Insulation Resistance of generator stator drops when the turbo-generator is charged with stator coil cooling water. To what value does it drop it? How come the gen is safe for production at that IR? To add detail, when the generator stator coil cooling water circuit is charged, if we measure the insulation resistance of the stator (phase to earth, say), the value is very less as compared to when it was before cooling water charging (due to the small levels of conductivity). I've been told, though this is not recommended to be measured, the value can be even as low as 1 Mega Ohm. I am curious as to why/how a generator can be declared ready for generation eventhough its insulation resistance in this condition is as low as noted above?