Ehv Protection Of A Number Of Issues

Distance relay is a key component in the extra-high voltage transmission line complete protection equipment. This paper concentrates on the study of the distance-relay scheme of the complete protection equipment for the EHV transmission line. Based on the analysis of characteristics and disadvantages of the current methods, the improved schemes are provided.This paper analyses the distance relay part of NARI RCS-901 EHV transmission line complete protection equipment, which uses a common and effective distance relay method. In this method, positive-sequence voltage polarized mho relay cooperates with zero-sequence reactance relay and export action signals through an AND gate. The power swing blocking and opening equipment works together with distance relay part and export action signals through an AND gate.This paper studies the condition for the unsymmetrical fault opening component: |(I|·)₀| + |(I|·)₂|>m×|(I|·)₁ |. This is a common and effective opening component but lack of meaningful study to provide the related theory. We analyze the fundamental mechanism of the opening condition, and give a feasible computing method to calculate the m value with respect to the real transmission lines.This paper analyses the cooperation of positive-sequence voltage polarized mho relay cooperates with zero-sequence reactance relay. The action characteristics of the former relay can be expressed in the measure impedance form while for the latter, it is infeasible. We also compare the two common cooperating methods for changing mho relay and zero-sequence reactance relay.This paper proposes a new criterion for the distance relay, which shares similar characteristics with the zero-sequence reactance relay and negative-sequence reactance relay, and theoretically resists infinite transition resistance. Since zero-sequence reactance relay, negative-sequence reactance relay, and many methods of self-adapt distance-relay, are derived based on the approximation that the phases of the whole system line's impedance Z_S , Z_L, Z_R are equal, it can not ensure the precision when I₀ replaces I_F to compare phase in zero-sequence reactance relay, and therefore miss operation and malfunction may occur in some self-adapt distance-relay. The newly proposed criterion is derived based on the precondition that the phases of Z_S , Z_L, Z_R are not equal, which is the most precise one among the self-adapt distance-relays.This paper proposes a practical condition to determine whether this kind of distance relay would cause the same-phase problem. The traditional condition is derived based on the precondition that the phase of I₀ and I_F are equal, while in reality this precondition is not precise. The condition proposed by this paper is more precise. It is not affected by the phase difference of I₀ and I_F,so it can be used as the dividing condition whether the same-phase problem occurs, and when it happens, an opposite motion equation is needed for zero-sequence reactance relay. Therefore, it realizes that no matter whether send-power side or receive-power side, no matter how large the phase difference of the two side of source of the system is, the zero-sequence reactance relay can resist infinite transition resistance.At last, this paper compares zero-sequence reactance relay, negative-sequence reactance relay and the new criterion. The experimental results prove that zero-sequence reactance relay and negative-sequence reactance relay is available for special kinds of fault, the new criterion proposed by this paper is available for single phase grounded fault, double phase fault, double phase grounded fault and even triple phase fault. The sub circuit impedance operating characteristic graph shows that it can resist infinite transition resistance.This project designed the "System Fault Simulation and Relay Criterion Analysis System" with MATLAB language and Simulink, this program can simulate all kinds of short-circuit circumstances in the 220kv two-side power system, get the transient value and virtual value for related electrical parameter values, and judge the motion condition for every relay, and draw sub circuit impedance operating characteristic graph for every distance relay.