Study Of Protective Relay On Series Capacitor Compensated Lines & Study Of Protective Relay And Reclosure On Double-circuit Lines On The Same Pole

With the development of large-scale complex interconnected power system, how to increase the efficiency of network, and how to enhance the transmission capability of lines have become signify tasks in many countries. New technologies such as Series Capacitor (SC) compensated lines; Double-circuit Lines on the Same Pole (DLSP) are introduced for this case. Those measures enhance the transmission capability of lines and utility efficiency of corridors. However, the widespread use of those measures has great influence on the performance of existing transmission line relaying protection at selectivity quick-action ability sensitivity and reliability. Methods used to resolve those problems, are brought out in this paper which includes: theory and technique that is suitable for protection on Series Compensated lines (SCL), configuration principle and problems that should pay attention to for protection on DLSP, a self-adaptive auto-reclosing mode that is suitable for DLSP.In the first part of this paper, protection on SCL is studied.1. Based on the analyzing of the configuration and attribute of SC , as well as the control mode and non-linear characteristics of its protection element—Metal Oxide Varistor(MOV), the influence of SC on the transmission line relaying protection is studied in this paper. The influence including: voltage reversal and current reversal due to the SC's capacitive impedance, thus affects the performance of relaying protection. SC makes it difficult to set distance zone I and easy to happen transient overreach. Low frequency component during transient process and unsymmetrical gap flashing also have negative influence on relaying protection. Existing solutions are also analyzed and compared in this paper.2. By the analyses of the performance of Ohm relays on SCL, it shows that Ohm relays which are polarized with memorizing positive-sequence voltage together with reactance relays can trip correctly on forward fault and not trip on backward fault whether the bus side or line side potential(relative to capacitor). But when memory time passed, the Ohm relays would wrongly trip if fault occurs on backward behind SC. Two Ohm relays with different memorizing-time are presented in this paper to resolve this problem. The overreach of distance relay zone I can be prevented by modifying the line relay's setting with the MOVprotective level online. Schemes forenamed have been verified by EMTDC stimulation.3. It indicates that Incremental Power Frequency (IPF) distance relay applied on SCL can operate correctly to the forward fault in the protection region, but misact to backward fault behind the SC. An overreach IPF distance relay and an underreach IPF distance relay that work together with logical "AND" are presented in this paper to prevent the reverse misoperation. The research indicates that adding the MOV protective level voltage to the IPF distance relay's threshold can prevent overreaching effectively when fault occurs behind the SC out of protection region.4. The performance of directional relays on SCL has also been studied in this paper. Forward fault may be judged as backward fault because of the capacitive equivalent source impedance backward the relay due to the effect of SC. Directional relays can operate properly when it is compensated by voltage. The influence of the transient low-frequency component on IPF directional relay is studied, and the method, which has been verified by the EMTDC simulation, is brought out also. Another theme is the influence of unsymmetrical flashing of the triggered gap on directional relay. The positive-sequence current is used to block relays in this situation. On the basis of the theoretical analysis and EMTP experiment , a special problem of the IPF directional relay on series compensated parallel double-circuit lines is brought out—the relay that applied on the fault line end without capacitor maybe fail to trip when a phase-ground fault via a high resistance occurs in the protection region near the SC.5. The research achievements mentioned above have been used into the research and development of new protection equipments on SCL. Configuration principle between main protection and back-up protection as well as requisition of hardware is explained in detail in the paper. Dynamic model experiment and RTDS experiment validate the feasibility of the research achievements. Protection equipments based on the new designed reliable hardware have been produced and put into operation in North China and South China electric systems.In the second part of this paper, protection on DLSP is studied1. Based on the analysis of the features and existing protection modes of the DLSP, protection configuration principle which is most applicable to our country's DLSP, basic requirement and problems which should pay more attention to are brought out in the paper.2. All existing Auto-reclosing modes on DLSP are discussed detailedly in the paper, and it reveals the fact that it would be inadvisable to adopt the "quasi-three phases" operation mode and unconditional multi-phase auto-reclosing in our country. On this basis, a scheme composed of tripping on phase, non-severe-faults orderly reclosing phase by phase is proposed in this paper, thus keep the system on operation as possible, increase the probability of successful auto-reclosing as well as avoid reclosing onto severe permanent faults.3. A detailed analysis has been made on the criterion used for distinguishing severe permanent faults and instantaneous faults. The terminal voltage criterion combined with operation information and distance measurement information is applied to distinguish instantaneous faults and severe permanent faults of unsymmetrical ground faults for the protection on DLSP. As the line without parallel reactor, the moment when the fault current arc extinguishes out in an instantaneous fault can be determined by the 3rd and 5th harmonics in the terminal voltage. Reclosing orderly phase by phase is proposed here to distinguish instantaneous and permanent phase-phase fault as well as prevent multi-phase reclosing from operating on multi-phase permanent fault.4. The scheme has been verified by EMTDC simulations using the parameters of Longwang—Honggou 500kV DLSP system in Sichuan province, China. And the protection equipments based on the scheme have passed the RDTS simulation experiments by Sichuan Electric Experiment and Research Institute. The scheme of the DLSP relay protection and self-adaptive auto-reclosing has been put into utility on the Longwang—HongGou DLSP. The protection equipments have experienced several faults in region or out region, which give the result that the protection equipments have achieved the design demand.