This standard covers certain electrical, dimensional, and mechanical characteristics and takes into consideration certain safety features of three-phase, 60-Hz, liquid-immersed, self-cooled, network transformers with a primary grounding switch. These transformers are rated 2500 kVA and below with high voltages of 34 500GrdY/19 920 volts and below. These transformers are generally used for step-down purposes from underground primary cables and supply a secondary network system through network protectors. These transformers are typically installed below ground level. This standard is intended for use as a basis for establishing the performance, electrical and mechanical interchangeability, safety of the equipment covered, and to assist in the proper selection of such equipment. Revision Standard - Superseded. This standard is intended for use as a basis for establishing the performance, interchangeability, and safety of the equipment covered and to assist in the proper selection of such equipment.