Pitfalls of partial discharge measurements on stator windings of turbine generators

The last decade shows a growing interest in the monitoring of partial discharges in stator windings of turbine generators. By monitoring discharges, one can follow possible deterioration of the insulation and detect serious faults at an early stage. Unfortunately, for the monitoring of discharges during regular operation, the standard technique according to IEC270 is not applicable. The main reasons for this are the complex propagation of discharge signals through a stator winding and the presence of many EM-disturbance sources in a power plant. In this paper, these important pitfalls are discussed; it is shown that a standard pd-detector can only be used if preceded by a sophisticated front-end. We illustrate with measurements on operating generators how interference and cross-talk can be rejected