Research On Controlled Opening Technology Of Shunt Reactors

As the power system having larger capacity,higher voltage and longer-distance transmission,there are some bad phenomena such as voltage-rising in the terminal of power grid.To eliminate voltage-rising phenomena,a certain number of inductive reactive power compensation devices(such as shunt reactors)need to be installed to compensate capacitive power in high-voltage transmission line.The power system is a dynamically balanced network which requires frequently switching on and switching off shunt reactors based on grid operation conditions.In the process of switching shunt reactors,there will be some electro-magnetic transient phenomena such as cut off overvoltage and re-ignition over-voltage,threatening the safe operation of power system.As the power switch being more and more intelligent,controlled switching technology has become an effective way to solve these problems.Controlled switching technology originated since 1970 s,after 20 years of continuous development,which has been widely used.The basic principle of controlled switching technology is controlling the circuit breakers to complete the closing and opening operation at the ideal electrical angle to avoid the energy amount of memory element in circuit changing as much as possible.And in this way,controlled switching technology can reduce the inrush current and overvoltage and avoid their bad impacts on power system.In this paper,the basic principle of controlled technology and electro-magnetic transient phenomena in the process of switching shunt reactor are briefly analyzed.Then,according to the connection configurations of the shunt reactors in power system,the best opening strategy of shunt reactors is deduced.And with the help of the EMTP/ATP,the electro-magnetic transient modeling and simulation software,the transient overvoltage of shunt reactor in random switching off and controlled switching off are compared in order to verify the rationality of the ideal opening strategy of shunt reactors.In this paper,the MOD modules in EMTP/ATP are established using FORTUNE coding language,the effect of raising rate of dielectric strength of the circuit breaker,the pre-arcing time and the maximum operating voltage in the power system on the controlled technology in engineering practice are explored,and this paper also gives some preliminary calculation method to direct the engineering practice.In the experimental part,FPGA is used as the core of the controlled switching system,working with the external circuit board,to complete the controlled switching function.The FPGA chip has the features of strong logic and high real-time.Software modeling and circuitboard are modularly designed,which will be convenient for field debugging and experiment,besides,secondary modification and re-development of this controlled switching system will also benefit from this.The controlled switching system could send qualified three-phase switching-off trigger signals when the shunt reactor are connected in different ways under the conditions of laboratory.Besides,the accuracy and stability of the trigger signals are also verified by experiment.In the end,single phase inductive load is switched off by this controlled switching system,and the results show that the control strategy and controlled switching system can work effectively and efficiently.