| Vacuum circuit breakers(VCBs)are widely used in 10-kV power distribution systems due to their excellent performance.However,in the process of frequently switching shunt reactors(SRs)for compensating reactive power,accidents often occur such as switch cabinet explosions and insulation breakdown of equipment including SRs and substation transformers(STs),which affect the stable operation of the power system.Limited by field test conditions,the research on switching overvoltage suppression mostly focuses on simulation.Besides,most simulation studies fail to establish an effective arc reignition and extinguishing model based on the measured voltage and current characteristics of VCB to carry out systematical and comprehensive simulation exploration about suppression measures.Through theoretical analysis,simulation calculation and field test,the paper studies the suppression methods for overvoltage caused by VCBs switching 10-kV SRs.The main work of the paper is as follows:Based on the Helmer's model,through the statistical analysis of the measured voltage and current data of VCB from the previous field test performed in Yunyang Substation,the typical values of the three characteristic parameters describing the arc extinguishing and reignition in the theory were obtained,and the real and effective VCB model was built in ATP-EMTP.Then a series of simulations were carried out,in which the factors(the V-I characteristics of the surge arrester,the capacitance value of the RC sunbber,and installation position and quantity of the protection device)affecting suppression performance were investigated.Finally,subsequent field test about suppression was implemented again in the same substation to verify the effectiveness of the simulation.Therefore,the most reasonable suppression measures were presented.The conclusions are as follows:(1)When the VCB switches off the SR,multireignition occurs in the first clearing pole and the probability is low,but the overvoltage magnitude is very high,which threats the insulation of system equipment severely;When the VCB switches on SR,three-phase prebreakdown usually occurs and the probability is very high.Although the overvoltage amplitude is not high,the equipment may be damaged under the condition of withstanding long-term overvoltage,so enough attention should be paid to it.(2)The surge arrester can only limit the overvoltage magnitude.The lower the V-I characteristic curve,the better the suppression performance.A single surge arrester can only suppress the overvoltage at the corresponding installation site.In order to suppress effectively,it is necessary to install multiple surge arresters.Because of the non-linearity of surge arrester,the suppression performance is obvious in the face of switching-off overvoltage while weak in the face of switching-on overvoltage.(3)The RC snubber can not only limit the overvoltage amplitude,but also reduce the oscillation frequency and rise steepness.The capacitance value is positively related to the suppression performance but has a saturation effect.Similar to the surge arrester,the installation position also has an influence on overvoltage suppression,but a single RC snubber has a better performance than a single surge arrester.The access of the RC snubber changes the high frequency oscillation circuit,result in an excellent suppression performance on both switching-off and switching-on overvoltage.(4)Considering the safety risks of the RC snubber and difference in suppression performance caused by V-I characteristics of the surge arrester,for the overvoltage caused by VCB switching 10-kV SR,the most reasonable suppression measures are as follows: two 12/32.4 kV surge arresters installed at the terminals of the cables for SR and ST. |
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