Oil filled bushing secrets revealed

Bushings provide a point of interface such that electrical current can pass to and from an electrical apparatus. Much like bridges on the highway, bushings are very critical and are the weakest link on any high voltage electrical apparatus such as power transformers, circuit breakers or instrument transformers. The integrate design and high areas of stress of bushings makes electrical testing, visual inspection and infrared inspection a vital part of any maintenance program. This paper describes the two elements of stress on bushings and breaks down a bushing into first principle components. Next, this paper details how portable test equipment can be used to examine these basic components of a bushing and gives guidelines for acceptance criteria. By understanding the basic construction of a bushing and applying testing methodologies of power factor, resistance, infrared inspection, and dissolved gas-in-oil, a good test and maintenance program can be established.