ANSI/IEEE C37.23-1969

The information in this Guide is applicable to all forms of isolated-phase buses operating in alternating-current power systems. It is not meant to apply to other forms of open or enclosed buses, although some of the material will be useful in most bus applications. Familiarity with Standards applying to metal-enclosed buses is assumed and provisions of those Standards are indicated only when necessary for clarity in describing limiting conditions

This Guide is intended for general use in the application of isolated-phase buses. It will serve as a ready reference of pertinent material for those responsible for determining losses and evaluating equipment. All conductors carrying electric current will produce power losses. This Guide covers methods for calculating conductor and enclosure losses at bus operating temperatures, including skin effect. In making power loss calculations, the I2R losses in the enclosure are considered. Means of determining such losses for various bus configurations are included. If the bus is fored-cooled, the power requirements of the cooling equipment will be included in the total power loss. For high-current installations, consideration should be given to the problem of induced magnetic heating and induced circulating current in nearby metallic members such as support beams and reinforcing rods. The Guide also contains references to assist in the estimation of heating effects of adjacent structural members. Such induced currents should be minimized to reduce extraneous losses. Methods of reducing eddy current and hysteresis losses and eliminating losses due to circulating currents are indicated.

New IEEE Standard - Superseded. Over the years, the isolated-phase bus has received widespread application in connecting the output of generators to step-up transformers. The trend toward generating units of larger capacity has dictated the need for higher rated isolated-phase bus designs. The increased losses associated with the higher capacity bus may be significant in the economic evaluation of alternate schemes or selection of equipment. The bus designer must know the magnitude and distribution of losses in order to keep temperature rises of bus components within the limits specified in USA Standard C37.20. In addition, the losses must be known to permit proper sizing of forced-cooling equipment whenever it is used. Various papers have been presented that deal with the determination of losses in isolated-phase bus enclosures. The difference in the results obtained for the same bus using various methods is of sufficient magnitude to cause concern. The industry has indicated the need for a guide for calculating losses to establish a common yardstick for establishing, evaluating, and applying different designs.