Assessment Method And Application Study For VCB Contact System Electrical Endurance

High voltage vacuum circuit breaker (VCB) is the security defender of power system,and it mainly plays key roles in control and protection. Its performance affects the reliableoperation of power systems. As a core component of VCB, the electrical wear of contactsystem directly influences the whole electrical endurance and breaking capacity. Thus it isvery necessary to assess and monitor electrical wear of VCB contact system. Firstly, thedefinition of VCB electrical endurance and the development of monitoring methods both athome and abroad are stated, and the methods that used for assessing electrical endurance ofVCB contact system are described in detail. Then various possible factors and techniqueproblems influenceing electrical wear and online monitoring of VCB are analyzed in depth.Furthermore, basing on the technology development of smart grid, probability-basedtesting and condition-based maintenance (CBM) of power equipment, the futureapplications and developing directions of electrical endurance assessment are prospected.This paper intensively studies methods for selecting and calculating key parameters ofbreaking current weighted cumulative method (BCWC), and BCWC is widely used forassessing electrical endurance. The research results show that breaking current index α,allowed total wear Qg, integral current coefficient K and the ascertainment of arcinginitialization are core factors influenceing the assessment accuracy. Referring to theelectrical endurance assessment methods and VCB electrical endurance curves, the leastsquares method is used to predict index α and Qgduring the researching process. Resultsshow that the index α and Qgare uniqueness and determinacy, when the material andstructure of contact ascertained, which meet up with the actual conditions. Basing oncalculation methods of integral current coefficient K, the theoretical analysis andexperimental verification are carried out. Results show that the K value is not a constantbut a dynamic physical quantity changing with breaking current, breaking number andarcing duration of three phases, when the material and structure of contact are ascertained.And the characteristic of K value appears to be an envelope interval, so it can not beforecasted by conventional equations. Therefor the LM-BP neural network algorithm isapplied to forecast and analyze K value dynamically, which based on the characteristic ofenvelope interval. The results appear to be a better adaptability and can be applied toonline monitoring of VCB electrical endurance.Considerable electromagnetic radiation and special modification process appearduring the breaking process. Thus, baseing on the electromagnetic character, the electricalinductor for arcing initialization is designed, and its working principles, design tactics andelectromagnetic compatibility method are deeply discussed. To test the designed inductor, circuit simulations and experiments verification are carried out in the lab, and researchsshow that the device has good characteristics of rapid reaction and smart sensitivity.Considering earlier stage researches, smart grid technology and CBM, the VCB electricalendurance online monitoring system is designed, which is based on the TMS320F2812microprocessor. At last, the simulation experiments for online monitoring device andarcing initialization inductor are carried out. Experimental results demonstrate that theparameters forecasting method and determination algorithm are practicable. The designedarcing initialization inductor has enough sensitivity and the online monitoring device ofVCB electrical endurance can realize the designed function, acts reliably, and can reach theobjective of assessing VCB electrical endurance. In brief, the study has a certainapplication prospects and reference value for engineering.