We are inspecting the rotor earthing on a frame 6B generator at the exciter end and request if someone could please explain how it is supposed to work and the theory behind it. We have a measurement brush, a check brush, a brush control power supply, a rotor earth test pushbutton, a timer set for a 10 second on pulse every 10 hours. Interpreting the drawing suggests that when the machine is running (field on) the measurement brush is engaged for 10 seconds then every 10 hours for another 10 seconds, or when the test pushbutton is pressed and when the machine is off the test pushbutton engages the test brush. We assume the test brush should bring up a rotor earth fault and the measurement brush should not - so it's testing the rotor earth protection which is why the test brush can only be engaged when the machine is off to prevent a trip.
Have I got this right? thanks.