Transformer switching transient elimination

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Becker Péter
Department of Electric Power Engineering

The inrush current that arose during the inrush of power transformers used in power systems can exceed the nominal current 8-10 times. This reduce the lifetime of the valuable transformer, and make it difficult to adjust the protections. The aim of my Thesis, to design a device, that can reduce the value of inrush current with the control of the switching.

First I present in my Thesis the phenomenon of inrush current, the factors that influence its value, and its effects on the transformer. I summarize the possible techniques of reducing the inrush transient, furthermore I examine with a simplified model, which timing is the most favourable in case of controlled inrush.

Then I examine the most favourable switch on and off phase sequence on a nonlinear transformer model with the ATP-EMTP network simulation program-system, and the most favourable timing. I examine also the effect of operation inaccuracy of the circuit breaker on the efficiency of the controlled switching.

After that I define the requirements for microcontroller based circuit breaker controller device, I prepare the block diagram of the device, then I detailed present the hardware of built breadboard-circuit. After the presentation of the hardware I present also the construction and operation of the software of the device with help flowcharts. Additionally I summarize the testing process of the device and the result of the testing.

Based on the test results, I examine finally the applicability of the device for reducing the inrush current of transformers.


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