To develop a standard for transformers serving semiconductor power rectifiers employing monochrystalline semiconductor diodes or thyristors. Excepted applications are welding equipment, static precipitators, HVDC converters, and low power applications; such as radio receivers and other non-linear loads. The standard includes loads rated: single phase 300 KW and above and three phase 500 KW and above. This standard will replace the lapsed ANSI C57.18-1964 for pool-cathode mercury-arc rectifiers. New IEEE Standard - Inactive-Reserved. Practices and requirements for semiconductor power rectifier transformers for dedicated loads rated single-phase 300 kW and above and three-phase 500 kW and above are included. Static precipitators, high-voltage converters for dc power transmission, and other nonlinear loads are excluded. Service conditions, both usual and unusual, are specified, or other standards are referenced as appropriate. Routine tests are specified. An informative annex provides several examples of load loss calculations for transformers when subjected to nonsinusoidal currents, based on calculations provided in the standard.