PREDICTION OF TEMPERATURE VARIATIONS FOR INDUSTRIAL BUS DUCT SYSTEM UNDER FORCED CONVECTION COOLING WITH VARIOUS ASPECT RATIOS USING MATLAB

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1 International Journal of Mechanical Engineering and Technology (IJMET) Volume 9, Issue 2, February 2018, pp Article ID: IJMET_09_02_076 Available online at ISSN Print: and ISSN Online: IAEME Publication Scopus Indexed PREDICTION OF TEMPERATURE VARIATIONS FOR INDUSTRIAL BUS DUCT SYSTEM UNDER FORCED CONVECTION COOLING WITH VARIOUS ASPECT RATIOS USING MATLAB S.Thirumurugaveerakumar Assistant professor Department of Mechanical Engineering, Kumuraguru College of Technology, Coimbatore C.Velmurugan Professor Department of Mechanical Engineering, Kumuraguru College of Technology, Coimbatore Kavitha Professor Department of Electronics and Communication Engineering, Kumuraguru College of Technology, Coimbatore ABSTRACT This paper presents an experimental and mathematical model of the heat transfer processes in an electric bus duct system. Factors affecting the thermal model of the bus bar are current carrying capacity of the bus bar, step changes of the electric load and cross selection area of the bus bar [1]. In this study the variation in aspect ratio is accomplished by varying the width of the rectangular busbar having a constant thickness of 6mm. The aspect ratio (a1-a5) has been selected in the range from 5 to 25[2]. Proximity and skin effect are much controlled which leads to the reduction of power consumption through thermal and electrical loading on electrical bus duct system [3]. An algorithm has been developed to predict and compare the sizes of the busbar with materials like copper and aluminium using MATLAB [4][5].It has been found that the forced convection along with perpendicular air flow reduces the power loss due to heat generation is also reduced in the bus bar conductor [6][7]. It is concluded that same ampacity level and variation of steady state temperature at different air velocity from 1 to 10 m/s and variation in aspect ratio of Copper and Aluminium busbar are predicted within the allowable temperature rise [8][9].The obtained results show that a variation in aspect ratio produces very satisfactory agreement between computed and experimental data editor@iaeme.com

2 Prediction of Temperature Variations for Industrial Bus Duct System under Forced Convection Cooling with Various Aspect Ratios Using MATLAB Keywords: heat transfer, air insulated bus bar, different air velocity, aspect ratioampacity, temperature rise. Cite this Article: S.Thirumurugaveerakumar, C.Velmurugan and Kavitha, Prediction of Temperature Variations for Industrial Bus Duct System under Forced Convection Cooling with Various Aspect Ratios Using MATLAB, International Journal of Mechanical Engineering and Technology 9(2), pp INTRODUCTION Busbar is the basic elements of a modern industrial power delivery systems made up of copper or aluminium, backbone of maintenance and protection functions, these devices are connecting various units such as generators, transmission lines and loads. Industrial power house panel board switch gear is employed in electrical installations in order to distribute power from one supply unit to different output circuits. busbars have to meet standards regarding their electrical, mechanical and thermal performance. The ampacity of a conductor is limited by the continuously permissible temperature of the system which depends on the properties of the conductor material. Magnetic field from the eddy current interacts with the original electromagnetic field resulting in the reduction of current flow in the centre of the conductor. These current tend to flow near the surface of the conductor which is referred as skin region (2).The inductance of a conductor varies with the depth of the conductor due to the skin effect. This inductance is further affected by the presence of another current-carrying conductor in the vicinity. R phase is situated in the outer layer, Y phase busbar is kept in between R and B busbars. Hence, from this arrangement, it is understood that Y phase will have the increased effect of eddy current due to the magnetic field of R and B phase busbars. Therefore, current flow through the Y phase busbar is greater than the R phase busbar and B phase busbar (1).The main goal in busbar development is to increase the ampacity of the components [2] and to reduce the material requirements. As a result of the current flow in busbars, power losses occur, which always turn into heat. The busbar heat dissipation has to be intensified, or the power losses in busbars must be reduced to remain within the temperature limits. Many studies that considered magnetic- and thermal-field solutions have already been published [5e10]. Fulfillment of the thermal standards is available only with sufficient heat dissipation capabilities. Hence, cooling is important to guarantee the maximum performance and reliability. Their application is manifold ranging from vertical risers, which distributes current to horizontal bars whose application is restricted within a distribution panel or an industrial process. The connection among the busbars and to the electrical apparatus is ensured through bolts, clamps and welding. 2. BUS BAR ARRANGEMENT IN THE POWER HOUSE The experiments have been conducted from the electric power facility of Sangeeth Textiles Mill, Coimbatore, which has the capacity of 2500A rating and 1500 KVA transformer substation. In the transformer, the voltage is stepped down to 440V for distribution to points of consumption. These arrangements are done in an enclosed chamber made of steel with minimum amount of ventilation with natural convection heat dissipation. The busbar is made of copper. Figure 1shows feeder and distribution arrangement editor@iaeme.com

