Arc Flash Hazard Analysis
Arc Flash Hazard Analysis
(OP)
While we carry the Arc Flash Analysis using SKM or ETAP, we will get the results for Incident energy, Arc Flash Boundry and PPE required for that particular switchgear. Now the results will depend upon Short Circuit and Coordination Studies.
The question I have is that now a days there are protective relays specially designed for Arc Flash Protection which require only Light & Current or only Current or Only Light input to detect the arc and trip the breaker. These systems are not dependent on Short Circuit or Coordination Studies. Can we model such systems in SKM or ETAP and see the impact. Anybody have such experience?
Thanks
The question I have is that now a days there are protective relays specially designed for Arc Flash Protection which require only Light & Current or only Current or Only Light input to detect the arc and trip the breaker. These systems are not dependent on Short Circuit or Coordination Studies. Can we model such systems in SKM or ETAP and see the impact. Anybody have such experience?
Thanks






RE: Arc Flash Hazard Analysis
To model this in Powertools or ETAP just create a custom relay with constant operating and clearing time over a large range (say 1A-100kA).
Careful with analyis of results however. Line side faults of feeding circuit breakers may still need overcurrent protection to trip on arcing faults, depending on how your system is set up.
RE: Arc Flash Hazard Analysis
RE: Arc Flash Hazard Analysis
Light sensors may additional aids, but not a substitute for OCPD, imho.
Rafiq Bulsara
http://www.srengineersct.com
RE: Arc Flash Hazard Analysis
As for trip multipliers, you can only use the results of the arc protection system if you're positive the compartment you're labeling is covered by the system and all sources are tripped. How this tripping is achieved (trip multipliers or not) does not really matter as they appear as instantaneous trips when properly setup.
Because SKM and ETAP don't support modeling systems like this you have to 'trick' them with instantaneous trip units on the incoming feeders and manually filter the results yourself. The danger here is that locations not covered by the system can give incorrect results.
A proper way might be to use a differential protection function in the software, but the issue of careful analysis remains.
RE: Arc Flash Hazard Analysis
Rafiq Bulsara
http://www.srengineersct.com
RE: Arc Flash Hazard Analysis
It is acceptable to use the protection relay for the arc-flash calculations. ie, a Multilin or SIPROTEC relay tripping curve is acceptable to use, as opposed to just using a fuse curve. So, why wouldn't a protection relay which integrates light sensing also be acceptable?
RE: Arc Flash Hazard Analysis
Rafiq Bulsara
http://www.srengineersct.com
RE: Arc Flash Hazard Analysis
Now lets suppose I model this switchgear in SKM and carry out arc flash analysis choosing IEEE-1584 medthod. I will have certain results for this analysis. These results will be dominated by my breakers tripping chracteristics.
Now in second step, I will add the Arc Flash Relays to the model. These relays operate in 7msec, so the total time will be 7 msec plus the breaker opening time to clear the arc flash. So after I model these relays in SKM and carry out arc flash analysis again as per IEEE, surely my tripping time will be faster and the resulting incident energy will be small.
So as explained above, can I use my simulation study to show that I have reduced the incident energy and hence the hazard by adding the arc flash relays???
RE: Arc Flash Hazard Analysis
RE: Arc Flash Hazard Analysis
RE: Arc Flash Hazard Analysis
I already indicated my opinion. You can do your own research or design.
Rafiq Bulsara
http://www.srengineersct.com
RE: Arc Flash Hazard Analysis
I don't see an issue with using arc detection relays to reduce incident energy - in principle. I do have concerns about attempting to retrofit the sensing fiber in existing equipment and having 99.99% certainty that the sensor will detect all possible arcing faults. If the arc detection relay is provided by a manufacturer in new equipment, then presumably they have designed and tested this, or at least they are assuming the responsibility for proper operation. For a field installation, who would bear the responsibility?
Using current relaying seems a little more fool-proof since an arcing fault will always have current to be detected. Of course anything can fail, but I'm not sure a "standard of care" has been established for retrofitting arc sensing fiber in existing equipment.
David Castor
www.cvoes.com
RE: Arc Flash Hazard Analysis
The section from the standard, "4.6 Step 5: Find the protective device characteristics and the duration of the arcs" does discuss using the fuse curve or breaker trip curve but I don't read anything that rules out using other means to clear the fault. I read it as saying that, ultimately, you need to know the clearing time however it is achieved.
David - Installation is always a concern but the manufacturers do have info on the proper installation of the sensor fiber, based on the proximity and amount of fiber that must be exposed to properly trip. Similar concerns about the actual detection and clearing of an arcing fault could also be voiced for any means of clearing an arc fault, since every detection and clearing method can fail.
RE: Arc Flash Hazard Analysis
Let me rephrase my view:
IEEE standard is based on trip time AND short circuit current. There is no way to tying the inception or detection of the "light" to the amount of short circuit current and hence the trip time. It does not fit in the IEEE method, the only recognized one I know of. I do not recommend "tricking" the software to arrive at a "desired" result.
If the mfr provides an arc flash label, based on their analysis/testing/theory and AHJ approves it, I have no issues. I will not be the one signing off on it. To that extent, yes it is a personal opinion as to how I would conduct my business. I perform a lot of short circuit and arc flash analysis on professional basis and only based on recognized software that follow IEEE.
This is not an opinion on effectiveness of light sensing and trip to minimize arc flash hazard.
Hope this clarifies my view point.
Rafiq Bulsara
http://www.srengineersct.com
RE: Arc Flash Hazard Analysis
RE: Arc Flash Hazard Analysis
RE: Arc Flash Hazard Analysis
RE: Arc Flash Hazard Analysis
The attached image shows that SKM provides the facility to model the Fiber/point sensor in Arc Flash Analysis. It require two parameters to be entered by the engineer carrying out the study, one is the operating time of the relay and the second is the breaker opening time.
Now suppose there is no relay, so arc detection will be based on the magnitude of current and the tripping will be dependent on the breakers tripping characteristics.
Now when I will add an Arc Detection Relay, It will detect the Arc based on the magnitude of current (which I will set above the FLA) and the arc flash. Since these devices will provide instantaneous tripping characteristics, so I can see the reduction of Incident Energy due to the reduced tripping time because of arc flash relays.
@dpc, Two main types of sensors are available as far as I know. Fiber and Point. I prefer point sensors because in case of an arc flash it gives you the exact location of the arc fault while since the fiber sensor runs throught out the switchgear compartments, it takes time to find the fault.
RE: Arc Flash Hazard Analysis
You should still enter the total trip time of the relay. The time will be dependent on which relay you are using and the style of contact/transistor outputs you are using. I've seen as fast as 2 to 2.5ms.
Be careful when using point sensors. Some relays do not monitor the point sensors for fiber breakage like they do with the loop sensors.
RE: Arc Flash Hazard Analysis
RE: Arc Flash Hazard Analysis
I agree with you, the image is just a reference. Actual trip time for breaker will be there.
RE: Arc Flash Hazard Analysis
Some people seem to have serious attitude problems related to light & overcurrent based systems which provide the fastest protection and lowest incident energy. Because several major manufacturers are turning to this well-known technology, there is a strong indication that this is the winning technology.