The Isolation Criterion For Serious Fault In Power Grid Based On Wide-area Information

With the growing scale of Chinese electric power system, the country hasentered the era of internet-style grid, our country has entered the era ofinterconnected power grid. Although the control of grid security and stability isgradually improved, but the possibility of unpredictable accidental factors in thepower grid and the size of the grid are growing, so the stability problem stillcannot be avoided totally. When power system is out-of-step, if the effectivemeasures were not taken in time, it will lead to accidents, causing widespreadblackouts. As the backup of power system security and stability control, theout-of-step separation can ensure the normal operation of the rest of the system,which is the most effective control measure to control the out-of-stepphenomenon.Out-of-step isolation uses the splitting device installed on the tie line，and theaction of splitting device is mainly determined by isolation criterion. For acomplex power grid, the limitations of the adaptability of the traditional isolationcriterion and the coordination of splitting device are gradually highlighted.Especially as the core part of the isolation control, isolation criterion plays adecisive role to the timeliness of out-of-step criterion and the accuracy of theisolation control, its limitations is an urgent problem to be solved. At present, theisolation criterion adopted by the power system basically has the followingquestions:1) most of the criterions are based on equivalent two-machine system model，cannot be accurately described the out-of-step process of a large-scaleinterconnected power system;2) by a single local measurement to locate the out-of-step center, the locationand the tracking of the out-of-step oscillation center cannot be accurate;3) it cannot make response according to the online operation mode of thesystem and fault forms.According to the above problems, this paper summarizes and analysis theout-of-step characteristics of power system electric parameters, using thesynchronous information provided wide-area measurement system (WAMS), puts forward the compound isolation criterion and control scheme based on wide-areainformation. The proposed isolation criterion, considering the features of thelarge-scale interconnected power system and multiple measured data, canaccurately locate out-of-step oscillation center and the out-of-step state of system,and also has good adaptability to the change of operation mode and fault form.The corresponding isolation control, with the isolation section optimization,reduce the impact to the grid when the system is splitting; the start criterion basedon generator power angle, prepared for isolation control in advance, can reduce thedecision time online. And with DIgSILENT/PowerFactory14.0as simulation tool,the IEEE-10machine39node system as simulation model, the paper verified theeffectiveness of the criterion and the feasibility of the control scheme.