Electric field method is one of most efficient method to defect composite insulator. But it is not be used widely on porcelain insulator. In this paper, research of using the electric field method on porcelain insulators was made. A space electric field probe measured the distribution of electric field around the insulators. Several faulty insulators were place on the
Electric field method can be used on porcelain insulator. To same faulty insulator, the electric field descent value AE at its position is increasing when it is closing to the high voltage line, the field electric rate-of-change AE/E is also increasing. But when faulty insulator is far from high voltage line, the AE/E has not obvious change. If the faulty insulator is exactly at the middle position of the string, its AE/E is the smallest. To one faulty insulator, the AE and AE/E are decreasing quickly with the increasing of the resistance of the faulty insulator. When the resistance of faulty insulator is up to 120MQ, the AE/E is down to zero. Thinking about measurement error at real transmission