| Most of load in the electrical power system,like electromotor and transformers,are reactive the reactive load will consume reactive power at work.The power voltage and terminal voltage will decrease if all reactive power is provided by power source,which will damage electrical equipment even cause the system to break down and large-scale power outage accident if the situation is severe enough.Therefore it is essential to use capacitor for reactive power compensation.To ensure the stability of the system the capacitors need to be switched according to reactive power requirement of the power system because the power system is a dynamic equilibrium system,and the reactive power consumption is changing at any time.The characteristics of capacitors make it easy to produce inrush current,overvoltage and reignition during switching on and off of capacitors,which will affect the power quality and the safe operation of the system.The inrush current generated by switching on capacitor and the overvoltage during opening can be restrained through phase controlled switching technology,that is making different switching strategies based on the different properties of the load,accomplishing circuit breaker switching operation at optimal phase to suppress electromagnetic transient process.With forty years development,phase-controlled switching technology has been applied in a certain rage,and the controlling of circuit breaker is more accurate and faster thus making the accuracy of phase control improvement drastically after the emergence of permanent magnetic mechanism.In this paper,the transient process of reactive power compensation line when circuit breaker switches on and off is analyzed briefly.And the inrush current when closing and the transient recovery voltage(TRV)and reignition when opening are researched,and the main factors affecting the inrush current and the recovery voltage are obtained.Previous researches are generally focused on switching of capacitor,and treated circuit breaker as ideal switch.Then a simulation model of controlled switching on and off of reactive power compensation line is established based on the electromagnetic transient simulation software ATP/EMTP according to topological structure and parameters of main wiring in a substation of China Southern power grid,the difference from the previous research is that the series reactor is considered in the simulation model.And a model of circuit breaker considering mechanical scatter and insulation characteristics is established based on the module of ATP in order to coincide with the actual situation.In this paper,the effect of three phase circuit breakers mechanical scatter on closing inrush current and series reactor is researched through controlled closing simulation.And the effect of series reactor in the compensation line and the chopping current of circuit breaker on the maximum TRV with no reignition when controlled opening is studied,and the relationship between reactance and maximum TRV and the relationship between chopping current and maximum TRV are discussed.A phase controlled switching controller based on FPGA is developed and debugged,and the validity of software and hardware of the controller are confirmed.Then the experimental circuit is built,and the permanent magnet vacuum circuit breaker is tested,to ensure that the mechanical scatter of circuit breaker can meet the requirement of controlled switching.Compared with three phases of circuit breaker switching simultaneously,it can be seen that the closing inrush current and the maximum TRV of opening can be decreased with application of phase controlled technology.In order to simulated actual situation of opening operation of reactive compensation line,setting series reactor in front of the capacitor.Switching off the compensation line at different phases of the current,the experimental results show that the reignition phenomenon of compensation line opening operation can be restrained through the application of controlled opening technology. |
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