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The effect of too high short-circuit current is discussed in the previous section. The short-circuit current should be around 20 times the rating of the circuit to ensure the branch circuit protection clears a fault quickly. Quick disconnecting is needed, because during a line-to-ground short circuit the grounding pin potential on the power ...
In an electric power system, a fault or fault current is any abnormal electric current. For example, a short circuit is a fault in which a live wire touches a neutral or ground wire. An open-circuit fault occurs if a circuit is interrupted by a failure of a current-carrying wire (phase or neutral) or a blown fuse or circuit breaker .
The current breaking capacity corresponds to a certain voltage, so an electrical apparatus may have more than one breaking capacity current, according to the actual operating voltage. Breaking current may be stated in terms of the total current or just in terms of the alternating-current (symmetrical) component.
In an electrical grid, the short circuit ratio (or SCR) is the ratio of: the short circuit apparent power (SCMVA) in the case of a line-line-line-ground (3LG) fault at the location in the grid where some generator is connected, to: the power rating of the generator itself (GMW).
A different form of short-circuit testing is done to assess the mechanical strength of the transformer windings, and their ability to withstand the high forces produced if an energized transformer experiences a short-circuit fault. Currents during such events can be several times the normal rated current.
A short circuit fault current can, within milliseconds, be thousands of times larger than the normal operating current of the system. [2] Damage from short circuits can be reduced or prevented by employing fuses, circuit breakers, or other overload protection, which disconnect the power in reaction to excessive current. Overload protection must ...
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the sub-transient state (″) is the one the generator enters immediately after the fault (short circuit). In this state the armature flux is pushed completely out of the rotor. The state is very brief, as the current in the damper winding quickly decays allowing the armature flux to enter the rotor poles only. The generator goes into transient ...