-In this paper, a thermal model is developed for the bus bar system to predict the temperature variation during the transient time period and to calculate both the steady-state and transient electrical current carrying capacity (ampacity) of bus bar. The bus bar system installed in the power house of Kumaraguru College of Technology, Coimbatore has been considered. Temperature variation predicted in the modelling is validated by observing the current and steady state temperatures in different feeders of the bus bar. Magnetic field of the extreme phases R and B induces more current in the middle phase Y. Hence, the steady state temperature in the phase Y is greater than other two phases. The transient capabilities of the bus bar are illustrated by calculating the variations in the bus bar temperature when it is subjected to a step change in current during the peak hours due to increase in hostel utilities and facilities (5.30 pm to 10.30 pm). The physical and geometrical properties of the bus bar and temperature variation in the bus bar are used to estimate the thermal time constants for common bus bar cross-sections. An analytical expression for the time constant of the bus bar is derived.

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The main objective of this paper is to propose an algorithm to predict and compare the sizes of the bus bar with materials like copper and aluminum by considering the allowable ampacity and allowable temperature rise with natural and forced convection cooling arrangement. Theoretical analysis is carried out with modified size of the copper bus bar using MATLAB, to analyze the ampacity and temperature variation under the natural and forced convection mode. The algebraic equation developed from thermal model is solved using MATLAB for the determination of the allowable temperature rise and ampacity of rectangular-section bus bars of copper and aluminum and also for different sizes of bus bar. An algorithm has been developed for the analysis. Experimental observations of temperature variation in copper bus bar with standard size under natural and forced cooling mode are validated with the algebraic equation developed from thermal model is solved using MATLAB. It is concluded that bus bar dimensions are compared for the materials copper and aluminum to predict the suitable equivalent dimensions for the same ampacity level and within the allowable temperature rise to reduce the cost of panel.

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