On-line condition monitoring of tap changers-field experience

In this paper we have described the field applications of a low-cost tap changer condition monitor to a type of old distribution tap changer. Monitoring systems have been applied to the on-line assessment of tap changers in a distribution network for over three years. From the results from long-term monitoring and subsequent plant inspection, we illustrate the ways in which the condition of a tap changer deteriorates. In some cases the deterioration is gradual, but in others there are sudden shifts in the condition. The monitoring system presented in this paper can accurately detect and track either type of degradation. The on-line condition monitoring can be applied to the optimisation of tap changer maintenance programs. Probabilities of rate of degradation, determined from long-term monitoring and results of short-term tests, can be used to establish a monitoring program that will minimise maintenance costs and maximise reliability