A Mathematical Approach to Evaluate Arc Immobility Time in Low Voltage Circuit Breakers

Abstract:
Immobility time of arc plays a major role in low voltage circuit breaking techniques. The mechanism of arc root movement is very complex, as it involves various electron - ion emission process and arc electrical conductivity. Efficient contact system design will have very low immobility time. This paper investigates a new mathematical approach in evaluating arc immobility period. This approach is based on the evaluation of characteristic contact gap for which arc remains immobile, for both normal and high current. The evaluation technique makes use of Newton's iterative method and is governed by the balance of electromagnetic and gas dynamic forces acting on the arc column. The simulation of interruption process has been realized using MATLAB. A set of equations that describe the contact movement, circuit parameter, magnetic and temperature field are used in the model. Various time dependent parameters like arc current, arc voltage, electric field, arc temperature etc., for fault currents greater than 1.5kA, can be obtained using this method. Direct as well as indirect parameters that are more sensitive towards arc immobility have been identified and evaluated. Experimental validation has shown that this model can predict the immobility time within a range of ± 10% accuracy.