Building heat load contributions from medium and low voltage switchgear - Part I: Solid rectangular bus bar heat losses

Heat dissipated by medium and low voltage switchgear is determined by use of a spreadsheet model. In the first part of this paper, mathematical models of a switchgear component that produces a significant portion of the total heat loss is examined. Rectangular bus bars are used in switchgear for carrying large current loads and the loss contribution of this one component is significant. The heat loss mechanisms of bus bars consist of eddy current loss, loss from proximity effect, and stray or enclosure loss. Each of these losses is considered in turn to develop a complete model of the bus bar loss process. Where possible, portions of the loss model are compared to information developed elsewhere with excellent agreement. The eddy current and proximity effect loss models are developed in such a way that the model allows evaluation with a spreadsheet. The same can be said for the stray or enclosure loss model. The goal of this work is to produce a switchgear power loss model suitable for use by HVAC engineers for heat load prediction.