| By Matt Polk, ABB|
Arc flash mitigation in our electrical equipment has become a major safety focus throughout the industry. With this growth, there has come an avalanche of information from various companies, articles and products. A lot of literature is available on how to calculate arc flash energy, personal protective equipment
(PPE) to wear and how to properly label equipment. Not much information is available on how to reduce the arc fault energy. In this white paper, we’ll try and simplify this and give you a few practical tips to help you reduce the risk of arc flash mitigation and the hazards to personnel.
When trying to mitigate the risks of arc flash, there are three overriding concepts that can be followed:
1. Move the people away from the gear (distance and space)
2. Redirect arc flash energy away from personnel
3. Reduce the time of the arc (time)
When looking to reduce arc flash energy levels, it is important to realize that your options are different for existing equipment that is already installed, as opposed to new equipment that you are purchasing. We will separate your options into these two categories.
Reducing arc flash energy levels for:
Existing Electrical Equipment
a) Move personnel away from the equipment whenever practical
- Use remote racking units for putting breakers into and out of cubicles.
Most manufacturers now have options for racking the breakers out with a motorized device where the operator can be 20 to 50 feet away.
- Use extended racking handles. With most equipment that is provided today, the racking handle is two to three feet long. Most suppliers can provide you an extended handle from four to 10 feet long that will move personnel farther away from the equipment.
b) Upgrade relay systems to reduce arc flash time
- Upgrade your system with an Arc flash mitigation relay system like ABB’s REA101 series. This type of relay uses a fiber optic sensor and can detect a trip in 2.5 milliseconds (msec).
Compare that to the 200 to 800 msec time frame for a main breaker to trip on overcurrent, and you can realize up to an 80 percent reduction in arc flash energy.
- Install a maintenance mode switch in your equipment, though this only works if you have microprocessor-based relays. Here, you can change all the relay settings to instantaneous overcurrent trip and reduce the arc flash energy.
c) Update and replace equipment
- The number one failure within switchgear is the breaker. Replacing older breakers with new roll-in replacement breakers can significantly reduce the risk of an arc fault.
- Have a certified provider do a full inspection of the gear, including the bushings, insulators, bus insulation and all grounding connections to ensure integrity of older equipment.
- There are a number of new technologies available for doing infrared (IR) sensing of buses and connections. They include wireless and wired sensors that are easy to install and can detect loose connection and failing insulation before an arc fault occurs.
Reducing arc flash energy levels for:
In addition to all the actions above, here are some additional options when purchasing new electrical equipment with an eye on reducing arc flash levels and hazard to personnel.
When specifying the new switchgear, there are a number of things you can do to reduce arc
-Specify that you have automatic secondary disconnects.
This will eliminate the need to open the door during racking to make the connections.
-If you don’t like remote racking units, you can order racking motors that can be mounted on each breaker. This will allow racking of breakers in and out of the gear without having someone present at the equipment.
-Specifying magnetic actuated breakers can limit the amount of service required and thus limit the time personnel are near the gear. Standard spring storage breakers generally require annual maintenance; magnetic breakers have a recommended service of five years or more.
-Having infrared (IR) viewing ports installed in switchgear when ordered will allow for routine inspection of the gear for hot spots.
a) Look for relay options in new switchgear
- Many new microprocessor relays have arc flash detection built into them as an option, or you can go with a specialized arc flash relay system.
- Installing a differential relay system will help to minimize arc flash levels similar to the aforementioned arc flash detection units (except for the cable compartment).
b) Specify arc resistant switchgear
There are different levels of arc resistant switchgear, so it’s important to select the one that is most appropriate to your needs.
- Type 2: This provides personnel protection in front of, behind and to either side of the switchgear lineup. As long as the doors to the switchgear stay closed, no PPE is required to operate or monitor the equipment.
- Type 2B: In addition to Type 2 protection, Type 2B also provides isolation of the Low Voltage compartment from the rest of the switchgear. This reduces the arc flash levels to that of the control circuits only.
- Type 2C: This provides compartment to compartment protection. If a fault occurs in one breaker compartment, only that compartment will be damaged, allowing for much faster system recovery.
FAMOUS LAST WORDS
None of the aforementioned concepts will completely eliminate the risk of an arc flash, and it is imperative that all operators use the proper PPE and follow the proper work procedures. With that said, it is the duty of all engineers and operators to minimize the risk whenever possible. Any of the above actions can help to significantly reduce the risk and extent of injuries to personnel.
Matt Polk is Account Manager for medium-voltage products
at ABB. Prior to his current role, Matt was Sales and Marketing
Manager for Medium-Voltage Switchgear at ABB. Matt
is based in
For more information, contact Lake Mary, Florida
Matt at firstname.lastname@example.org.