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4th Year Electrical - Machines > Alternators And Generators > Flashcards

Flashcards in Alternators And Generators Deck (19)
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1

On an AC machine, the armature windings are typically located on the _________, and the field windings are typically located on the ________.

On an AC machine, the armature windings are typically located on the STATOR, and the field windings are typically located on the ROTOR.

2

What is the role of the field windings in an AC or DC machine?

Create magnetic flux

3

The field windings of an AC alternator or synchronous motor may be connected to an external circuit by using __________.

Brushes

4

During the commutation process it is desirable to prevent arcing at the brushes. This is accomplished by:

Having the armature conductors cut the fewest lines of flux

5

The voltage induced into the armature conductor of a DC generator is _______ (ac/dc) voltage.

AC

6

A variable resistor connected in series with a field winding is called a:

Rheostat

7

Name the four (4) things that affect the amount of voltage produced by electromagnetic induction in a generator.

- Flux density or magnetic field intensity
- Length of conductor exposed to the field (which is affected by the number of turns)
- Relative speed of conductor to the field
- The angle at which the conductor cuts the lines of force

8

When the armature loop of an AC generator is at 180*, what is the value of the induced voltage.

Zero

9

Motors or generators must never be overloaded even for a brief period of time.

True or False?

False;

Most motors or generators can be overloaded for a brief time.

10

The temperature of the cooling medium associated with a motor or generator is called the ___________ temperature.

Ambient

11

The current rating (FLC) is the value of current that occurs at less than rated voltage and speed while operating with no load.

True or False?

False;

The alternator must be at rated speed and generating the rated voltage to produce FLC.

12

What are three (3) practical reasons for paralleling alternators?

- more kVa
- maintenance on prime mover
- operate a wider variety of loads

13

In order to properly synchronize and parallel alternators, what four (4) conditions must be met before both machines may be brought on the same system bus?

Same:
- voltage
- frequency
- phase position
- phase sequence

14

When using the three lamp dark method for paralleling, when all three lamps are flicking in unison, this would indicate which of the four conditions?

They all have the same phase sequence

15

A syncroscope is used to indicate two things when paralleling. They are:

- frequency
- phase position



Also, whether it's running faster or slower

16

Generally speaking, it is more desirable to have the incoming alternator running ________ (slower/faster) than the running alternator.

faster

17

Method of transferring all true power from Alt #1 (loaded) to Alt #2 (floating) without changing the system frequency.

Increase the prime mover on #2 and decrease on #1.

18

Method of transferring all reactive power from Alt #1 (loaded) to Alt #2 (floating) without changing the system voltage.

Increase the dc field rheostat on #2 and decrease on #1.

19

What is hunting?

The main alternator is trying to bring the secondary to synchronism causing high currents, potentially causing the OC to trip and losing the load.