It is currently Wed Feb 21, 2018 6:15 pm



Post new topic Reply to topic
Author Message
ekstra   ara
 Post subject: Arc flash study on 300 kV outdoor
PostPosted: Mon Jan 29, 2018 2:32 am 
Offline

Joined: Wed Nov 01, 2017 6:09 am
Posts: 13
What is best practice to evaluate outdoor high voltage equipment? In this case it a 300 kV overhead line and circuit breakers. It is quite similar to the ones showed on the picture below. This means that the service cabinet is available accessed during operation. A fence closes in the area. This is in Europe.


1. Would it be good practice to do a calculation and establish a cal/cm2 level? On the other hand, is this just way out of normal practice for these kind of operations? (Then I use the working distance from ground level)
2. The operator is also being curious about the arc flash boundary. Since there are many workers inside this fences during projects. They have no electrical skills or protection. Is this relevant?
3. I am considering to use the Lee equations for this? As I understand this would give very conservative results (I have a software that uses Lee for this kind of voltage). Have anyone done anything similar? Is this normal in the US?


You do not have the required permissions to view the files attached to this post.


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: Arc flash study on 300 kV outdoor
PostPosted: Mon Jan 29, 2018 5:05 am 
Offline
Plasma Level
User avatar

Joined: Tue Oct 26, 2010 9:08 am
Posts: 1878
Location: North Carolina
1. Lee is utterly invalid at 300 kV. It is off by 300% at 15 kV and gets worse as voltage increases. The inherent flaw is that arc voltage is almost a constant so since Lee is proportional, it is just plain wrong. This isn’t “conservative” for transmission voltages, it’s laughable. There is no test data either. It’s all guess work at this point. EPRI has started some testing and analysis but it is very preliminary. It is publicly available on their web site. A big problem is arc gap too. Anything from IEEE 1584 (Lee) is for short arcs where it can be modeled effectively as a point. At 300 kV the anode, cathode, and arc column are distinct and worker position and orientation to the arc matter as well as arc orientation. Arcpro is the best physics based modeling system we have to date for voltages above 10-15 kV. I’d recommend that but the caveat is nothing really covers your case. For line work (not at breakers) the arc is magnetically propelled down the line at several meters per second and you can see this on videos of traveling arcs so even if line workers initiate an arc, they are nowhere near it.

Another much simpler approach is IEEE standard C2 particularly chapter 400 which includes tables that go up to and include 300 kV and most if not all the work rules and requirements you are looking for.

In practice at distribution voltages I’ve found that standard insulated tool distances are more than sufficient. At 300 kV that’s impractical but with clearances what they are I’m at a loss how an arc could be initiated in the first place so your experience in the matter at transmission line distances should drive where arc flash becomes a concern in the first place.

US regulation is to dress in FR PPE for ALL utility work. This is for not just arc flash but also potential splashes from molten slag or sparks or other materials thrown by an arc.


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: Arc flash study on 300 kV outdoor
PostPosted: Mon Jan 29, 2018 6:32 am 
Offline
Plasma Level
User avatar

Joined: Wed May 07, 2008 5:00 pm
Posts: 711
Location: Rutland, VT
Here in the US, OSHA 1910.269 Appendix E lists the use of ArcPro software as an acceptable method for determining incident energy level above 15kV. I think that would still be appropriate to use in Europe.

_________________
Barry Donovan, P.E.
www.workplacesafetysolutions.com


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: Arc flash study on 300 kV outdoor
PostPosted: Mon Jan 29, 2018 9:01 am 
Offline
Sparks Level

Joined: Fri Apr 15, 2011 7:43 am
Posts: 164
Location: Colorado
You first need a power system study and an 3 phase arc flash study. Form that data you can then use ArcPro to get the single phase incident energy


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: Arc flash study on 300 kV outdoor
PostPosted: Mon Jan 29, 2018 10:57 am 
Offline
Plasma Level
User avatar

Joined: Wed May 07, 2008 5:00 pm
Posts: 711
Location: Rutland, VT
engrick wrote:
You first need a power system study and an 3 phase arc flash study. Form that data you can then use ArcPro to get the single phase incident energy


Not exactly clear on why this is so. ArcPro utilizes the SLG fault current and clearing time as inputs. Typically utilities have this information from their system modeling. So a full blown power system study is something the utilities should have on their system as well other studies such as load flow and contingency. For a 3 phase arc flash study in this situation, it is basically the SLG value multiplied by a factor but I see the new ArcPro has a drop down box to pick 3 phase in open air.

