As maglev is electrically powered, there is no direct air pollution as with airplanes and automobiles. The maglev causes lower CO2 emissions. It is also easier and more effective to control emissions at the source of electric power generation rather than at many points of consumption. Maglev is the quietest high-speed ground transportation system available today. Due to its non-contact technology, there is neither rolling nor gearing or engine noise. The frictionless operation of the maglev vehicle reduces vibration and maintenance resulting from wear. Comparing the noise levels at different speeds, the maglev vehicle is much quieter than the HSR trains. For example, The German TR07 maglev vehicle can travel about 25 percent faster than existing HSR trains before reaching the peak noise restrictions of 80 to 90 dBa. Such an advantage in speed will yield reduced the trip times along the noise-limited routes, which is most urban areas. At the speeds up to 200 km/h, the noise level compared to other noises from the surroundings can hardly be heard. At 250 km/h, the pass-by noise level is 71 dB(A), and from 250 km/h upwards, the aerodynamic noises begin to dominate the noise level. The result is that, at the speed of 300 km/h, the system is no louder than a light rail vehicle, and at 400 km/h, the noise level can be compared to a conventional train traveling at around 300 km/h. Even when at respective high speeds, data also indicates that maglev vehicle is 5 to 7 dBa quieter than the HSR train (Liu & Deng, 2004; Dai, 2005; Schwindt, 2006). The American JetTrain HSR train is almost twice as noisy as the maglev vehicle at the similar operational speeds (AMG, 2002). The results of the noise measurements of the TR08 Maglev System may be compared with similar data, documented by the Federal Railroad Administration (FRA, 1998), for other high-speed ground transportation systems (FRA, 2002a). The noise analysis associated with the Shanghai maglev train shows that the system is quieter than high-speed railway trains for comparable

A field experiment was conducted, to investigate the possible differences in perceived annoyance of noise caused by high-speed trains, both HSR and maglev. These results were evaluated for the TGV train at speeds of 140 km/h & 300 km/h and for the maglev vehicle at speeds of 200 km/h, 300 km/h and 400 km/h. The LAeq-annoyance relationships determined for the HSR and for the maglev train did not differ significantly. This study has shown that the noise annoyance caused by different types of trains at the same average

wasting time and damages such as environmental pollution.

distances from the track (Chen et al., 2007).

**7.5 Pollution**

close to a million passengers have ridden around the 40-kilometer closed loop. The maglev vehicle wraps around the guideway beam so it is virtually impossible to derail. Redundancies achieved through the duplication of components as well as the automated radio-controlled system ensure that operational safety will not be jeopardized. The principle of synchronized propulsion on the guideway makes collisions between vehicles virtually impossible. In general, no other obstacles can be in the way. If two or more vehicles were ever placed simultaneously in the same guideway segment, they would be forced by the motor in the guideway to travel at the same speed in the same direction. The vehicles are also designed to withstand collisions with small objects on the guideway. Energizing only the section of the guideway on which the train is traveling enhances operational safety and efficiency. The maglev vehicle is absolutely weatherproof and masters wind and adverse weather easily. Regarding the aspect of fire protection the maglev vehicle meets the highest requirements of the relevant standards. No fuels or combustible materials are on board. All used materials within the vehicles are PVC-free, highly inflammable, poor conductors of heat, burn-through-proof and heat-proof. The fire proof doors can be optionally used in order to separate the vehicle sections. The system is controlled in all the directions of the movement to ensure ride comfort throughout all the phases of the operation. The seat belts are not required, and passengers are free to move about the cabin at all speeds (AMG, 2002; Köncke, 2002; Liu & Deng, 2004; Dai, 2005).

### **7.4 Energy consumption and space requirement**

With non-contact technology, there is no energy loss due to the wheel-guideway friction. The vehicle weight is lower due to the absence of wheels, axles and engine (low mass of approx. 0.5 t per seat). In terms of energy consumption, the maglev vehicles are better than HSR trains. The maglev consumes less energy per seat-mile than HSR trains due to the utilization of lightweight materials and improvement in the advanced technology. The energy consumption of the maglev system with its non-contact levitation and propulsion technology, highly efficient linear motor and low aerodynamic resistance is very economical when compared to other transportation modes. The high-speed maglev system consumes 20 to 30 percent less energy per passenger than the very modest railroad. With the same energy input, the performance of the maglev system is substantially higher than HSR systems (Liu & Deng, 2004; Köncke, 2002).

As consumers of energy, the transportation sectors are vulnerable to environmental and global warming concerns and the increasing volatile oil market. Reducing dependency on foreign oil is also an important criterion. The system of the external power supply over the contact rail causes higher investment and operational costs. The energy costs of the maglev vehicle despite higher design speed, is lower than that of ICE3 train (Witt & Herzberg, 2004). The maglev vehicles running at 400 km/h has lower environmental impact indicators, such as system energy consumption, waste gas discharges, site area and the like, then the ICE trains running at 300 km/h (Baohua et al., 2008). They also have low running resistance of approx. 0.2 kN per seat at 400 km/h (Köncke, 2002).

Maglev is one of the first transportation systems to be specially developed to protect the environment. The system can be co-located with existing transportation corridors and needs a minimum amount of land for the support of the guideway beams. Use of the elevated guideway minimizes the disturbance to the existing land, water and wildlife, while flexible

close to a million passengers have ridden around the 40-kilometer closed loop. The maglev vehicle wraps around the guideway beam so it is virtually impossible to derail. Redundancies achieved through the duplication of components as well as the automated radio-controlled system ensure that operational safety will not be jeopardized. The principle of synchronized propulsion on the guideway makes collisions between vehicles virtually impossible. In general, no other obstacles can be in the way. If two or more vehicles were ever placed simultaneously in the same guideway segment, they would be forced by the motor in the guideway to travel at the same speed in the same direction. The vehicles are also designed to withstand collisions with small objects on the guideway. Energizing only the section of the guideway on which the train is traveling enhances operational safety and efficiency. The maglev vehicle is absolutely weatherproof and masters wind and adverse weather easily. Regarding the aspect of fire protection the maglev vehicle meets the highest requirements of the relevant standards. No fuels or combustible materials are on board. All used materials within the vehicles are PVC-free, highly inflammable, poor conductors of heat, burn-through-proof and heat-proof. The fire proof doors can be optionally used in order to separate the vehicle sections. The system is controlled in all the directions of the movement to ensure ride comfort throughout all the phases of the operation. The seat belts are not required, and passengers are free to move about the cabin at all speeds (AMG, 2002;

With non-contact technology, there is no energy loss due to the wheel-guideway friction. The vehicle weight is lower due to the absence of wheels, axles and engine (low mass of approx. 0.5 t per seat). In terms of energy consumption, the maglev vehicles are better than HSR trains. The maglev consumes less energy per seat-mile than HSR trains due to the utilization of lightweight materials and improvement in the advanced technology. The energy consumption of the maglev system with its non-contact levitation and propulsion technology, highly efficient linear motor and low aerodynamic resistance is very economical when compared to other transportation modes. The high-speed maglev system consumes 20 to 30 percent less energy per passenger than the very modest railroad. With the same energy input, the performance of the maglev system is substantially higher than HSR systems (Liu

As consumers of energy, the transportation sectors are vulnerable to environmental and global warming concerns and the increasing volatile oil market. Reducing dependency on foreign oil is also an important criterion. The system of the external power supply over the contact rail causes higher investment and operational costs. The energy costs of the maglev vehicle despite higher design speed, is lower than that of ICE3 train (Witt & Herzberg, 2004). The maglev vehicles running at 400 km/h has lower environmental impact indicators, such as system energy consumption, waste gas discharges, site area and the like, then the ICE trains running at 300 km/h (Baohua et al., 2008). They also have low running resistance

Maglev is one of the first transportation systems to be specially developed to protect the environment. The system can be co-located with existing transportation corridors and needs a minimum amount of land for the support of the guideway beams. Use of the elevated guideway minimizes the disturbance to the existing land, water and wildlife, while flexible

Köncke, 2002; Liu & Deng, 2004; Dai, 2005).

& Deng, 2004; Köncke, 2002).

**7.4 Energy consumption and space requirement**

of approx. 0.2 kN per seat at 400 km/h (Köncke, 2002).

alignment parameters allow the guideway to adapt to the landscape. Compared to roads or railway tracks, especially the elevated guideway does not affect wildlife movement. Even the ground-level guideway allows small animals to pass underneath due to the clearance planned under the guideway. Compared to all other land-bound transport systems, the maglev requires the least amount of the space and the land. The land area required for a ground-level double-track by either maglev or HSR systems is about similar so it is 14 m2/m and 12 m2/m, respectively. But for an elevated double-track guideway, approx. 2 square meter of land is needed for each meter of guideway (Schwindt, 2006). Considering the densely populated and limited land resources, an elevated structure is a preferred choice. The traffic effects on the land-use have been always considered by urban planner and transportation engineers. In the center of metropolitan areas with large economic activities, such as Mashhad, the increase of traffic volume has indirectly cost. It includes wasting time and damages such as environmental pollution.

### **7.5 Pollution**

As maglev is electrically powered, there is no direct air pollution as with airplanes and automobiles. The maglev causes lower CO2 emissions. It is also easier and more effective to control emissions at the source of electric power generation rather than at many points of consumption. Maglev is the quietest high-speed ground transportation system available today. Due to its non-contact technology, there is neither rolling nor gearing or engine noise. The frictionless operation of the maglev vehicle reduces vibration and maintenance resulting from wear. Comparing the noise levels at different speeds, the maglev vehicle is much quieter than the HSR trains. For example, The German TR07 maglev vehicle can travel about 25 percent faster than existing HSR trains before reaching the peak noise restrictions of 80 to 90 dBa. Such an advantage in speed will yield reduced the trip times along the noise-limited routes, which is most urban areas. At the speeds up to 200 km/h, the noise level compared to other noises from the surroundings can hardly be heard. At 250 km/h, the pass-by noise level is 71 dB(A), and from 250 km/h upwards, the aerodynamic noises begin to dominate the noise level. The result is that, at the speed of 300 km/h, the system is no louder than a light rail vehicle, and at 400 km/h, the noise level can be compared to a conventional train traveling at around 300 km/h. Even when at respective high speeds, data also indicates that maglev vehicle is 5 to 7 dBa quieter than the HSR train (Liu & Deng, 2004; Dai, 2005; Schwindt, 2006). The American JetTrain HSR train is almost twice as noisy as the maglev vehicle at the similar operational speeds (AMG, 2002). The results of the noise measurements of the TR08 Maglev System may be compared with similar data, documented by the Federal Railroad Administration (FRA, 1998), for other high-speed ground transportation systems (FRA, 2002a). The noise analysis associated with the Shanghai maglev train shows that the system is quieter than high-speed railway trains for comparable distances from the track (Chen et al., 2007).

A field experiment was conducted, to investigate the possible differences in perceived annoyance of noise caused by high-speed trains, both HSR and maglev. These results were evaluated for the TGV train at speeds of 140 km/h & 300 km/h and for the maglev vehicle at speeds of 200 km/h, 300 km/h and 400 km/h. The LAeq-annoyance relationships determined for the HSR and for the maglev train did not differ significantly. This study has shown that the noise annoyance caused by different types of trains at the same average

Maglev 171

The loading of the guideway is almost equal to the loading of each one of the four girders of the railroad bridge. In other words, taking into account the fact that the bridge consists of four girders, comparison of the results indicates that the load on the railroad bridge deck is four times greater than the load on the maglev guideway. This means that the guideway by itself can play the role of each one of the girders of the railroad bridge (Yaghoubi & Ziari,

Rapid increase in traffic volume in transport systems plus the need for improving passenger comfort have highlighted the subject of developing new transport systems. The recent required increases in the traffic volume in transport systems, as well as a need for the improvement of passengers' comfort, and required reductions in track life cycle costs, have caused the subject of the development of a new transportation system. One of the important systems which have attracted industries is maglev transport system. In this regard, maglev transport system turns out to be a proper choice for transportation industries around the world. Maglev systems have been recently developed in response to the need for rapid transit systems. The maglev system comes off clearly better and surpasses the HSR systems in almost most fields. These include the pollution, noise emission, vibration level, environmental issues, land occupations, loading, speed, acceleration and deceleration, braking, maintenance costs, passenger comfort, safety, travel time, etc. With the maglev guideway it is also possible to reach to the minimal radiuses for the horizontal and vertical curves. A maglev vehicle can as well travel at the steeper gradients compared with the HSR systems. This considerably reduces the total length of track for the maglev routes compared to the HSR systems. The possibility of traveling with the higher grade angles also reduces the number of tunnels that are required to travel through the mountainous areas. This can also shorten the total length for the maglev route. Therefore, construction of the maglev routes in the hilly areas, in addition to many other advantageous of these systems, can be considered as an attractive choice for the transportation industries. The lower energy consumption of the maglev vehicles in comparison with the HSR systems is also among major characteristics of the magnetically levitated trains. This can be easily associated with the absence of the wheels and the resulting situation of no physical contact between the maglev vehicle and its guideway. Therefore, the energy loss due to the unwanted friction is out of the equations. Furthermore, the vehicle weight is lower due to the absence of wheels, axles and engine. On the other hand, reduction in the travel time considerably reduces the energy consumption. The limited energy resources that are currently available to the nation have highlighted the fact that every individual has to be the energy conscious. The government had to take steps, and it started by setting the preventative rules and the tightening access to the cheap energy resources. Clearly, the widespread application of the magnetically levitated trains for the public transport, in short and long distances, can provide the nation with huge saving in the energy consumption. This is not a fact that can be easily

Effective parameters in the design of guideways including dead and live loads, dynamic amplification factor and deflection, and structural analysis and design criteria were investigated. According to AREMA regulations and UIC leaflets, live loading models for

2011; Yaghoubi & Rezvani, 2011).

ignored nor can it be bypassed.

