Estimation of the void content in HV stator coil insulation usingAC bridge measurements

摘要

It is shown that tan δ tip-up alone is not indicative of thevoid content of HV (high-voltage) stator coil insulation. A morereliable indication of the void content is obtained by calculating thedissipated energy from bridge measurements, assuming that all of it isdirectly due to partial discharges (PDs), and using the equivalent voidmodel circuit of Gemant. The significance of other dissipativemechanisms of interfacial and space-charge polarization, particularlyduring the occurrence of PDs, has been recognized, as have theshortcomings of the void model of Gemant, which does not account forthese phenomena. A modification to the circuit of Gemant is suggested byconsidering the effect of space charges. A method for calculating theeffective discharge inception voltage at a given test voltage isproposed