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SHORT CIRCUIT CHARACTERISTICS

Short-circuits can be defined according to three main characteristics:

– Their origin:

They may be mechanical: breakdown of conductors or accidental electrical connection between two conductors via a foreign body such as a tool or animal.

They may be electrical: following the degradation of the insulation between phases, or between phase and frame or earth, or resulting from internal over voltages (switching surges) or atmospheric overvoltage (stroke of lightning).

They may be due to an operating error: earthling of a phase, connection between two different voltage supplies or different phases or closing of a switching device by mistake.

– Their location:

The short-circuit may be generated inside equipment (cable, motor, transformer, switchboard, etc.) and it generally leads to deterioration.

The short circuit may be generated outside equipment (cable, motor, transformer, switchboard, etc.). The consequences are limited to disturbances which may, in the course of time, lead to deterioration of the equipment in question and thereby cause an internal fault.

– Their duration:

Self Extinguishing: the fault disappears on its own.

Fugitive: the fault disappears due to the action of protective devices and does not reappear when the equipment is started up again (the fault is “burnt out” after re energization);

Permanent: these faults require de-energization of a cable, machine, etc., and intervention by the operating personnel.

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