# A Workbench for Testing and Simulation Faults in Three-phase Electric Motors
with Intelligent Electronic Device and Microcontrolled System

Giovanni Faria, Michel Fernandes Peres,
Osmar Moreira da Silva Neto  Electrical Engineering Undergraduate Course
University Center of Araucária (UNIFACEAR)1
Araucária, Paraná, Brazil
<EMAIL_ADDRESS><EMAIL_ADDRESS>
<EMAIL_ADDRESS>Jefferson Rodrigo Schuertz, Edson Leonardo dos
Santos and Carlos Alexandre Gouvea da Silva1 Electrical Engineering Department
(DELT)
Federal University of Paraná (UFPR)
Curitiba, Paraná, Brazil
<EMAIL_ADDRESS>
<EMAIL_ADDRESS><EMAIL_ADDRESS>
###### Abstract

Electric motors can be damaged or operate improperly from a possible set of
failures. Such failures are related to high or very low voltage and current
levels, phase loss or blocked rotor. Therefore, it is important to protect
these equipments through appropriate mechanisms. Alternatively, a workbench
can simulate detectable failures related to the engines, allowing to change
parameters, in which maintenance operators are able to identify the results of
these changes. This work presents the development of a workbench as a tool for
testing electrical machines and drives. The workbench is based on the Arduino
programming platform (microcontroller system), in which it checks the
functioning of electric motors under the condition of failures that may occur
in this engine. Motor protections are carried out through an Intelligent
Electronic Device (IED), which are popularly known as intelligent relays. The
results show the development of a workbench that can test and identify several
faults in a small three-phase motor.

###### Index Terms:

Microcontroller System, Intelligent Electronic Device, Three-phase Motor,
Protection of Motor.

##  I Introduction

Electric motors contribute significantly to technological advances in
industries and encompass a large part of the energy consumption of countries.
In Brazil, according to data presented by the Brazilian National Electric
Energy Agency (ANEEL) at 2015, the industry consumed 43.7% of all national
electricity and 30% of all electric energy in the country is consumed by
electric motors. Industrial motor uses a major fraction of the total
industrial energy used around the world [1].

Electric motors are defined as devices that perform electromechanical energy
conversion [2]. This electromechanical conversion is explained based on the
principles of electromagnetism, in which conductors located in a magnetic
field and crossed by electric current are based on the action of a force
called torque. Electric motors are subdivided into two broad groups: the
direct current (DC) and the alternating current (AC) [3]. Alternating current
motors can be classified as induction or synchronous. The three-phase
induction motors are powered by three wires (phases) in which the voltages are
120∘ out of phase [4].

The basic construction of an alternating current motor is formed by a
stationary part, or stator and another rotating part, connected to the axis
that couples the motor to load. Stator is briefly a metal ring with slits that
wrap the coils in a steel core, in which the alternating current flows through
the coil producing a rotating magnetic field. The rotor, on the other hand, is
a rod where at its core, there are several conductive bars with uniformly
distributed spaces. When in operation, the rotor core interacts with the
magnetic field produced by the stator coils, causing the motor to rotate and
generate torque. These components are placed inside a housing to protect the
engine and control the heat, as showed in Fig. 1.

Figure 1: Three-phase motor.

Usually, most of the entire circuit must be protected by internal temperature-
sensitive and external devices that interrupt the current, when crossed by a
short circuit current. For the correct protection of the motors, relays are
used, which are defined as a wide range of devices that offer protection to
electrical systems in many different ways: overload, short circuit,
overvoltage, undervoltage and others [5]. Currently, there is a wide variety
of models manufactured from motor protection relays, one of which is the
digital relay or Intelligent Electronic Devices (IED).

In the beginning, the main applications of the first IEDs were the protection
of transformers, overhead lines and cables, motors and generators. However, it
has also been used in protection systems with high reliability as in
substations [6]. IEDs work by means of transformers, such as current
transformer (TC) and potential transformer (TP), in which upon receiving an
induction of the electric current that flows through the power cable of the
motor, it converts high currents and voltages into lower levels. Thus, the IED
receives this information and operates according a programming logic. Besides
to the circuit protections, the relays also perform functions of
communication, control, electrical measurements, signaling and others.
However, test workbenches for these engine protection devices still lack on
the market.

Therefore, the development of a workbench for protection of three-phase motors
using IED is presented in this paper. The solution is based on a real-time
microcontrolled system that analyzes the behavior of the IED, when typical
failures occur in this type of engine. Besides that, the workbench has a set
of commands, so that users can reproduce these failures.

