Revision Standard - Inactive-Withdrawn - Draft. This standard describes certain electrical and mechanical characteristics and takes into consideration certain safety features of three phase, 60-Hz, liquid-immersed, self-cooled, underground type distribution transformers rated 2500 kVA and smaller with high voltages of 34 500GrdY/19 920 volts and below and with low voltages of 480 volts and below. These transformers are generally used for step down purposes from an underground primary cable supply and are suitable for occasional submerged operation.