Steady-state and transient ampacity of bus bar

This paper presents a thermal model that can be used to calculate both the steady-state and transient electrical current carrying capacity (ampacity) of a power system busbar. Using a thermal model, a computer program has been formulated that can calculate the ampacity of busbar for any time-varying current and any variation in environmental conditions. Relations for the convection heat transfer coefficient for busbars with circular, rectangular and angular cross-sections are presented. The steady state values for ampacity predicted by the program are compared to accepted values. The transient capabilities of the program are illustrated by calculating the variation in busbar temperature when it is subjected to a step change in current. The predicted temperature histories of typical bus designs are compared to temperatures measured in the laboratory using thermocouples attached to the bus material