Research On Optimization Method Of Reclosing Sequence For Reducing Voltage Sag Depth

With the large-scale use of automatic control devices sensitive to voltage sag,such as computers and PLCs,the occurrence of voltage sag causes users to suffer huge economic losses.At the same time,the voltage sag will also cause a disconnection accident in the grid-connected new energy source.Automatic reclosing is widely used in transmission lines.Since the permanent fault identification method is not mature in practice,there is a case where the fault reclosing with the fault(ie,the coincidence failure),the sensitive load may be impacted again.In order to reduce the voltage sag depth at the sensitive load busbar when the reclosing failure fails and shorten the duration of the voltage sag,this paper studies the sequence of the adaptive reclosing optimization.Firstly,the optimization method of three-phase reclosing sequence is studied.After the short circuit fault occurs on line and the protection action on both sides open the circuit breaker,the node admittance matrix before the fault is corrected.Inverting the modified node admittance matrix to obtain the node impedance matrix.Compare the mutual impedance modulus between the node at both ends of the faulty line and the sensitive load node.The comparison result is used to determine the three-phase reclosing timing scheme,that is,the side with the smaller impedance value is the non-pressure side.Secondly,the optimization method of single-phase reclosing sequence is studied.When a single-phase grounding fault occurs on the line,the protections on both sides act and fault phase breakers trip.The concept of fault component is used to construct the fault additional state network.Additional source is added to each end of the line to calculate the fault component voltage of the sensitive load node.The reclosure sequence is determined according to the magnitude of fault component voltage of sensitive load node.The side with smaller magnitude is determined to reclose first.After one side of the line is reclosed,the magnitude of line voltage is used to judge whether the reclosure is open or not at the other side.Finally,an optimization method for reclosing sequence of grid transmission lines with multiple sensitive loads is studied.Through the simulation calculation,the voltage sag domain division map of each sensitive load node is obtained.After comparing the sag domain of each sensitive load,the line is divided into reclosing sequence without influence,the reclosing sequence affects a single sensitive load,the reclosing sequence affects multiple sensitive loads,and the reclosing sequence affects multiple sensitive loads and there are contradictions.After technical comparison,it is determined that there are contradictory transmission line reclosing sequence that affect multiple sensitive loads.The simulation results of PSCAD/EMTDC show that the research conclusions of this paper are not affected by the transition resistance and fault location,and can reduce the voltage sag depth and duration of sensitive loads.