Arc Flash

How to lower your risk of arc flash

In this interview with Tony Locker, we explore how plant managers are lowering arc flash incident energy to make their workplace safer.

Tony Locker received his Bachelor of Science electrical engineering degree from Rose Hulman in 1995 and his MSCE from Georgia Institute of Technology in 2005. Tony is active in the IAS and PES of IEEE, where he serves on several subcommittees and working groups. He is a registered professional engineer in Ohio and has two patents.

Plant Services:  What is the life of the arc flash relay, and what maintenance is required and how often?

Tony Locker: The arc flash relay is built on the same platform and standards as any other protective relay. So the lifespan of an arc flash relay is very long. It’s well over 10+ years. Different manufacturers have different warranties.  Maintenance is relatively low. There are no moving parts. It’s not like an older-style electromechanical relay. The maintenance of the sensors depends on the application. It’s no different than how often you would maintain your circuit breaker or CTs or other relays in that device. If the electrical equipment is in a very hazardous or corrosive environment and every six months you’re doing PM on the gear, you do the same on a sensor. If it’s in a very clean environment such as a data center, where you’re doing PM every 3-5 years, that would be the same PM you do on the sensor itself.

PS: Are there control systems available that truly eliminate or control arc flash?

TL: There are a lot of different design techniques you can use. You can design in smaller transformers so the let-through current is much smaller. There are a lot of other design techniques you can also do to reduce the arc flash hazard. But there’s not one silver bullet, not one single thing you can do. It takes all different types of products and/or design techniques to really truly reduce the arc flash hazard.

PS: How can I tell if the arc flash relay will reduce dangerous-category levels, and will that change the amount of PPE required?

TL: Arc flash relays detect an arc and send a signal to the circuit breaker to trip faster than any other device out there today, period. Nothing can operate faster than 1 millisecond, that I’ve seen. Most arc flash relays now are in the power system software. I showed the model in there with RK5 and RK1 using power system software. So if your company just completed an arc flash study, it’s very simple. You just use the same study, same library. Open back up your report from the library in the power system software and add in the arc flash relay, and it will quickly go through, rerun the calculations based on the 1-millisecond detection time, and then you have to add in the clearing time of the circuit breaker. it will rerun the study and you will see the reduction of arc flash energy, and in doing so, your PPE should be lowered.  But again, it’s extremely easy to do. All these arc flash relays are in these software libraries. Simply rerun the study and add in the arc flash relay. It’s that simple. You’ll see the proof in the calculations in the software how much incident energy can be lowered, and hopefully it lowers it to a level where you can use less PPE.

PS: If you have a neutral grounding resistor, is an arc flash relay also recommended?

TL: Absolutely. It depends on what you’re trying to do, your level of control. The NGR depends on what level you’re at. If you’re over 5 amps, it will reduce the incidence of ground faults, but it’s not going to eliminate it. 5 amps is sort of the line in the sand there that’s been well-documented. And there are additional studies going on that say 5 amps really applies for low voltage versus medium voltage. A lot of different things are happening there. But for low voltage, 5 amps is the standard. If you were to keep it less than 5 amps, you’ll find that’s only 95 percent of the time. You need to worry about the other 5 percent. Current-limiting fuses or arc flash relays come into play there. So even though you can put an NGR in, you’re 95 percent safe, so you’re still not quite there. You need something to get over that last couple percent. That’s where current-limiting fuses and arc flash relays come into play. 

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