3 S.Thirumurugaveerakumar, C.Velmurugan and Kavitha Figure 1 Feeder and distribution arrangement Figure 2 Thermocouples and temperature indicator The current rating of the busbar depends on the volt ampere rating. Busbar with rectangular shape cross section is being used in the panel board. The size of the busbars is 100 X 6 mm Copper for Phases (RYB). It passes horizontally along the length of the panel board. For heavy load on the bus bar, load from a textile industry has been selected where the loading effect would have high transient variation in the current. This variation causes huge amount of thermal stress on the electrical busbar. The physical and geometrical properties of the bus bar and temperature variation are employed to predict the thermal time constant of common bus bar. Presently, heat dissipation from bus duct system has been predicted in forced convection mode. Figure 3 Forced convection heat dissipation arrangements editor@iaeme.com

4 Prediction of Temperature Variations for Industrial Bus Duct System under Forced Convection Cooling with Various Aspect Ratios Using MATLAB Figure Error! No text of specified style in document. Experimental arrangement in the power house of Sangeeth Textiles Temperature variation predicted in the modelling of busbar is validated by experimental observation. Thermal time constant has been predicted to find the steady state temperature of the bus duct system using analytical expression. Many factors are involved for choice of selecting appropriate temperature measurement instrument for the given application. Here, calibrated thermocouples are to be used for measuring the temperature in R, Y, B phases. The thermocouples are connected to the four channel temperature indicator as shown in figure 2.The selected K-Type thermocouple can be used to measure temperature up to 1200 C and are also recommended in high moisture, dust, fog, smoke, liquid, high pressure, and corrosive environments. Figure 3 shoes forced convection heat dissipation arrangements and figure 4 shows experimental arrangement in the power house of Sangeeth Textiles. 3. THERMAL MODEL OF THE BUS BAR The energy balance equation for the bus bar is written as dt C pv I Rt has T T As T T dt Equation (1) is simplified and given as dt dt hasas 2 T T T T I R t ha A T T T T s s T T C V p C pv Equation (2) is similar to the differential Equation dt at C dt Solution for the above given differential Equation is c at at Ti 1 1 e Ti e a Where has A a s T T T T C V p C V 2 I R t has As T T C C pv C pv p T T T (1) (2) (3) (4) editor@iaeme.com

5 S.Thirumurugaveerakumar, C.Velmurugan and Kavitha Thermal time constant is the function of geometrical, physical and thermal properties of the busbar material. The thermal time constant is, C h p V A s T T T T T T t 2 T T e For the forced convectional cooling with air flow perpendicular to the busbar, the correlation used is, x 1 3 Nu x 0.205Re Pr ;Re 4000 ~ 15000,Pr 7 Algorithm for busbar forced convection with perpendicular air flow system The algorithm developed carried out in the research work is being given in fig 3. The experimental work was conducted in a textile mill and a suitable thermal model is developed to determine the temperature of the busbar under forced convection mode. The program has been written in MATLAB for the algebraic equation developed from thermal model. Analytic algorithm t (5) (6) editor@iaeme.com

6 Prediction of Temperature Variations for Industrial Bus Duct System under Forced Convection Cooling with Various Aspect Ratios Using MATLAB 4. RESULT AND DISCUSSION Figure 5 Comparisons of experimental and numerical temperature rise of Y Phase busbar with velocity from 1 to 10 m/s under forced convection with air flowing perpendicular to the copper busbar. Figure 5 shows the comparisons of experimental and numerical temperature rise of Y Phase busbar with velocity from 1 to 10 m/s under forced convection with air flowing perpendicular to the copper busbar. Copper busbar is perceived to be more efficient in enhancing the heat transfer at all velocities. The experimental and numerical results match with an error of2.78 C. When we increase the air velocity from 7 m/s to 10 m/s the steady state temperature will be stable. Figure 6 Comparisons of different standard width numerical temperature rise of Y Phase busbar with velocity from 1 to 10 m/s under forced convection with air flowing perpendicular to the copper busbar editor@iaeme.com

