A novel algorithm of online monitoring for three-phase ac bushing system concerning its dielectric properties

Abstract:
The bushing is one of the key components in high voltage power transformers. The insulation systems of the bushings are usually exposed to high electric field stress and may suffer from accelerated material aging in service. Therefore it is of increasing interest for transformer operators to evaluate the online conditions of the transformer bushings, especially the conditions of their insulation systems. In this paper, a novel algorithm for online monitoring of three phase ac bushing systems is described as well as an application concept suggested: In order to detect the symmetry of electrical power systems, voltage transformers are applied for examining the line voltage. However, other than in the majority of conventional bushing monitoring setups, they do not serve as a separate reference system due to the possible influence of temperature change. This influence is compensated by using “phase vs. phase” measurement principle for the three-phase bushing system. It can be seen that the impact of temperature and voltage fluctuation on the measuring results is hereby effectively limited. Finally, simulations with field data are carried out for validation of the algorithm developed for bushing monitoring. This paper shows a promising approach to realizing an effective online monitoring system of transformer bushings.