In recent years, arc flash has become a hot topic for the data center industry because of the increasing awareness of its dangers, both to personnel and equipment. Regulations and standards, such as the NFPA 70E Standard for Electrical Safety in the Workplace, are becoming more stringent. They provide guidance on analysis procedures, requirements for documentation and equipment labeling, and the proper selection of Personal Protective Equipment (PPE).
However, while attention has focused on system analysis and the selection of appropriate PPE, the application of product or design solutions intended to mitigate the risk of arc flash events has received relatively little attention. The most effective arc flash safety programs do not rely solely on worker training, warning signs, and PPE. They should also incorporate engineering controls because they reduce the degree of hazard and do not depend completely on workers following proper procedures and practices.
Fundamental design choices can impact the ultimate levels of arc flash hazard when the system is in operation. Consideration of these issues in the initial design stage can help engineers more effectively design safety into a system rather than trying to develop patchwork solutions after the fact.
Since incident energy is proportional to arcing time, one effective tool is the selection of breaker settings that strike an optimal balance between arc-flash reduction and maximizing selectivity. In addition to selection of proper device types and settings, a protective relaying scheme can also help reduce arc flash levels in a system.
A relatively new concept is the use of relays that detect the presence of arcing faults by looking for the associated flash of light. When both a high current and a burst of light are present, the relay operates very quickly to clear the fault.
The method of system grounding can have an impact on arc-flash hazards. High-resistance grounded (HRG) systems are not new, but recently they have been promoted as an arc-flash mitigation means. The idea is that HRG systems inherently limit the energy delivered to a ground fault by limiting the available fault current to just a few amperes, providing a great deal of protection.
Arc Resistant Switchgear
Worker safety can also be increased by containing and redirecting the effects of an arcing fault that occurs in a piece of electrical equipment. Arc-resistant switchgear provides protection from internal arcing faults to workers performing normal operations while standing in front of or around the perimeter of the equipment.
Increasing the effective working distance (distance between a worker and the location of the arc) is also a very effective mitigation strategy, since energy levels drop off exponentially as the working distance is increased.
Properly-maintained electrical equipment is less likely to fault and more likely to be able to clear faults that do occur. Proper maintenance practices are an important part of an electrical safety program and must be employed along with other mitigation techniques.
Ideally, arc flash safety is taken into consideration when a facility’s electrical distribution system is designed, but many techniques are equally applicable as retrofits to existing systems. Although the application of some solutions results in increased costs, the financial impact of even a single serious injury makes arc flash mitigation an ultimately wise investment.
If you would like further information arc flash mitigation techniques in the data center, please refer to the application theory, Arc Flash Mitigation
9 years ago
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