**8. Conclusion**

outdoor façade exposure level is not significantly different. In particular, the magnetic levitation systems are not more annoying than the HSR trains, which is in agreement with earlier research (Coensel et al., 2007).

Whatever the kind of transport system, a passing maglev vehicle always creates ground vibrations due to dynamic loading of the track. Depending on the speed, load transfer, load dispersion and the nature of the ground, these vibrations are transmitted through the ground to different degrees and may thus be felt as shocks in neighboring buildings. For especially sensitive areas, technical solutions are currently being investigated, which minimize the dynamic loads that are transferred from the vehicle to the guideway and then to the bearings in the supports and foundations (Schwindt, 2006).

TR08 vibration levels for both the concrete elevated and concrete at-grade (AG) guideways are compared with those of the TGV, the Italian Pendolino, the Swedish X2000, and the Acela at 240 km/h. The vibration levels for the TR08 traversing the at-grade guideway structures are comparable to those from HSR trains measured in Italy (Pendolino) and France (TGV), whereas the levels for the elevated structure are considerably lower for the distances measured. Vibration levels measured at 15 m for the TR08 traversing the at-grade guideway at 400 km/h are less than those previously measured at 15 m for the Acela traveling 240 km/h. These comparisons, however, are representative of data collected at various sites and are generally typical of local geological conditions. In general, groundborne vibration levels from trains on elevated structures tend to be lower than those from atgrade operations (FRA, 2002b). The curves for European HSR trains are taken from the FRA high-speed ground transportation guidance manual (FRA, 1998), and for the Acela from measurements conducted by HMMH (FRA, 2000).

### **7.6 Loading**

In this part of research, maglev guideways and road and railroad bridges are compared from loading and design aspects. The optimal design of all bridges, including road, railroads and maglev elevated guideways is really vital. Majority of the existing maglev guideways are elevated and completely built on the bridge. In fact, a maglev elevated guideway is one kind of bridges. Therefore, it can be compared with any bridge, including railroad and road.

According to the AREMA regulations and the UIC leaflets, the live loading models for the rail tracks, is a combination of the concentrated and distributed loads. However, the live loading models for the maglev trains, in the absence of wheels and pursuant to uniformity in the intensity of magnetic forces due to the magnets, are uniformly distributed on the guideways. The lateral magnetic force in maglev is less than the lateral force in the rail tracks. The low level of this force in maglev is due to the absence of the rails and wheels, lower weight of the vehicle and the presence of lateral restoring and equilibration magnetic force.

In general, vertical loadings (dead and live) in the spans of maglev guideways are much lower than those of the railroad bridges. The intensity of the uniform distributed load in live loading of the railroad bridges is almost four times that in maglev. One reason for this difference is the lower weight of the maglev vehicle due to the absence of wheels, axles and transmission parts plus the overall short length of the vehicle. The amount of the earthquake lateral force on the maglev guideway is less than one third of its value for the road bridge.

outdoor façade exposure level is not significantly different. In particular, the magnetic levitation systems are not more annoying than the HSR trains, which is in agreement with

Whatever the kind of transport system, a passing maglev vehicle always creates ground vibrations due to dynamic loading of the track. Depending on the speed, load transfer, load dispersion and the nature of the ground, these vibrations are transmitted through the ground to different degrees and may thus be felt as shocks in neighboring buildings. For especially sensitive areas, technical solutions are currently being investigated, which minimize the dynamic loads that are transferred from the vehicle to the guideway and then

TR08 vibration levels for both the concrete elevated and concrete at-grade (AG) guideways are compared with those of the TGV, the Italian Pendolino, the Swedish X2000, and the Acela at 240 km/h. The vibration levels for the TR08 traversing the at-grade guideway structures are comparable to those from HSR trains measured in Italy (Pendolino) and France (TGV), whereas the levels for the elevated structure are considerably lower for the distances measured. Vibration levels measured at 15 m for the TR08 traversing the at-grade guideway at 400 km/h are less than those previously measured at 15 m for the Acela traveling 240 km/h. These comparisons, however, are representative of data collected at various sites and are generally typical of local geological conditions. In general, groundborne vibration levels from trains on elevated structures tend to be lower than those from atgrade operations (FRA, 2002b). The curves for European HSR trains are taken from the FRA high-speed ground transportation guidance manual (FRA, 1998), and for the Acela from

In this part of research, maglev guideways and road and railroad bridges are compared from loading and design aspects. The optimal design of all bridges, including road, railroads and maglev elevated guideways is really vital. Majority of the existing maglev guideways are elevated and completely built on the bridge. In fact, a maglev elevated guideway is one kind of bridges. Therefore, it can be compared with any bridge, including railroad and road. According to the AREMA regulations and the UIC leaflets, the live loading models for the rail tracks, is a combination of the concentrated and distributed loads. However, the live loading models for the maglev trains, in the absence of wheels and pursuant to uniformity in the intensity of magnetic forces due to the magnets, are uniformly distributed on the guideways. The lateral magnetic force in maglev is less than the lateral force in the rail tracks. The low level of this force in maglev is due to the absence of the rails and wheels, lower weight of the vehicle and the presence of lateral restoring and equilibration magnetic

In general, vertical loadings (dead and live) in the spans of maglev guideways are much lower than those of the railroad bridges. The intensity of the uniform distributed load in live loading of the railroad bridges is almost four times that in maglev. One reason for this difference is the lower weight of the maglev vehicle due to the absence of wheels, axles and transmission parts plus the overall short length of the vehicle. The amount of the earthquake lateral force on the maglev guideway is less than one third of its value for the road bridge.

to the bearings in the supports and foundations (Schwindt, 2006).

measurements conducted by HMMH (FRA, 2000).

**7.6 Loading**

force.

earlier research (Coensel et al., 2007).

The loading of the guideway is almost equal to the loading of each one of the four girders of the railroad bridge. In other words, taking into account the fact that the bridge consists of four girders, comparison of the results indicates that the load on the railroad bridge deck is four times greater than the load on the maglev guideway. This means that the guideway by itself can play the role of each one of the girders of the railroad bridge (Yaghoubi & Ziari, 2011; Yaghoubi & Rezvani, 2011).

### **8. Conclusion**

Rapid increase in traffic volume in transport systems plus the need for improving passenger comfort have highlighted the subject of developing new transport systems. The recent required increases in the traffic volume in transport systems, as well as a need for the improvement of passengers' comfort, and required reductions in track life cycle costs, have caused the subject of the development of a new transportation system. One of the important systems which have attracted industries is maglev transport system. In this regard, maglev transport system turns out to be a proper choice for transportation industries around the world. Maglev systems have been recently developed in response to the need for rapid transit systems. The maglev system comes off clearly better and surpasses the HSR systems in almost most fields. These include the pollution, noise emission, vibration level, environmental issues, land occupations, loading, speed, acceleration and deceleration, braking, maintenance costs, passenger comfort, safety, travel time, etc. With the maglev guideway it is also possible to reach to the minimal radiuses for the horizontal and vertical curves. A maglev vehicle can as well travel at the steeper gradients compared with the HSR systems. This considerably reduces the total length of track for the maglev routes compared to the HSR systems. The possibility of traveling with the higher grade angles also reduces the number of tunnels that are required to travel through the mountainous areas. This can also shorten the total length for the maglev route. Therefore, construction of the maglev routes in the hilly areas, in addition to many other advantageous of these systems, can be considered as an attractive choice for the transportation industries. The lower energy consumption of the maglev vehicles in comparison with the HSR systems is also among major characteristics of the magnetically levitated trains. This can be easily associated with the absence of the wheels and the resulting situation of no physical contact between the maglev vehicle and its guideway. Therefore, the energy loss due to the unwanted friction is out of the equations. Furthermore, the vehicle weight is lower due to the absence of wheels, axles and engine. On the other hand, reduction in the travel time considerably reduces the energy consumption. The limited energy resources that are currently available to the nation have highlighted the fact that every individual has to be the energy conscious. The government had to take steps, and it started by setting the preventative rules and the tightening access to the cheap energy resources. Clearly, the widespread application of the magnetically levitated trains for the public transport, in short and long distances, can provide the nation with huge saving in the energy consumption. This is not a fact that can be easily ignored nor can it be bypassed.

Effective parameters in the design of guideways including dead and live loads, dynamic amplification factor and deflection, and structural analysis and design criteria were investigated. According to AREMA regulations and UIC leaflets, live loading models for

Maglev 173

American Magline Group (AMG). (2002). Technology comparison: high speed ground transportation, Transrapid superspeed maglev and bombardier JetTrain. Baohua, M., Rong, H. & Shunping, J. (2008). Potential applications of maglev railway technology in China. *Journal of Transpn Sys Eng & IT*, Vol. 8, No. 1, pp. 29−39. Behbahani, H. & Yaghoubi, H. (2010). Procedures for safety and risk assessment of maglev

Cai Y., Chen, S. S., Rote, D. M., & Coffey, H. T., (1996). Vehicle/guideway dynamic

Coensel, B. D., Botteldooren, D., Berglund, B., Nilsson, M. E., Muer, T. D. & Lercher, P.

Dai, H. (2005). Dynamic behavior of maglev vehicle/guideway system with control. Ph.D.

FRA (Federal Railroad Administration). (1998). High speed ground transportation noise and

FRA. (2000). Acela trainset noise and vibration measurements on the northeast corridor.

FRA. (2002a). Noise characteristics of the Transrapid TR08 maglev system. Report No. DOT-

FRA. (2002b). Vibration characteristics of the Transrapid TR08 maglev system. Report No.

Federal Transit Administration (FTA), Office of Research, Demonstration, and Innovation,

FTA, Office of Research, Demonstration, and Innovation, (2004). Urban maglev technology

FTA, Office of Mobility Innovation, (2005a). Proceedings of the Federal Transit

FTA, Office of Research, Demonstration, and Innovation, (2005b). General Atomics low

Grossert, E. (2006). Actual development in guideway constructions at the example of the

Guangwei, S., Meisinger, R., & Gang, S. (2007). Modeling and simulation of Shanghai

(2002). Assessment of CHSST maglev for U.S. urban transpn., *U. S. Department of*

development program Colorado maglev project, *U. S. Department of Transportation*,

Administration's urban maglev workshop, *U. S. Department of Transpn.*,

speed maglev technology development program (supplemental #3), *U.S.*

Transrapid Munich project, *The 19th Int. Conf. on Magnetically Levitated Sys. and*

maglev train Transrapid with random track irregularities. *Sonderdruck Schriftenreihe*

*Acta Acustica united with Acustica*, Vol. 93, No. 4, pp. 589-601.

Report No. 295450-3, *U.S. Department of Transportation*.

VNTSC-FRA-02-13, *U.S. Department of Transportation*.

*der Georg-Simon-Ohm-Fachhochschule Nürnberg*, Nr. 39.

DOT-VNTSC-FRA-02-06, *U.S. Department of Transportation*.

Thesis, *Department of Civil Engineering, Case Western Reserve Uni*.

systems: a case-study for long-distance and high-speed maglev project in Mashhad-Tehran route. *The 1st International Conference on Railway Engineering, High-speed Railway, Heavy Haul Railway and Urban Rail Transit*, Beijing Jiaotong University, Beijing, China, China Railway Publishing House, pp. 73-83, ISBN 978-7-113-11751-

interaction in maglev systems. *ASME, Journal of Dynamic Systems, Measurement, and*

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**10. References**

1.

*Control*, Vol. 118, pp. 526-530.

*Transportation*.

*Transpn.*, Final Report.

