Towards improved calibration in the measurement of partial discharges in rotating machinery

It is pointed out that an improved calibration strategy for partial-discharge (PD) detectors in rotating machine applications can only be achieved if the propagation characteristics of PD pulses are clearly understood, thus enabling the calibration pulse to simulate the discharge pulse more accurately as it appears at the detector terminals. The results of a pulse propagation study are reported, and the available models which may be of use in explaining the observed phenomena are discussed. Two forms of experimental procedure were adopted. In both, a 6.6-kV motor stator was utilized. In the first, a discharge simulating/calibration pulse was injected at one phase terminal and detected at different intercoil links. In the second, similar pulses were injected at the intercoil links and detected at the phase terminals. Pulse response was monitored on a 400-MHz-bandwidth oscilloscope and stored with an associated digitizing camera. Stator models developed in the area of surge propagation are reviewed, providing useful insight into the mechanisms for pulse propagation and providing the basis for the development of a general pulse propagation model. Digital signal processing considerations are also examined