DEVELOPMENT OF A PROGRAM FOR THE DETERMINATION OF THE TEMPERATURE AT TRANSFORMERS COPPER BUS BARS BY CALCULATING THEIR DIMENSIONLESS NUMBERS

Abstract

The present technical study aims to demonstrate how to make the determination of the temperature at Transformers Copper Bus Bars by calculating their dimensionless numbers its will explain about the development of a thermal software that represents a viable and cost-effective to dimensioning the transformers Bus Bars due the temperature rise generate by the current. In this environment, the program is basically a virtual lab where is only necessary the cost of specialized engineering analysis and the critical time analysis. This program allows to be done a large number of tests with different types of Bus Bars and different positions of this Bus Bars with the main objective of loss and temperature reduction, material and final cost of the equipment it can also be used to avoid a possible re-work, non-acceptance or disapproval in heating tests, improving the overall performance of the equipment. To find the temperature at the Bus Bar was necessary to calculate the losses at the Bus Bars and the dimensionless numbers of Prandtl which is the ratio of momentum diffusivity (kinematic viscosity) to thermal diffusivity, Grashof which is a dimensionless number in fluid dynamics and heat transfer which approximates the ratio of the buoyancy to viscous force acting on a fluid, Rayleigh which is associated with buoyancy driven flow (also known as free convection or natural convection) and is the product of the Grashof number and the Prandtl number also and finally Nusselt which is the ratio of convective to conductive heat transfer across (normal to) the boundary. The conductive component is measured under the same conditions as the heat convection but with a (hypothetically) stagnant (or motionless) fluid. All dimensionless numbers were considered for natural convection. To do this calculation an analytical program using Visual Basic at MSExcel was created. To find this temperature some variables are dependent. In that case, this variables need to be fixed after the first temperature found at copper Bus Bars. Some iterations must be done using the program starting from this first temperature to find the correct final temperature. After this procedure is possible to determinate the temperature considering the paper layer of the copper Bus Bars when it exists. The measured results show the reliability of the proposed model by calculating the dimensionless numbers for the determination of the temperature at Transformers copper Bus Bars.