Alternators

Question 1

Name the two other names for Alternators.

Answer 1

Synchronous Generators
Alternating current generators

Question 2

Describe a rotating field alternator.

Answer 2

Has rotating field windings
Excitation current is supplied through brushes and slip rings from an external dc source
Armature directly connected to an external load

Question 3

The two distinct types of synchronous-generator rotating field structures are?

Answer 3

Cylindrical - smooth exterior, long, well balanced
Salient (projecting) - shorter in length, wide

Question 4

What sort of conversion of energy happens in the armature winding?

Answer 4

Mechanical to Electrical

Question 5

A one-turn stator winding in an alternator generates one-quarter the voltage of a comparable four-turn winding. T or F?

Answer 5

True
E•G
One Turn Coil= 30V
Four Turn Coil= 120V

Question 6

In regards to a parallel delta-connected, three-phase, twelve-lead alternator, how would you find the current in a winding?

Answer 6

Divide Iphase by two to get the current per winding

Question 7

How do you reduced Hysteresis Losses?

Answer 7

Alloys such as silicon steel or iron with silicon in it are used in the core material.

Question 8

Heat losses produced by current in windings of the alternator are called?

Answer 8

Copper Losses

Question 9

The power required to drive the built-in cooling fan of an alternating current generator is known as what type of losses?

Answer 9

Mechanical Losses

Question 10

In an alternator, the slip rings are stationary. T or F?

Answer 10

False. Slip rings are attached to the rotor.

Question 11

The Output Voltage of an Alternator is due to three factors:

Answer 11

Armature: Resistance, Reactance & Reaction

Question 12

A solid state rectifier is an example of a external dc supply. T or F?

Answer 12

True

Question 13

In a brush-type, self-excited alternator, a small shunt is mounted on the same alternator shaft that supports the main alternator rotor and field windings. T or F?

Answer 13

True

Question 14

A brushless excitation system does not require a commutator. T or F?

Answer 14

True

Question 15

Four conditions must be met before syncing two parallel alternators. State them:

Answer 15

Phase Sequence
Terminal Voltages
Frequencies
Phase Position

Question 16

Using the “three-dark lamp method” the lamps must be suitable for what rating?

Answer 16

Twice the alternators phase voltage value

Question 17

A synchroscope indicates what values?

Answer 17

Frequency and Phase Position of the incoming alternator relative to the running alternator or supply voltage

Question 18

If a synchroscope pointer moves CCW, what does that indicate?

Answer 18

The frequency of the incoming alternator is lower than that of the running alternator.

Question 19

The 12 o’clock position of a synchroscope means the frequency and phase position have all matched up. T or F?

Answer 19

True

Question 20

How do you transfer the power load of ALT 1 to ALT 2 without changing frequency?

Answer 20

Increase the power input or the torque of the prime mover of ALT2 and simultaneously decrease the power input to ALT1

Question 21

To increase the output voltage of a system supplied by two paralled alternators, the field excitation of both alternators needs to be increased. T or F?

Answer 21

True

Question 22

A heavy flywheel reduces hunting. What other application reduces hunting?

Answer 22

Embedded amortisseur (dampen) windings in the surface of the alternator’s rotor pole faces produce an induced current that opposes and limits the action of hunting.

Question 23

What kind of connection is this? And how many lead Alternator?

Answer 23

A Series Wye Connection

Twelve Lead

Question 24

What is Phase Sequence? What is another name for it?

Answer 24

It’s the direction of the magnetic field rotation.

Phase Rotation

Question 25

Describe what is happening in the diagram below.

Answer 25

Three-Dark Lamp Method to parallel two alternators.

The lamps turn on if there’s any difference in phase voltage between the two alternators.

When the phase voltage from each Alternator have the same phase sequence, frequency and phase position there is no potential difference in their phase voltages at any point in cycle and all three lamps will remain dark. Usually the lamps will flash slowly and you can close the switch when they’re dark.