QUE-ANS:10-30 words
[1] What is the function of commutator in a dc machine?
The function of commutator is to convert the alternating emf induced in the armature into unidirectional (dc) current in the external circuit.
[2] What are the types of dc generators?
The generators are classified into separately excited and self excited generators. The self excited
Generators are further classified into shunt, series, long shunt (cumulative and differential) and short shunt (cumulative and differential).
[3] What are the various losses in a dc machine?
Copper loss: both armature and field
Iron loss: hysteresis loss + eddy current loss
Constant or mechanical losses: friction losses + windage losses.
[4] What are the conditions for the voltage to build up in a dc shunt generator?
- A) There must be residual magnetism.
- B) Shunt field coils should be properly and correctly connected to the armature terminals.
- C) Shunt field resistance should be less than the critical resistance.
[5] What is direct-connected alternator?
One in which the alternator and engine are directly connected. No intermediate gearing such as
Belt Chain etc. is installed between them.
30-60 words
[1] What are the characteristics of dc generator?
- Open circuit characteristics or magnetic characteristic
(emf generated under no load Vs field current)
- Total or internal characteristics (generated emf Vs armature current)
- External characteristics or voltage regulation curve (terminal voltage Vs load current)