Research On Load Model And Transient Stability Modeling Of Isolated Network System Of Hydropower Plants

With the rapid development of the electric power industry,the power grid becomes more complex.When disturbances and power failures occur in large power system,the system may be divided into several small isolated systems.At this moment,the situation that a single power plant drives concentration load could happen.Therefore,it is particularly important to study the transient stability of the isolated network system.Selecting suitable load model is crucial for the transient stability analysis and simulation of the isolated network system.An over-optimistic or over-pessimistic load model will have a significant impact on the simulation results.This will directly affect the decision of grid-connected hydropower plants under isolated operation,the operational safety and economic benefits of hydropower plants subsequently.Firstly,the possible operation status for the isolated grid in the operation of the hydropower station is discussed.Then the influence of different load models on the transient stability is analyzed in this paper.Secondly,aimed at the needs of the modeling for the isolated-network systems with hydropower plants,the models of turbine,governor,generator,excitation system and power system stabilizer are respectively built using the Matlab/Simulink software.Finally,taking a practical hydropower station in Yunnan Power Grid as an example,the isolated-network system with two hydroelectric generator units in parallel operation is modeled.And the constant impedance load model,the constant impedance load model in parallel with induction motor and the composite load model are used for simulation analysis.The results show that the system is transiently stable when a short-time disturbance occurs in the isolated network system.If the constant-impedance load model is adopted,the simulation results obtained are the most optimistic.If the constant impedance load in parallel with parallel induction motor is used as the isolated system load,the simulation results are the most pessimistic.