The Key Technology Research And Application Of Out-of-step Protection Based On The Double Circular Arc Algorithm

With the development of energy saving and theBelt and theRoadpolices,small and old generating units is shut down,supercritical large generating units are built to run,extra high voltage direct current transmission project has been vigorously carried out in recent years,long distance transmission of large power unitsare normal.At the same time,the capacity of newenergyintegrated into power gridsmaintains the fast growth.Wind energy,solar energy and other large scale renewable energy power generation into the grid impact on the stable operation of power grid.Oscillation of power system is difficult to avoid.Once the disposal measures are not properly,it is likely to cause significant damage to the generator set out and a large area of the region,resulting in significant economic losses.As an important part of generator and transformer unit protection system,generator out-of-step protection is closely related to the stability of electrical power system.The research of generator out of step protection is ofgreat significance.This paper introduces the existing principle of out of step protection and points out the existing problems.analyzes the cause of the loss of step,and gives out the voltage and current,the track of the oscillation center and the law of its voltage variation in the process of out of step.A linear formula and a circle formula for measuring the trajectory of the impedance at the end of the machine are derived.Because of the existence of the system impedance angle,it is found that the jumping phenomenon of the oscillation center.In this paper,the angle between the angle of the angle formed by the reverse vector of the system impedance and the reactance of the transformer is illustrated by the graph analysis.Protection collects generator terminal voltage and current.According to the measured impedance locus,the change process of energy angle is calculated.The lost step is determined by the double arc boundarycriterion.Due to the whole set of multiple angle boundary,the power angle can be arbitrarily set.The circular arc can correspond to the static stability and the dynamic angle.When the loss step is not completely formed,Protection can sent out the alarm signal,and has early warning function.By detecting the change of power angle between the arcs,the algorithm of out-of-step prediction can beresearched with the polynomial curve fitting.In this paper,a single machine to infinite system model is established in MATLAB,combined with equal area rule and rotor motion equation,the generator oscillation and out of step simulation is carried out.It is found that the active power output and fault duration are the main factors leading to the loss of step and oscillation.The double circular arc algorithm is proved to be correct by putting the simulation parameters into the program written by MATLAB language.The simulation research of out of step early warning in the case of the circuit breaker is considered in two cases without coincidence and coincidence,and the appropriate warning time is given.Wave record files are generated with the comtrade format,using the playback function of the testing system,simulation waveform isplayed backin the devicewhich uses the double circular arc algorithm,the feasibility of the algorithm is verified.