Automation of the measurement and evaluation of turn-to-turn overvoltage tests on dry-type high voltage reactors according to IEC 60076-6 Appendix E
Today all non-high-frequency reactors rated 1 kvar (single phase) or 5 kvar (three phase) and above are tested according to IEC 60076-6. Part of these tests is a routine test using lightning impulse voltages. For drytype reactors, having a rated voltage of Um less or equal to 35 kV, the standard allows an alternative turn-to-turn overvoltage test, which is described in Appendix E of the document. The basic procedure of the test is to apply a minimum of 7200 voltage pulses with either 1,33 or 1 times the peak value of the rated voltage for outdoor and indoor reactors, respectively, which need to be applied within one minute. To conduct these tests, a special impulse generator consisting of a DC source, a charging capacitor and a spark gap is used as generator.
In order to pass the test, the frequency of the waveshape of the reactor's response to the first impulse (or an reference impulse with lower voltage) must not differ from the response to the last of the 7200 impulses. Recording these waveforms to date is done with oscilloscopes, triggered manually, or by the generator, to record the first and the last oscillogram. These recorded data is then compared and the test result is determined.
By using a PC-oscilloscope, the measurement data can be acquired onto a personal computer for further analysis, allowing detailed real-time insight into the reactor under test. In the scope of this paper, using this data, an algorithm to ascertain detailed parameters of the reactor, like inductance and resistance, are developed and presented.
Data of the measurement are analysed in real-time and shown graphically and in text on screen for the test operator to monitor. The algorithm is used as a basis for a demonstration software. Running on a modern computer, the software is able to capture and evaluate data of the running test in real-time and show, if the behaviour of the reactor changes during the test. In case of a faulty reactor, it is possible to see how the reactor's response to the impulse changes over time.
Using the software introduced in this paper, the behaviour of faulty reactors can be observed live during the turn-to-turn overvoltage test. With further research, finding the exact cause and reason of damage for faulty reactors may be possible without conducting additional tests.