Field experience with online monitoring of three-phase AC bushing system concerning its capacitance

Bushing is one of the important HV-components in power transformers. The insulation systems of the bushings are subjected to electric stress and environmental effects such as heat and moisture. In order to avoid the field distortion, graded capacitive control layers are widely used in the design of HV-bushings. So, the main capacitance (C) of the bushings is regarded as a key indicator for finding the possible partial breakdowns in the insulation systems. It is of increasing interest for transformer operators to evaluate the online conditions of the bushings, especially the conditions of their insulations in operation. According to an innovative algorithm for online monitoring of three phase ac bushing systems, an application concept is realized: Voltage transformers are applied for…