Improving PD detection in long cable routes through advanced analysis technique

Attenuation phenomena in power cables increase with frequency, thus reducing the optimum bandwidth for PD detection. Therefore, in order to assess PD amplitude with maximum signal-to-nose (SNR) ratio, it is fundamental to know cable propagation constants. In this paper two methodologies have been chosen to determine cable propagation constant and characteristic impedance. The first is one-port measurement configuration to determine the open and short circuit impedance of the cable in function of the frequency. The second one is a two-port measurement configuration to determine the scattering matrix. The two measurement techniques have been applied and compared on splices of a 20 kV power cable with EPR insulation. It was found that one-port measurements provide more accurate results and should, therefore, be preferred.