DC Generators
For a D.C. machines laboratory following type of D.C. supply will be suitable

Rotary converter
Mercury are rectifier
Synchronous motor D.C. generator set
Induction motor D.C. generator set

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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.
So that two similar machines will pass approximately equal currents to the load
To reduce the combined effect of armature reaction of both machines
To increase the series flux

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