In a recent survey conducted by Littelfuse, Inc., 85% of plant professionals agree or strongly agree that arc flash safety is their top priority. How do plant professionals reduce arc flash hazards and keep workers safe?
Here are the four most popular solutions, according to the Littelfuse survey, as well as a complete system for detection and prevention using Littelfuse technology from Easter-Owens.
1) Current-Limiting Fuse
Well established in the industry as a method to control the SCCR (Short Circuit Current Rating). SCCR is basically a measure of the damage a device can withstand without severe damage. Current limiting fuses aid in restricting the amount of energy a system will see during a catastrophic incident which could lead to an arc flash. A current limiting fuse can react to a very high current within ½ cycle or around 8 msec which makes these devices a crucial part of your arc flash prevention plan.
2) Arc-Resistant Switchgear
Arc-resistant switchgear does not prevent arc flash, instead directs the arc flash energyaway from the workers and other equipment. With sealed joints, top-mounted pressure relief vents, baffles, and reinforced hinges, the switchgear contains the energy and heat from the arc flash and directs the energy via ducts away from workers (generally upward). Arc resistance gear is only effective when the doors are closed, giving workers little added protection when the doors are open during maintenance operations. It can be difficult to retrofit in existing installations.
A requirement for many switchgear installations (NEC 240.87) forces new systems to include an arc flash energy reduction system. A popular method for manufacturers of switchgear to provide is an Energy-Reducing maintenance switch. The principle of this solution is to temporarily reduce the trip time delay of the feeder breaker to as near zero as possible whenever personnel are working around live equipment of the system. This reduction in the ‘clearing time’ of the breaker makes it very sensitive to overload thereby reducing the energy available during an arc flash incident.
This method requires operator action before and after maintenance and does not mitigate arc flash on a continuous basis.
3) High-Resistance Grounding
High-resistance grounding (HRG) systems are another solution plant professionals use to reduce arc flash hazards. These systems monitor and reduce current flow between any single phase and ground. They generally limit current flow to between 5 and 10 amps during a phase to ground incident. HRG sensing equipment generally allow continued operation when a ground fault is detected allowing the operator to locate the fault.
Arc flash reduction is not the main function of HRG systems and considering they do not detect phase to phase shorting they should not be depended upon to protect against arc flash incidents.
4) Arc Flash Relays
Arc flash relays are growing in popularity as they offer 24/7 mitigation of low, medium, and high voltage systems. The relays immediately detect light from the arc and send a trip signal to the circuit breaker to disconnect power. The relay shuts off power quick enough to reduce incident energy drastically. It’s easy to install, costs less than other solutions, and requires a simple yet reliable operation.
5) A Complete System for Detection and Prevention
The Easter-Owens Arc Flash Detection System (AFDS) using Littelfuse technology utilizes the speed to light (versus the slower speed of electron flow) to detect then reduce the severity of an arc flash incident. Light detection sensors are placed in the areas prone to arc flash and connected to the AFDS. When an arc flash incident occurs the sensor detects the massive spike in light energy informing the controller. The arc flash detection controller electrically trips the feeder breaker and removes the energy from the area.
The AFDS will not prevent an arc flash incident, but used in conjunction with other arc flash reduction methods can greatly reduce damage, protect personnel, and reduce down time.
The AFDS comes complete with relay installed within a UL listed enclosure and sensors to fit your needs. Startup and commissioning assistance is available upon request.