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Washington, DC.

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*Linear Drives*, Dresden, Germany.

loading of rails, is a combination of concentrated and distributed loads. However, live loading models for maglev trains, in the absence of wheels and as a result of uniformity in the intensity of lifting magnetic forces due to support magnets, are uniformly distributed on the guideways. The guideway loading is modeled as dynamic and uniformly distributed magnetic forces to account for the dynamic coupling between the vehicle and the guideway. In general, vertical loadings (dead and live) in the spans of maglev are much lower than those of the railroad bridges. The railroad bridge dead load is four times larger than the maglev guideway dead load, and the intensity of the uniformly distributed live load on the railroad bridge is almost four times that of the maglev guideway. Moreover, loading of guideway is four times that in the railroad bridge. One reason for this difference is the lower weight of the maglev vehicle due to the absence of wheels, axles and transmission parts plus the overall short length of the vehicle. The lateral force on the maglev guideway is also much lower than that on the railroad bridge. Also, it is predicted that on the straight routes as a result of negligible lateral magnetic force, there is no considerable amount of torsion created in the cross-section. Therefore, if the beam cross-section and the vertical loading are symmetrical, special design of guideway crosssections to overcome torsion, is not necessary. Moreover, there usually is no need for the design of deck-shaped cross-sections to care for tension lateral magnetic forces and for the moments due to vertical magnetic forces. Compared to the road and railway bridges, the amount of lateral earthquake force on maglev guideway is lower. Maglev guideways have high resistance against earthquake forces. Maglev vehicles are lighter compared to conventional railway vehicles. These lighter vehicles cause less centrifugal force. The absence of wheels and wheel/rail contact, lighter vehicles and presence of compensating magnetic forces opposing any lateral deviation are the main reasons behind the lower centrifugal forces. A distributed-load vehicle model is better than a concentrated-load model. Multicar vehicles have less car-body acceleration than does a single-car vehicle, because of intercar constraints. This indicates that the multicar vehicle would provide better ride comfort. Weight of required longitudinal bars of guideway is also one-fourth that in the railroad bridge. Deflections due to the vertical loads (dead and live) are also lower in guideways than in rail tracks. Torsion reduction, deflection reduction due to vertical loads, reduction in the costs of construction and operation, increase in resistance and technical justification, possibility of motion in higher speeds are among main reasons to utilize beams with a U-shaped cross-sections and structural continuity in the guideways. Therefore, as noticeable improvements and developments are made in structural optimization of these cross-sections, they could be considered as a good choice among other sections and could be used with a relatively high safety factor. Also, it is shown that the lower loads on the maglev guideway lead to lower bending moments and sheer forces in comparison with the railroad bridge. This indicates that the maglev support structure requires less mechanical strength than the railroad bridge support structure for the same loading pattern. A dynamic simulation for maglev vehicle/guideway interaction is essential to optimize the vehicle design and reduce the cost.

#### **9. Acknowledgment**

This chapter of book was performed and financially supported completely by Iran Maglev Technology (IMT).

loading of rails, is a combination of concentrated and distributed loads. However, live loading models for maglev trains, in the absence of wheels and as a result of uniformity in the intensity of lifting magnetic forces due to support magnets, are uniformly distributed on the guideways. The guideway loading is modeled as dynamic and uniformly distributed magnetic forces to account for the dynamic coupling between the vehicle and the guideway. In general, vertical loadings (dead and live) in the spans of maglev are much lower than those of the railroad bridges. The railroad bridge dead load is four times larger than the maglev guideway dead load, and the intensity of the uniformly distributed live load on the railroad bridge is almost four times that of the maglev guideway. Moreover, loading of guideway is four times that in the railroad bridge. One reason for this difference is the lower weight of the maglev vehicle due to the absence of wheels, axles and transmission parts plus the overall short length of the vehicle. The lateral force on the maglev guideway is also much lower than that on the railroad bridge. Also, it is predicted that on the straight routes as a result of negligible lateral magnetic force, there is no considerable amount of torsion created in the cross-section. Therefore, if the beam cross-section and the vertical loading are symmetrical, special design of guideway crosssections to overcome torsion, is not necessary. Moreover, there usually is no need for the design of deck-shaped cross-sections to care for tension lateral magnetic forces and for the moments due to vertical magnetic forces. Compared to the road and railway bridges, the amount of lateral earthquake force on maglev guideway is lower. Maglev guideways have high resistance against earthquake forces. Maglev vehicles are lighter compared to conventional railway vehicles. These lighter vehicles cause less centrifugal force. The absence of wheels and wheel/rail contact, lighter vehicles and presence of compensating magnetic forces opposing any lateral deviation are the main reasons behind the lower centrifugal forces. A distributed-load vehicle model is better than a concentrated-load model. Multicar vehicles have less car-body acceleration than does a single-car vehicle, because of intercar constraints. This indicates that the multicar vehicle would provide better ride comfort. Weight of required longitudinal bars of guideway is also one-fourth that in the railroad bridge. Deflections due to the vertical loads (dead and live) are also lower in guideways than in rail tracks. Torsion reduction, deflection reduction due to vertical loads, reduction in the costs of construction and operation, increase in resistance and technical justification, possibility of motion in higher speeds are among main reasons to utilize beams with a U-shaped cross-sections and structural continuity in the guideways. Therefore, as noticeable improvements and developments are made in structural optimization of these cross-sections, they could be considered as a good choice among other sections and could be used with a relatively high safety factor. Also, it is shown that the lower loads on the maglev guideway lead to lower bending moments and sheer forces in comparison with the railroad bridge. This indicates that the maglev support structure requires less mechanical strength than the railroad bridge support structure for the same loading pattern. A dynamic simulation for maglev vehicle/guideway interaction is essential to optimize the vehicle design and reduce the

This chapter of book was performed and financially supported completely by Iran Maglev

cost.

**9. Acknowledgment**

Technology (IMT).

### **10. References**

Maglev 175

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**Part 2**

**Modelling for Railway Infrastructure**

**Design and Characterization**

## **Part 2**

**Modelling for Railway Infrastructure Design and Characterization**

176 Infrastructure Design, Signalling and Security in Railway

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**7**

*Colombia*

**Power System Modelling for Urban Massive**

Urban Massive Transportation Systems (UMTS), like metro, tramway, light train; requires the supply of electric power with high standards of reliability. So, an important step in the development of these transportation systems is the electric power supply system planning

Normally, the trains of a UMTS requires a DC power supply by means of rectifier AC/DC substations, know as traction substations (TS); that are connected to the electric HV/MV distribution system of a city. The DC system feeds catenaries of tramways or the third rail of metros, for example. The DC voltage is selected according to the system taking into account power demand and length of the railway's lines. Typically, a 600 Vdc – 750 Vdc is used in tramways; while 1500 Vdc is used in a metro system. Some interurban-urban

Fig. 1 presents an electric scheme of a typical traction substation (TS) with its main components: AC breakers at MV, MV/LV transformers, AC/DC rectifiers, DC breakers, traction DC breakers. As, it is shown, a redundant supply system is placed at each traction substation in order to improve reliability. In addition, some electric schemes allow the power supply of the catenaries connected to a specific traction substation (A) since the neighbour traction substation (B) by closing the traction sectioning between A and B and opening the traction DC breakers. In this way, the reliability supply is improved and allows

So, an important aspect for the planning and design of this electric power supply is a good estimation of power demand required by the traction system that will determine the required number, size and capacity of AC/DC rectifier substations. On the other hand, the design of the system requires studying impacts of the traction system on the performance of the distribution system and vice versa. Power quality disturbances are present in the

This chapter presents useful tools for modelling, analysis and system design of Electric Massive Railway Transportation Systems (EMRTS) and power supply from Distribution Companies (DisCo) or Electric Power Utilities. Firstly, a section depicting the modelling and simulation of the power demand is developed. Then, a section about the computation of

operation of these systems that could affect the performance of the traction system.

**1. Introduction**

systems use a 3000 Vdc supply to the trains.

flexibility for maintenance of TS.

and design.

**Transportation Systems**

Mario A. Ríos and Gustavo Ramos *Universidad de los Andes, Bogotá, D.C.,*

## **Power System Modelling for Urban Massive Transportation Systems**

Mario A. Ríos and Gustavo Ramos *Universidad de los Andes, Bogotá, D.C., Colombia*

### **1. Introduction**

Urban Massive Transportation Systems (UMTS), like metro, tramway, light train; requires the supply of electric power with high standards of reliability. So, an important step in the development of these transportation systems is the electric power supply system planning and design.

Normally, the trains of a UMTS requires a DC power supply by means of rectifier AC/DC substations, know as traction substations (TS); that are connected to the electric HV/MV distribution system of a city. The DC system feeds catenaries of tramways or the third rail of metros, for example. The DC voltage is selected according to the system taking into account power demand and length of the railway's lines. Typically, a 600 Vdc – 750 Vdc is used in tramways; while 1500 Vdc is used in a metro system. Some interurban-urban systems use a 3000 Vdc supply to the trains.

Fig. 1 presents an electric scheme of a typical traction substation (TS) with its main components: AC breakers at MV, MV/LV transformers, AC/DC rectifiers, DC breakers, traction DC breakers. As, it is shown, a redundant supply system is placed at each traction substation in order to improve reliability. In addition, some electric schemes allow the power supply of the catenaries connected to a specific traction substation (A) since the neighbour traction substation (B) by closing the traction sectioning between A and B and opening the traction DC breakers. In this way, the reliability supply is improved and allows flexibility for maintenance of TS.

So, an important aspect for the planning and design of this electric power supply is a good estimation of power demand required by the traction system that will determine the required number, size and capacity of AC/DC rectifier substations. On the other hand, the design of the system requires studying impacts of the traction system on the performance of the distribution system and vice versa. Power quality disturbances are present in the operation of these systems that could affect the performance of the traction system.

This chapter presents useful tools for modelling, analysis and system design of Electric Massive Railway Transportation Systems (EMRTS) and power supply from Distribution Companies (DisCo) or Electric Power Utilities. Firstly, a section depicting the modelling and simulation of the power demand is developed. Then, a section about the computation of

Power System Modelling for Urban Massive Transportation Systems 181

The power consumed by one railway vehicle depends on the velocity and acceleration that it has at each instant of time. Its computation is based on the traction effort characteristic (supplied by the manufacturer of the motors), the number of passengers and the distances between the passengers' stations (Vukan, 2007), (Chen et al., 1999), (Perrin & Vernard, 1991). The duty cycle of an urban train between two passengers' stations is composed by four operation states: acceleration, balancing speed, constant speed and deceleration. Fig. 2 shows the behavior of the speed, traction effort and power consumption of a traction vehicle

Fig. 2. Velocity, Traction Effort, and Power Consumption of an Urban Train Travel between

During the first state (I), the vehicle moves with constant positive acceleration, so the speed increases. When the vehicle reaches a determined speed lower than the constant speed, the second operation state starts. In this state, the acceleration decreases, but the speed keeps increasing. In the third state (III), the cruise speed is reached and the acceleration is zero. In the fourth state (IV), the braking operation starts with negative acceleration until the moment it decelerates with a constant rate and finally it stops at the destination station

The parametric construction of the traction and braking effort curves is based on the traction theory already implemented in locomotives and high speed rails. Three factors limit the traction effort versus velocity: the maximum traction effort *Fmax* conditioned by the number of passengers that are in the wagon, the maximum velocity of the vehicle, and the maximum power consumption. The maximum traction effort used by the acceleration, and then

*<sup>m</sup> axis wnnTMm axle* (1)

(Vukan, 2007), (Chen et al., 1999), (Perrin & Vernard, 1991), (Hsiang & Chen, 2001).

transferred to the rail, is limited by the total weight of the axles given by:

during each operation state elapsed either time or space (Hsiang & Chen, 2001).

**2.1 Power consumption model of an urban train**

adjacent Passenger Stations (Hsiang & Chen, 2001)

**2.1.1 Net force of a traction vehicle**

the placement and sizing of TS for urban railway systems is presented where the modelling is based on the power demand model of the previous section. After that, two sections about the power quality (PQ) impact of EMRTS on distribution systems and grounding design are presented. Both subjects make use of the load demand model presented previously.

Fig. 1. A Typical Traction Substation (TS)

### **2. Power demand computation of electric transportation systems**

This section presents a mathematical model useful to simulate urban railway systems and to compute the instantaneous power of the Electric Massive Railway Transportation Systems (EMRTS) such as a metro, light train or tramway, by means of computing models that take into account parameters such as the grid size, acceleration, velocity variation, EMRTS braking, number of wagons, number of passengers per wagon, number of rectifier substations, and passenger stations, among other factors, which permit to simulate the physical and electric characteristics of these systems in a more accurate way of a real system.

