DC Generators Objectives part 02
21 . If a is the degree of multiplicity and p is the number of poles, the number of parallel paths in a wave winding will be 2a.
22 . Hysteresis loss in a dc machine depends on Volume and grade of iron ,Max value of flux density and frequency of magnetic reversals .
23 . The effect of iron losses on dc machines is loss of efficiency, excessive heating of core.
24 . In dc machines the losses which has the highest proportion is armature copper loss
25 . In dc machines the losses which has the least proportion is mechanical losses.
26 . Armature copper loss in dc generator significantly varies with the load current.
27 . In dc generator the loss which has a least proportion is windage loss.
28 . A properly designed dc generator can have an overall efficiency of 95%.
29 . Eddy current loss will increase rapidly as compared to others when the number of magnetic reversals is increased.
30 . For a shunt generator copper loss is considered as constant.
31 . For reducing the hysteresis loss in a dc generator armature core material should have low hysteresis coefficient.
32 . When B is the maximum flux density then eddy current loss varies as 𝑩𝟐.
33 . The armature voltage control is considered as suitable in case the dc machine is driven at constant torque.
34 . Two dc generators have similar characteristics. The essential condition for stable parallel operation of these two generators is that they should have same drooping voltage characteristics.
35 . While pole flux remains constant, if the speed of a shunt wound dc generator is doubled its generated emf will be doubled.
36 . As a result of armature reaction, the total mutual air gap flux in a dc generator is approximately 5%.
37 . Interpoles are usually wound with heavy guage copper wire.
38 . Cool armature by ventilating air is not the function of the interpoles in dc generators.
39 . In dc generators the change in voltage when the load is reduced from rated value to zero, expressed as a percentage of the rated load voltage, is known as regulation.
40 . If θm be the mechanical degree θe be the electrical degree and Pbe the numbers of poles on a dc generator, then relation will be θm=2θe/P.