Jonathan, you are effectively describing high-resistance system grounding, that although not “mainstream,” is frequently used in industrial settings. There is a paper that discusses the application, although not specifically for a generator as sole power source. See
www.neiengineering.com/papers/paper1JN.pdf. The idea is to use a resistor connected from the generator-neutral point of stator windings to equipment ground. At 480V and under 1000kVA, the resistor is sized to limit ground-fault current to roughly one ampere. That is about a 280-ohm, 300-watt device, with a 480:120 potential transformer with primary connected across the grounding resistor with secondary connected to the relay.
Typically used is a two-setpoint protective (ANSI device 59N or 59G) voltage relay—one setting is configured to alarm/annunciate for initial manual intervention. A higher setting that can be applied to shunt-trip associated circuit breakers for ground faults. One example of the relay is a Basler BE1-59N at
www.basler.com/html/pcs59-87.htm#BE1-59N The relay has adjustable- voltage pickups of a few volts with time curves set for the application, to continuously withstand phase-to-ground voltage {scaled by the PT} without damage. The relay also has third-harmonic restraint to improve security.
[This message has been edited by Bjarney (edited 12-13-2004).]
