Research On The Out-of-step Oscillation Center Characteristics And Location Method

Recently,as the construction of ultra-high voltage(UHV)lines,many factors that may influence the safe operation of the power system are introducing into the grid.The local faults may spread over a long distance through the connection lines between regional power grid and severe cascading failure may occur.The out-of-step modes of the power system are turning from the traditional two-frequency out-of-step mode to the multi-frequency out-of-step mode.So the conclusions derived from the two-frequency scene may be unsuitable for the multi-frequency scene.So it is urgent to study the characteristics of out-of-step center in the multi-frequency scene.Based on the reference of a great deal of documents and the major project of the State Grid(2012-2015)and science and technology project of the State Grid(2016-2018),research of this paper centers around the characteristics of out-of-step center of the multi-frequency scene.The main research is as follows:(1)The construction of two typical out-of-step models in the multi-frequency scene.Based on the out-of-step models,expressions of voltage,current and frequency is derived and the it is observed that the electrical factors of any point in the power system is related with the voltage amplitude ratio,the frequency difference and the location of the point.(2)Based on the expressions of electrical factors,characteristics of out-of-step center in the multi-frequency scene are gained.When out-of-step center occurs on a line,frequency curves of the points locating on the same side of the out-of-step center fluctuate towards the same direction.Frequency curves of the points locating on the different sides of the out-of-step center fluctuate towards the opposite directions.(3)Inside factors of the power system that may influence the migration are analyzed.It is observed that the change of power system network frame and the series compensators may cause the migration of out-of-step center through the change of impedance.Unsuitable operations of cutting machine or cutting load can also change the dominant out-of-step mode of the power system,and the migration of out-of-step center will also be influenced.As for the SVC,it will be locked in the out-of-step process because of the low voltage,so the SVC has no influence on the migration of out-of-step center.(4)Based on the characteristics of out-of-step center in the multi-frequency scene,the location method of out-of-step center is proposed in this paper.First,the voltage frequency is preprocessed to reduce the calculation load.Then the characteristics parameters for locating out-of-step center are calculated.The correctness of the proposed locating method is proved by the simulations.