Synchronous Generator

Question 1

Stator

Answer 1

Outer part of machine that is stationary

Question 2

Rotor

Answer 2

Inner shaft of machine that is free to rotate

Question 3

Field Winding

Answer 3

Produces main magnetic field (rotor for AC)

Question 4

Armature Winding

Answer 4

Where main voltage is induced (stator for AC)

Question 5

Synchronous machine

Answer 5

Magnetic field current supplied by separate DC source

Question 6

Induction machine

Answer 6

Field current supplied by magnetic induction into field winding

Question 7

What produces rotating magnetic field

Answer 7

Rotor is supplied with DC current for rotor magnetic field and moved by prime mover like turbine

Question 8

Salient pole

Answer 8

Protruding from surface (4+ poles)

Question 9

Nonsalient pole

Answer 9

Flush with surface (2-4 poles)

Question 10

Why is rotor constructed of thin laminations

Answer 10

To reduce eddy current losses from changing magnetic field

Question 11

Slip rings

Answer 11

Metal rings commonly encircling shaft of machine, but insulated from it

Question 12

Brush

Answer 12

Block of graphite like carbon compound that conducts electricity freely but has very low friction

Question 13

Smaller machines are supplied by

Answer 13

Slip rings and brushes

Question 14

Larger machines are supplied by

Answer 14

Brushless exciters

Question 15

Brushless exciters has field cirucit on ______ and armature circuit on _____

Answer 15

Stator
Rotor

Question 16

Why is it called synchronous generator

Answer 16

Electrical frequency produced is locked in with mechanical rate of rotation

Question 17

Internal generated voltage Ea is directly proportional to

Answer 17

Speed and flux

Question 18

Flux depends on

Answer 18

Field current in rotor circuit

Question 19

The graph of Ea over If is called

Answer 19

Magnetization curve or Open Circuit Characteristics

Question 20

VT = Ea if

Answer 20

Generator is at no load

Question 21

What effects Vt under load conditions

Answer 21

Armature reaction
Self inductance of armature
Resistance of armature
Effect of salient pole rotor shape

Question 22

What is Armature reaction

Answer 22

Distortion of air gap magnetic field by current flowing in stator

Question 23

Estat ____ the plane of maximum current

Answer 23

Lags by 90 degrees

Question 24

For given phase voltage and armature current we need ______ Ea for lagging loads

Answer 24

Larger

Question 24

For given field current and load current Vt is ______ for lagging loads

Answer 24

Lower

Question 25

What is the power flow for synchronous generator

Answer 25

Input mechanical power first loses stray losses then it goes into the rotor where friction and windage losses occur, then the core is magnetized causing core losses after which power is converted to electrical. Here we have copper losses, then finally output power

Question 26

What is torque angle

Answer 26

Angle between Vphi and Ea (power depends on this)

Question 27

What is static stability limit

Answer 27

Maximum power of generator

Question 28

Why is the short circuit characteristics linear

Answer 28

In short circuit, rotor and stator magnetic fields almost cancel each other and net magnetic field is very small so the machine is unsaturated

Question 29

Why is value of Xs calculated only an approximate

Answer 29

Ea taken from OCC is different from Ea at same If for short circuit

Question 30

Short circuit ratio

Answer 30

Ratio of If for rated voltage at open circuit to If for rated Ia for short circuit

Question 31

Adding lagging load ______ Vt

Answer 31

Decreases