Investigation of white powder found on pump motor stator winding

During a routine physical inspection of pump motor unit P7 at the Little Harquahala pumped storage power plant in Central Arizona, USA, a very fine, white powder was found on the surface of the stator winding. A series of inspections, tests, and analyses was performed to determine whether the particles were caused by electrical, chemical, or mechanical breakdown of the stator winding insulation system, or the result of contamination by a foreign material. The course and outcome of the stator winding investigation are presented.