Signal transmission and calibration of on-line partial discharge measurements

Relevant standards such as the IEC60270 concentrate on a measurement frequency band below 1 MHz and on lumped, i.e. non-distributed test objects. On-line partial discharge measurements often require using higher frequencies to avoid noise interference. With respect to the basic gas discharge physics, the rise time of an electron avalanche under nitrogen atmosphere results in a partial discharge signal bandwidth of several hundreds of MHz at its origin. However, in terms of high frequency properties, distributed test objects, such as the stator winding of a rotating machine, for instance, act as a highly complex network. Mismatch of impedance, dispersion, attenuation, and other effect influence the applicability of different frequency bands and calibration techniques for partial discharge testing.