ON-LINE DETECTION AND LOCATION OF LOW-LEVEL ARCING FAULTS IN METAL-CLAD ELECTRICAL EQUIPMENT
Sagoo, Gurinder Singh
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Modern metal-clad electrical equipment are built with tight insulation tolerances and are consequently subjected to severe electrical and thermal stresses. Insulation failure as a result of higher electrical and thermal stresses leads to arcing faults. Large numbers of equipment fire and burndown cases, arising from the low-level arcing faults, have been reported in the past. It has been found that a low-level arcing fault does not cause significant changes in the system voltages and currents. Therefore, conventional protective devices that rely on sufficient changes in system voltages and currents may not detect the inception of an arcing fault. The consequence is that the damage due to the arcing fault is substantial. Three techniques have been suggested in the past for the detection of electric arcs. Two techniques are based on detection of light and magnetic fields associated with an electric arc whereas the third technique is based on three different physical phenomena associated with an electric arc. These techniques have limitations that impact on the reliability, cost and practicality of their use in detecting arcs in electrical equipment. A new system for detecting and locating low-level arcs in metal-clad electrical equipment is proposed in this thesis. The proposed system detects the inception of an arcing fault by analyzing ultrasonic, infrared, radio-frequency and acoustic radiation associated with arcing. The system uses sensitive sensors and signal conditioning units to process the information collected by sensors on the occurrence of an arcing fault. The collected information is analyzed using a modern digital signal processing system. The system also locates the arcing fault by obtaining the video images of the arc using a miniature video camera. The proposed system is a stand-alone system and does not require physical contact with the fault. Extensive testing of the proposed system was done by creating arcing faults in a metal-clad dry-type 15kVA step-down transformer and a 230V, 600A MCC switchgear panel in the Power Systems Laboratory at the University of Saskatchewan. Performance of the developed system was studied under a variety of operating conditions. The effect of load current and external interference from a non-arcing source was investigated. The performance of the proposed system was also tested for simultaneous arcing faults inside the enclosure and for arcing faults outside the enclosure. The results show that the developed system performs satisfactorily in all the cases. It is concluded that the proposed system can detect and locate arcing faults in metal-clad electrical equipment. The system has potential application in the metal-clad equipment industry and can provide significant benefits with little additional cost.