An arc fault is the most serious fault within a switchgear system. A new, active arc fault protection system from ABB not only effectively eliminates risk to people, it also offers protection against damage or destruction of system components.
There are rare cases where failure inside a medium-voltage switchgear cabinet, due to a defect, exceptional service condition or incorrect operation can cause an internal arc – a short circuit current flowing through the air - which presents a significant hazard. This is due to the instantaneous increase in temperatures at the fault location to around 20,000C, well above the melting point of steel, copper and insulation materials. Internal components are vaporized and the sudden release of heat and plasma (ionized gas) creates an explosive blast.
Absolute protection of all personnel during an arc-fault is of course the number one priority. However, it is even better to take active measures to prevent such an event from happening in the first place. This not only eliminates risk to people, it also offers protection against damage and even destruction of system components. There is now a solution in the form of the ultra-fast earthing switch (UFES) internal arc protection system that combines ABB’s fast acting vacuum interrupter and the world’s fastest limiting and switching device, the Is-limiter.
The UFES operates on the principle that the uncontrolled release of energy from an internal arc fault is prevented by rapid metallic 3-phase earthing. Characterized by a significantly low impedance, this type of connection causes the short-circuit current of an arc fault to commutate immediately to the fast-acting earthing switch and this extinguishes the arc
The UFES system, suitable for rated voltages up to 40.5 kV and rated short-time withstand currents up to 63 kA, is an active internal arc fault protection solution for new internal arc classified medium-voltage switchgear as well as for existing older generation switchgear. It helps to avoid serious damage to the switchgear, the equipment and the direct environment. Therefore, it greatly increases both system availability and personnel safety in the event of internal arc fault. Furthermore it enables the minimization of pressure relief arrangements in switchgear installation rooms with limited access.
The UFES primary switching elements can be installed in the switchgear cable connection compartments or simply in each separate busbar section to ensure the entire system is covered. The UFES is available as a complete unit in a type-tested ABB service box for simple installation in existing ABB and non-ABB switchgear systems, on draw-out units as a plug&play solution and as a “loose device” (ie, the electronic unit and three primary switching elements) for project driven integration.
Internal arc test 100 ms without and with UFES intervention (UniGear ZS1 50 kA)
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Robert Clua
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