Factory of wooden panels MDF Lesonit d.o.o. from Ilirska Bistrica, covers its electricty needs by using 9 power transformers which transform power from 20 kV voltage level to 6 kV and 230 V. On the 6 kV voltage level operates a high voltage electric motor with 3,65 MW of power. At the moment, two out of nine transformers have outdated over-current protection. The results of measurements made yearly by the Institute Milan Vidmar (EIMV) show that protection still works within regulations, but in the near future it should be replaced with modern electronics.
In the theoretical part of the thesis, we first write about protection of transformers and 6 kV electric motors in the company Lesonit. Theoretical part is followed by the calculation part in which we will explain the current situation in the network. With help of software package Matlab Simulink we simulated network condition when occurs the short-term overloading of transformers and when occurs various short-circuit faults. According to the obtained data an analysis was made, on the basis of which, the decision about possible replacement of transformer overcurrent protection will be taken.
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