Deck 18: Ac Generators Alternators

Question 1

The rotating field of a large alternator receives its energy from the DC exciter, through slip rings.

Answer 1

True

Question 2

Direct current is less expensive to produce and transmit than alternating current.

Answer 2

False

Question 3

The standard frequency for power distribution in the U.S. is 120 Hz.

Answer 3

False

Question 4

What is one factor that affects the output voltage of an alternator?

A) Resistance of the stator windings
B) The frequency of the emf produced
C) The type of coil connection
D) The phase sequence

Question 5

The ____ method for synchronizing alternators is generally used only for small operations or for laboratory experiments.

A) phase sequence
B) frequency meter
C) lamp dark
D) lamp dim

Question 6

Another name for a rotary converter is a(n) _____.

A) dynamotor
B) multiphase alternator
C) dynamometer
D) alternator

Question 7

The phase sequence describes the order in which the currents follow one another.

Question 8

What instrument is used to determine whether the frequency of an alternator to be brought on line matches the frequency of the bus?

A) Phase sequence meter
B) Prime mover
C) Period meter
D) Synchroscope

Question 9

The prime mover in a motor-generator set is the _____.

A) generator
B) motor
C) dynamotor
D) armature

Question 10

Frequency is calculated by taking the number of field poles on the alternator, multiplying by ____, and then dividing their product by 120.

A) resistance of the stator windings in ohms
B) winding current in amperes
C) rotor speed in rpm
D) field strength in volts

Question 11

The wye connection, sometimes called a star connection, is a method of connecting coils together inside the alternator.

Question 12

In a delta-connected alternator, the line voltage is equal to ____ times the phase voltage.

A) 1.0
B) 1.25
C) 1.73
D) 2.0

Question 13

When alternators are connected in parallel, the phase rotation of the alternator and the distribution bus must be ____.

A) 90 degrees out of phase
B) 120 degrees out of phase
C) 180 degrees out of phase
D) the same

Question 14

In a wye-connected alternator, the line voltage is equal to ____ times the phase voltage.

A) 1.0
B) 1.25
C) 1.73
D) 2.0

Question 15

In a balanced three-phase system, the power factor is the____ of the angle between the phase current and the phase voltage.

A) sine
B) cosine
C) tangent
D) hypotenuse