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Flashcards in Generator and Components Deck (40):
1

Generator Theory

-The exciter supplies dc current to the field winding (rotor) of the main generator rotor making an electromagnet of the rotor. As the turbine drives the rotor, the magnet rotates through the magnetic field which cuts the lines of flux then inducing a voltage in the stator windings. If the circuit is closed electricity will flow.

2

Collector Ring
(Slip Ring)

-dc current from the exciter is brought to the ________ through carbon bushes and then through the conductors to the field windings(rotor).
-A metal ring mounted on an electric machine that conducts current into or out of the rotating member.

3

Exciter

-Supplies current through slip rings to the rotor windings to produce the magnetic field causing the rotor to become an electromagnet.

4

Watt Meter

-Shows how many kilowatts the generator is producing and the kilowatt hours produced.

5

What does the stator consist of?

-Core
-Stator Windings
-Frame

6

Stator Windings

-3 phase windings are installed in the stator 120 degrees apart.
-All of the output current of the generator flows through the conductors made of copper.

7

If the rotating part of the generator has one pair of poles (1 north and 1 south) what rpm must it travel to match 60 Hz?

-3600 rpm

8

What happens with voltage and current in a Capacitive Load?

-Current leads voltage.
-Voltage peaks and current peaks are not in phase.

9

What happens with voltage and current in a Resistive Load?

-A load whose total reactance is zero, so that the alternating current is in phase with voltage.
-voltage peaks and current peaks are in phase.

10

What 2 elements does Excitation relaying recognize?

1. Low Voltage
2. Low Current Flow

11

What happens with voltage and current in an Inductive Load?

-Current lags behind voltage.
-Voltage peaks and current peaks are not in phase.

12

3 Types of Loads

1. Resistive Load
2. Inductive Load
3. Capacitive Load

13

What is the purpose of the Generator Stator

-Provides a place for the phase conductors.

14

What parameters must be met before putting the generator online?

1. generator voltage must match system voltage.
2. Frequency must be the same as operating system frequency.
3. Generator voltage must be in phase with the voltage of the system.
4. Voltage phase angles must match.
5. Rated Speed

15

Functions of Auxiliary Equipment

-Provide field excitation
-Generator cooling
-Lubricate the shaft bearings
-Protect generator from fault conditions

16

Synchroscope

-Used to match the frequency of the voltages.
-Compares the generator voltage waveform to the system voltage waveform by measuring the phase angle between the two voltages.

17

Line Voltage Meter

-Indicates the bus voltage in the switchyard.

18

Differential Relaying

-During normal operation no current flows through the relay because the amount of current flowing into and out of the windings is equal.
-If a fault occurs in the windings, the flow of the current is no longer balanced. The difference between current flow in and current flow out causes current to flow through the relay, then causing the generator to trip.

19

Generator Amps A, B, and C

-Shows how many amps are on each phase of the generator.
-Amps the generator is producing.
-Should all read about the same.

20

DC Ammeter

-Shows the amount of amps being produced by the exciter.

21

Field Rheostat

-Used to raise and lower the voltage to the generator from the exciter.

22

Reverse Power Relaying

-A loss of flow to the turbine causes the power flow from the generator to drop to zero. Under this condition, since the generator is still connected to the system power from the system drives the generator motor.
-The relay recognizes the reversal of power flow and operates after a preset short time delay.

23

Generator Rotor

-Field that revolves within the stator.
-The copper windings are made into bars similar to those in the stator.

24

What is the standard Electrical "speed" for electrical power in the US?

-60 Hz

25

Stator Core

-Consists of a stack of thin steel sheets made of a special alloy.

26

Negative Phase Sequence Relaying

-Negative phase current is caused by an unbalance in the three phase system (such as a short circuit in the system) in which all 3 phases are not involved.

27

Automatic Voltage Regulator

-Designed to change the exciter field current to hold the generator output voltage at the prescribed value.
-Control terminal voltage of the associated generator.

28

What does sparking of the brushes indicate?

-Brush pressure is too weak or that the brush is too short.

29

Brushes

-Press lightly on the slip rings and provide a conductive path from the exciter to the slip rings.
-conductor, usually composed in part of carbon, serving to maintain an electric connection between stationary and rotating parts of an electrical machine.

30

Lockouts

-Type of relay that, when tripped, the generator OCB will also trip.
-Will trip on overvoltage, loss of oil and water pressure, bearing temperature, low battery voltage, overspeed, and any bently alarm.

31

Generator Voltage

-Shows the voltage being produced by the generator.

32

Governor Control

-This control is used to operate the actuator which controls the opening and closing of the wicket gates.

33

3 things that control the amount of voltage induced into the conductor?

1. Strength of the magnet
2. Number of turns of the conductor
3. Rotational speed of the conductor through the field

34

Generator DC Volts

-Shows the DC voltage coming from the exciter to the generator.

35

Generator OCB

-Control to close the generator breaker when up to synchronous speed.

36

Air Gap

-A separating space between two paths of magnetic material through which the magnetic flux must pass.
-A typical representation of this space is the clearance between the rotor and stator of an electrical machine.

37

Alternator

-A device for converting mechanical energy into alternating current electrical energy.
-May be called a synchronous generator.

38

Field

-A region of magnetic lines of flux.
-May be produced by electrical current or permanent magnet.

39

Field Coil

-Insulated electric winding to be mounted on a field pole.

40

Field Pole

-Part of a magnetic structure of an electric machine on which the field coils are located.