Research On Application Of Active Arc-Suppression Technology In Resonant Grounded System

With cable widely being used in the grid, the grid-to-ground capacitance current is rapidly increased today, the influence of which to the stability of the power system and equipment insulation becomes larger and larger, so the focus of research is changed from the neutral point ungrounded and low resistance grounded way to the resonant grounded way for most developed countries. In recent years, the harmonic content of earth shot ciucuit current is increased with power electronic and associated nonlinear equipments’ wide application, because of which the arc-suppression device is considered not only to achieve the purpose of the capacitance current compensation, but also eliminating harmonic. Therefore, a relatively quick, stable and accurate compensation arc-suppression device developed to get rid of the traditional way’s own defects and insufficiency is of great significance.An improved measuring method associated with the commonly used injecting signal for the measurement of capacitance current is put forward in this paper based on the background above. The changes of injecting amplitude current with constant frequency twice directly into the grounded transformer and the neutral point zero sequence voltage it brings are measured to calculate the capacitance value. The improved method is applied to both the neutral point ungrounded and resonant grounded system for accurate capacitance current measurement, which is verified by theory, simulation and actual distribution network. Simulation results show that the improved method can be used to accurately measure capacitance current over a wide range of unbalance. Subsequently, the influence of load side harmonic source to failure point voltage and the relevance among failure point harmonic voltage, harmonic component of neutral point zero sequence voltage and grounding short-circuit current are analyzed theoretically using the zero sequence equivalent circuit. A new active arc-suppression device is improved in this paper based on active inverter technology, accurate capacitance current measured and harmonic detected when single-phase ground fault occurs. Main and secondary arc-suppression devices are contained in the new active arc-suppression device, the former one is used to compensate the capacitance current, and the latter one is used to compensate harmonic current. This device has two operating modes, working in capacitance current measurement mode using improved injecting signal method when the system is normal, and working in the fully compensated mode to compensate the capacitance, harmonic component when single-phase ground fault occurs, which makes the device’s value achieved as much as possible. Finally, capacitance,5th and 7th harmonic component content in short circuit current is comparised between new arc-suppression device being put into the single-phase ground fault system before and after based on an actual steel factory distribution network model, and the result shows the new device has achieved the desired compensation effect.