On-line monitoring and diagnoses of power transformer bushings

Power transformers have been in service for many years under different conditions. Statistical studies have shown that failures of bushings are one of the main causes for long duration outages of transformers. The development of an instrument for supervising the conditions of transformers bushings is, therefore, of special interest. In this contribution two methods are introduced for monitoring of bushings. In the first method, using summation voltage of transformer bushings from bushing taps with and without neutral point voltage are considered. In the second method a new sensor is used which can give voltage signal as a signal reference from the high voltage conductor in each bushing. Comparing the signal reference with using tap voltage signal can evaluate the condition of transformer bushing. In addition a software for monitoring and diagnostic of transformer bushing is presented.