Stator Earth Fault for High Voltage Generator

The thing to do is to read the manual, then pick up the telephone, and ring the equipment manufacturer's technical helpline.

The Lightening arrestor can be checked with and ohm meter an should be wide open. That is the simplest. The better way is to put an amp meter& arrestor in series with a dc voltage source and bring the voltage up slowly. If you get any current, shut it off because it's broken. If you attain your operating voltage without current draw it's probably OK. This of course does not check for spikes or surges. For them you must go higher.

A conventional ohmmeter (or DMM) isn't going to be able to diagnose the OP's problem if he actually has stator insulation breakdown going on, unless it's practically a bolted fault to ground. What he needs is to do a DC insulation resistance test with an instrument made for that purpose, usually called a "megger" or megohm meter.

For the voltage rating of his equipment, he should use at least a 5000V megger. Test the stator insulation to ground with all other items disconnected (including disconnect the neutral grounding transformer and the arresters). Test the neutral grounding transformer from primary winding to ground and primary to secondary winding (at 5000V) and secondary winding to ground (at 500V). Test the arresters to ground at 5000V.

These are the simplest tests to perform, and will show most gross problems. If they all come out okay, then more diagnostics are needed, such as is the stator ground relay set properly and operating properly, is the resistor on the neutral transformer secondary the proper value (or exists at all), and so on. This will need the services of a qualified HV testing company, which is the OP's best course of action anyway.

do you know recommanded setting (ISO based lists of differents generators ratings and trasformers ???it will help me in future problem.My generator has 12.5 MVA with neutral grounding transformer of proximate 9kva ) after Meggering using 5000kv or any other megger.????when u troubleshoot earthling fault at stator terminals(ie neutral grounding transformer and Lightening arrestor or some generator low resistance maybe used) of generator.

synchronized connection is easy just connect the the genset to the MCB bus bar togehter with the national public power then your done !!! and to make an automatic trasfer you need to get or install automatic transfer switch and for installing the autotrasfer switch the line/ neutral cable connect to the genset line / neutral so when the genset will shutdown the autotrasfer switch will closed he will trigger the contactor to swift in national power . but if you are not qualified to do the job just call me oppppssss!!! not me call your eletrician,