Study On The Transition Process Of Closing Shunt Capacitors In 10kV Power System

To find out the reasons of the explosion of breakers while putting parallel compensation capacitor into operation in 10kV power system, transition process of closing has been studied and discussed in depth in this article. ATP-EMTP is used for simulating the transition process and verifying the conclusions. The following work has been carried out.Reanalyzed the symmetrical three-phase circuit which be used to study the transition of breakers closing. With solving the whole solution of differential which describe second-order RLC series circuit response to sinusoidal excitation, this article studied the second-order circuit parameters (R, L and C) and the early closing phase angle how to impact the transition process. Found that the decrease of L would make the current significantly increased while the voltage is slightly reduced in the transition process, at the same time the transition time will be slightly smaller. The early closing phase angle is an important factor in causing the over-current and over-voltage. And then, ATP-EMTP is used to verify the above conclusion.A new circuit model containing Three-phase coupled inductors is established to analyze over-voltage and over-current in the transition of closing three-phase circuit breaker. Through decoupling and Laplace and inversely transforming the circuit, the influence of mutual inductance and different inductor polarities on the process of transition is discussed. In this paper, ATP-EMTP Power System Simulation Software is employed into calculating the over-voltage and over-current with the actual parameters, and the transition process under different situation of decoupling the circuit is contrasted.A new circuit model is established to analyze the over-voltage and over-current while breakers asynchronous closing. By selecting a set of practical operation 10kV system parameters and taking numerical solution to it, cause of the higher over-voltage and over-current in the transition of asynchronously closing is investigated. This paper simulated and analyzed the circuit with the ATP-EMTP simulation software and obtained a series of over-voltage and over current actual waveforms. The paper summarizes the law how breakers-closing interval and the value of capacitance and inductance impacted on the transition.Described the production of circuit breaker resistance, the equivalent model of resistance is established to study the role of which to the transition of closing. A new method to simulation the equivalent resistance designed in ATP-EMTP, simulated three phase circuit and got the conclusion that the longer the compression process, the more significant damping effect.In summary, the paper summarizes the following conclusions. Both coupled inductors and breakers asynchronous closing could increase the voltage, even in extreme cases did not exceed the insulation with the setting value. In terms of the over-current, the change is more sensitive. It appears much higher current, up to 6 times of the steady state. Therefore, Breaker failure is more likely caused by the over-current.