A practical life assessment technique for aged oil paper systems

A significant percentage of the transformer population is now aged beyond a nominal design life of 25 to 30 years. As much of this equipment is performing quite satisfactorily, economic factors usually favour continued operation for as long as possible. The operating environment in which the following studies were undertaken is an extensive transmission system operating at voltages up to 275 kV. The climatic conditions are tropical and subtropical, which are conducive to the ageing mechanisms of oil impregnated paper insulation. The author studies insulation condition monitoring and life assessment techniques. One research project has been particularly useful in providing a practical method for estimating the remaining reliable life of ageing power transformers employing oil/paper insulation