Condition monitoring of 132 kV transformers

Approximately 30% of the 132 kV grid transformers in the UK are over 40 years old. Some 80% are over 20 years old. Transformer loads are increasing and reserved capacities are decreasing. Consequently, it is imperative to have some simple and practical means of assessing the insulation integrity of high voltage power transformers. The objectives of the present investigation were (a) to determine an acceptable level of insulation integrity for the large population of aged transformers, and (b) to develop or implement a diagnostic technique which could be used to monitor the rate of deterioration of the oil-paper composite insulation. The degraded oil can readily be refurbished or replaced. The degradation of the insulating paper, however, is nonreversible. The effects of thermal ageing on the paper matrix are accentuated by the presence of air and moisture