This model connects the physical and dynamic variables of the traction behaviour with electrical characteristics to determine the power consumption. The parametric construction of the traction and braking effort curves is based on the traction theory already implemented in locomotives and urban rails. Generally, there are three factors that limit the traction effort versus velocity: the maximum traction effort (*Fmax*) conditioned by the number of passengers that are in the wagons, the maximum velocity of the train (or rail), and the maximum power consumption. Based on these factors, a simulation model is formulated for computing the acceleration, speed and placement of each train in the railway line for each time step (1 second, for example). So, the power consumption or re-generation is computed also for each time step and knowing the placement of each train in the line, the power demand for each electric TS is calculated.

### **2.1 Power consumption model of an urban train**

180 Infrastructure Design, Signalling and Security in Railway

the placement and sizing of TS for urban railway systems is presented where the modelling is based on the power demand model of the previous section. After that, two sections about the power quality (PQ) impact of EMRTS on distribution systems and grounding design are

presented. Both subjects make use of the load demand model presented previously.

**2. Power demand computation of electric transportation systems**

This section presents a mathematical model useful to simulate urban railway systems and to compute the instantaneous power of the Electric Massive Railway Transportation Systems (EMRTS) such as a metro, light train or tramway, by means of computing models that take into account parameters such as the grid size, acceleration, velocity variation, EMRTS braking, number of wagons, number of passengers per wagon, number of rectifier substations, and passenger stations, among other factors, which permit to simulate the physical and electric characteristics of these systems in a more accurate way of a real

This model connects the physical and dynamic variables of the traction behaviour with electrical characteristics to determine the power consumption. The parametric construction of the traction and braking effort curves is based on the traction theory already implemented in locomotives and urban rails. Generally, there are three factors that limit the traction effort versus velocity: the maximum traction effort (*Fmax*) conditioned by the number of passengers that are in the wagons, the maximum velocity of the train (or rail), and the maximum power consumption. Based on these factors, a simulation model is formulated for computing the acceleration, speed and placement of each train in the railway line for each time step (1 second, for example). So, the power consumption or re-generation is computed also for each time step and knowing the placement of each train in the line, the power

Fig. 1. A Typical Traction Substation (TS)

demand for each electric TS is calculated.

system.

The power consumed by one railway vehicle depends on the velocity and acceleration that it has at each instant of time. Its computation is based on the traction effort characteristic (supplied by the manufacturer of the motors), the number of passengers and the distances between the passengers' stations (Vukan, 2007), (Chen et al., 1999), (Perrin & Vernard, 1991). The duty cycle of an urban train between two passengers' stations is composed by four operation states: acceleration, balancing speed, constant speed and deceleration. Fig. 2 shows the behavior of the speed, traction effort and power consumption of a traction vehicle during each operation state elapsed either time or space (Hsiang & Chen, 2001).

Fig. 2. Velocity, Traction Effort, and Power Consumption of an Urban Train Travel between adjacent Passenger Stations (Hsiang & Chen, 2001)

During the first state (I), the vehicle moves with constant positive acceleration, so the speed increases. When the vehicle reaches a determined speed lower than the constant speed, the second operation state starts. In this state, the acceleration decreases, but the speed keeps increasing. In the third state (III), the cruise speed is reached and the acceleration is zero. In the fourth state (IV), the braking operation starts with negative acceleration until the moment it decelerates with a constant rate and finally it stops at the destination station (Vukan, 2007), (Chen et al., 1999), (Perrin & Vernard, 1991), (Hsiang & Chen, 2001).

### **2.1.1 Net force of a traction vehicle**

The parametric construction of the traction and braking effort curves is based on the traction theory already implemented in locomotives and high speed rails. Three factors limit the traction effort versus velocity: the maximum traction effort *Fmax* conditioned by the number of passengers that are in the wagon, the maximum velocity of the vehicle, and the maximum power consumption. The maximum traction effort used by the acceleration, and then transferred to the rail, is limited by the total weight of the axles given by:

$$m\_m = TM - \left(n\_{axis} - n\right) \times \omega\_{axle} \tag{1}$$

Power System Modelling for Urban Massive Transportation Systems 183

 *<sup>i</sup> F t*

The velocity is assumed an independent variable, which determines the path time of the traction vehicle, with steps fixed by velocity and acceleration (Jong & Chang, 2005b). So, the

*v v t t*

The motor torque and the velocity for an EMRTS are linear functions of the acceleration and the angular velocity. So, the instantaneous power consumption by the EMRTS, for the first three operative states (Chen et al., 1999), (Perrin & Vernard, 1991), (Hsiang & Chen, 2001), is:

*Pt B v v e B*

which describes the braking effort multiplied by the velocity in the range of 0≤*v*≤*vmax* and a multiplicative factor *ηB* which describes the efficiency of the regenerative braking which it is considered of 30% for this type of systems (Perrin & Vernard, 1991), (Jong & Chang, 2005a),

The model presented at section 2.1 allows the computation of the power consumption and travel time characteristics (*t, x*) for each train *i* in the railway line. Naturally, a railway line simulation must include a number *n* of passengers' stations and *k* trains travel in the line (go

The integration of these characteristics requires modelling the mobility of passengers associated at each train. It can be simulated in a probabilistic way, computing the number of passengers coming up and leaving the train (*i*) in each passenger's station (*j*) and the stopping time of the train in each station. This first part, stated here as Module 1, uses the following parameters: the passengers' up (*rup*) and down (*rdown*) rates, and up (*tup*) and down

The number of passengers in the first station and the number of passengers waiting in each station (*paxwait*) are modelled as random variables of uniform distribution. As, the railway line simulation includes a number *n* of passengers' stations; Module 1 computes for each

train *i* the number of passengers that the train transport between station *j* and *j+1* as:

1

*i i*

*i*

*a*

*TM t* (6)

(7)

*i i ii i* 1 1 *s s vt t* (8)

*P t TM t a t MR v v <sup>i</sup>* (9)

(10)

*a t*

1

For the last operative state where the braking acts, the consumption is given by:

*i i*

time steps and the incremental travelled distance are given by:

**2.1.3 Power consumption computation**

(Hill, 2006).

and return).

**2.2 Simulation model**

(*tup*) times per passenger.

where *TM* is the total vehicle mass, *n* is the number of motor drives, *naxis* the number of axles in the vehicle, and *waxle* the weight per axle (Buhrkall, 2006). The total vehicle mass is:

$$TM = w\_v + \left(n\_p \times w\_{pas}\right) \times M\_{DYN} \tag{2}$$

where *wv* corresponds to the weight per wagon without passengers, *np* the number of passengers per wagon, *wpas* the average weight per passenger, and *MDYN* the dynamic mass of the railway, which represents the stored energy in the spinning parts of the vehicle, typically of 5-10% (Buhrkall, 2006). Then, the maximum traction effort is calculated as:

$$F\_{\text{max}} = \mu \times m\_m \times \text{g} \tag{3}$$

Where *µ* corresponds to the friction coefficient between the wheels and the rail, which is about 15% for the ERMTS, and gravity *g* equals to 9.8 m/s2 (Buhrkall, 2006). The force needed to move a traction vehicle (*TM* times the acceleration (*a*)) is:

$$F = TM \times a = TM \frac{dv}{dt} = TE(v) - MR(v) - B\_e(v) \tag{4}$$

Where *TE(v)* is the traction effort in an EMRTS that provides the necessary propulsion to exceed inertia and accelerate the vehicle, *MR(v)* is the movement resistance as an opposite force to the vehicle movement, *Be(v)* is the braking effort used to decelerate the vehicle and stop it permanently (Vukan, 2007).

The traction and braking effort act directly in the vehicle wheels edges. The movement resistance is given by:

$$MR(v) = 10^{-3} \times \left(2.5 + 10^{-3} \times k(v + \Delta v)^2\right) \times TM \times \text{g} \tag{5}$$

Where *k≈0.33* for passengers' vehicles, *∆v*≈15km/h is the wind velocity variation, *TM* is the total mass of the vehicle, and g the gravity. Table 1 presents the action forces in an EMRTS that makes its path between two passengers' stations. As a result, there are four regimens of operation: stopping, acceleration, constant velocity, and deceleration. This is how the difference between the traction effort, the movement resistance, and the braking effort, which are not velocity variants, represent the net force of the vehicle (Jong & Chang, 2005b).

Table 1. Net Force and Velocity as function of the Operative Regimen (Jong & Chang, 2005b)

#### **2.1.2 Computation of dynamic variables**

The incremental acceleration (*ai*) is obtained from the net force and the total mass of the vehicle (Jong & Chang, 2005b) computed for each instant *t*, as:

$$a\_i(t) = \frac{F(t)}{TM(t)}\tag{6}$$

The velocity is assumed an independent variable, which determines the path time of the traction vehicle, with steps fixed by velocity and acceleration (Jong & Chang, 2005b). So, the time steps and the incremental travelled distance are given by:

$$t\_{i+1} = t\_i + \frac{v\_{i+1} - v\_i}{a\_i} \tag{7}$$

$$\mathbf{s}\_{i+1} = \mathbf{s}\_i + \upsilon\_i \left( t\_{i+1} - t\_i \right) \tag{8}$$

#### **2.1.3 Power consumption computation**

The motor torque and the velocity for an EMRTS are linear functions of the acceleration and the angular velocity. So, the instantaneous power consumption by the EMRTS, for the first three operative states (Chen et al., 1999), (Perrin & Vernard, 1991), (Hsiang & Chen, 2001), is:

$$P(t) = \left(TM(t) \times a\_i(t) + MR(v)\right) \times v \tag{9}$$

For the last operative state where the braking acts, the consumption is given by:

$$P(t) = B\_\varepsilon(\upsilon) \times \upsilon \times \eta\_B \tag{10}$$

which describes the braking effort multiplied by the velocity in the range of 0≤*v*≤*vmax* and a multiplicative factor *ηB* which describes the efficiency of the regenerative braking which it is considered of 30% for this type of systems (Perrin & Vernard, 1991), (Jong & Chang, 2005a), (Hill, 2006).

#### **2.2 Simulation model**

182 Infrastructure Design, Signalling and Security in Railway

where *TM* is the total vehicle mass, *n* is the number of motor drives, *naxis* the number of axles in the vehicle, and *waxle* the weight per axle (Buhrkall, 2006). The total vehicle mass is:

where *wv* corresponds to the weight per wagon without passengers, *np* the number of passengers per wagon, *wpas* the average weight per passenger, and *MDYN* the dynamic mass of the railway, which represents the stored energy in the spinning parts of the vehicle, typically of 5-10% (Buhrkall, 2006). Then, the maximum traction effort is calculated as:

> *F mg* max

Where *µ* corresponds to the friction coefficient between the wheels and the rail, which is about 15% for the ERMTS, and gravity *g* equals to 9.8 m/s2 (Buhrkall, 2006). The force

*dv F TM a TM TE v MR v B v*

Where *TE(v)* is the traction effort in an EMRTS that provides the necessary propulsion to exceed inertia and accelerate the vehicle, *MR(v)* is the movement resistance as an opposite force to the vehicle movement, *Be(v)* is the braking effort used to decelerate the vehicle and

The traction and braking effort act directly in the vehicle wheels edges. The movement

Where *k≈0.33* for passengers' vehicles, *∆v*≈15km/h is the wind velocity variation, *TM* is the total mass of the vehicle, and g the gravity. Table 1 presents the action forces in an EMRTS that makes its path between two passengers' stations. As a result, there are four regimens of operation: stopping, acceleration, constant velocity, and deceleration. This is how the difference between the traction effort, the movement resistance, and the braking effort, which are not velocity variants, represent the net force of the vehicle (Jong & Chang, 2005b).

Operative Regimen Net Force Velocity Stopping *TE(v) – MR(v) – Be(v)=0 v=0*  Acceleration *TE(v) – MR(v) – Be(v)>0 0 < v < vmax* Constant Velocity *TE(v) – MR(v) – Be(v)=0 v > 0*  Deceleration *TE(v) – MR(v) – Be(v)<0 0 < v < vmax*

Table 1. Net Force and Velocity as function of the Operative Regimen (Jong & Chang, 2005b)

The incremental acceleration (*ai*) is obtained from the net force and the total mass of the

needed to move a traction vehicle (*TM* times the acceleration (*a*)) is:

stop it permanently (Vukan, 2007).

**2.1.2 Computation of dynamic variables**

vehicle (Jong & Chang, 2005b) computed for each instant *t*, as:

resistance is given by:

*TM w n w M <sup>v</sup> p pas DYN* (2)

() () () *<sup>e</sup>*

3 3 <sup>2</sup> *MR v*( ) 10 2.5 10 *k v v TM <sup>g</sup>* (5)

*dt* (4)

*<sup>m</sup>* (3)

The model presented at section 2.1 allows the computation of the power consumption and travel time characteristics (*t, x*) for each train *i* in the railway line. Naturally, a railway line simulation must include a number *n* of passengers' stations and *k* trains travel in the line (go and return).

