Critical cavity size producing internal discharges in stator bar ground wall insulation

Partial discharges (PDs) cause degradation of the generator stator bars insultation. The use of mica in this insulation system prevents small internal PDs from reducing the expected life of the equipment. However, some cavities may be the cause of a more significant PD presence and accelerate the aging of the insulation system. A method that uses the Paschen law and numerical simulations is presented for determining critical cavity sizes that produce significant PDs.