Power supply arm protection scheme of high-speed railway based on wide-area current differential

When fault occurs on cross-coupling autotransformer(AT)power supply traction network,the up-line and down-line feeder circuit breakers in the traction substation trip at the same time without selectivity,which leads to an extended power failure.Based on equivalent circuit and Kirchhoff’s current law,the feeder current characteristic in the substation,AT station and sectioning post when T-R fault,F-R fault,and T-F fault occur are analyzed and their expressions are obtained.When the traction power supply system is equipped with wide-area protection measurement and control system,the feeder protection device in each station collects the feeder currents in other two stations through the wide-area protection channel and a wide-area current differential protection scheme based on the feeder current characteristic is proposed.When a short-circuit fault occurs in the power supply arm,all the feeder protection devices in each station receive the feeder currents with time stamp in other two stations.After data synchronous processing and logic judgment,the fault line of the power supply arm can be identified and isolated quickly.The simulation result based on MATLAB/Simulink shows that the power supply arm protection scheme based on wide-area current differential has good fault discrimination ability under different fault positions,transition resistances,and fault types.The verification of measured data shows that the novel protection scheme will not be affected by the special working conditions of the electrical multiple unit(EMU),and reliability,selectivity,and rapidity of relay protection are all improved.

An adaptive supervised wide-area backup protection scheme for transmission lines protection

Maloperation of conventional relays is becoming prevalent due to ever increase in complexity of conventional power grids.They are dominant during power system contingencies like power swing,load encroachment,voltage instability,unbalanced loading,etc.In these situations,adaptive supervised wide-area backup protection(ASWABP)plays a major role in enhancing the power system reliability.A balance between security and dependability of protection is essential to maintain the reliability.This paper proposes multi-phasor measurement units(MPMU)based ASWABP scheme that can function effectively during faults besides power system contingencies.MPMU is an extended version of Phasor Measurement Unit(PMU).It is an intelligent electronic device which estimates the synchronized predominant harmonic phasors(100Hz and 150Hz)along with the fundamental phasors(50Hz)of three phase voltages and currents with high precision.The proposed ASWABP scheme can detect the fault,identify the parent bus,determine the faulty branch and classify the faults using MPMU measurements at System Protection Center(SPC).Based on these MPMU measurements(received at phasor data concentrator(PDC)at SPC)the appropriate relays will be supervised to enhance the overall reliability of the power grid.Numerous case studies are conducted on WSCC-9 bus and IEEE-14 bus systems to illustrate the security and dependability attributes of proposed ASWABP scheme in MATLAB/Simulink environment.Also,comparative studies are performed with the existing conventional distance protection(Mho relays)for corroborating the superiority of the proposed scheme regarding security and dependability.Comparative studies have shown that the proposed scheme can be used as adaptive supervised wide-area backup protection of conventional distance protection.