DC Generators Objectives Part 03

41 . The number of mechanical and electrical degrees for a dc generator will be the same when the generator has 2 poles.

42 . A dc generator running at 1600 rpm gives 240 V dc. If the speed is dropped to 1400 rpm without change in flux. The new emf will be 210V.

43 . In dc generators, an interpole field coils are connected in series with armature.

44 . In a dc generator the polarity of interpole is same as the polarity of the main pole that precedes in the direction of rotation. (In motor, reverse)

45 . When a dc generator is operating at constant speed, variable load, copper loss is likely to vary significantly.

46 . Total losses in a properly designed 1kW dc generator may be of the order 50W.

47 . If the no load voltage of a certain generator is 220V and the rated load voltage is 200V, then the voltage regulation is 10%.

48 . In a duplex winding for a 4-pole machine, the number of parallel paths will be 8.

49 . In dc generator External characteristics = magnetization characteristics-armature reaction-Ohmic drop.

50 . Series generator cannot start if there is no residual magnetism.

51 . The direction of rotation of a shunt generator can be reversed by interchanging the polarity of field winding.

52 . A shunt generator running in 600 rpm has an induced emf of 200 volts. If the speed increases to 750 rpm, the induced emf will be 250V.

53 . A sinusoidal voltage of frequency 1 Hz is applied to the field of a dc generator. The armature voltage will be 1 Hz sinusoidal.

54 . Equalizer rings in lap wound dc generators are used to avoid unequal distribution of current at the brushes thereby helping to get sparkles commutation.

55 . Hysteresis loss in a dc shunt generator varies as 1.6 power flux density.

56 . The critical resistance of the dc generator refers to the resistance of field.

57 . In a dc generator if field winding attains the critical resistances the voltage generated will be zero.

58 . In a 4-pole dc machine alternate poles are north and south.

59 . If A be the commercial efficiency, B be the electrical efficiency and C be the mechanical efficiency of a dc generator then A=BxC relation is valid.

60 . Overall efficiency of a well-designed generator may be expected to be around 90 to 95%.