AC Theory 3: Lesson 7 - Understsanding The Design And Function Of AC Generators

Question 1

Another name for an AC generator is the alternator.

True or False

Question 2

The primary difference between a simple DC generator and a simple AC generator is the method by which the voltage is removed from the armature; in a DC generator, the voltage is removed by using brushes on ______. In an AC generator, the voltage is removed by using ______.

a. a commutator / sliprings
b. sliprings / a commutator

Question 3

There are two basic types of alternators. These are the revolving ______ type and the revolving ______ type.

a. armature / field
b. rotor / field
c. rotor / stator
d. stator / rotor

Question 4

______ are constructed as a continuous ring, with each end of the armature loop connected to a separate ring.

a. Brushes
b. Commutators
c. Slip rings

Question 5

In a 3-phase generator, the three sets of windings are placed ______ apart.

a. 60°
b. 90°
c. 120°
d. 180°

Question 6

There is no limit to the amount of power that can be generated with the revolving armature type of generator.

True or False

Question 7

There ______ real advantage to using a rotating field and a stationary armature on commercial generators.

a. is a
b. is no

Question 8

The ______ is the rotating member of a generator or motor.

a. armature
b. commutator
c. rotor
d. stator

Question 9

When the armature is held stationary in a generator, it is called the ______.

a. armature
b. commutator
c. rotor
d. stator

Question 10

Two types of rotating field construction are the ______ pole rotor and the ______ rotor.

a. salient, round
b. salient, stator
c. stator, turbo
d. turbo, stator

Question 11

Pole faces that jut out and are very pronounced are called ______ poles.

a. extended
b. protruding
c. round
d. salient

Question 12

The ______ rotor uses a smooth, longer, and narrower construction to minimize wind resistance and centrifugal forces.

a. aerodynamic
b. high velocity
c. round
d. salient pole

Question 13

Exciters are made in ______ ways including stationary and rotating.

a. a variety of
b. only a few

Question 14

A rotating exciter mounted on the same shaft as the main generator is usually called a(n) ______ exciter.

a. armature type
b. brushless
c. integral
d. internal

Question 15

Alternators with small kilovolt-ampere ratings are usually ______ cooled.

a. air
b. hydrogen
c. nitrogen
d. oxygen

Question 16

Air-cooled alternators usually have a ______ attached to one end of the rotor to help circulate air.

a. compressor
b. fan
c. propeller
d. turbo

Question 17

Large-capacity generators are often enclosed in a(n) ______ atmosphere for cooling purposes.

a. air
b. hydrogen
c. nitrogen
d. oxygen

Question 18

Which dissipates heat faster, hydrogen or air?

a. air
b. hydrogen

Question 19

Select the factors that determine the frequency of an alternator.

I. Number of stator poles
II. Voltage level
III. Phase
IV. Speed of rotation.

a. I., II., and III.
b. I., II., and IV.
c. II., III., and IV.
d. I. and IV.
e. II. and IV.

Question 20

Match the appropriate variables with the correct locations to create the formula for determining the frequency of an alternator.

Question 21

To generate 50 hertz with an 8-pole generator, the speed of rotation must be ______ revolutions per minute.

Question 22

How many poles are required for a generator to have a frequency of 60 hertz at 1,200 revolutions per minute?

Question 23

A generator has four poles and a speed of 1,500 revolutions per minute. What is the output frequency?

Question 24

Select the factors that determine the output voltage of an alternator.

I. The length of the armature conductors
II. The speed of rotation of the conductor in the magnetic field
III. The strength of the magnetic field
IV. The size of the conductor

a. I., II., and III.
b. I., II., III., and IV.
c. II., III., and. IV
d. I., III., and IV.

Question 25

If the number of turns of the coil is fixed by the generator’s design, and speed of rotation is fixed by the output frequency requirements, the most practical option for voltage control is by increasing or decreasing the strength of the magnetic field of the rotor.

True or False

Question 26

Three conditions that must be met when connecting two 3-phase alternators in parallel are:

I. Each generator must have the same frequency.
II. The output voltages of the two machines must be equal.
III. The phase rotation of the two machines must be the same. Phases A, B, and C of one machine must be in sequence with the same phase of the other machine.

True or False

Question 27

A common method of detecting when the direction of the magnetic field of one alternator is matched with the phase rotation of a paralleled alternator is with the use of three lights.

True or False

Question 28

When using the “three-lamp” method, how does an Electrical Worker know when the two alternators are in-phase with each other?

a. All three lamps will be off.
b. All three lamps will be on.
c. One lamp will be off.
d. One lamp will be on.

Question 29

Another method of paralleling two alternators is with the use of a synchroscope.

True or False