DC Generators
The overall efficiency of a dc generator is maximum when its variable loss is equal to

Stray loss
Iron loss
Mechanical loss
Constant loss

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DC Generators
When two D.C. series generators are running in parallel, an equalizer bar is used

To reduce the combined effect of armature reaction of both machines
To increase the speed and hence generated e.m.f.
So that two similar machines will pass approximately equal currents to the load
To increase the series flux

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