Development of test methods for microprocessor-based protection

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Dr. Petri Kornél
Department of Electric Power Engineering

Nowadays the modern microprocessor based protections simultaneously perform multiple functions. Continuous testing of these equipment during their development is an essential but complex task. Some of these tests can easily be done by new relay test equipment however others are still very labor-intensive and time-consuming. The frequent need for intervention by engineers opens the door to human mistakes.

My work focuses on the distance protection function, regarding to which the

IEC 60255-121 standard includes detailed description of the investigations to be carried out by the manufacturers. One of them – the measuring for current transformer transient dimensioning – is particularly complex, and requires a lot of care during the work.

I set the complete automation of the above mentioned test as the goal of my thesis. To achieve this, the programmed control of an OMICRON CMC356 relay test equipment is necessary. My C# program performs the calculation of transient time functions, the control of voltage and current outputs of the test equipment and the protection function evaluation by using the own programming language of OMICRON, and the preparation of the output files for documentation.

After the theoretical review I introduce the implemented application and its structure. I provide insight into the inner details of the program and the basics of the operation of the required functions. I demonstrate by the measurement results that the application can correctly carry out a full standard test. Finally, I present the dimensioning of the current transformer by IEC 60255-121 standard through a numerical example.


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