Study On The3^rd Line Defense Of Frequency Stability Coordinating Control For Sending-end Power System

As the energy resource is distributed intensively and load-adversely in China, large-scale regional energy bases such as thermal power base in Shanxi, hydropower base in Western Sichuan, wind power base in Gansu are all away from load center, which makes power grid with large installed capacity, small local power loads and great amount of power transmission more and more common. Limited transmission lines dealing with a large demand of power output, the sending-end power grid may endure cascading trip when serious failing occurs, which will lead itself to disconnected from the main power grid. In that circumstance, with a great amount of imbalance power, the isolated sending-end power system will face the challenge of frequency instability.In this paper, the mathematical models of frequency-related elements are studied. By making use of parameter aggregation and model identification, the one-machine piecewise linearization model is proposed to analysis the frequency response of sending-end power system. According to the comparison with the result of full-state simulation model, this model is proved to be valid and convenient. By synthesizing the assessment methods of transient frequency stability and that of frequency deviation acceptability, a new transient frequency assessment index is proposed. The test of different frequency response curves verifies this index to be valid and accurate. The traditional configuration methods of frequency stability control strategy mainly rely on operational experience and off-line simulation calculation. In this paper a technological process based on the model and index mentioned before is summed up, which includes principle formulation, setting and optimization of high frequency generator trip (HFGT) scheme. A strategy using df/dt criterion is introduced to accelerate the trip. Simulations are performed on an actual power grid using PSD-BPA. Simulation shows that the optimized HFGT scheme can adapt to different operation mode, suit for the condition that security and stability control system out of work, and coordinating with other control measures enhance the frequency stability of sending-end power system.