New high temperature insulation for oil-filled transformers

Traditionally, oil-filled transformers have utilized densified cellulose paper as the primary conductor insulation. However, cellulosic insulation is a relatively low temperature material and thermal degradation due to overload conditions and/or long-term aging can led to transformer failures. Materials with better thermal capabilities than cellulosic paper have been evaluated with varying results. For example, calendared aramid paper exhibits excellent high temperature resistance, but it requires excessive drying time, and is considerably more costly than cellulosic insulation. A new, cost effective polyester composite insulation has been specifically developed to meet the physical, electrical, and thermal requirements for oil-filled power transformers. The design and development of this insulation is discussed to demonstrate the combination of properties that make this product uniquely suited for high performance conductor insulation. Coil impulse testing comparing the polyester composite material with cellulosic and aramid papers is discussed, as well as preliminary 180°C heat aging data