Power Stages in a d.c. generator
The various power stages in a d.c. generator are represented diagrammatically in Fig. (1.39).
A – B = Iron and friction losses
B – C = Copper losses
(i) Mechanical efficiency
(ii) Electrical efficiency
(iii) Commercial or overall efficiency
Unless otherwise stated, commercial efficiency is always understood.
Now, commercial efficiency
,
Condition for Maximum Efficiency
The efficiency of a d.c. generator is not constant but varies with load. Consider a shunt generator delivering a load current IL at a terminal voltage V.
The shunt field current Ish is generally small as compared to IL and, therefore, can be neglected.
The efficiency will be maximum when the denominator of Eq.(i) is minimum i.e.
The load current corresponding to maximum efficiency is given by;
Hence, the efficiency of a d.c. generator will be maximum when the load current is such that variable loss is equal to the constant loss. Fig (1.40) shows the variation of η with load current.
Written by arjun on May 7th, 2009 with
2 comments.
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ravi
#1. May 15th, 2009, at 6:25 AM.
calculations about emf equation power stages & losses