If for some reason the generator breaker should not trip and the generator begins acting as a motor, would a voltage and current be seen on the instruments for the excitation system?

 

That would depend.

(I presume we're talking about a three-phase, synchronous generator with some an exciter regulator.)

One condition would be whether the exciter regulator (AVR) remained in operation or not. In the case where the exciter regulator didn't trip and remained in operation, there would be an indication of current and voltage on the exciter regulator.

Though if the exciter regulator didn't continue to run the rotor would likely overheat pretty quickly due to inductive effect of the stator magnetic field acting on the rotor punchings, etc. And in this case, there would likely be no readings on the exciter instruments.

 

Ibamez... although sparse in substance, CSA's final comment about exciter instruments is correct! Typically, a generator can be "motored" for two types of events: 1) sudden loss of its prime-mover; or 2) inadvertent energization due to human or equipment failure. Your question is best answered by a brief explanation of what happens in both the stator and rotor circuits.

In either case, stator current causes a rotating flux to be induced thru certain rotor paths. Some are the rotor-iron (mostly surface), slot wedges, and retaining rings. The rotor winding is also affected, but usually via eddy-currents, to a lesser degree.

The resultant currents are AC in nature, hence undetectable by instruments normally assigned the task of monitoring the rotor's electrical parameters.

Let me know if additional detail is required.

Regards, Phil Corso