7 S.Thirumurugaveerakumar, C.Velmurugan and Kavitha Figure 7 Comparisons of different standard width numerical temperature rise of Y Phase busbar with velocity from 1 to 10 m/s under forced convection with air flowing perpendicular to the aluminum busbar In the aspect of optimizing the size of the steady state temperature of the busbar, the algebraic equation developed from thermal model is solved using MATLAB by considering different standard width sizes of 35 mm, 50 mm and 100 mm and keeping thickness as constant of 6mm for copper and aluminium busbar materials under the forced convection arrangement as shown in figure 6 and 7. It is inferred from the figure 6, the heat transfer rate is almost same for35 mm and 50mm width when compared to 100 mm width of the copper busbar. The temperature is reducing continuously upto the velocity of 7 m/s, but after 7 m/s the temperature decreases gradually for the copper and aluminium busbar. The opitimized width of 35 mm for copper and aluminium busbar has maximum temperature of 42 C and 54 C respectively, which in turn reduces the power loss to 45% as compared to natural convection. Figure 8 Variation of steady state temperature at different velocity and aspect ratio Figure 8shows the variation of temperature with respect to velocity for copper and aluminium busbars at various aspect ratios having defined it to be the ratio between width and thickness of the busbar. In this study the variation in aspect ratio is accomplished by varying the width of the busbar having a constant thickness of 6mm. The aspect ratio (a1-a5) has been selected in the range from 5 to 25. It is inferred from the diagram that heat transfer rate has been augmented with increase in aspect ratio for both copper and aluminium busbar. The editor@iaeme.com

8 Prediction of Temperature Variations for Industrial Bus Duct System under Forced Convection Cooling with Various Aspect Ratios Using MATLAB velocity has an influential effect on heat transfer only at low aspect ratio and its effect gradually diminishes at higher aspect ratio. The velocity has no effect especially at higher aspect ratio even in copper busbar. Copper busbar is perceived to be more efficient than aluminium busbar in enhancing the heat transfer at all aspect ratio and velocity. 5. CONCLUSION An experimental observation of temperature variation for standard size copper busbar is validated with theoretical analysis using MATLAB. An algorithm has been developed to perform analysis to determine the temperature variations in the busbar of different materials of copper and aluminium with different standard size using MATLAB. Then, with forced convection cooling arrangement, the temperature variation of copper busbar is observed and it is found that the temperature variation is well under the safety range. Hence a theoretical analysis is carried out with different size of copper and aluminium busbar with different air velocities to predict the temperature rise which is also under the safety range. It is suggested that by reducing the size of busbar, cost of panel can be saved. During the course of validation of the analytical algorithm, it is confirmed that due to forced convection (perpendicular airflow) heat dissipation, response time (time constant) for attaining steady state condition is improved. Hence, proximity and skin effect are much controlled which leads to the reduction of power consumption in the load. REFERENCES [1] Bedkowski, M., Smolka, J., Banasiak, K., Bulinski, Z., Nowak, A. J., Tomanek, T., &Wajda, A. (2014).Coupled numerical modelling of power loss generation in busbar system of low-voltage switchgear. International Journal of Thermal Sciences, 82, [2] M. Bedkowski, J. Smolka, Z. Bulinski, A. Ryfa (2016), 2.5-D multilayer optimization of an industrial switch gear busbar system, applied thermal modelling 101 (2016) [3] M. Bedkowski, J. Smolka, Z. Bulinski, A. Ryfa(2017), Simulation of cooling enhancement in industrial low-voltage switch gear using validated coupled CFD-EMAG model, international journal of thermal science 111 (2017) [4] Thirumurugaveerakumar, S., Sakthivel, M., Valarmathi, S., Experimental and Analytical Study on the Bus Duct System for the Prediction of Temperature Variations Due To the Fluctuation of Load, Journal of Electrical Engineering and Technology., 9(2014), 6, pp [5] Thirumurugaveerakumar, S., Sakthivel, M., Rajendran, S., Experimental and Analytical Study of Effect of Forced Convectional Cooling of Bus Duct System in the Prediction of Temperature Rise, International Journal of Advances in Engineering and Research.,10(2015), 21, pp [6] Thirumurugaveerakumar, S., Sakthivel, M., SharmilaDeve V.,Prediction and Comparison of size of the copper and aluminium bus duct system based on ampacity and temperature variations using MATLAB, Thermal Science 9 (2016), pp [7] Robert Coneybeer, T., Black, W.Z., Bush, R.A., Steady-state and Transient Ampacity of Bus bar, IEEE Trans. Power Delivery., 9(1994), 4, pp [8] Klimenta, D. O., Perović, B. D., Jevtić, M. D., Radosavljević, J. N., An analytical algorithm to determine allowable ampacities of horizontally installed rectangular bus bars, Thermal Science 20 (2016), 2, pp [9] Kim, J. K., Hahn, S. C., Park, K. Y., Kim, H. K., Oh, Y. H., Temperature rise prediction of EHV GIS bus bar by coupled magneto-thermal finite element method, IEEE Trans. on Magnetics 41(2005), 5, pp editor@iaeme.com