Transformer Insulation Materials and Ageing

Sufficient insulation between different active parts of the transformer is necessary for its safe operation. The insulation system in a transformer can be categorized as follows: major insulation, and minor insulation. The solid insulation materials widely used in the transformer are paper, pressboard, and transformer board, which are formed from the cellulose found in plants. The main concern with using dry paper as an insulating material is that it is very hygroscopic. The presence of cellulose insulation affects the voltage distribution in heterogeneous dielectric systems: it contributes to the dielectric loss; determines the short-term dielectric strength; and, to a major extent, the life of the total insulated system. Oil is an equally important part of a transformer's overall insulation. The insulation system of a transformer undergoes ageing due to transformer operating conditions. This chapter provides an overview of the key concepts discussed in the subsequent chapters of this book.