A New Method for Detection and Location of Distributed Partial Discharges (Cable Faults) in High Voltage Cables under External Interference

Existing partial discharge (PD) detection and location methods in high voltage cables are limited by the influence of external inter¬ ferences as well as by the type and properties of the cable and by the nature of PD impulses The problems of the existing methods.the frequency spectrum analysis and the traveling wave method.could be overcome by the development of a new electronic PD detection and location method based on the traveling wave method To exploit the PD impulses for an electronic location, several conditions have to be fulfilled The first is that PD impulses propaga ting along a cable are influenced by the low-pass behavior of the cable, the high-frequency components being highly attenuated The travel-time through the cable is a longer one for the reflected im¬ pulse than it is for the original impulse Therefore, the reflected impulse is attenuated more than the original one Its distortion and diminution grow with increasing cable length and with increasing fault distance from the far end of the cable The electronic recording of the time interval between the original and the reflected impulse therefore requires a preceding pulse amplification In this case, how¬ ever, the amplifier may be overdriven by the original impulse, while the reflected one is not yet sufficiently amplified This problem was solved by employing a controlled amplifier within the electronic location system Further, the shapes of both the original and the reflected impulses respectively could be matched to one another by various filters Furthermore, recorded PD or calibration impulses respectively might show overshoot due to the existence of different energy stor¬ age elements The overshoot then being caused by the electrical properties of the leads, ground connections or measuring units as well as the reflection coefficients of the connection points of the various circuit components An original impulse with positive over¬ shoot higher than the reflected impulse makes the electronic measurement of the time interval between both impulses impos¬ sible To solve this problem, high-pass filters are employed, sup¬ pressing low-frequency interference and largely eliminating undesired overshoot With the built PD location system which is de¬ scribed in detail, extensive investigations have been performed on coaxial HF cables with various lengths (model cables) as well as on various HV cables under 3 to 60kV ac voltage in order to determine the sensitivity and the accuracy of the new system compared to