Synchronous Generator Objectives Part 08

141 . Consider the following statements about a three-phase synchronous generator synchronized to an infinite bus when its mechanical input is increased gradually with field current held constant: 1. The power factor of the current supplied becomes more lagging. 2. The power factor of the current supplied improves. 3. The power factor remains unity. 4. The load angle is increased. Of these statements (B) 2 alone is correct

142 . A 3-phase synchronous generator, with its armature resistance and the leakage reactance being neglected, is synchronized to an infinite bus and its field excitation is kept constant thereafter. Now the machine is loaded by Supplying mechanical input to the shaft so that the load-angle δ reaches a value of 60° Under this condition, the operating power-factor would be 0.866 lagging

143 . A round rotor synchronous generator has a leakage reactance of 10%, armature reaction reactance of 90% and negligible armature resistance. With the machine initially running at rated speed and terminal voltage of 1.0 p.u., a 3-phase short-circuit is applied. The sustained armature current will be 1.11 p.u

144 . Following a sudden short-circuit at the terminals of a 3-phase unloaded synchronous generator, the initial effect of the pole-face damper windings, is to allow only partial linkage of the armature flux with the main field winding

145 . In a synchronous generator operating at zero pf lagging, the effect of armature reaction is demagnetizing

146 . which of the following limit the reactive power output of a synchronous generator ? 1. Armature current 2. Field current 3. Load angle 4. Prime mover input. Select the correct answer using the codes given below: (B) 2 and 3

147 . The steady-state stability limit of a synchronous generator can be increased by an increase in the excitation of the machine

Synchronous Generator: Fill in the blanks with appropriate words:

01 . When a turbine drives an alternator it is termed as Turbo alternator.

02 . A two pole alternator running at 1500 rpm will generate emf at 25 Hz.

03 . The stator winding of a three poles alternator is always Star connected.

04 . The rotor of an alternator has Two slip rings for DC supply.

05 . In an alternator, with the fall in leading power factor, its voltage. RISES from no load to full load.

06 . In large alternators damper winding is used to improve Stability.

07. The rating of an alternator is expressed in terms of KVA or MVA.

08. A six pole alternator running at 1200 rpm will generate voltage at the frequency of 60 Hz.

09. In case of an alternator having negative regulation, the terminal voltage will rise kW output of the alternators Increases.

10. A synchronous generator’s ability to produce electric power is primarily limited by Heating within the machine.

11 . When a generator is connected to infinite bus-bars, its Frequency and Voltage are fixed.

12 . A generator has two different windings, Armature field and winding.

13 . The maximum allowable heating in the armature winding sets the maximum KVA allowable from the machine.

14 . A generator with a service factor of 1.1.15 can actually be operated at 115 percent of the rated load Indefinitely without harm.

15 . 15. High capacity generators are usually Hydrgen cooled.

16 . In a synchronous generator, the Armature is always a stationary member, and the Field structure moving member.

17. In a fractional-pitch winding the coil span is less than180 electrical degrees.

18 . Salient-pole synchronous generators normally operate at Lower speeds.

19. Fields of synchronous generators have high Inductance inductance.

20 . Aircraft alternators generate High frequency voltage high.

21 . The synchronous reaction is made up of and reactances magnetization

22 . In order to get sinusoidal wave output the airgap under the salient pole machine should be proportional to 1 cosθ

23 . For unity power factor load, the effect of armature reaction in alternator will be cross magnetising.

24 . In alternators is stationary armature.

25 . The winding tends to maintain balanced 3φ voltages under unbalanced load conditions damper.

26 . Armature windings in alternators are from those used in DC machines different .

27 . In connections, third harmonic, components are additive round the mesh delta connection.

28 . In alternators of the load has a considerable effect on armature reaction power factor.

29 . In case of leading load p.f. regulation is negative.

30 . For proper synchronization of alternator, speed of incoming machine must be such that its frequency bus-bar frequency equal.

31 . Infinite bus-bars are constant and constant bus-bars frequency voltage .

32 . Synchronous generators have a voltage regulation large .

33 . Synchronous of a synchronous generator is not constant over entire operating range impedance.

34 . A synchronous generator could be build by replacing the Commutator in a DC machine by slip rings commutator.

35 . The factor by which the EMF of a distributed winding must be multiplied to give the total generated EMF is called Distribution factor for the winding distribution factor.