PD-pulse characteristics in rotating machine insulation

In this contribution will be presented results from investigations on partial discharges (PD) in insulation systems, resembling the stator insulation in high voltage rotating machines. A model, simulating a stator winding in a slot, has been developed, consisting of simple rotating machine insulation test bars with epoxylmica insulation, mounted between steel sheets forming a slot, in order to investigate the fundamental behaviour of PD in insulation defects in epoxylmica insulation and the characteristics of the resulting electrical pulses. Stator slot couplers (SSC) were used to detect pulses coming from artificial defects implemented in the model as well as from the existing voids in the test bars' insulation. Some characteristic pulse shapes were found, which partly could be related to the defect type. The high frequency detection method, with directional couplers, made it possible to localize the defects thereby determining the pulse distortion in the chosen geometry. The influence of some parameters was investigated, such as the voltage applied, the location of the defect with respect to the sensor and the orientation of the defect in the slot. These informations are essential for PD-detection systems where the noiselsignal separation is based on the pulse shape, such as the SSC-technology used in the present investigations.