Research On Control Of Automatically Compensating Earth Capacitive Current For Arc Suppression Coil By Switching Parallel Connected Capacitors

In china, resonance grounding is commonly adopted in distribution network, by which power supply reliability and security can be enhanced. The earth capacitive current is therefore increased with the expansion of network scales. When the current is greater than the permitted value, it is recommended to install arc suppression coil(ASC) equipment by which the earth capacitive current can be counteracted with perfectly compensating inductive current. However regulation of ASC turns manually is hard to follow the variation of capacitive current and it is unable to ensure the suppressed fault current value in the permitted range when one phase to ground fault occurs.Under this circumstance the auto-turning ASC equipment is required to be installed in the distributions network which can automatically follow variation value in zero sequence capacitance due to network changes of topology to compensate fault current when single phase to ground fault occurs.Out of all auto-turning ASC equipment concepts, the method of arc suppression coil that inductance value is changed by switching parallel connected capacitors distinguishes itself as a very attractive option with grounding capacitive current compensating demand. The fundamental feature of novel ASC is no noise, fast, flexible, no rash. In this paper the working principles of the auto-turning novel ASC as well as implementation of the prototype are described.Fist, the principles of ASC that inductance changes by switching parallel connected capacitors and its compensating characteristic are specified .It is sharply different for switching frequency of each of capacitors of ASC that inductance changes by switching parallel connected capacitors when each capacity is arranged in the past binary manner. To solve this problem, a new manner is proposed that each parallel capacitor of ASC is arranged in nearly equal capacity. Secondly, to ensure ASC automatically to follow the earth capacitive current, there are two key problemswhich is automatically measurement of capacitive current flowing to ground and identifying occurrence of single phase to ground fault in network. According to two problems, the new method identifying single phase to ground fault is proposed that the equipment monitors zero sequence current directions of very load line in the single source supply distributions under the maximum and minimum turn of arc suppression coil by automatically switching parallel connected capacitors. Following this theory, the novel controller based on dual CPUs is designed to fulfill the job of compensation control.At last, the simulation system module is established according to the practice case of 10kV, 210kVar and 190kVar capacitors auto-turning ASC that inductance is changed by switching parallel connected capacitors, based on PSCAD/EMTDC software. And also the sample equipment of the 190kVar capacitors is designed and implemented, as well as its each circuit Thyristors Switched capacitors (TSC) is tested at rated voltage 400V in the lab. According to two simulation cases, the system can automatically turning arc suppression coil which is used to generate the switching pulses for thyristors to regulate the inductive current of ASC by switching parallel connected capacitors following the value of automatically measurement, when single phase is observed. The test result prove that its design of capacitors based on TSC technique is rational and the process of switching capacitors is rapidly and surgeless.