Switching on Short Circuit Current in an Electric Circuit

Closing or opening the contacts of a electrical switches is normally done in a totally random fashion and consequently, transient current and voltage disturbances may appear in the electrical system. A way for controlling this transient behavior is possible by operating the switch in synchronism with either the current or the voltage oscillations, depending upon the type of switching operation at hand. So, generally the closing of the contact should take place at voltage zero (when energizing capacitor banks) or that the opening the contacts should occur at a current zero when interrupting short circuit currents. During a closing operation and as the contacts approach each other, a point is reached where the gap equals the minimum flashover distance and therefore an electric arc is initiated. As the distance between the contacts continues to diminish the arc gradually shortens until finally the contacts engage and the arc disappears. The switching-on arc glowing time depends hence on the value of the intensity of electric field in the contact area, and on the velocity of contacts closing. Relations between the electric field strength and design parameters of contact system for different values of contact gap is presented. The paper describes the problems of calculation the arc switching time in contact switches during making of a current in current paths and test circuits. Conical contacts used in making switches, circuit-breakers, and earthing switches, have been chosen for analysis.