Damage resulting from long term slot discharge activity in a hydrogen environment

Two 17-kV, 160 MVAr hydrogen-cooled synchronous condensers were recently rewound. They had operated since original installation with significant slot discharge activity. At the time of rewind the original stator bars were inspected to determine the extent of the slot discharge and vibration related damage to the groundwall insulation. It was found that inadequately side packed and wedged stator windings are subject to significant erosion from slot discharge and vibration even in a hydrogen environment. A semiconducting coating painted over the cured groundwall insulation may not be durable. It is concluded that wedging materials should be chosen to better enable a stator winding to withstand short-circuit forces.<
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