Research On Large Capacity Synchronous Condenser Loss-of-excitation Protection And Its Impact On AC/DC System Protection

In order to solve the problems of insufficient dynamic reactive power reserve and deterioration of voltage regulation characteristics of UHVDC,State Grid Corporation of China plans to put a number of large capacity synchronous condenser(LCSC)units into operation during the 13th Five-Year Plan period.This paper focus on LCSC and the research includes four parts,they are configuration of LCSC loss-of-excitation(LOE)protection,impact of LCSC on generator LOE protection、distance protection and DC system.Firstly,the LOE simulation model of LCSC is established in this paper,and the electrical quantity characteristics of LCSC are studied systematically.Then,the principle and method of LOE protection are introduced,the existing problems are analyzed,and a new LOE protection scheme of LCSC is proposed.The new scheme uses the absorbing reactive power rate as a new criterion,which can identify the LOE fault reliably,and maximum exert the reactive power regulation function of LCSC.Then,according to the reactive power response characteristics of LCSC and the basic principle of distance protection,the expression of measured impedance after LCSC accessing is deduced,and the characteristics of measured impedance are qualitatively analyzed.When the injection current of LCSC acts on the transition resistance,the measured impedance of distance protection at the access side will decrease and that at the other side will increase.In AC system,the impact of LCSC access is obvious,but in AC/DC hybrid power system,the impact is limited.In view of the adverse effects of LCSC on distance protection,the action characteristics of the measuring elements that can allow a large transition resistance can be adopted,so as to improve the action performance of distance protection.The physical process and dynamic response characteristics of generator LOE fault are analyzed from two aspects:theory and simulation.And the time characteristic of equal active power process in LOE fault is mainly analyzed.A single machine infinite bus system model with LCSC,and a multi machine system with LCSC are established in PSCAD/EMTDC and the operation of LOE protection under different generator loadings and different LOE modes is simulated.The research shows that the access of LCSC extends the equal active power process,but does not affect the correct operation of LOE protection.Therefore,the access of the LCSC has little impact on the machine which is loss of excitation.In the multi machine system,the access of LCSC increases reactive power reserve of the system,which is conducive to the synchronous operation of the unit.Finally,this paper establishes a simulation environment of AC/DC hybrid power system with LCSC access.From the system level,it analyzes the different requirements for dynamic reactive power caused by serious faults of the power grid at the sending and receiving ends,and verifies the impact of LCSC on the stability of the power grid through simulation.Then combined with theoretical derivation,the influence of the initial reactive power output of LCSC on its transient reactive power output capacity is analyzed.On this basis,the optimal scheme of the initial reactive power output of LCSC in HVDC converter station is proposed.