Hi

kindly inform:

why we ground the rotor and what is the danger if did not ground it?

regards
neger
nubaria power station
Egypt

Hello the reason why the rotor is grounded is to prevent circulating currents on the rotor. Only one side should be grounded..typically opposite of the collector, As is the bearing. The rotor grounding brush will dissipate any stray or induced voltages that are on the rotor itself.
thanks