Rotor ground faults without slip rings

[NickParker]

What are the methods for detecting ground faults in rotor windings without using slip rings? This is for diesel generators with a capacity of 3 to 5 MVA.
Does the current injection principle for detecting ground faults require slip rings?
Is rotor earth fault detection necessary for generators in this capacity range? Can I use loss of excitation for detecting rotor earth fault detection?

 

[waross]

Disconnect the rotating diodes and megger-test the rotor.
Also test the diodes while you have the chance.

 

[edison123]

No, you cannot detect rotor ground fault without sliprings. Rotor can run with single earth fault but will have damaging vibrations if it develops a second earth fault.
Loss of excitation is harder to detect and will not detect rotor earth fault.

 

[wcaseyharman]

GE on their 6A3 generators with brushless exciters in the 90s (and I am assuming others had this although I haven’t seen them) used a rotor mounted unit that would light an indicator when the rotor insulation was present. The light would turn off when a ground fault was detected. A stationary receiver would reset a timer when the light triggered the indicator, when the timer expired it would trigger a rotor ground fault alarm. This allowed rotor ground detection be provided without slip rings.