Development Of Thyristor-Switched Capacitor Based Arc Suppression, Resonance Elimination And Fault Line Selection Integrated System

Single-phase grounding fault is the most frequent fault of distribution network, in this fault case, line voltages are still symmetrical,so it's no influence to continuous power supply, but all the capacitance current of network will flow through the ground point and produce electric arc. Along with the expansion of network scales,the capacitance current increases rapidly,and the electric arc often can't be extinguished by itself, so it needs installing arc suppressing device. At the same time, single-phase grounding fault also causes non-fault phase voltage to raise,it will reduce the strength of isolation if the time of single-phase grounding fault is too long. According to the rules in safety regulations, the fault line must be selected and cut off in one to two hours. Besides,various resonance over-voltage maybe happen on the conditions of open-conductor,switch closing and developing new line,it will influence the safety of power network. For this reason, this paper does some research on arc suppression and resonance elimination and fault line selection in distribution network.Firstly, this paper analyses the physical mechanism of single-phase grounding fault and resonance over-voltage, based on the analyze, brings forward a new method identifying single phase to ground fault, and improves the two point method for measuring capacitance current, then designs a sort of arc suppression, resonance elimination and fault line selection integrated system based on Thyristor-Switched Capacitor. It switches the parallel connected capacitors to the capacitor-tuning arc-suppression coil's secondary windings by micro-controller, consequently adjusts the inductance of arc suppression coil immediately and flexibly. The principles of arc suppression, resonance elimination and fault line selection are as follows: When single-phase grounding fault occurs, the device decreases the grounding current and extinguishes grounded arc by adjusting the inductance of arc suppression coil to resonance state; If the single-phase grounding fault is permanent, the device adjuststhe inductance of arc suppression coil, and identifies the fault line by the different changes of each line's zero-sequence current.; In the same way, when resonance over-voltage appears, the device breaches resonance condition and suppresses resonance over-voltage by adjusting the inductance of arc suppression coil.This paper clearly introduces the hardware design and the software design of the system, and analyses the Model-View-Controller mode of software development. At last, a digital simulation model is established in EMTDC/PSCAD software, and some tests of the equipment have been completed in the lab. The results of simulation and tests prove that the method can effectually eliminate electric arc, suppress resonance over-voltage and correctly identify fault line.