Monitoring of Exciter and Rotor winding insulation resistance

[NickParker]

The specification states: "There should be provisions for brushless continuous monitoring of the exciter and rotor winding insulation resistance. Additionally, provisions should be made for monitoring the rectifier diodes, with alarms triggered for both open and shorted diodes."

This is for marine main diesel generators with a capacity of around 3.5MW. While I have already asked the vendor for clarification, I wanted to ask here in the meantime:
How do vendors typically achieve this?

 

[Gr8blu]

First - I think the specification should read "There should be provisions for continuous monitoring of the brushless exciter stator and exciter rotor winding insulation resistance...".

Note that the way the specification is worded (or at least the excerpt supplied by the OP), it is unclear whether the intent is to monitor the exciter rotor or the main synchronous rotor winding for insulation resistance.

For the diodes, there's usually some additional computing power on the rectified wheel that looks at the output waveform from the diodes and checks against known failure modes (e.g. one diode is short-circuited, etc.). If such a "bad" waveform is detected, the alarm is sounded.

I know there are at least two different ways that the exciter windings are checked for insulation resistance - but I couldn't explain them if I tried. My guess is that they are looking at a capacitance-to-ground measurement or some sort of leakage current and flagging changes that may be associated with deteriorating insulation resistance.

Converting energy to motion for more than half a century

 

[thermionic1]

This paper describes a Basler Diode monitor

https://docs.ips.us/docs/W1002340.pdf