Investigation into the possibility of partial discharge damage in a synchronous generator supplying a thyristor bridge load

The loading of a small synchronous generator with a thyristor bridge causes harmonic currents to flow in its windings. This can lead to an increase in the generator´s working temperature. This temperature increase promotes additional thermal stressing of the machine, and acts to lower the partial discharge (PD) inception and extinction voltages of its insulation system. The use of a thyristor bridge also produces notches in the generator phase-to-neutral and line-to-line voltage waveforms, the leading edges of which are sufficiently fast fronted to cause a non-linear distribution over the phase winding. Furthermore, the use of thyristor snubbers can produce an oscillating overvoltage at the trailing edge of the notch. It has been suggested that these overvoltages and fast fronted transients may produce PDs in the generator insulation, possibly leading to damage and premature failure. The paper details a laboratory investigation into the PD performance of the insulation in a 16 kVA, three phase synchronous generator when loaded with a thyristor bridge.