The integration of these characteristics requires modelling the mobility of passengers associated at each train. It can be simulated in a probabilistic way, computing the number of passengers coming up and leaving the train (*i*) in each passenger's station (*j*) and the stopping time of the train in each station. This first part, stated here as Module 1, uses the following parameters: the passengers' up (*rup*) and down (*rdown*) rates, and up (*tup*) and down (*tup*) times per passenger.

The number of passengers in the first station and the number of passengers waiting in each station (*paxwait*) are modelled as random variables of uniform distribution. As, the railway line simulation includes a number *n* of passengers' stations; Module 1 computes for each train *i* the number of passengers that the train transport between station *j* and *j+1* as:

Power System Modelling for Urban Massive Transportation Systems 185

On the other hand, Module 2 considers the maximum velocity, the braking and traction effort curves as input variables. These curves are parameterized by means of (1), (2), and (3) and are given by manufacturers of traction equipment. Each curve is used to establish the net force at each operative regime, I to IV in Fig. 2. Fig. 4. shows an example of the simulation of placement and power consumption for a train in a metro line using a power

Finally, the simulation of Module 2 is run for the total number of *k* vehicles in the railway line, taking into account the dispatch time of each one. Then, the power consumption at each TS is computed as Fig. 5. shows. Each TS supplies the power to trains (going or returning)

Active Power (kW)

a) Graphical Interpretation of x(i,t) b) Graphical Interpretation of P(i,t)

<sup>0</sup> <sup>1000</sup> <sup>2000</sup> <sup>3000</sup> <sup>4000</sup> <sup>5000</sup> <sup>6000</sup> <sup>7000</sup> <sup>8000</sup> <sup>9000</sup> -1500

Time(s)

placed for its specific portion of the railway line (the DC section connected to the TS).

demand simulator reported at (Garcia et al., 2009).

<sup>0</sup> <sup>1000</sup> <sup>2000</sup> <sup>3000</sup> <sup>4000</sup> <sup>5000</sup> <sup>6000</sup> <sup>7000</sup> <sup>8000</sup> <sup>9000</sup> <sup>0</sup>

Time(s)

Fig. 4. Example of Simulation of Train *i* Travel – Module 2

Fig. 5. Simulation of Power Consumption of a Railway Line

Position(m)

$$\max\left(i,j\right) = \left(1 - r\_{down}\right) \times \max\left(i, j-1\right) + \max\_{unit}\left(j\right) \times r\_{up} \tag{11}$$

The number of passengers is constrained to be less or equal than the maximum capacity of passengers at the train. In addition, this module gives the stopping time for each train at each passenger's station (*tstop*(*i*,*j*)) based on passengers up and down times, as:

$$\mathbf{t}\_{stop}\left(\mathbf{i},j\right) = \mathbf{t}\_{down} \times \left(\mathbf{1} - r\_{down}\right) \times \max(\mathbf{i},j-\mathbf{1}) + \mathbf{t}\_{up} \times \max\_{uuit}(j) \times r\_{up} \tag{12}$$

The second part of the model, called Module 2, simulates the overall travel of train *i*. This means, the simulation gives the power consumption of train *i* for each instant of time *t* for a complete travel (go and return). At the same time, the placement (*x***(***t***)**) of the train is get for each *t*. If the line railway has a length *L*, then the total travel of one train is *2L*, and *x* will be between *0* and *L* in one sense and between *L* and *0* in the another sense.

So, Module 2 computes the train's time of travel between passengers' stations and the instantaneous power demand for one train based on equations (1) to (10) and the number of passengers and stopping time obtained from (11) and (12), respectively; as Fig. 3 shows. As, it is shown, the simulation considers the initial dispatch time and computes the initial value of passengers using the second term of equation (11).

Fig. 3. Simulation of Train *i* Travel – Module 2

The number of passengers is constrained to be less or equal than the maximum capacity of passengers at the train. In addition, this module gives the stopping time for each train at

The second part of the model, called Module 2, simulates the overall travel of train *i*. This means, the simulation gives the power consumption of train *i* for each instant of time *t* for a complete travel (go and return). At the same time, the placement (*x***(***t***)**) of the train is get for each *t*. If the line railway has a length *L*, then the total travel of one train is *2L*, and *x* will be

So, Module 2 computes the train's time of travel between passengers' stations and the instantaneous power demand for one train based on equations (1) to (10) and the number of passengers and stopping time obtained from (11) and (12), respectively; as Fig. 3 shows. As, it is shown, the simulation considers the initial dispatch time and computes the initial value

each passenger's station (*tstop*(*i*,*j*)) based on passengers up and down times, as:

between *0* and *L* in one sense and between *L* and *0* in the another sense.

Computation the travel of train *i* between stations *j* and *j+1* using (1) to (8)

Computation of power consumption travel of train *i* between stations *j* and *j+1* using (9) and (10) considering the Operative Regimen (Table 1)

> Update travel vectors: Placement x(i,t) Power Consumption P(i,t) Update Total travel time

Fig. 3. Simulation of Train *i* Travel – Module 2

of passengers using the second term of equation (11).

Initial data: Placement of passenger's stations *x(j)* Train characteristics (number of wagons, axles and motors; weight of wagons, axles and motors), efficiency of the regenerative braking.

, 1 ( , 1) ( ) *down wait up pax i j r pax i j pax j r* (11)

, 1 (, 1) ( ) *stop down down up wait up t i j t r pax i j t pax j r* (12)

Simulation for Train *i* Initial values: Passenger station *j*=1 Computes *pax(i,j)* Total travel time=*tdispatch*

> Last Passengers' station?

Add to Total travel time the stopping time of train *i* at station *j+1.* Computes *pax(i,j+1)*.

End

yes

j = j +1

no

On the other hand, Module 2 considers the maximum velocity, the braking and traction effort curves as input variables. These curves are parameterized by means of (1), (2), and (3) and are given by manufacturers of traction equipment. Each curve is used to establish the net force at each operative regime, I to IV in Fig. 2. Fig. 4. shows an example of the simulation of placement and power consumption for a train in a metro line using a power demand simulator reported at (Garcia et al., 2009).

Finally, the simulation of Module 2 is run for the total number of *k* vehicles in the railway line, taking into account the dispatch time of each one. Then, the power consumption at each TS is computed as Fig. 5. shows. Each TS supplies the power to trains (going or returning) placed for its specific portion of the railway line (the DC section connected to the TS).

Fig. 4. Example of Simulation of Train *i* Travel – Module 2

Fig. 5. Simulation of Power Consumption of a Railway Line

Power System Modelling for Urban Massive Transportation Systems 187

In this section, a methodology of placement and sizing of traction substations under an electric connection scheme, in which high reliable levels are guaranteed, is presented. In this scheme, each traction substation (TS) is able to support the load of each adjacent substation. That means that in the case when a fault occurs in one TS, there is a support system based on automatic switches normally opened that close and allow the two neighbour substations to supply the power to the associated load with the faulted substation (each one would feed half of the load of the faulted one). The input data to calculate the sizing of substation is obtained from the power demand computation,

On the other hand, the placement of each TS is obtained by a heuristic optimization problem. This problem minimizes the total cost of a given configuration, that is composed of investment costs (rectifiers, transformers, and protection and control cells), the cost of energy losses composed by AC losses (associated with the transformer) and DC losses (associated to rectifiers) and the failure cost, that represents the cost of the annual expected

A scheme of supply of an urban railway system must satisfy electric conditions, such as: operating limits, voltage drops through the catenaries or third rail (called here, in general, DC section), and maximum capacity of transformers. These conditions must be satisfied for supplying the power demand independently of the operating state of the system, i.e., normal state or a post-contingency state after a fault of a HV/MV substation, or TS, or one DC section. So, the TS location and configuration's selection are strongly linked problems. Fig. 8 shows three possible schemes of connection of the MV network to a set of TS. Each TS

The way of behave in a fault condition determines the following three possible

1. **One transformer-rectifier unit with possibility of power supply from the adjacent TS**. Each TS acts as a support of its adjacent TS. This implies that the substations must be able to supply at least 1.5 times the length of the normal DC section length (3L/2). 2. **Two transformer-rectifier units in each traction substation**. This configuration means the redundancy in the main equipment of the TS. In case of a fault in one transformer and/or rectifier, the parallel unit must supply the total power demand of the TS. This scheme assumes that there is not possibility of support of adjacent substations. The wide dotted line if Fig. 8 remarks the parallel unit of transformer-

3. **Two transformer-rectifier units in each TS and support of adjacent DC section**. This is the combination of configurations 1 and 2. This means that there is redundancy in each traction substation and there is also possibility of support of adjacent DC section

is designed to supply (in normal operation state) a DC sector of length L.

**3. Placement and sizing traction (rectifier) substations in urban railway**

**systems**

explained in the previous section.

energy not supplied (EENS).

configurations:

rectifier unit.

feeder.

**3.1 Traction substation (TS) configurations**

### **2.3 Simulation example**

This section illustrates the application of the power consumption mathematical and simulation model in a possible metro line for the city of Bogota of 13.2 km and 13 passenger stations. Fig. 6 shows one section of the possible line 1 to be developed in Bogotá. Fig. 7. presents the results of a simulation of the Metro Line of Fig. 6 using the previous algorithms.

Fig. 6. Example Case of Power Consumption for a Metro Line

Fig. 7. Power Demand of a Traction Substation – Estimation by Simulation

The simulation establishes the trajectories of 17 trains-vehicles at the Metro Line (Fig. 7.a). The power is supplied by 3 TS. Fig. 7.b shows the power demand at the first traction substation that supplies all trains placed between position 0<x(t)<4400 m.

This section illustrates the application of the power consumption mathematical and simulation model in a possible metro line for the city of Bogota of 13.2 km and 13 passenger stations. Fig. 6 shows one section of the possible line 1 to be developed in Bogotá. Fig. 7. presents the results of a simulation of the Metro Line of Fig. 6 using the

Calle\_19

<sup>0</sup> <sup>1000</sup> <sup>2000</sup> <sup>3000</sup> <sup>4000</sup> <sup>5000</sup> <sup>6000</sup> <sup>7000</sup> <sup>8000</sup> <sup>9000</sup> -2000

(seg)

Consumo de Potencia de la Subestacion Rectificadora No: 1

NQS

Av\_Carrera\_22

Plaza\_Bolivar

Zona \_Industrial

**2.3 Simulation example**

previous algorithms.

Portal\_Am

ericas Kennedy Tim

 iza

> A

v\_Villavicencio

Plaza\_Am

Fig. 6. Example Case of Power Consumption for a Metro Line

Av\_68

Canal\_Fucha

a) Train's Trajectories x(i,t) b) Power Demand P(i,t) substation 1

The simulation establishes the trajectories of 17 trains-vehicles at the Metro Line (Fig. 7.a). The power is supplied by 3 TS. Fig. 7.b shows the power demand at the first traction

Fig. 7. Power Demand of a Traction Substation – Estimation by Simulation

substation that supplies all trains placed between position 0<x(t)<4400 m.

(kW)

Tranv\_49A

 ericas

### **3. Placement and sizing traction (rectifier) substations in urban railway systems**

In this section, a methodology of placement and sizing of traction substations under an electric connection scheme, in which high reliable levels are guaranteed, is presented. In this scheme, each traction substation (TS) is able to support the load of each adjacent substation. That means that in the case when a fault occurs in one TS, there is a support system based on automatic switches normally opened that close and allow the two neighbour substations to supply the power to the associated load with the faulted substation (each one would feed half of the load of the faulted one). The input data to calculate the sizing of substation is obtained from the power demand computation, explained in the previous section.

On the other hand, the placement of each TS is obtained by a heuristic optimization problem. This problem minimizes the total cost of a given configuration, that is composed of investment costs (rectifiers, transformers, and protection and control cells), the cost of energy losses composed by AC losses (associated with the transformer) and DC losses (associated to rectifiers) and the failure cost, that represents the cost of the annual expected energy not supplied (EENS).

### **3.1 Traction substation (TS) configurations**

A scheme of supply of an urban railway system must satisfy electric conditions, such as: operating limits, voltage drops through the catenaries or third rail (called here, in general, DC section), and maximum capacity of transformers. These conditions must be satisfied for supplying the power demand independently of the operating state of the system, i.e., normal state or a post-contingency state after a fault of a HV/MV substation, or TS, or one DC section. So, the TS location and configuration's selection are strongly linked problems. Fig. 8 shows three possible schemes of connection of the MV network to a set of TS. Each TS is designed to supply (in normal operation state) a DC sector of length L.

