Fault location in power transformers during impulse tests

In this paper we present a new approach to detect, and investigate the feasibility of locating winding faults with also determining the percentage of shorts within windings of power transformers. There has not been much emphasis on methods of assessing the extent of failure and in the estimation of the location of failure during such tests. However, this is a very important aspect since all faults involving nonself-restoring insulation are destructive in nature and hence have to be necessarily rectified. In case of failure of a transformer during an impulse test, manufacturers have to untank the winding in order to locate the fault. Often the destructive 1-minute power frequency test is done in order to visually locate the fault. It would be appropriate to develop a method for fault location so that results are available prior to the untanking of the transformer. This paper discusses methods for fault location based on frequency domain approach. Windings of a transformer behaviour at very high frequency, is essentially that of a capacitive ladder network. At lower frequency standing wave behaviour is obtained. Based on a choice of filters, the appropriate behaviour of the winding during a fault can be studied. In this work, we develop methods for fault location based on simulations on layer windings using a circuit simulation model. The results are validated experimentally on a specially constructed layer winding