Research On Line Protection And Fault Location Based On The Distributed Parameters Model

A new fault location function is generated based on the matching idea of selecting a reference point to match the fault position, which phase characteristics is determinated by the phase characteristics of hyperbolic tangent function or by the phase characteristics of hyperbolic sine function. The accurate fault location for N-terminal (N≥2) transmission lines and parallel transmission lines can be achieved by using the phase characteristics of the function.(1) The function has different phase characteristics between reference point located at the left of fault position and reference point located at the right of fault position, and the phase of the function equals to zero when the reference point matches the fault position. Based on the phase characteristics of the function, a novel fault location algorithm for two terminals transmission lines is proposed. The presented algorithm has less calculation burden, and the accuracy is independent of fault transition impedance and its property, fault type, fault position. The fault location function has no false root in theory.(2) The function has different phase characteristics between the fault branch and the healthy branches, and phase of the function equals to zero when the reference point matches the fault position on the fault section. Based on the phase characteristics of the function, a novel fault location algorithm for three-terminal tranimission lines is proposed. The method breaks the mold of traditional methods that it must identify the fault section before locating the fault. The method can locate the fault without identifying the fault section first. And the method doesn't have dead zone of fault location, it can accurately locate the fault occurring near the teed node. Therefore, the method perfectly solves the disadvantage of currently used methods that there is a dead zone of fault location near the teed node. Th·e presented algorithm has less calculation burden, and the accuracy is slightly affected by transition resistance and its property, fault types and load current.(3) Due to the defects of existing synchronized phasor measurement (SPM) based fault location methods for multi-terminal transmission lines, such as the adopted lumped parameter models of transmission line cannot reflect correctly actual condition, there is dead zone of fault location while the high resistance fault occurred near the teed node, or the algorithm is too complex to implement, the adopted algorithms are affected by operation modes of power system, etc., the faulty branch cannot be correctly judged when high resistance fault occurred near the teed node. For this reason, a new fault location algorithm for multi-terminal transmission lines using SPM is proposed. Firstly, the voltage and current of the teed node that is the nearest to the reference bus are calculated by the voltage and current data of the bus that is the farthest to the reference bus, and by use of two-terminal fault location algorithm the fault location between the teed node and reference bus is solved; then based on the distribution characteristic of this fault location, the fault location problem of original N-terminal transmission lines is changed into the fault location of a teed transmission line; finally, a new fault location algorithm without dead zone for teed transmission line is given. The given algorithm remedies the defect of traditional fault location methods in which dead zone of fault location exist. The accuracy of the given algorithm is slightly affected by transition resistance, fault types and load current.(4) A new fault location algorithm for parallel transmission lines using two terminals unsynchronized data is proposed based on the phase characteristics of the function. The synchronization is achieved by using one terminal current's phase to adjust the other terminal current's phase in the differential component net. Since voltages are not be used in this algorithm, the measurement error of PT and CT will not affect on location accuracy. The presented algorithm has less calculation burden, and the accuracy is independent of fault transition impedance and its property, fault type, fault position and load current. The fault location function has no false root in theory.Due to the fact that the distributed capacitive current in three-terminal transmission lines significantly influences the protection performance of current differential protection, such influence should be taken into account in the protection principle. On the basis of new research findings of current differential protection for two-terminal transmission lines, a new distributed parameter model based principle of current differential protection for three-terminal transmission lines is proposed. Translating original current differential protection for three-terminal transmission line into two current differential protections for two-terminal transmission lines, which are similar in principle, the correctness of such a translation is strictly proved by distributed parameter model. Comparing with traditional post-fault current differential protection for three-terminal transmission lines, new protection criterion is not influenced by distributed capacitive current, so it is suitable to three-terminal high voltage transmission lines.The estimation error in the fault current phase angle based on the zero sequence current at the relay installed location is the key influential factor for the zero-sequence reactance relay and its improved ground reactance relay to be applicated in Ultra-high-voltage long AC transmission lines. To tackle the problem, an improvement of zero sequence reactance relay with applications in Ultra-High-Voltage long AC Transmission Lines is proposed. It is based on the principle that the negative current phase angle in fault path can be precisely estimated by the negative sequence current phase angle at the relay installed location with single-phase-to-ground faults.The protection has very strong ability against transient resistance and stability protective zone and high operation sensitivity with single-phase-to-ground faults.