Research On Some Key Issues Of Protection For Series Compensated Transmission Line

As the electric power resources in our country are distributed in centralized region which are far away from the load center, the high voltage and long distant transmission lines have an important place in our developing power system. There are two techniques:series compensated method and parallel lines method, which are usually used for improving the transmission capacity and efficiency. Although they are of many merits in normal work condition, they may cause protection issues in lines relays during fault condition for their complicated structure and changeable action situations. In this dissertation, some researches are given in protection issues of the series compensated line, which are included the series compensated parallel line. The main achievements and contributions of this dissertation are as follows:(1) Based on the analysis of the model for series compensated device and the main characteristics of series compensated line, a new generalized and unified RLC model of the series compensated line is given, which is well considered the effect of the MOV actions. Compared with the traditional research idea which is dividing the series compensated line into series compensated device and transmission line, the model given in this dissertation viewed the series compensated line as the integrated unit which can provide a new theoretical foundation for the further research.(2) A new fault location detecting method considering the effect of the MOV actions is proposed in this dissertation for series compensated line. During the fault, the series compensated device is generally simplified as series capacitor in tradition fault detecting methods, which is not always proper in fact. The new fault location detecting method is based on the new initial model which is considering more characteristics of the series compensated in practical situation, so it is more complete and simple in theoretical analysis and more advanced in practice application than the traditional fault detecting methods.(3) A new interphase distance relaying algorithm (Zone-1) for series compensated transmission lines is proposed in this dissertation. The algorithm is based on the unified model of the series compensated line during the interphase fault, which is not required iterative calculation, and not needed to know the series capacitor parameters and the operating states of SC/MOV/GAP. Meanwhile, the over-reaching and under-reaching problems caused by the MOV action can be solved effectively. Numerical simulations results show that the accuracy and reliability of the new algorithm proposed in this dissertation are satisfactory.(4) Two new single-phase ground fault location algorithms which are respectively based on one end data and two end data are proposed for series compensated line protection. The two algorithms are both based on the unified model of the series compensated line during the single phase ground fault, which is well considered of the effect of non-linear MOV and compensated capacitor impact on actual transmission line reactance. Compared with conventional fault location algorithm for series compensated line, they do not need to identify whether SC/MOV is in fault loop, and not need to know the parameters and the operating states of MOV. Furthermore, the two algorithms only use the filtered sample data, and do not need iterative calculation. The simulation results show that the proposed algorithms can obtain more accurate and fast results than conventional fault location algorithms.(5) Two new distance relaying algorithms (Zone-1) which are respectively realized by one end data and two end data are proposed for single phase to ground fault on series compensated parallel transmission lines in this dissertation. The two algorithms are both based on the unified model of the series compensated parallel lines during the single phase ground fault, which is well considered of the effect of the compensated capacitor protected by MOV and the zero-sequence mutual coupling on actual reactance of transmission line. As the algorithms do not need the phase calculation of the electric quantity, not needing the parameters of mutual coupling and series capacitor device, they are characteristic of the lucidity in principle and the simplicity and rapidity in calculation.