An improved technique to determine the wave propagation velocity of medium voltage cables for PD diagnostics

Investigation of wave propagation characteristics for high frequency pulses is an important aspect for the partial discharge (PD) diagnostics in medium voltage cables. Precision in determining the electromagnetic wave propagation velocity in the cables determines the accuracy of developing cable model and localization of partial discharge initiation site. It has been observed that commonly used time domain reflectometry (TDR) and time difference of arrival (TDA) methods pose certain limitations while finding out the propagation velocity of the cables. This can cause serious inaccuracy during localization of PD faults. This paper presents an alternative quarter wave length (QWL) method in frequency domain to measure the propagation velocity. It is based on transmission line model of the cables and eliminates the practical limitations of TDR and TDA techniques. The comparative assessment of these methods is presented based on experimental measurements. The comparison asserts the improved performance of proposed technique. This improved technique can be used to enhance the diagnostics capability for power networks.