DC Generators Objectives Part 01
01 . In lap winding the number of brushes is equals to number of poles.
02 . Rotor of a motor is usually supported on ball or roller bearings.
03 . Each commutator segment is connected to the armature conductor by means of copper lug.
04 . A two-layer lap wound 4 pole generator with 16 coils will have a pole pitch of 8.
05 . Dummy coils in generators are provided to mechanically balance the rotor.
06 . In a dc machine if p is the number of poles, n is the armature speed in rpm, then the frequency of magnetic reversal will be PN/120.
07 . For parallel operation the generators normally preferred are shunt generators.
08 . The residual magnetism of a dc shunt generator can be regained by connecting the shunt field to a battery.
09 . Lap winding on dc generators is preferred for generating the large current.
10 . Load saturation characteristics of a dc generator gives relation between V and If.
11 . In an ideal dc generator, the regulation is zero.
12 . The decrease in terminal voltage of a shunt generator is due to armature resistance.
13 . In a dc generator the effect of armature reaction on the main pole flux is to reverse it.(in other sources the answer is reduce it and distort it)
14 . In a 10-pole, lap wound dc generator the number of active armature conductors per pole is 50. The number of compensating conductors per pole required is 5.
15 . Maximum efficiency in machines occurs when constant losses = variable losses.
16 . ifyf is the front pitch ,yb is the back pitch yc is the commutator pitch then in wave winding yf+yb=2 yc.
17 . Maximum power output is given by a machine at an efficiency of 50%.
18 . Equalizer rings are required in a lap winding dc machine to prevent flow of circulating current through the brushes.
19 . For a fixed number of poles and armature conductor, wave winding will give higher emf.
20 . For wave winding the average pitch must be even or odd.