Study On Turn-to-turn Short Circuit Fault On-line Monitoring System For 66kV Dry-type Air-core Shunt Reactors

Dry-type air-core shunt reactor plays a role in improving the quality of power,reducing line losses, providing reactive power compensation, restricting over-voltage,it is occupied important position in the power system. However, since the dry-type air-core shunt reactor has been put into operation, there have been a lot of fire accidents, a large number of analysis results show that the majority of fire accident is mainly due to turn-to-turn short circuit fault. The existing turn-to-turn short circuit fault monitoring methods have some defects such as low sensitivity or poor reliability. In order to solve this problem, it is significant to explore a kind of on-line monitoring method for turn-to-turn short circuit with high sensitivity and good reliability.Circuit models under strand-to-stand short fault and turn-to-turn short fault of66 k V dry-type air-core shunt reactor are established in this paper, and the numerical method is applied to analyze overall current, current distribution, variations of equivalent resistance and equivalent reactance in different positions of two kinds of short circuit faults reactor. The turn-to-turn short circuit monitoring method based on the impedance variation is determined according to the variation of size of these electrical parameters. The harmonic analysis method and the quasi-synchronization sampling method are adopted to calculate the equivalent resistance and equivalent reactance of reactor. Monitoring method extract the voltage signal and current signal through voltage transformer(PT) and current transformer(CT) in power system secondary side. The single-chip microcomputer is used as the core of data processing and logic control, which control the A/D converter and collect the reactor three-phase voltage signal and current signal, then the collected data are uploaded to the PC. Thereceived impedance of reactor is carried out number conversion, display and storage.The impedance variation of the reactor is calculated at the same time. The alarm function will come true, though the threshold and historical data to judge whether a reactor turn-to-turn short circuit fault occurs. Finally, the turn-to-turn short circuit online monitoring system based on impedance variation is studied by experiment.The research results show that, when strand-to-stand short fault and turn-to-turn short fault of 66 k V dry-type air-core shunt reactor occur, the variation of the equivalent resistance and equivalent reactance is related to fault types and location,and the variation of equivalent resistance is more obvious than equivalent reactance.The harmonic analysis method and the quasi-synchronization sampling method have the features of strong anti-interference capacity, the impedance of reactor can be calculated accurately. The feasibility of the reactor turn-to-turn short circuit on-line monitoring system is verified and the on-line monitoring system is of 1% accuracy, it satisfies the requirements of the field test.