IEEE C57.12.2-2016 IEEE Standard for Submersible, Three-Phase Transformers, 3750 kVA and Smaller: High Voltage, 34 500 GrdY/1 9 920 Volts and Below; Low Voltage, 600 Volts and Below.
5. Rating data 5.1 Cooling class The cooling class shall be as specified in IEEE Std C57.12.00-2015. 5.2 Kilovolt-ampere ratings The kilovolt-ampere ratings shall be continuous for an insulation system thermal class of 120 as defined in IEEE Std C57.154 and are based on not exceeding an average winding temperature rise of 55 °C and a hottest-spot temperature rise of 70 °C. The temperature rise of the insulating liquid shall be measured near the top of the tank and shall not exceed 55 °C. Nonsymmetrical unbalanced excitation or loading of wye-wye-connected units may cause heating of their tanks in excess of that which would be produced by balanced conditions. To reduce the probability of this tank heating, such a unit shall be provided with a core construction that will not saturate when 33% zero sequence voltage is applied. 5.3 Voltage ratings Voltage ratings are shown in Table 1.
6.2 Reference temperature The reference temperature to which load losses, impedance, regulation, and efficiency shall be corrected to is 85 °C. The no-load losses shall be corrected to 20 °C. 7. Construction 7.1 General Devices such as separable connectors, switch handles, tap changers, plug-in terminators, and replaceable fuses, which are designed for operation after the transformer is in place, shall be located on the transformer cover so that they can be operated from above with hot-line tools. Unless otherwise specified, the insulating liquid shall be mineral oil. Insulating liquid immersed transformers shall have dimensions not exceeding those as shown in Figure 1, unless agreed upon between the end user and manufacturer. The plan view of the transformer shall be in accordance with Figure 2 for the purpose of locating terminations and operating devices. Parking stands of series 304L or 316L stainless steel shall be provided in accordance with Figure 3, and shall be centered to the rightmost of the high-voltage connectors as shown in Figure 2.IEEE C57.12.2 pdf download.