Heat dissipation is always a problem in large power transformers. Increased market competency demands for accurate determination of the thermal profile across the transformer. This paper presents a thermal model to simulate the thermal behavior of the electrical utility transformers.
The thermal model is arrived at using the principle of thermal electrical analogy and the fact that the losses in the transformer are distributed rather than lumped. In this paper, the model is implemented for single phase transformer and the same model can be extended to three phase transformer. Simulation results are presented.
INTRODUCTION:
Power transformers represent the largest portion of capital investment in transmission and distribution substations. One of the most important parameters governing a transformer’s life expectancy is the hot-spot temperature value.
To the user, temperatures in a transformer are important to determine the amount and duration of over load it can sustain, and to estimate the effects on the life of the transformer by operation at various temperatures.
For a designer, prediction of temperatures at all points becomes important to determine the amount of copper to place in the coils, leads and outlet bushings, type of cooling and ducts, position of ducts, insulation class, design and settings of control equipment.
A transformer is provided with a cooling system which is designed for normal operations. But actually, the transformer might run on over load for a longer duration or frequently for shorter durations. Further, there are stray losses in transformer, which are usually under estimated. Also, the iron loss may change because of change in grain orientation due to punching and clamping actions.
For all these reasons, the losses actually may be larger than the calculated ones. Though safety factors are included because transformer is a remotely installed and frequent maintenance is not feasible, still we cannot go for large safety factor for economic reasons. This results in temperature rise in the transformer beyond normal value.
Source: IIT-H
Author: Haritha VVSS | T R Rao | Amit Jain | M Ramamoorty
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