Our 3 phase induction motors winding burn last week. Three motors, 160kw4poles, 37kw4poles,90kw4poles. we found the grains of copper under the DE turn coil of all motors. All DE turn coil was black but NDE turn was clean just like nothing happen there. at the bottom of DE turn coil such wet oil or something. I found no grease on the winding due excess grease, but I think this oil came from grease. We used omega 77 for 160 and 90kw, and alvania R3 for 37kw motor. Any one please explain to me, did the oil from melt grease harm to winding? how to avoid this problem. thank in advance.