Probability Of Reignition Research Articles

Development of switching performance evaluator and arc modelling tool for low-voltage switching devices

PurposeThe purpose of this paper is to investigate a reliable evaluator of arc re-ignition and to develop a numerical tool for accurate prediction of arc behaviour of low-voltage switching devices (LVSDs) prior to empirical laboratory testing of real products.Design/methodology/approachTwo types of interruption tests have been carried out in the investigation of re-ignition evaluators. Arc modelling tool coupled with the load circuit has been developed to predict arc characteristics based on conventional magnetohydrodynamics theory, with special attention given to Lorentz force acting on the arc column and surface phenomena on the splitter plate. The model assumptions have been validated by experimental observation of arc motion and current and voltage waveforms.FindingsIt is found that the exit-voltage across the switching device and the ratio of system to exit-voltage at the current zero point are reliable evaluators for prediction of re-ignition. Where the voltage ratio is positive, instantaneous re-ignition does not occur. Further, the probability of re-ignition is very low if the voltage ratio is in the rage of −1.3 to 0.Originality/valueIt is observed that the voltage ratio can be considered as a reliable global evaluator of re-ignition, which can be used for various types of LVSD test conditions. In addition, it is shown that arc modelling allows a good prediction of the current and voltage waveforms, arc motion as well as the exit-voltage, which can be used to obtain the evaluator of re-ignition.

Field Experiments on Overvoltage Caused by 12-kV Vacuum Circuit Breakers Switching Shunt Reactors

Insulation failures in dry-type distribution transformers occur frequently and severely when 12-kV vacuum circuit breakers are applied to switch shunt reactors. However, the reason for this phenomenon is unclear. Based on the test platform for the failure circuit of a running 10-kV power system, a series of field tests was conducted to investigate the overvoltage mechanism of this type of failure. Field tests successfully recorded the prestrike and reignition waveforms during the transient processes of switching shunt reactors, based on which transient process and phenomena were analyzed. The prestrike probability was as high as 60% during the transient process of switching on shunt reactors. However, the probability of reignition was significantly lower than that of prestrike. The phase-to-ground and interphase maximum overvoltages during the switching transient processes have approximately the same amplitude. The prestrike caused phase-to-ground overvoltages beyond 6.0 p.u., whereas the reignition caused overvoltage beyond 8.0 p.u. The mechanisms of overvoltage generation of the switching transient processes were analyzed based on circuit analysis. Multiprestrikes and multireignitions, cable length, switching conditions, and system configurations were the main reasons for severe overvoltages.

Phenomena and Mechanism Analysis on Overvoltages Caused by 40.5-kV Vacuum Circuit Breakers Switching Off Shunt Reactors

In view of frequent and severe overvoltage failures of 40.5-kV vacuum circuit breakers (CBs) while switching off the shunt reactors in the 35-kV distribution systems in China, a series of field tests was carried out to determine the mechanism of this kind of disruption. The transient process and phenomena were analyzed and summarized based on the overvoltage waveforms obtained from the field tests. The experimental results indicated that the probability of reignition is greater for a 40.5-kV CB than in a 12 kV one. The interphase overvoltage was especially critical. The causes of severe overvoltages were analyzed, and it was indicated that the difference of CBs, multireignitions by the interphase coupling, and the different application conditions were the main effect factors. In addition, some suggestions were given.

Simulation of the Venting Configuration Effects on Arc Plasma Motion in Low-Voltage Circuit Breaker

A 2-D magnetohydrodynamic (MHD) arc model is developed to simulate the influence of the venting configuration on air arc plasma motion in a low-voltage circuit breaker. It is demonstrated that the fully closed back venting is helpful to accelerate the arc motion due to the propagation of a pressure wave. Side- and central-type front-venting configurations are also compared. It is found that the arc velocity is higher, and yet the probability of reignition is increased for the central-type front venting, as a consequence of differences in the current density distribution. Using an arc chamber with different venting configurations, short-circuit interruption experiments are carried out. These verify the arc reignition trends predicted in the simulations.