Stability Analysis And Control Strategies Of UHV Access Zhejiang Grid

With economic of Zhejiang developing rapidly, power load increasing fast, the power network construction is developing towards large network, large units, ultra high voltage, and long distance transmission. The strength of using the generating, transmitting and distributing equipments is increasing to the limit. When UHV transmission lines access Zhejiang grid, large power will be transmitted to Zhejiang. So the research on angle stability and voltage stability has practice signification for the safety of electric network.According to the planning data of Zhejiang grid, there will be 5 UHV AC lines and 1 UHV DC lines in 2015, and 6 UHV AC lines and 2 UHV DC lines in 2030, so large power will be transmitted to Zhejiang, and it certainly will influence the safety and stable operation of existing grid. Based on the planning data, this paper uses BPA as analysis tool. Firstly calculate the power flow distribution of Zhejiang Grid and draw out the power flow diagram. Then do a fault simulation to Zhejiang ultra high voltage transmission lines. Combining with angel and voltage stability curves, analysis the effects of UHV AC and DC line fault to Zhejiang grid. Then list out the transient instability. Analyzing which instability plays the leading role, angle instability or voltage instability.Power system transient stability includes transient angle stability and transient voltage stability. The power system will be guaranteed under stable operation only when both of them are met. This paper discusses several criterions of transient angle stability and transient voltage stability, puts forward transient angle stability and transient voltage stability constraints for preventive control, and establishes a refined OPF-based transient stability preventive control model. Based on optimal control theory and functional variation theorem, generator dynamic equations and co-state equations are computed. This algorithm is realized on small power system. But for this study of Zhejiang Grid, the program is temporarily unable to realize. So aiming at grid instabilities, some control strategies are designed based on sensitivity analysis method. In the end, a summary of this paper is made. And the author also points out that more work needs be done in the future.