Insulation systems and monitoring for stator windings of large rotating machines

The condition of the insulation system frequently limits the useful life of the windings of a rotating machine. This is a function of thermal, electrical, environmental, and mechanical factors plus the type of duty to which the machine is subjected. The thermal classifications of the variety of insulating materials that make up an applied insulation system are presented. Strand and turn insulation, common groundwall insulation systems, armor tapes and coatings, side packing and wedging methods, are discussed. Four factors that influence insulation life are identified: thermal, electrical, ambient (environmental), and mechanical plus performance (intended) and duty (mode of operation). Finally, accelerated aging tests, inspections and diagnostic test during service outages, and online monitoring of partial discharges are discussed.<>