Deck 12: Alternating-Current Generators

Question 1

____________________ causes the current to surge back and forth between alternators operating in parallel.

Answer 1

Hunting

Question 2

Why is the practice of operating several alternators in parallel preferred by power-generating stations?

Answer 2

Power-generating stations operate several alternators in parallel. This practice is preferred to the use of a single large generator for the following reasons:
1. The use of several ac generators means that periodic maintenance and repairs can be made to one alternator. Because the other machines are operating in parallel, they can supply the load and prevent a power interruption due to a generator failure.
2. The load requirements for any central generating station change continually. During light-load periods, the load demands can be met by one or two alternators operating at a high efficiency. This means that these alternators will be operating at a high efficiency. As the load demands increase during certain periods of the day, other alternators can be connected in parallel to meet the peak demands. This procedure is more economical than the use of one huge machine operating, at certain periods of each day, at only a small fraction of its full-load capacity. Such operation results in a low efficiency.
3. Electrical power requirements are continually increasing. To meet these increased demands, utility companies can increase the physical size of their generating plants so that more alternators can be installed. These machines can be operated in parallel with the existing generating equipment. This procedure is a convenient and economical way of increasing the generating capacity of a utility.

Question 3

All of the coils of one single-phase winding are collectively known as a(n) ____________________.

Answer 3

phase belt

Question 4

Describe the two bright, one dark method.

Question 5

The arithmetic sum of the two alternator currents equals the total current supplied to the load.

Question 6

Explain hunting and how it can be corrected.

Question 7

AC generators are also known as ____________________ because they supply electrical energy with an alternating voltage.

Question 8

A(n) ____________________ is a single-phase instrument that indicates synchronism accurately.

Question 9

Explain the effect of lagging power factor.

Question 10

Alternators operating in parallel in various central stations often will operate in a network power system.

Question 11

In an AC generator, the direct voltage induced in the armature conductors is changed to an alternating voltage at the brushes by means of the commutator.

Question 12

The capacity of an alternator is given in kilowatts rather than kilovolt-amperes.

Question 13

A(n) ____________________ is generated in stationary armature conductors when the field poles rotate past the conductors.

Question 14

How is the division of the load between dc generators obtained?

Question 15

DC generators and alternators have nearly the same losses.