The first 110 kV /35 kV - 31.5 MVA cast resin transformer

In electricity distribution system, engineers of the power industry and utilities for general distribution applications have commonly used oil-immersed transformers. Other insulation options of transformers such as cast resin transformer (CRT), and SF6 gas-insulated transformer have also been mainly employed by engineers for the purpose of meeting environmental consideration and fire risk protection requirement. However most engineers might like to see the availability of an alternative option to SF6 gas transformer. A 110 kV cast resin transformer, which is now commercially available, may be considered as an ideal option for application in a fire risk-free 110 kV substation in urban areas with dense population. This paper attempts to describe the design and development of the proto-type CRT in different key technical aspects. The solutions to technical barriers due to resin insulation v.s. voltage level limitations were based on technical research, operation experience and supported by comprehensive tests. The construction and the technical characteristics of the CRT are therefore described in brief details. The paper discusses the general design aspects namely winding structure, heat dissipation, insulation compound structure capability to withstand high impulse voltage and short-circuited forces.