MODELLING OF THE POWER TRANSFORMERS TO THE DETERMINATION OF THE HOT-SPOT POINT POSITION UNDER THE DIFFERENT OPERATING CONDITIONS

Abstract

Purpose. Research of the position changing of the hot-spot point of the oil-immersed power transformers using simulation. Methodology. The theory and practice of calculation of power transformers, standardized mathematical models of calculation of the hot-spot point temperature and the mathematical modeling were used. Results. At Figures 4 - 6 under the number 1 indicate the initial conditions, namely the rated load of the transformer; eddy loses at rated load and 20 ° C ambient temperature. Under initial conditions, the hot-spot point is located on the surface of the low voltage winding at the middle leg. Ambient temperature changing and correction of eddy losses to the load factor of the each phase, numbers 2 - 4, cause the movement of the hot-spot point on the surface of this winding. The main factor that causes the movement of the hot-spot point is the load factor of each phase, numbers 3 or 4 and 5 or 6. If there is an overload of some phase, then the hot-spot point will be on the surface of the low voltage winding of this overloaded phase. Originality. According to the information obtained from [1-4] it is seen that the movement of the hot-spot point is not paid attention at all. For example, in [2] the position of this point is considered unchanged and already known. The results obtained from the research have shown that this provision is not true. Practical value. The obtained results is seen in the possibility of providing recommendations for paying additional attention to monitoring the insulation of windings at a certain point during the current maintenance or post-accident inspection of the transformer. Tracking data of the position of the hottest point should be stored, especially if the overheating in this point take place. Conclusions. The research was performed on transformers S13-MRL-40, S13-MRL-160 and S13-MRL-1000 with primary voltage evel 10 kV. The fact of movement of the hot-spot point on the insulation surface of the windings of these transformers under different operating conditions is established and demonstrated. Six operating conditions were considered. As can be seen from Figures 4 – 6, the hot-spot point responds to a change in operating conditions by changing its position. In case of the change in ambient temperature or eddy loss the point moves on the surface of the winding within a single phase. In case of the change in load losses, the point can move between phases. The movement of the point between the phases takes place under the load asymmetry.