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Navy Electricity and Electronics Training Series (NEETS)
Module 5 - Introduction to Generators and Motors
Chapter 1:  Pages 1-21 through 1-30

NEETS   Module 5 - Introduction to Generators and Motors



Formulas - RF Cafe

NOTE: The lower the percent of regulation, the better the generator. In the above example, the 5% regulation represented a 22-volt change from no load to full load. A 1% change would represent a change of 4.4 volts, which, of course, would be better.
Q20.   What term applies to the voltage variation from no-load to full-load conditions and is expressed as a percentage?
VOLTAGE REGULATION should not be confused with VOLTAGE CONTROL. As described previously, voltage regulation is an internal action occurring within the generator whenever the load changes. Voltage control is an imposed action, usually through an external adjustment, for the purpose of increasing or decreasing terminal voltage.
Manual Voltage Control



Hand-operated field rheostat - RF Cafe

 Figure 1-21. - Hand-operated field rheostat.



Automatic Voltage Control
Q21. What term applies to the use of two or more generators to supply a common load?



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Ordinary dc generator - RF Cafe

Figure 1-22. - Ordinary dc generator.


Brushes shorted in a dc generator - RF Cafe





Amplidyne load brushes - RF Cafe

Figure 1-24. - Amplidyne load brushes.

precisely by something very small, almost insignificant.
Q22.   What is the purpose of a dc generator that has been modified to function as an amplidyne?


Q23.   What is the formula used to determine the gain of an amplifying device?
Q24.   What are the two inputs to an amplidyne?


You must always observe safety precautions when working around electrical equipment to avoid injury to personnel and damage to equipment. Electrical equipment frequently has accessories that require separate sources of power. Lighting fixtures, heaters, externally powered temperature detectors, and alarm systems are examples of accessories whose terminals must be deenergized. When working on dc generators, you must check to ensure that all such circuits have been de-energized and tagged before you attempt any maintenance or repair work. You must also use the greatest care when working on or near the output terminals of dc generators.


This chapter introduced you to the basic principles concerning direct current generators. The different types of dc generators and their characteristics were covered. The following information provides a summary of the major subjects of the chapter for your review.
MAGNETIC INDUCTION takes place when a conductor is moved in a magnetic field in such a way that it cuts flux lines, and a voltage (EMF) is induced in the conductor.
THE LEFT-HAND RULE FOR GENERATORS states that when the thumb, forefinger, and middle finger of the left hand are extended at right angles to each other so that the thumb indicates the direction of movement of the conductor in the magnetic field, and the forefinger points in the direction of the flux lines (north to south), the middle finger shows the direction of induced EMF in the conductor.



AN ELEMENTARY GENERATOR consists of a single coil rotated in a magnetic field. It produces an ac voltage.


A BASIC DC GENERATOR results when you replace the slip rings of an elementary generator with a two-piece commutator, changing the output voltage to pulsating dc.


A MULTIPLE COIL ARMATURE (adding coils to the armature) decreases the ripple voltage in the output of a dc generator, and increases the output voltage.




 A MULTIPOLE GENERATOR is the result of adding more field poles to a dc generator. They have much the same effect as adding coils to the armature. In practical generators, the poles are electromagnets.


COMMUTATION is the process used to get direct current from a generator. The coil connections to the load must be reversed as the coil passes through the neutral plane. The brushes must be positioned so that commutation is accomplished without brush sparking.




ARMATURE REACTION takes place when armature current causes the armature to become an electromagnet. The armature field disturbs the field from the pole pieces. This results in a shift of the neutral plane in the direction of rotation.


COMPENSATING WINDINGS AND INTERPOLES are used to counteract the effects of armature reaction. They are supplied by armature current and shift the neutral plane back to its original position.




MOTOR REACTION is caused by the magnetic field that is set up in the armature. It tends to oppose the rotation of the armature, due to the attraction and repulsion forces between the armature field and the main field.


ARMATURE LOSSES in dc generator armatures affect the outputs. These losses are as follows:
1.    Copper losses are simply I2R (heat) losses caused by current flowing through the resistance of the armature windings.
2.    Eddy currents are induced in core material and cause heat.
3.    Hysteresis losses occur due to the rapidly changing magnetic fields in the armature, resulting in heat.


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