All stator windings are not created equal

It is noted that modern high-voltage stator windings in very large hydro generators are subject to attack from many sources-thermal aging, high-intensity slot discharge, low-intensity partial discharge (corona), mechanical vibration, oil, and high electrical bar forces. Any of these can be detrimental to the total insulation system, and together can sometimes cause insulation failure. Each failure mechanism has its own preventive measure. Each of these must be refined and incorporated into the total insulation system of the machine to enable it to operate successfully in service for a long period of time. Some of these failure mechanisms are discussed in association with pertinent laboratory studies and field experience