SYNCHRONOUS MACHINES

Construction & types of synchronous machines	Armature reaction	Phasor diagram	Two axis theory
Voltage regulation	Parallel operation of alternators	Synchronous motors	Hunting
		Internet website: Simulator for synchronous generator	Objective questions

HOME takes you to the start page after you have read these Topics. Start page has links to other topics.

http://powerlearn.ee.iastate.edu -- Simulator for synchronous generator

Construction & types of synchronous machines

Types of synchronous machines, simple working of synchronous machine as a generator and motor, expression for induced emf. Generator & motor operation

Armature reaction

Resultant mmf vector, armature reaction reactance, synchronous impedance, simple equivalent circuit

Phasor diagram

Phasor diagram for cylindrical rotor machine, synchronous impedance from open circuit & short-circuit tests, short circuit ratio, generator load characteristics, armature reaction ampere turns and leakage reactance, Potier method

Two axis theory

Two-reaction theory of salient pole machine, phasor diagram & power angle relations, reluctance machine

TOP

Voltage regulation

Voltage regulation by different methods

TOP

Parallel operation of alternators

Synchronous machine on infinite bus (generator & motor action) and synchronization, synchronous machine operation on infinite bus at

1. Constant excitation with variable load

2. Constant load under variable excitation (O-curves & V-curves) TOP

Synchronous motors

Starting of synchronous motors, V-curves, Torque & power angle curves

TOP

Hunting

Hunting in synchronous machines, damper winding

TOP

Objective questions

1. The damper winding in the synchronous moor is often used to

a) prevent hunting only

b) prevent hunting & provide the starting toque

c) maintain synchronism

d) provide the starting torque only.

Ans. b

2. Which of the following statements is true?

Short-pitched coils in the alternators are used to

a) reduce the size of the machine

b) reduce the harmonics or to eliminate the harmonics from the generated emf

c) provide accurate phase difference of 120 degrees between phases

d) reduce copper losses.

Ans. b

3. The armature flux of an alternator at unity power factor load will be

a) demagnetizing

b) of square waveform

c) cross-magnetizing

Ans. c

4. The armature reaction of an alternator will be completely magnetizing when

load power factor is

a) unity

b) zero lagging

c) zero leading

d) 0.8 lagging

Ans. c

5. If two alternators are running in parallel and he voltage of one machine is suddenly increased

a) the machine winding will burn

b) both machines will stop

c) synchronizing torque will be produced to restore synchronism

Ans. c

6. If the input to the prime mover of an alternator ( in a system of three alternators) is kept constant, and the excitation is changed, then

(1) the reactive component of the output is changed

(2) the active component of the output is changed

(3) the power factor of the load remains the same

(4) (a) and (b) occur simultaneously.

Ans. a

7. The coupling angle or load angle of a synchronous motor is defined as the angle between the

a) rotor and the stator poles of same polarity

b) rotor and the stator poles of opposite polarity

c) rotor and stator teeth

Ans. b