Submersible Dry-Type Transformer

This paper describes the concept and development of dry-type transformers for underground distribution networks, capable of operating in the open air, partially submerged or completely submerged without enclosure and in contact with water. The rating is in the range of 500 kVA to about 2000 kVA and 15- or 25-kV voltage. Immersion depth is limited to 3 m, due to the limits of the plug-in connectors on the high-voltage (HV) side of the transformer. A tap panel is provided on HV coils for ±5.0%. Dimensions and losses are comparable to those of liquid-immersed transformers. Electrical insulation is fully solid. The HV coils are shielded and the shield is grounded.