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Cheap flash mitigation techniques
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Author:  amohammed [ Mon Jun 22, 2009 9:32 pm ]
Post subject:  Cheap flash mitigation techniques
Gentlemen,

Would you know of methods which can be used to mitigate flash hazard with little to no cost? For a start ... I know changing protective device settings will help a lot.

Regards
Aleen,
Author:  JPEG [ Tue Jun 23, 2009 12:32 pm ]
Post subject: 
You can look for remote racking/operation devices.
Author:  amohammed [ Tue Jun 23, 2009 1:04 pm ]
Post subject: 
JPEG wrote:
You can look for remote racking/operation devices.


Ever checked the cost of owning a racking system? I've called CBS for a quote of ArcSafe racking unit....its upwards of $15000. I do not know if this price is common on similar racking equipment.

I guess my actual question is vague and very general but definately would make a great sticky thread :)
Author:  acobb [ Tue Jun 23, 2009 1:19 pm ]
Post subject: 
Maybe your lowest first cost option is to shut it down. Bet the boss won't like that option either!
Author:  Zog [ Wed Jun 24, 2009 6:17 am ]
Post subject: 
amohammed wrote:
Ever checked the cost of owning a racking system? I've called CBS for a quote of ArcSafe racking unit....its upwards of $15000. I do not know if this price is common on similar racking equipment.

I guess my actual question is vague and very general but definately would make a great sticky thread :)


Well if you have 10 substations that is a $1,500 per sub solution, thats as cheap as a solution can get. Besides chaging settings there is not a free or cheap solution.
Author:  powerengineer [ Wed May 02, 2018 2:05 pm ]
Post subject:  Re: Cheap flash mitigation techniques
Paying engineers to develop settings isn't always cheap.
Author:  wbd [ Wed May 02, 2018 2:41 pm ]
Post subject:  Re: Cheap flash mitigation techniques
I would say that the method would depend on the system configuration and where you are trying to reduce the IE. In some cases it may be as simple as changing a Class RK5 fuse to a A6D Class RK1 fuse. In other cases it may require installation of an arc flash relay system.

I don't think there is one global answer and there may be several ways to reduce the IE for a particular system configuration.
Author:  Flash [ Mon Oct 08, 2018 2:37 pm ]
Post subject:  Re: Cheap flash mitigation techniques
wbd wrote:
I would say that the method would depend on the system configuration and where you are trying to reduce the IE. In some cases it may be as simple as changing a Class RK5 fuse to a A6D Class RK1 fuse. In other cases it may require installation of an arc flash relay system.

I don't think there is one global answer and there may be several ways to reduce the IE for a particular system configuration.



Let us go one step further, both Mersen (A6D-R) and Buss (LPS-R) have two styles of Class RK1 fuses. Class R takes you through 600 amperes and 600 volts. The A6D-R and LPS-R have some intentional time-delay, that can be a problem at low fault currents. in general, either of these fuses will get you below 1.2 cal/sq cm incident energy (IE) if the fuse size does not exceed 200 amperes. If the fault current is high, they can can be used through 400 amperes to reduce the IE.

For IE reduction it is far better to use the Mersen A6K-R or the Buss KTS-R all the way through 600 amperes. In most cases you will get below 1.2 cal/sq cm, even at 600 amperes. The only limitation is you cannot use these fuses on a single across-the-line start motor or a transformer primary. On the other hand they do an excellent job feeding a bus duct or MCC. If your plug plugs or fuseible switchboard feeders are 600 amperes or less you typically can get all the process control panels under 1.2 cal/sq cm.

Over 600 Amperes and 600 Volts:
Another technique is to insert the the Mersen A50QS fuse in the circuit upstream of the equipment to be protected. This works very well in front of a large drive cabinet. The problem is, finding a switch that accepts this style of fuse. Boltswitch Company makes fuse adapters all the way through 1200 amperes that fit their switches. I have been involved in multiple installations when 400A-1200A drive cabinets have the IE reduced to less than 1.2 cal/sq cm with this technique.

Drive Isolation Transformers (DIT):
When you add a DIT in front of the drive cabinet you are typically increasing the IE by more than four times, that is conservative. The above technique works very well on the secondary of the DIT.
Author:  PaulEngr [ Thu Oct 11, 2018 3:07 pm ]
Post subject:  Re: Cheap flash mitigation techniques
If the breaker supports it, "maintenance switches" are very cheap and can be effectively "zero". By this I mean let's say you have a feeder breaker that has LSI or LSIG tripping. You don't need "I" for a feeder breaker normally because it's a coordination issue. But as a maintenance function it's perfect. Set up the instantaneous trip feature and turn it on when you need it, off when you don't.

In high (>600 A) current 480 V systems I've successfully installed Class L fuses in an enclosure feeding the equipment. These have the high let through needed for motor starting but still effectively lower incident energy to reasonable though not necessarily <1.2 cal/cm2 values.

Another cheap option I've found is to install a panelboard, fused disconnect, or breaker upstream of an existing MCC or similar equipment. In practice you have the breaker/switch on the primary side of the transformer to shut off the transformer primary and secondary power. On the low side you have the existing MCC or panelboard or whatever you want to call it with a main breaker or switch, but since the very high incident energy is blocked by the upstream device that was added, the incident energy at the normal point of use and operating location is drastically reduced. So basically you'd never actually operate the intervening layer of protection by hand due to the high incident energy. You always de-energize or re-energize equipment downstream or upstream of it, and then reset, change fuses, etc. If designed and set up correctly (avoiding coordination issues) the only time it should ever trip is in the event of an arcing fault or maybe a dead short.

Two more low cost options I've used. First consider "virtual breakers". In this scheme you install bushing CT's on the transformer secondary terminals which go to a 50/51 relay. The output of the relay trips the feeder breaker on the primary side. Since the CT's are right on the transformer itself, there is effectively almost no typical secondary side high incident energy hazard. Second and similar scheme is if your primary side breaker has a high end protective relay such as an SEL 751A, program it with two settings. When you command the breaker to close in, it uses the usual high settings to avoid transformer inrush. Once the inrush passes detected through the breaker's current sensors, reduce the breaker settings to much lower settings that do not need to consider inrush.

Another low cost/cheap option: hot sticks. A lot of larger switchgear in particular is set up for utility use and has loops specifically for hot stick operation. Standing 8 feet away and operating equipment with a hot stick is vastly different from standing directly in front of it.

When designing one basic rule is that in 600 V class equipment (230, 480, 600), try not to exceed 1500 kVA for transformer size. You definitely will end up in the world of >40 cal/cm2 without mitigation if you don't in almost every case. And if that's already the case, it's always a challenge trying to knock it down.

I've never used arc flash relays and never found a need for them. They aren't actually all that expensive any more and they're not bad to add if you already have switchgear with separate protective relaying but there are always questions about it and I just haven't found much use for it. Usually the trick that seems to work best for me every time in the low cost category is to either improve the existing protective device settings, or add an extra layer of protective devices, or move the operator out of the area.
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