##  II Protection Techniques and Related Works

Overcurrent is the most common cause of failure in an electrical system,
causing a higher level of wear, which reduces the useful lifetime of the
components used in the motor supply. The overcurrent can be classified as
overloads or short circuits. Overloads are softened variations in the current
flowing in the electrical system. Short circuits, on the other hand, are
extreme variations in current flowing in the electrical system. However, it is
challenging to detect and locate these types of failures and interrupting it
as quickly as possible [7]. For induction motors, Zhang et al. [8] suggest
investigate five areas of faults for protection methods: thermal protection
and temperature estimation, stator insulation monitoring and fault detection,
bearing fault detection, broken rotor bar/end-ring detection, and air gap
eccentricity detection.

The IEEE Std C37.2$\texttrademark$-2008 [9] is used as a set of function codes
and acronyms for equipments used in the equipment installations, generating
plants, power substations and power conversion. This standard also includes a
set of functions used to electric motors protection [10]. The protection
relays required to keep AC motors running are based on type, size and
application. These relays are identified and summarized in IEEE Std
C37.96$\texttrademark$-2012 [11].

In general, work related to the creation and development of test workbenches
for electric motors is limited to the use of applications in educational
environments, improving teaching in engineering courses [12]. In these cases,
protection simulator designs or the use of electric motors are used by
[13][14][15][16].

##  III Proposed System and Results

Fig. 2 shows the main parts of the proposed workbench. It is used a three-
phase induction motor of 220 Volts and 1 HP (horse power) in order to test and
verify the accuracy of the proposed system. At the motor, a blocking system
was built and coupled to the axis in order to verify the blocked rotor test.
This mechanism was manufactured from an electromechanical brake and, when
energized, interrupts the rotation of the movable motor axis. The operating
conditions of the motor are monitored in real time by the IED. In this work,
an IED manufactured by Schneider using the LTMR 100PBD Tesys model was
employed. This IED is an equipment for monitoring and control motors, in which
can provide the following type of protection: load fluctuation, reverse
polarity protection, locked rotor, thermal protection, overload (long time),
power factor variation, earth-leakage protection, thermal overload protection,
phase unbalance, and phase loss.

Figure 2: Workbench for Protection Motor Diagram.

From each type of failure that the IED can identify and protect the motor, it
sends a notification message to Arduino. This message is identified by the
microcontroller, which in turn sends a response to the fault identified by the
IED to the user panel. This response can be of three types: a message written
on a liquid crystal display (LCD), on indicative LEDs or an audible signal
from a buzzer.

In order to develop and implement the workbench, we focus the main types of
failures that occur in three-phase motors. The main types of faults are
indicated by: (1) Overvoltage; (2) Undervoltage; (3) Overcurrent; (4) Phase
loss; (5) Locked rotor; (6) Extended start; (7) Voltage unbalance; and (8)
Current unbalance. The motor protection used in the workbench was based on the
specifications available in the IEEE C37.2$\texttrademark$-2008 e IEEE
C37.96$\texttrademark$-2012 standards. To simulate the failures are used input
elements such as on/off keys, buttons and a potentiometer that allow increase
or decrease voltage at the motor. In order to simulate a blocked rotor
failure, a key is used to block the motor rotation system.

###  III-A Microcontroller System

The programming of the intelligent relay (IED) was developed in the software
that accompanies the relay called Tesys T, which uses block diagram language.
In this programming, values were set that parameterize the relay, where for
each failure a value is pre-established.

The criteria configured via software at IED for fault detection are shown as
follows:

  * •

For the overcurrent fault to occur, the current must vary between 20% to 800%
of the rated current value. For the fault operation in the project, the value
of 120% of the nominal current was parameterized.

  * •

In the case of blocked rotor failure, the same current variation occurs,
however the value set in the parameterization was 130% of the nominal current.
In the current unbalance fault, this interval varies between 10% to 70% the
value of the percentage of unbalance, where the value defined in the project
to occur the fault was 10%.

  * •

In the extended start, the variation occurs between 100% to 800% of the
nominal current value, where the value of 150% was defined for the failure
action in the project.

  * •

In the case of undervoltage failure, the ideal interval should occur if the
nominal voltage is greater than or equal to 70% and less than or equal to 99%.
In the case of overvoltage, this range varies from 101% to 115%. For
parameterization purposes, the value of 85% for undervoltage and 110% for
overvoltage was selected.

  * •

In the case of voltage unbalance failure, the voltage analyzed is not the
nominal voltage, but the motor phase voltage, where the variation is at least
3% and at most 10%, with the value being 10%.

The program was developed in C language and built-in Arduino microcontroller
to receive the IED signals, as well as send messages and failure states on the
user panel. This panel is illustrated in Fig. 3.