The way of behave in a fault condition determines the following three possible configurations:

Power System Modelling for Urban Massive Transportation Systems 189

1 ( ) , , *m op Energy loss loss i C j Cost j AC i j DC i j*

*loss iron loss copper loss*

On the other hand, the DC losses are power losses in the rectifiers (AC/DC converters):

*P i <sup>j</sup> <sup>t</sup> AC i j t P i UF j t P i P i*

 0

*To loss dem*

0

instantaneous demanded power (*Pdem(i,j,t)*) and the transformer rating (*Pnom*).

*cooper loss nom Cu nom Cu*

*o*

power demanded at year *j* hour *t*. It varies from 95.4% to 95.7% (Hill, 2006).

**3.3 Technical constraints**

\* In the case of regenerative braking, 800 V is admissible. \*\* In the case of regenerative braking, 800 V is admissible. Table 2. Voltages in DC Traction Systems (White, 2009).

*o*

*To*

*To* is the operation time of the urban rail during the year. The "iron losses" in the transformer are constant (Institution of Electrical and Electronic Engineers [IEEE], 2007) and computed as it is established in (IEEE, 1992). The "copper losses" are directly proportional to the square of the utilization factor (*UF*), and the constant of proportionality is the nominal copper losses of the transformer (*Pnom\_Cu*) (IEEE, 2007). The *UF* is defined as the ratio of

<sup>1</sup> , , (, ,)

*AC i j AC i j AC i j t dt <sup>T</sup>* (16)

*DC i j eff i j t P i j t dt <sup>T</sup>* (18)

*C T PC ENS NS av fault* (19)

2 \_ \_ (, ,) (, ,) ( ( , )) *dem*

<sup>1</sup> , 1 ( , , ) ( , , ))

The *eff(i,j,t)* is the DC efficiency of the rectifier of the TS *i* and depends on the instantaneous

The third term of the objective function of the minimization problem is the cost of energy not supplied (*CENS*), computed as function of the time of no-supply in hours/year (*TNS*), the unitary cost of fault in USD\$/kWh (*Cfault*) and the average power not supplied by TS (*Pav*):

The voltage drop between a supply point and a utilization point must not be more than 15% in normal operation and as maximum 30% in special cases (Arriagada & Rudnick, 1994). These specials cases may be the outage of a substation or the last DC section in the route. Table 2 presents the voltage margins according to the different used DC system voltages.

DC system voltage (V)<PHONE_NUMBER> 3000 Lowest voltage. Undefined duration (V)<PHONE_NUMBER> 2000 Nominal design system voltage (V)<PHONE_NUMBER> 3000 Highest voltage. Undefined duration (V)<PHONE_NUMBER> 3600 Not-permanent highest voltage. Duration of 5 minutes (V) 770\* 950\*\* 1950 3900

2

(17)

*nom*

(15)

Fig. 8. Configurations of Traction Substations' Connection

#### **3.2 Optimization problem**

A minimization of the total project cost is solved for determining the quantity of traction substations, their connection configurations, and their locations. The optimization is a constrained problem that guarantees the electrical requirements, like voltage levels and high reliability requirements. The distance between TS is assumed to be equal, and each TS is located at the middle point of the DC section that it supplies, as Fig. 8 shows.

The cost function (*TC*) includes investment costs, operation costs *Cop* (associated with losses) and reliability cost or cost of energy not supplied (*CENS*). So, the total cost for each configuration is given by:

$$TC = C\_{inv} + \sum\_{j=1}^{T} \left( \frac{C\_{op}(j)}{(1+r)^j} + \frac{C\_{ENS}(j)}{(1+r)^j} \right) \tag{13}$$

Where *T* is the number of years of the project, and *r* is the discount rate of the project. The investment cost depends on the length of the DC network, and is given by:

$$\mathbf{C}\_{inv} = \left(\mathbf{L}\_{cat} \times \mathbf{C}\_{cat}\right) + \sum\_{i=1}^{m} \left(\mathbf{N}\_{Mod}(i) \times \mathbf{C}\_{Mod}(i) + \mathbf{C}\_{Place}(i)\right) \tag{14}$$

Where, *Lcat* and *Ccat* are the total length and the unitary cost of the catenaries or rail (DC section, in general). *NMod* is the number of modules in one traction substation (1 or 2). *CMod* is the cost associated to one module; *Cplace* is the cost of the terrain where the substation is built; *m* is the number of substations.

The annual operation cost (*Cop(j)*) is computed as the sum of annual AC and DC losses in the year *j* multiplied by the energy cost. Transformer losses are defined as the sum of the instantaneous iron losses (*ACiron-loss*) and copper losses (*ACcopper-loss*) during the year. Then, the total losses cost for *m* substations is:

A minimization of the total project cost is solved for determining the quantity of traction substations, their connection configurations, and their locations. The optimization is a constrained problem that guarantees the electrical requirements, like voltage levels and high reliability requirements. The distance between TS is assumed to be equal, and each TS is

The cost function (*TC*) includes investment costs, operation costs *Cop* (associated with losses) and reliability cost or cost of energy not supplied (*CENS*). So, the total cost for each

> ( ) ( ) (1 ) (1 )

(14)

(13)

*op ENS*

*inv j j <sup>j</sup> C j C j TC C*

( ) () () ()

Where *T* is the number of years of the project, and *r* is the discount rate of the project. The

*C L C N iC iC i*

Where, *Lcat* and *Ccat* are the total length and the unitary cost of the catenaries or rail (DC section, in general). *NMod* is the number of modules in one traction substation (1 or 2). *CMod* is the cost associated to one module; *Cplace* is the cost of the terrain where the substation is built;

The annual operation cost (*Cop(j)*) is computed as the sum of annual AC and DC losses in the year *j* multiplied by the energy cost. Transformer losses are defined as the sum of the instantaneous iron losses (*ACiron-loss*) and copper losses (*ACcopper-loss*) during the year. Then, the

*r r*

1

1

*i*

*m inv cat cat Mod Mod Place*

*T*

located at the middle point of the DC section that it supplies, as Fig. 8 shows.

investment cost depends on the length of the DC network, and is given by:

Fig. 8. Configurations of Traction Substations' Connection

**3.2 Optimization problem**

configuration is given by:

*m* is the number of substations.

total losses cost for *m* substations is:

$$\text{CC}\_{op}(j) = \text{Cost}\_{Energy}(j) \times \sum\_{i=1}^{m} \left( A \text{C}\_{loss} \left( i, j \right) + D \text{C}\_{loss} \left( i, j \right) \right) \tag{15}$$

$$AC\_{loss}\left(\mathbf{i}\_{\prime},\mathbf{j}\right) = \frac{1}{T\_o} \times \int\_0^{To} \left(AC\_{iron-loss}\left(\mathbf{i}\_{\prime},\mathbf{j}\right) + AC\_{copper-loss}\left(\mathbf{i}\_{\prime},\mathbf{j},\mathbf{t}\right)\right) d\mathbf{t} \tag{16}$$

*To* is the operation time of the urban rail during the year. The "iron losses" in the transformer are constant (Institution of Electrical and Electronic Engineers [IEEE], 2007) and computed as it is established in (IEEE, 1992). The "copper losses" are directly proportional to the square of the utilization factor (*UF*), and the constant of proportionality is the nominal copper losses of the transformer (*Pnom\_Cu*) (IEEE, 2007). The *UF* is defined as the ratio of instantaneous demanded power (*Pdem(i,j,t)*) and the transformer rating (*Pnom*).

On the other hand, the DC losses are power losses in the rectifiers (AC/DC converters):

$$AC\_{\text{copper}-loss}(i, j, t) = P\_{\text{nom\\_Cu}}(i) \times \left( \text{LIF}(j, t) \right)^2 = P\_{\text{nom\\_Cu}}(i) \times \left( \frac{P\_{\text{dem}}(i, j, t)}{P\_{\text{nom}}(i)} \right)^2 \tag{17}$$

$$DC\_{loss}\left(i,j\right) = \frac{1}{T\_o} \times \int\_0^{T\_o} \left(1 - \epsilon \mathcal{G}\left(i,j,t\right)\right) \times P\_{dem}\left(i,j,t\right) \right) dt\tag{18}$$

The *eff(i,j,t)* is the DC efficiency of the rectifier of the TS *i* and depends on the instantaneous power demanded at year *j* hour *t*. It varies from 95.4% to 95.7% (Hill, 2006).

The third term of the objective function of the minimization problem is the cost of energy not supplied (*CENS*), computed as function of the time of no-supply in hours/year (*TNS*), the unitary cost of fault in USD\$/kWh (*Cfault*) and the average power not supplied by TS (*Pav*):

$$\mathbf{C}\_{\rm ENS} = T\_{\rm NS} \times P\_{\rm av} \times \mathbf{C}\_{\rm fault} \tag{19}$$

#### **3.3 Technical constraints**

The voltage drop between a supply point and a utilization point must not be more than 15% in normal operation and as maximum 30% in special cases (Arriagada & Rudnick, 1994). These specials cases may be the outage of a substation or the last DC section in the route. Table 2 presents the voltage margins according to the different used DC system voltages.

\* In the case of regenerative braking, 800 V is admissible.

\*\* In the case of regenerative braking, 800 V is admissible.

Table 2. Voltages in DC Traction Systems (White, 2009).

Power System Modelling for Urban Massive Transportation Systems 191

*P P t It Lt It Lt*

*Ij* is the current in each DC section that is defined as the catenaries/rail between two vehicles or between a vehicle and the TS (in the case of the nearest vehicle to the feeding point of the TS). The total losses at the DC section takes into account all vehicles placed at left and right of the TS. is the resistivity of the DC section [Ω/km or Ω/mi]; *To* is the total annual operation time.

The analysis was developed for the metro line showed in Fig. 6 corresponding to the study case of section 2.3. The study was developed as function of the number of substations and

The unitary cost of fault was assumed 1074 US\$/kWh, from reliability analysis. Simulations were done for three levels of load: high (the maximum number of vehicles in service), medium (half of the total vehicles in service), and low (with no vehicles in service). The simulator allows the calculation of power losses in N-0 state, and the demand of each

Simple contingencies (N-1) at the maximum load were made in order to sizing the TS when configurations 1 and 3 are used, to give support of adjacent TS. While, normal state

Table 3 presents the total cost computed as function of the number of TS and configuration of connection. Additionally, the investment cost (C\_inv) and the net present value of the

The investment cost (without the cost of catenaries/rail that is common for all alternatives), noted C\_inv, includes the switchgear in SF6, rectifiers, transformers, having into account the number of each equipment depending on the configuration (see Fig. 8). The NPV\_Oper

In the second column, in brackets, the rating commercial capacity of each substation is shown, based on the results of simulations and the algorithm for finding catenaries/rail losses. The capacities of each substation for configurations 1 and 3 are the same, due to the

> 1 (5MW) 8.8 6.11 0.81 7.95 2 (4 MW) 4.4 9.75 1.63 12.4 3 (5MW) 8.8 11.9 1.62 14.5

1 (5 MW) 6.6 6.73 0.90 8.65 2 (3.75MW) 3.3 12.3 1.79 15.1 3 (5 MW) 6.6 13.0 1.79 15.8

1 (3.75MW) 5.28 7.97 0.98 9.97 2 (3.75MW) 2.64 14.3 1.97 17.3 3 (3.75MW) 5.28 15.4 1.96 18.3

operation cost (NPV\_Oper) is shown. The fault cost was of 155.000 USD\$/year.

Maximum length of catenary/rail (km)

Table 3. Cost Comparison of Several Configuration of TS's Connections – Study Case

includes the operation cost for a useful life of the project of 20 years.

2 2

(26)

Millions of dollars C\_inv NPV\_Oper Total Cost

() () () () ()

'

**3.4 Application to the study case**

the three possible configurations explained in section 3.1.

substation for N-0 and N-1 contingencies state.

operation was used for sizing TS in configuration 2.

high electrical similitude between both schemes.

