Have you ever wondered how disastrous an internal arc fault in low- or medium-voltage switchgear (e.g. in not internal arc classified / arc resistant switchgear) can be?
An internal arc fault is rare, but it is the most severe fault within a switchgear system. The destructive impact of such an arc fault event can lead to severe injuries or even fatalities of operating personnel as well as costly damage to the switchgear and long outages of the switchgear/power system. Relative to the loss of a human life or a severe injury, the possible subsequent investigations by the authorities or financial implications due to supply interruption as well as equipment replacement appear to be irrelevant.
Besides harsh environmental conditions and old equipment, human “interference” is one of the predominant reasons that may cause an internal arc with disastrous consequences. Even well trained and experienced engineers are by no means immune to making mistakes – dropping tools and making improper cable terminations are two main causes of an internal arc fault.
In the past arc protection could only have been achieved by conventional passive protective measures i.e. maintaining the IP code (Ingress Protection, or International Protection, Marking), safety procedures for dead working, protective clothing or integrated disconnector/earthing switches. Available active arc detection systems eg pressure sensors or fast relays such as ABB’s REA or TVOC-2 system can already significantly improve the protection by reducing the arcing time to 55 – 75 milliseconds (ms).
Today’s intelligent technologies like the ultra-fast earthing switch (UFES) immediately mitigate the effects of internal arc faults and raise safety standards to a whole new level. The UFES not only acts as an active protection for personnel, but also saves the equipment from heavy damage, minimizing the necessary repair work and downtime.
The UFES is a smart combination of an arc detection system and the corresponding primary switching elements (PSE), which initiate a three-phase short-circuit to earth in the event of an arc fault. The extremely short switching time of the primary switching element, less than 1.5ms, in conjunction with the rapid and reliable detection of the fault, ensures that an arc fault is extinguished almost immediately after it arises. With a total extinguishing time of less than 4ms after detection, an active protection concept with the UFES enables switchgear installations to achieve the highest possible level of protection for personnel and equipment.
Designed for rated voltages up to 40.5 kV and rated short-time currents up to 100 kA, the UFES can, in principle, be installed in any new or existing installation of medium- or low-voltage equipment. And there is already a wide range of type tested solutions for several applications available. UFES is included in the accessory portfolio of various low- and medium-voltage AIS solutions from ABB, and is also available as an integral part of an enclosed Resibloc dry-type transformer solution. Outside ABB, other firms benefit from the active protection approach through OEM (original equipment manufacturer) arrangements.
Besides switchgear applications, manufacturers of capacitor banks or drives, also see a high potential to significantly increase safety of their equipment.
Andreas Peters is head of the project development team at ABB’s medium voltage factory in Ratingen, Germany