Research On Zero-crossing Prediction Of Controlled Short Circuit Interruption

Controlled switch，also called phasing-control switch or synchronous switch，is one ofthe newest subjects of intelligent apparatus techniques. It’s an intelligent control methodthat can make the switch open or close at an optimum phase of the associated current orvoltage waveform, based on the load characteristic and control strategy. In recent years, ithas been be widely used in the field of conventional equipment, such as capacitor bank,reactor bank and so on, which can effectively eliminate over voltage and inrushphenomenon. But for controlled fault interruption, there isn’t an effective solution.With the continuous development of power system, the increasing short circuit currenthas been greatly testing the breaking capacity of the switch. The contact is also seriouslyablated by the arc energy that injected to the chamber during the short circuit time. Thecontrolled fault interruption is an important way to improve the breaking capacity,reliability and lifetime of the circuit breaker by controlling the initial time and duration ofthe arc. But the aperiodicity of the short-circuit current and the speed request of theprotective relaying is a challenge for the prediction of the fault current zero-crossings.Focused on the zero-crossing prediction of the fault current, this paper carries out thetheoretical and experimental study.An improved half-wave Fourier algorithm is presented. By increasing two extrasampling points and shifting the data processing window twice, the algorithm can extractthe initial value and time constant of the decaying DC component, amplitude and phase ofthe fundamental and three-order wave components. Current break arithmetic is presented topredict the initial time of the fault. The sudden-change of phase current differential is usedto judge the fault type. The result of fault recorder data simulation shows that the algorithmcan quickly realize the zero-crossing point prediction, and the errors are less than±1ms.At last, the control system of controlled fault interruption is developed, in which thedigital signal processor TMS320F2812is used as the kernel. The system can control thecircuit breaks to interrupt in right position cooperated with the proper control strategy. Thetest result shows that the control system is accurate and stable and the statistical result ofprediction errors (3σ) are [-0.6ms,0.6ms].