Thermal network theory for switchgear under continuous current

Abstract

All electrical equipments generate heat through I2R loss within a specified volume resulting in temperature rise. The regulating bodies define the temperature rise limits for all equipments for safe operation. So during the design phase of any electrical equipment thermal analysis is mandatory to predict the temperature rise. The objective is to develop an analytical tool based on thermal networking method by exploiting the similarity between thermal and electrical analogy to calculate steady state temperatures in less time along current carrying path in electrical equipments. As a later part, the tool developed is used to predict change in temperatures for change in geometry of the components in the electrical equipment. The problem is considered as two parts. As first part, an Excel tool is developed with Visual Basic backend, based on thermal networking method to calculate steady state temperatures in electrical equipments. Here the numerical method used is Elementary Balance Method, in which every element is represented by a node and relevant energy balance equations are formulated for it. Temperatures are calculated using the Excel tool for frame 1 and 3. Test (Thermal Run) is conducted on AKD-12 switch gear (frame 1 and frame 3) under continuous current to find out temperatures. Analytical results from the tool are then validated against the test data. As second part, dimensions of components in the switch gear are varied and variation in temperatures of components, particularly at moving contact (highest temperature point) with respect to original temperatures is observed. Good matching is observed in temperature profile between analytical and experimental results. The maximum percentage error is 15%.By analyzing the results, it can be concluded that thermal network theory helps engineers to predict temperatures easily for changes in design reducing design cycle time and it is flexible as to expand its application to any heat generating equipment.