Research On Generator Protection Related To Power Grid And Related Issues

As power electronic devices are being largely applied and high-voltage direct current(HVDC)s with large capacity are being commissioned,the characteristics of “power electronization” and “strong DC and weak AC” of the grid are being presented.On one hand,the new characteristics affect the operation of generator directly.On the other hand,with the increasing of capacity of generator,its operation status also has an influence on the safety of power system directly.Therefore,it is of great significance to strengthen the research on the coordination between generators and grid under new situation.As gridrelated protection of generator is one of the key factors impacting on the coordination between generators and grid,it is necessary to study on the grid-related protection of generator deeply.Firstly,the coordination principle between LOE protection and over-excitation limit of adjacent generator is obtained by investigating the behavior of loss-of-excitation in the power system with several generators in this paper.Secondly,this paper focuses on the operation of LOE protection in the presence of Unified Power Flow Controller(UPFC),on the base of which,the operations of LOE protection in the presence of synchronous condenser and capacitor are also analyzed.Furthermore,aiming at synchronous condenser,the effect of its position in the grid on LOE protection is discussed and its effect on the behavior of loss-of-excitation in the power system with several generators is also studied.Besides,aiming at capacitor,the impact of its capacity on LOE protection is discussed.Finally,the influence of extending the single-phase reclosing time of transmission line on the protections of generator is studied in this paper.Then,take a practical pumped storage power plant in East China Grid as an example,the protections of generator/motor are readjusted.In addition,on the base of the three-area AC/DC equivalent system model,the mechanism of short single-phase reclosing time leading to instability of sending system after single-phase permanent fault in AC transmission lines of receiving system is theoretically analyzed.