A New Approach Of Short-circuit Current Reduction Considering Power Losses

Transformers adopt the planning and design concept of "large capacity,less distribution points",With the continuous close of power grid,the problem of short-circuit current exceeding the standard is becoming increasingly serious,which not only threatens the safety of transformers,circuit breakers,buses and other electrical equipment,but also often causes the problem of voltage sag and affects the power continuity of sensitive loads.In order to ensure the safe,reliable and stable operation of the power grid,the economic and effective short-circuit current limiting measures must be taken.As an effective current limiting measure,the fault current limiter is widely concerned by the electrical sector.Firstly,based on the analysis of the principle structure and current limiting process of the conventional Non-Loss Fault Current Limiter(NLFCL),it is pointed out that the maximum short-circuit current peak cannot be effectively restrain under the adverse fault phase angles,the accuracy of the analysis conclusion is verified by PSCAD/EMTDC platform.In order to solve above the problem,a light loss fault current limitation technology is proposed,in which,a fast switch is only paralleled with a certain proportion of the current limiting reactor.It can restrain the maximum short-circuit current and operation loss.Secondly,based on the study of the structure and principle of Light Loss Fault Current Limiter(LLFCL),The way to obtain the best proportion of the current limiting reactor paralleled with the fast switch is described,in which,the peak of the maximum short-circuit current,the duration time of the current exceeding the allowed value,the loss and the voltage drop in normal operation are taken as evaluation indexes.At the same time,under the condition of minimum operation loss,the best ratio is determined.Thirdly,based on the simulation software PSCAD/EMTDC,the system simulation model and controller module are established,and the best proportion range and final value are obtained through four evaluation indexes.The short-circuit current restrain effect of NLFCL and LLFCL are compared and analyzed when the natural arc-extinguishing is adopted under different fault phase angles,the results show that LLFCL has better current limiting effect and solves the existing shortcomings of NLFCL.The peak of short-circuit current limitation effects of LLFCL with natural arc-extinguishing and artificial arc-extinguishing technology are compared and analyzed at various fault phase angles,the conclusion shows that the current limiting effect is better and the running loss is smaller under artificial arc-extinguishing.The voltage changes at the reactor ends of NLFCL and LLFCL are compared and analyzed,the conclusion shows that the LLFCL can protect the reactor wellFinally,combined with typical cases,the short-circuit current restrain effect under the unfavorable fault phase angle is compared and analyzed when NLFCL and LLFCL are used respectively,which proves the feasibility and effectiveness of the proposed light loss current limiting technology.