Unit 30: DC Generators

Question 1

What is a generator?

Answer 1

A generator is a device that converts mechanical energy into electric energy.

Question 2

What type of voltage is produced in all rotating armatures?

Answer 2

AC is produced in all rotating armatures.

Question 3

What are the three types of armature winding?

Answer 3

1. Lap-wound armatures.
2. Wave-wound armatures.
3. Frogleg-wound armatures.

Question 4

What type of armature winding would be used for a machine intended for high- voltage, low-current operation?

Answer 4

Wave-wound armatures are used in machines designed for high-voltage and low-current operation.

Question 5

What are interpoles, and what is their purpose?

Answer 5

Interpoles are small pole pieces connected between the main field poles used to help correct armature reaction.

Question 6

How are interpoles connected in relation to the armature?

Answer 6

Interpoles are connected in series with the armature.

Question 7

What type of field winding is made with many turns of small wire?

Answer 7

Shunt field windings are made with many turns of small wire and have a high resistance.

Question 8

How is the series field connected in relation to the armature?

Answer 8

Series field windings are connected in series with the armature.

Question 9

How is the shunt field connected in relation to the armature?

Answer 9

Shunt field windings are connected in parallel with the armature.

Question 10

What is armature reaction?

Answer 10

Armature reaction is the twisting or bending of the main magnetic field.

Question 11

What is armature reaction proportional to?

Answer 11

Armature reaction is proportional to armature current.

Question 12

What are eddy currents?

Answer 12

Eddy currents are currents that are induced into the metal core material by the changing magnetic field as the armature spins through the flux lines of the pole pieces.

Question 13

What condition characterizes overcompounding?

Answer 13

When a generator is overcompounded, the output voltage is higher at full load than it
is at no load.

Question 14

What is the function of the shunt field rheostat?

Answer 14

The shunt field rheostat is used to control the output voltage.

Question 15

What is used to control the amount of compounding for a generator?

Answer 15

The amount of compounding is controlled by connecting a low-value variable resistor in parallel with the series field. This resistor is known as the series field shunt rheostat, or the series field diverter.

Question 16

Explain the difference between cumulative- and differential-compounded connections.

Answer 16

In a cumulative compound connection the shunt and series fields are connected in such a manner that when current flows through them they aid each other in the production of magnetism, whereas a differential-compound generator has its fields connected in such a manner that they oppose each other in the production of magnetism.

Question 17

What three factors determine the amount of output voltage for a DC generator?

Answer 17

1. the number of turns of wire in the armature.
2. the strength of the magnetic field of the pole pieces.
3. the speed of the armature.

Question 18

What is the voltage regulation of a DC generator proportional to?

Answer 18

The voltage regulation of a DC generator is proportional to the resistance of the armature.

Question 19

What is countertorque proportional to?

Answer 19

Countertorque is proportional to the armature current if the field excitation current remains constant.

Question 20

What is countertorque a measure of?

Answer 20

Countertorque is a measure of the useful electric energy produced by the generator.