Propagation of partial discharge signals in stator windings of turbine generators

• Published in: IEEE transactions on energy conversion 2006-03, Vol.21 (1), p.155-161
• Main Authors: Pemen, A.J.M., van der Laan, P.C.T., Wout de Leeuw
• Format: Article
• Language: English
• Subjects: Couplings; Fault location; High-voltage techniques; insulation testing; machine windings; Partial discharge measurement; Partial discharges; partial discharges (PDs); Propagation; Pulse generation; Pulse measurements; Signal generators; Stator windings; Transmission line measurements; Turbines; turbogenerators
• ISSN: 0885-8969; 1558-0059
• DOI: 10.1109/TEC.2005.847949

We studied the propagation of partial discharge pulses in a stator winding by means of measurements on a dismantled 35-MW generator and found that a stator winding acts as a transmission line. Therefore, a partial-discharge (PD) signal manifests itself at the generator terminals after a transit time that depends on the location of the discharge. Due to capacitive and inductive couplings in the end-winding region, a second propagation mode is present for higher frequencies. This "fast mode" manifests itself at the terminals without appreciable time delay. The capacitive and inductive couplings also cause crosstalk between the phases. As a consequence, a signal measured in one phase does not necessarily originate from a discharge in that phase. The amplitudes of the fast mode and, to a lesser extent, the slow mode (or transmission-line mode) are heavily damped when the discharge occurs further away from the measuring terminal. The consequence is that only discharges close to the measuring terminal can be observed. The propagation of a PD signal is not only influenced by the construction of the generator but also by its external connections.