IEEE C57.12.23-2009 IEEE Standard for Submersible Single-Phase Transformers: 167 kVA and Smaller; High Voltage 25 000 V and Below; Low Voltage 600 V and Below.
7. Construction 7.1 General The transformers covered in this standard shall include high-voltage connectors and low-voltage terminals as described in 7.2. The high-voltage connectors and low-voltage terminals shall be welded to the cover or tank. The transformer tank, cover, and all external appurtenances shall be of corrosion-resistant material, unless they are otherwise rendered corrosion-resistant. Corrosion-resistant base bars or other suitable means shall be provided on the transformer tank to protect the bottom of the tank while in transit and when installed in the underground enclosure. Minimum bar height is 25 mm (1 in). Construction of the units shall be such that they can be lifted and lowered into place in a suitably designed and constructed enclosure having a minimum diameter of 910 mm (36 in). To allow for cabling space and proper air flow for cooling, the transformers covered by this standard shall not have overall diameters in excess of 760 mm (30 in) for sizes 100 kVA and smaller, or overall diameters in excess of 840 mm (33 in) for 167 kVA. For the purpose of locating terminations and operating devices, the plan view of the transformer is divided into four segments with the segments numbered in a clockwise direction. See Figure 1. All neutral connections shall be suitably sized for the short-circuit rating of the transformer as defined in IEEE Std C57.12.00-2000.
7.2.2 High-voltage connectors The electrical characteristics of the completely assembled high-voltage connectors shall be as shown in Table 1. On phase-to-ground transformers, the H 2 end of the high-voltage winding shall be connected to the tank internally. This connection shall be independent of all other electrical connections. The high-voltage connectors shall consist of either bushing wells, bushing wells with bushing inserts, or integral bushings, as specified. One cable accessory parking stand shall be provided for each phase of supplied high-voltage. Separable insulated high-voltage connectors that are designed for operation after the transformer is in place shall be located so that they can be operated with hot-line tools. For specific details concerning high-voltage separable connectors and cable accessory parking stands, refer to IEEE Std 386-1995.
IEEE C57.12.23 pdf download.