In this case, the capacitance, disconnected from the source, will be charged with a voltage three times as great as before. The arc may be again extinguished at the moment when the voltage is at its maximum and the recharging current has the value zero. Should the arc in the switch be ignited again after half a period, when the source voltage will have changed its polarity, the capacitance C will be recharged through the inductance of the source L source. When the arc is extinguished, the capacitance C is disconnected from the source and remains charged at the maximum voltage. When such a line is disconnected, an arc ignited between the contacts of the switch K will be extinguished when the arc current is passing through its zero value and the source voltage is passing through its maximum value (Figure 1,b). In a certain approximation, an unloaded line can be considered to be a capacitance (Figure 1, a). Such voltage surges are obtained, for example, in disconnecting unloaded lines or by the grounding through an arc of one of the phases of a three-phase system with an insulated neutral conductor. Switching surges can be produced by the repeated igniting and extinguishing of electric arcs in circuits with capacitive susceptance. Consequently, a distinction is made between brief, switching surges lasting several microseconds or tens of microseconds and prolonged surges that occur under steady-state conditions. Switching is accompanied by transient processes, after which new operating conditions are established within the system. The principal causes are switching events such as the connection or disconnection of a current and short-circuiting to ground. System-generated voltage surges are surges that appear in electric equipment when abrupt changes occur in operating conditions. There are two types of voltage surges-lightning surges and system-generated surges. A correct calculation of voltage surges is of great economic and practical importance in the selection of insulation and of measures for power-supply system protection, particularly for voltages above 10 kilovolts (kV). In electrical engineering, a voltage rise that endangers the insulation of electric equipment.
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