#TS's Configuration

3

4

5

(rating/TS)

*To To n n LOSS loss j j j j t tj j*

0 01 1

A voltage drop of 30% between the TS and the last vehicle can be tolerated in a suburban system, where the vehicles are constantly accelerating, but a voltage drop over the principal line of a *metro* during any time interval might exceed all the established limits. Therefore, the maximum voltage drop allowed is limited to 15% on nominal voltages under normal conditions. A voltage drop in the farthest point of a section supplied by TS is defined as:

$$V\_T = V\_S - L\_2 Z n I - Z\_x (n + n') I - \frac{1}{4} (Z n \times I \times L \text{Cat}(i) - Z \times L\_2) \tag{20}$$

$$Z\_x = (R\_u + R\_T)\cos\phi + (X\_u + X\_T)\sin\phi \quad \text{and} \quad Z = R\cos\phi + X\sin\phi \tag{21}$$

Where *Vs* is the DC voltage at the TS (p.u), *VT* is the minimum DC voltage in the DC section for correct vehicle operation (p.u.); *I* is the current demanded by a vehicle (p.u.); *Ru* and *Xu* are the equivalent resistance and reactance, respectively (p.u.); *RT* and *XT* are the transformer resistance and reactance, respectively (p.u.); is the angle of power factor (zero for DC systems); *R* and *X* are the DC section resistance and reactance, including the return way, in p.u./mi; *L2* is the distance between the TS and the nearest vehicle at the right; *n* and *n'* are the number of vehicles at the right and the left, respectively, of the TS.

Voltage drop in the farthest point is determined by the maximum length of the sector supplied. In normal conditions, this value is the length *L* (see Fig. 8). However, when a contingency occurs, the sector length must be modified to almost twice the original length. Then, for normal conditions, the voltage must satisfy:

$$V\_T \le V\_S(i) - Z(i, L \mid \mathcal{D}) \times I\_{TS}(i) \tag{22}$$

Where *ITS* is the current delivered by the TS depending on the number of vehicles in sector *i* supplied in a determined time by the substation. Under a contingency of the TS, the voltage must satisfy the constraint for the sector *i-1* and sector *i+1* (adjacent sectors):

$$V\_T(i \pm 1) \le V\_S(i \pm 1) - Z(i \pm 1, \Im L \ne 2) \times I\_{TS}(i \pm 1) \tag{23}$$

The minimum capacity of transformers and rectifiers is calculated from the maximum demanded current in each TS. The transformers and rectifiers size must be chosen as the nearest superior value to the demanded power, depending on the commercial capacities. As previously, normal conditions and post-contingency operation must be considered. In normal operation with 2 transformers, the power capacity of transformers must satisfy:

$$\Pr\left(\text{MVV}\left(\text{i}\right)\right) \ge I\_{\text{TS}}\left(\text{i}, L\right) \times V\_{\text{DC}} + P\_{\text{Loss}}\left(\text{L}\right) \tag{24}$$

Meanwhile, when the traction substation *i* is unavailable, the capacity of active power of the 2 transformers in the *i-1* and *i+1* sector must satisfy:

$$\Pr\left(\text{MWV}\right)\left(\mathbf{i}\pm\mathbf{1}\right) \ge I\_{\text{TS}}\left(\mathbf{i}\pm\mathbf{1}, \Im\left.\mathbf{L}\right/\mathbf{2}\right) \times V\_{\text{DC}} + P\_{\text{Loss}}\left(\Im\mathbf{L}/\mathbf{2}\right) \tag{25}$$

The capacity in MVA of the transformer is computed dividing the capacity in MW by the power factor (p.f.). As shown in (24) and (25), the power loss (*Ploss*) in the DC section feeder for the maximum demand must be determined for each section. The total power loss in DC section associated to the TS for a round trip is:

$$P\_{LOSS} = \sum\_{t=0}^{To} P\_{loss}(t) = \sum\_{t=0}^{To} \left[ \sum\_{j=1}^{n^\star} I\_j(t)^2 \times \rho \times L\_j(t) + \sum\_{j=1}^n I\_j(t)^2 \times \rho \times L\_j(t) \right] \tag{26}$$

*Ij* is the current in each DC section that is defined as the catenaries/rail between two vehicles or between a vehicle and the TS (in the case of the nearest vehicle to the feeding point of the TS). The total losses at the DC section takes into account all vehicles placed at left and right of the TS. is the resistivity of the DC section [Ω/km or Ω/mi]; *To* is the total annual operation time.

### **3.4 Application to the study case**

190 Infrastructure Design, Signalling and Security in Railway

A voltage drop of 30% between the TS and the last vehicle can be tolerated in a suburban system, where the vehicles are constantly accelerating, but a voltage drop over the principal line of a *metro* during any time interval might exceed all the established limits. Therefore, the maximum voltage drop allowed is limited to 15% on nominal voltages under normal conditions. A voltage drop in the farthest point of a section supplied by TS is defined as:

*Z R R X X and Z R X x uT uT* ( )cos ( )sin

Where *Vs* is the DC voltage at the TS (p.u), *VT* is the minimum DC voltage in the DC section for correct vehicle operation (p.u.); *I* is the current demanded by a vehicle (p.u.); *Ru* and *Xu* are the equivalent resistance and reactance, respectively (p.u.); *RT* and *XT* are the transformer

systems); *R* and *X* are the DC section resistance and reactance, including the return way, in p.u./mi; *L2* is the distance between the TS and the nearest vehicle at the right; *n* and *n'* are

Voltage drop in the farthest point is determined by the maximum length of the sector supplied. In normal conditions, this value is the length *L* (see Fig. 8). However, when a contingency occurs, the sector length must be modified to almost twice the original length.

Where *ITS* is the current delivered by the TS depending on the number of vehicles in sector *i* supplied in a determined time by the substation. Under a contingency of the TS, the voltage

The minimum capacity of transformers and rectifiers is calculated from the maximum demanded current in each TS. The transformers and rectifiers size must be chosen as the nearest superior value to the demanded power, depending on the commercial capacities. As previously, normal conditions and post-contingency operation must be considered. In normal operation with 2 transformers, the power capacity of transformers must satisfy:

Meanwhile, when the traction substation *i* is unavailable, the capacity of active power of the

The capacity in MVA of the transformer is computed dividing the capacity in MW by the power factor (p.f.). As shown in (24) and (25), the power loss (*Ploss*) in the DC section feeder for the maximum demand must be determined for each section. The total power loss in DC

the number of vehicles at the right and the left, respectively, of the TS.

must satisfy the constraint for the sector *i-1* and sector *i+1* (adjacent sectors):

resistance and reactance, respectively (p.u.);

Then, for normal conditions, the voltage must satisfy:

2 transformers in the *i-1* and *i+1* sector must satisfy:

section associated to the TS for a round trip is:

2 2

<sup>1</sup> ( ') ( () ) <sup>4</sup> *V V L Zn I Z n n I Zn I LCat i Z L T S <sup>x</sup>* (20)

( ) ( , /2) ( ) *V V i ZiL I i T S TS* (22)

( 1) ( 1) ( 1,3 / 2) ( 1) *V i V i Zi L I i <sup>T</sup> <sup>S</sup> TS* (23)

( )( ) ( , ) ( ) *CapT MW i I i L V P L TS DC Loss* (24)

( )( 1) ( 1,3 / 2) (3 /2) *CapT MW i I i L V P L TS DC Loss* (25)

cos sin (21)

is the angle of power factor (zero for DC

The analysis was developed for the metro line showed in Fig. 6 corresponding to the study case of section 2.3. The study was developed as function of the number of substations and the three possible configurations explained in section 3.1.

The unitary cost of fault was assumed 1074 US\$/kWh, from reliability analysis. Simulations were done for three levels of load: high (the maximum number of vehicles in service), medium (half of the total vehicles in service), and low (with no vehicles in service). The simulator allows the calculation of power losses in N-0 state, and the demand of each substation for N-0 and N-1 contingencies state.

Simple contingencies (N-1) at the maximum load were made in order to sizing the TS when configurations 1 and 3 are used, to give support of adjacent TS. While, normal state operation was used for sizing TS in configuration 2.

Table 3 presents the total cost computed as function of the number of TS and configuration of connection. Additionally, the investment cost (C\_inv) and the net present value of the operation cost (NPV\_Oper) is shown. The fault cost was of 155.000 USD\$/year.

The investment cost (without the cost of catenaries/rail that is common for all alternatives), noted C\_inv, includes the switchgear in SF6, rectifiers, transformers, having into account the number of each equipment depending on the configuration (see Fig. 8). The NPV\_Oper includes the operation cost for a useful life of the project of 20 years.

In the second column, in brackets, the rating commercial capacity of each substation is shown, based on the results of simulations and the algorithm for finding catenaries/rail losses. The capacities of each substation for configurations 1 and 3 are the same, due to the high electrical similitude between both schemes.

Table 3. Cost Comparison of Several Configuration of TS's Connections – Study Case

Power System Modelling for Urban Massive Transportation Systems 193

Fig. 9. PQ Phenomena and Railways' Electrical System Components Relationships

The identification of PQ problems in power systems represents an important issue to the distribution utilities. The harmonic distortion is one of the main PQ phenomena in the electrical system feeding an EMRTS because the injection of harmonics by its nonlinear loads flows through the network and affects other consumers connected to the distribution system. According to the conceptual diagram of Fig. 9, the production of harmonics in the EMRTS is a PQ phenomenon at steady state caused by the rectifier substations, normally, a

In addition, the computation of the total harmonic distortion (THD) in the AC side of the rectifier substation at the railway system must take into account the time load variability at each TS. So, the instantaneous power load must be computed as function of time and distance as it was explained at section 2. Once the current consumption in each TS is

Generally, deterministic models have been adopted for network harmonic analysis; however, these models can fail for modelling the load variation in systems such as the railways' electrical system (Chang et al., 2009). So, a probabilistic analysis to characterize the harmonic current loads properly must be used in order to obtain an accurate model.

An EMRTS is characterized by fluctuating loads due to the different operation states of the trains in the traction system (See Fig. 7 b). Thus, the harmonics injection from the rectifier substations to the MV network causes that the current harmonic spectrum at the distribution system's connection point (PCC) varies over time. So, each traction substation can be represented as a harmonic current source that provides a probabilistic spectral content at the

obtained, it is possible to identify the variation of the THD during the time.

**4.2 Harmonic distortion analysis**

controlled rectifier of 6 or 12 pluses.

**4.2.1 Probabilistic model**

PCC (Rios et al., 2009).

The third column shows the maximum length of the DC section that each TS can supply. TS in configurations 1 and 3 must have a capacity to supply even twice the total length of the line divided by the number of considered substations. Instead, TS in configuration 2 supply the maximum length of catenaries/rail, just the normal operation length because this configuration is not able of supporting of adjacent substation in case of fault.

The lowest total cost at Table 3 is presented in the case of three 5 MW TS because, in the study case of section 2.3, the investment cost weights more in the final cost than the operation cost. That is, looking just the configuration 1, it is evident that even though the operation costs do not grow up linearly as more TS are considered, the difference between investment costs is higher than operation costs, so the optimal solution is the location of 3 TS of 5 MW, under the configuration 1.

### **4. Power quality impact of urban railway systems on distribution systems**

Power quality phenomena originated in power distribution systems impacts on the electrical power supply system of UMTS and, at the same time, power electronics used in the traction system impacts on the power quality (PQ) service of the distribution system.

In addition, the power demand of UMTS presents high and fast variations as consequence of the operation cycles of each train-vehicle and the non-coincidence of operational cycles among several vehicles. So, PQ phenomena are time variable (Singh et al., 2006).

### **4.1 PQ Phenomena and railways' electrical system components**

Fig. 9 shows the existing relationships between the different PQ phenomena and the railways' electrical system components. As it is shown, the main electrical components in the railway system are: the train-vehicle as an electric load that involves a great use of power electronics, rectifier substations, the electric HV/MV substation, and the distribution network system (White, 2008).

On the other hand, the main PQ phenomena involved in the interaction between the railways' electrical systems and the power distribution system are: electromagnetic interference (EMI/RFI) at high frequency (HF); harmonics, flicker, and voltage regulation at low frequency (LF) (Sutherland et al., 2006). Also, PQ phenomena include sags at instantaneous regime, unbalance of the three-phase power system, and transients' phenomena (Lamedica et al., 2004).

Fig. 9 (Garcia & Rios, 2010) presents also where the cause of the phenomena is, what are the affected or perturbed systems, and where a solution of the problem can be implemented. For example, the electromagnetic transients occur in microseconds and they are caused by capacitor switching or lightning. Hence, they can be generated in the distribution network, MV side of the rectifier substation or in the train (represented by X in Fig. 9). The main problems are related to the rectifier substation or the train (represented by circle in Fig. 10) where the electronic sensitive equipment are susceptible to misuse or damage due to the transient overvoltage. An effective overvoltage transient protection could be located at the rectifier substation and, finally, at the train (represented by triangle Fig. 9).

