Detection of Multiple Partial Discharge Faults in Switchgear and Power Cables

Partial Discharge (PD) measurements are considered as the early detection of insulation degradation in power system equipment. In switchgear and power cables, multiple PD faults may exist, which make the detection and location of such incipient faults challenging. This paper deals with identification of multiple PD faults by a hybrid detection technique, by combining conventional and unconventional measurement methods.Unconventional PD measurements rely on detection of physical emissions due to such faults, e.g. detection of radio frequency (RF) electromagnetic (EM) fields in the vicinity of PD activity, ultrasonic waves, optical emissions and heat produced by the PD, whereas the conventional measurement methods are based on detection of high frequency current and voltage, superimposed on the power frequency current and voltage.In this paper, the apparent charge of PD events is calculated by using conventional measurement technique and EM signal energy is calculated based on unconventional method. The high frequency electric field was measured using a D-dot sensor. The comparison between the two parameters show that a second degree polynomial relation exists between the EM energy and apparent charge. The scatter plots between the two variables show a number of patterns due to the number of PD faults. Therefore, the detection of multiple faults is possible.