Building heat load contributions from medium and low voltage switchgear - Part II: Component and overall switchgear heat gains

Utility power sub-stations, industrial plants, and buildings use electrical power equipment in low voltage (LV) and medium voltage (MV) levels. A large number of electrical brands and products together with a lack of power efficiency information provide complications for HVAC engineers and designers in predicting power equipment heat loss. This is very true for LV and MV switchgear. Environmental heat gain information is very important for sizing HVAC equipment. The objectives of this paper are to update information on heat loss by LV and MV switchgear and to show these losses can be predicted. Two spreadsheet models are presented that calculate the power loss for low and medium voltage switchgear and practical examples are shown for each case using realistic information. The spreadsheets provide an approximation of the dissipated power losses if actual current loadings are used. However, if breaker and bus amp ratings (unknown loading case) are used in place of the actual loadings, the dissipated power loss ofthe L V and MV switchgear will be overestimated. This emphasizes the need of using the actual loadings for each bus and circuit breaker to obtain realistic results.