Figure 3: Control panel of the workbench.

Fig. 4 shows the engine with the electromechanical brake system. For safety
reasons, this motor is protected in a housing with a safety sensor. If the
engine is running and the case is opened, the system will shut off the
engine’s power supply.

Figure 4: The overview of motor and break system.

Fig. 5 shows the final result of the workbench construction. From the
transparent material on the front of the workbench, users can check the main
internal components and their connections, which can prompt and encourage
users to ask questions related to the protection of the motor and its devices.

Figure 5: The overview of full workbench. Figure 6: LCD with workbench message
ON.

###  III-B Test Procedures

First, to start the fault simulation, it is necessary to turn on the workbench
switch, where the green LED will light. In addition, the LCD displays a
“Workbench Working” message, as shown in Figure 6. Next, it should be shown
that the IED is operational in order to identify the faults that are sent by
the user. To create a motor fault, the yellow fault reset LED cannot be lit.
If the LED is on, the IED must be reset using the reset button failure.

####  III-B1 Overvoltage Failure

Overvoltage occurs when there is a voltage above the nominal motor supply. To
perform the overvoltage failure, a three-phase transformer (II) was connected
to one of the contactors (8). When the overvoltage button (D), this contactor
coil is activated, allowing the transformer to send 380 Volts to the motor.
Thus, when the IED identifies that there is a voltage above the nominal motor
voltage (220 Volts), it triggers the motor trip, sending a digital signal to
the Arduino to indicate on the display (L) the occurrence of the failure.

####  III-B2 Undervoltage Failure

To simulate this fault, it is necessary that the three-phases of the motor
supply are interrupted abruptly. In this way, the drive relays were
interconnected to the power contactors, so that when the undervoltage switch
is activated, the coil of the three relays is powered, making it impossible to
supply voltage to the motor.

####  III-B3 Overcurrent Failure

To simulate this load, a braking system was connected to the motor axis;
therefore, when the motor is already running and the potentiometer is turned
slightly to the point of overcurrent event, the voltage will decrease at the
magnetic brake. Then, lightly locking the motor axis so that it is not
completely locked.

####  III-B4 Phase Loss Failure

When the phase failure selector switch is activated, the coil of the two
command relay is powered, making it impossible for the three-phases to reach
the motor.

####  III-B5 Locked Rotor Failure

To simulate this failure, the magnetic brake was used again, but this time
this brake will be activated through the locked rotor selector. When moving
the key to the right side, the motor axis will be completely locked, as the
voltage is 0 Volts.

####  III-B6 Extended Starting Failure

For complete blocking of the motor, the same selector switch is used that
generates the failure of the blocked rotor; however, for extended starting
failure, the switch must be moved to the left. Thus, the IED recognizes that
the motor is stopped and after programmed timeout in the IED, that the motor
does not start is disarmed.

####  III-B7 Voltage Unbalance Failure

To simulate this failure, the drive relays were interconnected to the power
contactors, so that when the voltage unbalance selector switch is activated, a
relay coil is powered, making it impossible for the relay voltage phase to
reach the motor.

####  III-B8 Current Unbalance Failure

In order to simulate the driver relays, they were interconnected with the
power contactors, so that when the current unbalance selector switch is
activated, a relay coil is powered, making it impossible for the voltage of
this phase to reach the motor.

For each type of fault, 30 repetitions were performed in total to check the
reliability of the system in identifying each type of fault and in protecting
the motor. Only two types of failure did not reach full success: undervoltage
with 70% and phase loss with 86.6%. This is due to the fact that there is a
great similarity between the two types of failure, where sometimes the EDI
interpreted that the undervoltage occurs and other times it identified that
the failure occurred was phase loss.

Considering that this test workbench can be used as a teaching tool, it is
possible to make a comparison with [12]. The main advantage of the work
proposed by [12] is the low cost due to the use of virtual simulators or
emulators only. Otherwise, our work can be used in real practical classes and
not just simulated. In addition, it also allows the study of real equipments,
unlike the use of only simulators.

This workbench is limited to the use of three-phase motors based on the
nominal motor voltage and also does not provide support for DC motors. For
motors with a high power level, it is necessary to update the IED firmware.

##  IV Conclusion

In this work, a test workbench and fault simulation in induction motors was
proposed. System control is based on the Arduino programming platform, whereas
motor protection is performed by an Intelligent Electronic Device. In a
control panel, it was possible to verify the performance of the IED in eight
types of common faults in the motor under test. The results showed that the
workbench was able to identify most of the failures implemented with a high
level of confidence. As a future work, it is suggested to use this workbench
as an educational teaching tool in electrical engineering courses.

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