Calculation Of Switching Transients Electro-magnetic In Substation And Their Effects On Secondary Equipment

Ultra UHA is the development direction of China’s power grid,which makes theelectromagnetic environment in substation more complex,also requirements ininsulation and electromagnetic compatibility is higher. With the measurement,monitoring and other secondary equipment decentralization to switch venue,thesecondary equipment exposed to switching field directly and severely disrupted as thefield has compex electromagnetic environment. Therefore,effective evaluation due toswitching transient field and research of its impact on secondary equipment is crucial.In this paper,the disconnectors operating model is the main researchobject.First,combined FDTD method with the transmission line theory to study thecoupling interference of transient field;Second,established the ATP model of entiresubstation to study conducted interference and propose the corresponding protectivemeasures.On this basis,analysis software for transient electromagnetic field estimatingand calculation caused by the switching operation in substation was developed. Themain research work carried out as follows:①The equivalent circuit model of disconnectors operation was established,current waveform due to switching operations were calculated by using the Bergeronmethod,to determine the mathematical expression of bus current;FDTD is superiorityin the study of transient problems,combined it with electric dipole method andantenna theory to calculate the distribution of spatial transient field;Due to thesymmetry of the switching operation model,a discrete FDTD method in cylindricalcoordinates is eatablished and Mur absorbing boundary conditions is setted;Resultsshow that: to calculate the space electric field,floor effect need to be taken intoconsideration,ground and below the regional electric field is small,little effect inelectric field if changes in soil properties, only shielding and other measures canreduce electric field.②For the characteristics of coupling of transient electromagnetic field caused bythe bus transient currents when switching operation to the secondary cables,using animproved method of Agrawal transmission lines,making the space electric field asmotivation,considering the perspective of the incident plane wave,to calculatecoupling interference of space field to the cable.Results showed that:when thetransmission line perpendicular to the bus,coupling voltage in it is minimum,thetransmission line should avoid parallel bus. ③A method to verify the theory:literature actual measurement date,applied thealgorithm in this paper,under the same bus current incentives,waveform calculated bythe theory comparison with the measured waveform.The results show that:thetheoretical results is consistent with the measured waveform,witch can meet theaccuracy requirements of practical engineering,transient electromagnetic environmentcan be estimated in actual substation.④The simulation study for wave processes of first system and its conductedinterference to secondary cables.Set up a first system and secondary systemmodel,calculate the transient overvoltage generated by first system and interferencevoltage in secondary cable ends under different operational forms;Several protectivemeasures for interference voltage were proposed and its protective effect wassimulated.The results showed that:the disconnectors shunt resistor and installation offilter capacitor can reduce the interference voltage at secondary cable effectively.⑤Analysis software for transient electromagnetic field estimating andcalculation caused by the switching operation in substation was developed.Softwarecan achieve three functions:single-point field calculation,spatial field calculation andtransmission-line overvoltage calculation.Respectively,to achieve a single point ofswitching transients field calculation,space field calculation and its couplingovervoltage for transmission-line,it was effective to evaluate switching transientsfield.