Fig. 9. PQ Phenomena and Railways' Electrical System Components Relationships

### **4.2 Harmonic distortion analysis**

192 Infrastructure Design, Signalling and Security in Railway

The third column shows the maximum length of the DC section that each TS can supply. TS in configurations 1 and 3 must have a capacity to supply even twice the total length of the line divided by the number of considered substations. Instead, TS in configuration 2 supply the maximum length of catenaries/rail, just the normal operation length because this

The lowest total cost at Table 3 is presented in the case of three 5 MW TS because, in the study case of section 2.3, the investment cost weights more in the final cost than the operation cost. That is, looking just the configuration 1, it is evident that even though the operation costs do not grow up linearly as more TS are considered, the difference between investment costs is higher than operation costs, so the optimal solution is the location of 3 TS

**4. Power quality impact of urban railway systems on distribution systems**

Power quality phenomena originated in power distribution systems impacts on the electrical power supply system of UMTS and, at the same time, power electronics used in the traction system impacts on the power quality (PQ) service of the distribution

In addition, the power demand of UMTS presents high and fast variations as consequence of the operation cycles of each train-vehicle and the non-coincidence of operational cycles

Fig. 9 shows the existing relationships between the different PQ phenomena and the railways' electrical system components. As it is shown, the main electrical components in the railway system are: the train-vehicle as an electric load that involves a great use of power electronics, rectifier substations, the electric HV/MV substation, and the distribution

On the other hand, the main PQ phenomena involved in the interaction between the railways' electrical systems and the power distribution system are: electromagnetic interference (EMI/RFI) at high frequency (HF); harmonics, flicker, and voltage regulation at low frequency (LF) (Sutherland et al., 2006). Also, PQ phenomena include sags at instantaneous regime, unbalance of the three-phase power system, and transients'

Fig. 9 (Garcia & Rios, 2010) presents also where the cause of the phenomena is, what are the affected or perturbed systems, and where a solution of the problem can be implemented. For example, the electromagnetic transients occur in microseconds and they are caused by capacitor switching or lightning. Hence, they can be generated in the distribution network, MV side of the rectifier substation or in the train (represented by X in Fig. 9). The main problems are related to the rectifier substation or the train (represented by circle in Fig. 10) where the electronic sensitive equipment are susceptible to misuse or damage due to the transient overvoltage. An effective overvoltage transient protection could be located at the rectifier substation and, finally, at the train (represented

among several vehicles. So, PQ phenomena are time variable (Singh et al., 2006).

**4.1 PQ Phenomena and railways' electrical system components**

configuration is not able of supporting of adjacent substation in case of fault.

of 5 MW, under the configuration 1.

network system (White, 2008).

phenomena (Lamedica et al., 2004).

by triangle Fig. 9).

system.

The identification of PQ problems in power systems represents an important issue to the distribution utilities. The harmonic distortion is one of the main PQ phenomena in the electrical system feeding an EMRTS because the injection of harmonics by its nonlinear loads flows through the network and affects other consumers connected to the distribution system. According to the conceptual diagram of Fig. 9, the production of harmonics in the EMRTS is a PQ phenomenon at steady state caused by the rectifier substations, normally, a controlled rectifier of 6 or 12 pluses.

In addition, the computation of the total harmonic distortion (THD) in the AC side of the rectifier substation at the railway system must take into account the time load variability at each TS. So, the instantaneous power load must be computed as function of time and distance as it was explained at section 2. Once the current consumption in each TS is obtained, it is possible to identify the variation of the THD during the time.

### **4.2.1 Probabilistic model**

Generally, deterministic models have been adopted for network harmonic analysis; however, these models can fail for modelling the load variation in systems such as the railways' electrical system (Chang et al., 2009). So, a probabilistic analysis to characterize the harmonic current loads properly must be used in order to obtain an accurate model.

An EMRTS is characterized by fluctuating loads due to the different operation states of the trains in the traction system (See Fig. 7 b). Thus, the harmonics injection from the rectifier substations to the MV network causes that the current harmonic spectrum at the distribution system's connection point (PCC) varies over time. So, each traction substation can be represented as a harmonic current source that provides a probabilistic spectral content at the PCC (Rios et al., 2009).

Power System Modelling for Urban Massive Transportation Systems 195

Then, a process called "Vector Sum - Phasor" is run through Monte Carlo simulations. Finally, the probabilistic characterization is obtained; where the probability distribution function of current THD, the probability distribution function of rms current and the

Table 10.3 of Std. IEEE - 519 (IEEE, 1993) contains the current distortion limits in the voltage range of 120 V to 69 kV, which applies for typical railways' electrical systems connected to distribution systems at MV. So, based on this standard, a comparison between the current distortion levels at 95% and 50% of probability and the given limits must be realized to assess if the current distortion must be reduced or not. If a current THD distortion must be reduced, it could be used several filters methods. The next section presents the application

The harmonic distortion produced by railways' systems at the distribution system's connection point can be reduced using passive or active power filters (APF). However, due to the random and time variability of the harmonic distortion in traction systems, it is required an active power compensation with the ability of adaptation to different load conditions. Passive filters are designed with fixed parameters and for specific harmonics, so this type of filter does not have the required ability. By contrast, APFs based on the p-q theory became an effective solution in traction systems; normally, they are used for dynamic harmonic suppression (Xu & Chen, 2009). This type of compensation presents the advantage

On the other hand, the traction system has several rectifier substations and from the economic point of view it is difficult to install an APF in each TS due to its high cost. Then, it is necessary to allocate APFs in the most sensitive positions in the own power system of the EMRTS using the least number of filters and minimizing their size. An important factor to be considered in the decision of harmonic compensation in traction system is the sudden fluctuation of traction load because this dynamic behavior is also observed in the harmonic

The allocation methodology of APFs in distribution systems supplying a traction load is based on probabilistic data of harmonic distortion presented in all traction substations. According to the Std. IEEE - 519 (IEEE, 1993), using a 15 minutes time interval it is enough to understand the dynamic behavior of the traction load because in this interval there are 900 different data of the load behaviour in each TS. Fig. 11 shows the proposed

As, it was shown in section 3.4, for the study case of this Chapter, the metro line can be supplied by three TS at MV. The total harmonic distortion in the distribution system is analyzed with and without active compensation. The APF is allocated in the low voltage side of the transformer in the TS. As, the railway line has three TS, there are seven possible

Table 4 shows the THD distortion at levels of 50% and 95% of probability when the system is without active power compensation and when APFs compensation is used according to the seven different configurations. This table shows the effectiveness of the APFs to reduce

probability distribution of each harmonic component are obtained.

of active power filtering to reduce THD distortion.

**4.2.2 Active power filter allocation methodology**

of eliminating a wide range of harmonics simultaneously.

distortion, as it has been explained in the previous section.

methodology of allocation of APF in urban railways systems.

allocations of APF, as Table 4 shows at the first column.

Then, it is necessary to perform the vector sum of several harmonic sources (i.e. traction substations) at the distribution system's connection point to determine the total harmonic distortion. There are two methods to evaluate the effect of different non-linear loads: the analytical method and Monte Carlo simulation method. The complex implementation of analytical methods for large power systems studies involves little practical application in real systems. By contrast, Monte Carlo simulation has proved to be a practical technique (Casteren & Groeman, 2009) based on the low correlation between different harmonic loads (independence of the sources). Fig. 10 presents the methodology useful for probabilistic harmonic distortion analysis of railways' electrical systems with different harmonic sources.

The methodology for probabilistic analysis of harmonic starts from values obtained from deterministic simulations. Once the different conditions of loads are defined in the behaviour of the traction system, it is possible to use probability distribution plots to evaluate the harmonic level in the system during the travel time. So, the next step is to determine the probability density function to fit the harmonic components of each harmonic source and its phase angle.

Fig. 10. Methodology for Harmonic Distortion Probabilistic Analysis of EMRTS

Many studies agree that the normal function is suitable as probability density function to use in the case of a random behaviour (Wang et al., 1994). In addition, according to the Std. IEEE - 519 (IEEE, 1993) the recommended window time to evaluate the harmonic distortion is 15 or 30 minutes. Therefore, it is recommended the selection of random time intervals of 15 minutes to make a probabilistic characterization of the THD distortion.

Then, it is necessary to perform the vector sum of several harmonic sources (i.e. traction substations) at the distribution system's connection point to determine the total harmonic distortion. There are two methods to evaluate the effect of different non-linear loads: the analytical method and Monte Carlo simulation method. The complex implementation of analytical methods for large power systems studies involves little practical application in real systems. By contrast, Monte Carlo simulation has proved to be a practical technique (Casteren & Groeman, 2009) based on the low correlation between different harmonic loads (independence of the sources). Fig. 10 presents the methodology useful for probabilistic harmonic distortion analysis of railways' electrical systems with different harmonic sources. The methodology for probabilistic analysis of harmonic starts from values obtained from deterministic simulations. Once the different conditions of loads are defined in the behaviour of the traction system, it is possible to use probability distribution plots to evaluate the harmonic level in the system during the travel time. So, the next step is to determine the probability density function to fit the harmonic components of each harmonic

Fig. 10. Methodology for Harmonic Distortion Probabilistic Analysis of EMRTS

15 minutes to make a probabilistic characterization of the THD distortion.

Many studies agree that the normal function is suitable as probability density function to use in the case of a random behaviour (Wang et al., 1994). In addition, according to the Std. IEEE - 519 (IEEE, 1993) the recommended window time to evaluate the harmonic distortion is 15 or 30 minutes. Therefore, it is recommended the selection of random time intervals of

source and its phase angle.

Then, a process called "Vector Sum - Phasor" is run through Monte Carlo simulations. Finally, the probabilistic characterization is obtained; where the probability distribution function of current THD, the probability distribution function of rms current and the probability distribution of each harmonic component are obtained.

Table 10.3 of Std. IEEE - 519 (IEEE, 1993) contains the current distortion limits in the voltage range of 120 V to 69 kV, which applies for typical railways' electrical systems connected to distribution systems at MV. So, based on this standard, a comparison between the current distortion levels at 95% and 50% of probability and the given limits must be realized to assess if the current distortion must be reduced or not. If a current THD distortion must be reduced, it could be used several filters methods. The next section presents the application of active power filtering to reduce THD distortion.

### **4.2.2 Active power filter allocation methodology**

The harmonic distortion produced by railways' systems at the distribution system's connection point can be reduced using passive or active power filters (APF). However, due to the random and time variability of the harmonic distortion in traction systems, it is required an active power compensation with the ability of adaptation to different load conditions. Passive filters are designed with fixed parameters and for specific harmonics, so this type of filter does not have the required ability. By contrast, APFs based on the p-q theory became an effective solution in traction systems; normally, they are used for dynamic harmonic suppression (Xu & Chen, 2009). This type of compensation presents the advantage of eliminating a wide range of harmonics simultaneously.

On the other hand, the traction system has several rectifier substations and from the economic point of view it is difficult to install an APF in each TS due to its high cost. Then, it is necessary to allocate APFs in the most sensitive positions in the own power system of the EMRTS using the least number of filters and minimizing their size. An important factor to be considered in the decision of harmonic compensation in traction system is the sudden fluctuation of traction load because this dynamic behavior is also observed in the harmonic distortion, as it has been explained in the previous section.

The allocation methodology of APFs in distribution systems supplying a traction load is based on probabilistic data of harmonic distortion presented in all traction substations. According to the Std. IEEE - 519 (IEEE, 1993), using a 15 minutes time interval it is enough to understand the dynamic behavior of the traction load because in this interval there are 900 different data of the load behaviour in each TS. Fig. 11 shows the proposed methodology of allocation of APF in urban railways systems.

As, it was shown in section 3.4, for the study case of this Chapter, the metro line can be supplied by three TS at MV. The total harmonic distortion in the distribution system is analyzed with and without active compensation. The APF is allocated in the low voltage side of the transformer in the TS. As, the railway line has three TS, there are seven possible allocations of APF, as Table 4 shows at the first column.

Table 4 shows the THD distortion at levels of 50% and 95% of probability when the system is without active power compensation and when APFs compensation is used according to the seven different configurations. This table shows the effectiveness of the APFs to reduce

Power System Modelling for Urban Massive Transportation Systems 197

A primary requirement to ensure the appropriate operation of any electrical system is to guarantee personnel and system safety, either under normal and fault conditions. So,

Grounding in electric traction systems requires a different treatment than in typical AC electrical systems, because of the existence of traction substations AC/DC of high capacity, the high variable load characteristic in time and distance, the direct contact of the rails with the earth, the current flow through the ground during normal operating conditions that can cause corrosion of underground metallic elements, the appearance of step and touch voltage

The grounding system is composed by two subsystems. The first one (subsystem 1) assures the personnel safety and the protective device operation; while, the second one (subsystem 2) is used to ground the negative pole in the DC side of the railway's traction substation.

The grounding subsystem 1 is used to ground all metallic structures: boxes, protective panels, pipeline, bridges, passenger platforms, etc. There are two ways to connect this