Alternators And Generators

Question 1

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

Answer 1

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

Question 2

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

Answer 2

Create magnetic flux

Question 3

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

Answer 3

Brushes

Question 4

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

Answer 4

Having the armature conductors cut the fewest lines of flux

Question 5

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

Answer 5

AC

Question 6

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

Answer 6

Rheostat

Question 7

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

Answer 7

• 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

Question 8

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

Answer 8

Zero

Question 9

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

True or False?

Answer 9

False;

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

Question 10

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

Answer 10

Ambient

Question 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?

Answer 11

False;

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

Question 12

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

Answer 12

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

Question 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?

Answer 13

Same:

• voltage
• frequency
• phase position
• phase sequence

Question 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?

Answer 14

They all have the same phase sequence

Question 15

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

Answer 15

• frequency
• phase position

Also, whether it’s running faster or slower

Question 16

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

Answer 16

faster

Question 17

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

Answer 17

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

Question 18

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

Answer 18

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

Question 19

What is hunting?

Answer 19

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