Deck 9: Three-Phase Alternators

Question 1

Why are rotating fields more commonly used than stationary fields?

Answer 1

Rotating fields are more commonly used than stationary fields because generating large amounts of current would require larger sizes of conductors and iron to rotate. Therefore, it is more practical to make the armature stationary and rotate the magnetic field.

Question 2

The field leads for both alternators and generators are indicated by what markings?

Answer 2

The field leads for both alternators and generators are indicated by the markings F₁ and F₂.

Question 3

There are 120 electrical degrees between each voltage ____________________ waveform.

Answer 3

sine

Question 4

Two phase is the most common polyphase electrical system.

Question 5

Armatures may be either the rotating piece of the alternator or the stationary component of the alternator.

Question 6

The voltage output of an alternator decreases as the speed of rotation accelerates.

Question 7

Two principal types of ____________________ alternators are (1) the rotating-armature alternator and (2) the rotating-field alternator.

Question 8

What is the purpose of a field discharge switch?

Question 9

The field windings in large generators are typically ____________________ than the armature windings.

Question 10

The frequency in cycles per second, or ____________________, is the number of pairs of poles passed by the conductor in a second.

Question 11

Why are rotating-field alternators used extensively?

Question 12

The alternator converts the mechanical energy of a(n) ____________________ to electrical energy.

Question 13

The frequency of an alternator is a direct function of what two things?

Question 14

The rotating-armature alternator generally is used for high-power installations.

Question 15

DC must be used in the electromagnetic field circuit of an alternator.