Solid insulation distribution transformer

Underground transformer with insulating oil as the insulating and cooling medium has been used since the early 1960s.

byK. Lee, B. Mun, C. Ballard


Introduction

Underground transformer with insulating oil as the insulating and cooling medium has been used since the early 1960s. It uses mineral oil, as well as ester and silicone oil, and the enclosure is made of corrosion-resistant stainless steel. Underground, submersible and environmental conditions in which the transformer is installed are exposed to sewage, rain and surrounding chemicals. If liquid-filled transformers leak due to corrosion or other damage to the tank, liquid can contaminate the surrounding soil and underground water. In addition, the potential risk of explosion and fire caused by the transformer failure is a fire spreading factor, which further increases the safety concerns. Therefore, there has been a demand for new technology to solve these problems. SIDT has many advantages such as eco-friendliness, safety and reliability. It can be installed not only for underground and submersible applications but also for areas impacted by natural disasters such as mountains, as well as wildfire, hurricane, typhoon and flood-prone areas.

 

  1. Insulation system

The insulation system is made entirely of solid materials and does not use liquids or gases. The use of Nomex® aramid paper provides a 220 °C insulation class that limits the potential thermal degradation of windings due to insufficient ventilation in the vault or direct burial.

Epoxy resin improves the structural integrity of the transformer and creates a self-supporting structure for the core, coil and terminals.

The optimized ratio of mineral filler and epoxy resin reduces the mechanical stress caused by the thermal expansion and contraction of copper or aluminium conductors. The combination of high thermal conductivity of 0.7 W/mK of epoxy resin and a low load loss design eliminates the need for a separate external radiator for heat dissipation. In addition, the distance from low voltage to high voltage can be relatively small due to grounded high voltage and layer winding in the HV coil.

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