Synchronous Generator Objectives Part 02

21 . Voltage characteristic of an alternator is shown in figure. Which curve represents the characteristics for leading power factor? D

22 . In the above figure, the characteristic for unity power factor is represented by the curve maked – C

Questions 23 to 26 refer to the following data:

In a 50 kVA, star connected 440 V, 4-phase 50 Hz alternator, the effective armature resistance is 0.25 ohm per phase. The synchronous reactance is 3.2 ohm per phase and leakage reactance is 0.5 ohm per phase.

23 . Full load output current at unity power factor will be- 65.6 A 24) Full load line voltage will be- 471 V

25 . No load line voltage will be- 592V

26 . Percentage regulation of the alternator is approximately-25%.

27 . In order that two alternators be put in parallel, which of the following factors should be identical for both

(A) Voltage

(B) Frequency

(C) Phase sequence

28 . When two alternators are running in parallel, their RKVA load share is changed by changing their excitation while their kW load share is changed by changing their driving torque

29 . Two-alternators are running in parallel. If the driving force of both the alternators is changed, this will result in change is frequency

30 . A three phase alternator has a phase sequence of RYB for its three output voltages. In case the field current is reversed, the phase sequence will become RYB

31 . The armature reaction of an alternator influences generated voltage per phase

32 . For the same power rating, a lower voltage alternator will be larger in size

33 . An alternator is supplying 10A to an inductive load at 220 V, while running at 1000 rpm. Now if the speed of the alternator is reduced to 750 rpm but the field current remains unchanged, the load current will become 10 A

34 . Dampers in a large generator increase stability

35 . An alternator is rated for 75 kW at 0.8 power factor. It means that alternator can supply 75 kW at 0.8 power factor

36 . The regulation of an alternator is the increase in terminal voltage when load is thrown off

37 . A magnetization curve represents the relationship between exciting currents and terminal voltage

38 . In an alternator if the armature reaction produces demagnetization of the main field, the power factor should be Zero, lagging load

39 . In an alternator if the armature reaction produces magnetization of the main field the power factor should be Zero, lagging load

40 . When an alternator is supplying unity power factor load, the armature reaction will produce demagnetization of the main field