The Study of a Secondary Ferroresonance Elimination Method Based on Combined Detection of the Zero-sequence Voltage and Potential Transformer Current

2019 
Eelectromagnetic potential transformers (PTs) are widely used in 10-35kV distribution networks for monitoring and protecting. However, the PT's magnetic saturation often induces ferroresonance issues in the networks, breaking PT fuses and even exploding PTs. In this paper, a secondary resonance elimination method was mainly studied. Firstly, the 10/35 kV ferroresonance simulation circuits based on PSCAD/EMTDC software were founded in this paper and the calculated results show that the PT current waveform under the fundamental resonance behaves the distinct characteristic with respect to the normal current waveform, which can be used to recognize the fundamental resonance. Then a secondary elimination control model based on the combined detection of the zero-sequence voltage and PT current was established, specifically with which it could be controlled to close the switch device by detecting the zero-sequence voltage combined with PT current, and to open the switch device by detecting the PT open-delta current combined with the Joule heat of the damping resistor. Furthermore, the influence of the damping resistances and the threshold value of PT open-delta current on effectiveness of anti-ferroresonance were discussed and the appropriate ranges of the two values were given correspondingly. Finally, the validity of this secondary resonance elimination method has been verified by the simulating experiments in the testing platforms and the substation.
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