Research On The Influence Of Generator Excitation Limit Functions On The Stability Of Power System

With the development of ultra-high voltage power network,the increase of voltage level,the complexity of electric network and the enlargement of single unit capacity of generator unit,the problem of the power system stability becomes increasingly prominent.There are many improvement measures for reliability and stability of generator and power system.Improving control characteristics of generator excitation system is considered as one of the most economical and effective measures for enhancing the stability level of power systems.Fault case of power grid through domestic and international countries showed that not only main part of the rapid voltage control,but also various excitation limit elements will play additional restrictions effect on power system in and after long processes of the power grid failure.Therefore,it is of great significance to study the action characteristics of additional function excitation restriction and the effect on the stability level of power system.Firstly,the thesis researches the estimation value of the phase-lead depth of generator,and provides a reference for the setting value of under excitation limiter.The basic principle and limiting factors of phase-lead operation of generator has been derived.Based on the scenario of voltage rise in the actual power grid,the simulation calculation method of the phase-lead depth of generator is proposed.And the phase-lead depth of the unit is simulated and calculated by typical examples.Secondly,the thesis introduces the UEL access mode.The transient stability of power system under four different excitation modes is analyzed in typical single-machine infinite-bus system.The transient stability of the actual power system is analyzed under AVR without UEL voltage regulation mode,AVR with UEL voltage regulation mode by select gate type and AVR with UEL voltage regulation mode by superposition type.The influence of different voltage regulation modes on the transient stability of the actual power grid model is illustrated.Finally,the thesis analysis the action characteristics of OEL and the coordination relationship between OEL and rotor overload protection.For example,a dynamic model based on FDS is established and simulated with the case that the voltage is easily on the low side after it is disturbed by fault.The influence of OEL action and different number of OEL on system stability is compared and analyzed,and reasonable suggestions for maintaining stable operation of receiving end grids under low voltage scenario are given.