DC Generators
Carbon brushes are used in a dc machine because _______

None of the listed here
Carbon lubricates and polishes the commutator
Contact resistance is decreased
Carbon is cheap

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

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

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