Historical
IEEE C57.12.40-2017
IEEE Standard for Network, Three-Phase Transformers, 2500 kVA and Smaller, High Voltage, 34 500 V and Below, Low Voltage, 600 V and Below, Subway and Vault Types (Liquid Immersed)
This standard is intended for use as a basis for establishing the performance, interchangeability, and safety of the equipment
Institute of Electrical and Electronics Engineers [ieee]