_________________
Barry Donovan, P.E.
www.workplacesafetysolutions.com


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: Arc flash study on 300 kV outdoor
PostPosted: Fri Feb 02, 2018 8:08 am 
Offline

Joined: Wed Nov 01, 2017 6:09 am
Posts: 13
Thanks for all answers. I don't have the arcpro software.
But the following data applies:
Ik3p=6kA
Ik1p=7 kA
disconnection time is:
Circuit breaker open time: 20ms(very fast)
Arcing time=15ms(?)
Relay time:25ms(no intended delay)
Total time=60ms.
This is 50Hz, so that gives 3 cycles

If I whant to use the IEEE C7 as suggested. Can I then use table 410-2. And since there are no voltage that includes 300kV(only 230-242 and 345-362) I must round up to 345-362. And current below 20kA
When I use the table i then get a 4 cal system.

Does this mean that a ATPV value of 4cal/cm2 will protect from Arc-flash hazard at a distance of 2.77m(table 441-2 at T=3.0 and voltage 241-362 kV).

Would these numbers be ok for circuit breaker as mention in the first post(above)?


Would these assumptions be the same for an ungrounded system?


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: Arc flash study on 300 kV outdoor
PostPosted: Fri Feb 02, 2018 11:37 am 
Offline
Plasma Level
User avatar

Joined: Wed May 07, 2008 5:00 pm
Posts: 711
Location: Rutland, VT
I did a quick run using ArcPro for a fault using your values except the arcing time for total clear time and at 2.77m and got:
SLG: 0.03 cal/cm2
3ph: 0.06 ca;/cm2

So your 4 cal PPE will work but a formal study should be done.

Also, I think you meant C2 not C7

_________________
Barry Donovan, P.E.
www.workplacesafetysolutions.com


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: Arc flash study on 300 kV outdoor
PostPosted: Sat Feb 03, 2018 1:54 am 
Offline

Joined: Wed Nov 01, 2017 6:09 am
Posts: 13
Thanks for answer you are right it suppose to be C2 :)
In general it thought the arcing time has to be included since the arc flash would be presented until the current is totally blown off(not just use open time for the CB?)

But my real question is do I understand the table 410-2 correctly? Can I round up to fit the voltage?
And is the 2.7m correctly understood?

The Lee equation's gives higher values at the same input


You do not have the required permissions to view the files attached to this post.


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: Arc flash study on 300 kV outdoor
PostPosted: Sat Feb 03, 2018 6:17 am 
Offline
Plasma Level
User avatar

Joined: Wed May 07, 2008 5:00 pm
Posts: 711
Location: Rutland, VT
The clearing time of the circuit (breaker, relay, LOR) is the arcing time. The arc starts, relay senses, sends trip signal, breaker opens, all that time until arc is extinguished is the arcing time.

The table in C2 was created by use of ArcPro. ArcPro's inputs are current, duration, arc gap, source voltage, distance to arc. The source voltage is basically a check to see if the voltage would sustain an arc. The arc gap is the L-G voltage divided by 10 (dielectric strength of air is 10kV per inch).

So for your voltage, I would use the voltage range in the table which would have the arc gap closest to the arc gap at 300kV.

230-242 kV, arc gap: 13.3-14 in
345-362 kV, arc gap: 19.9-20.9 in
300 kV, arc gap: 19.1 in

So the 345-362 kV range utilizes an arc gap closest to the one used for 300 kV. I think that as long as you are outside the minimum approach distance the incident energy level will be well below 4 cal/cm2.

_________________
Barry Donovan, P.E.
www.workplacesafetysolutions.com


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: Arc flash study on 300 kV outdoor
PostPosted: Sat Feb 03, 2018 11:34 am 
Offline
Plasma Level
User avatar

Joined: Tue Oct 26, 2010 9:08 am
Posts: 1878
Location: North Carolina
There really isn't anything on the market in terms of FR PPE that is below 4 cal/cm2 and IEEE C2 assumes that all workers are at least wearing FR PPE of some kind for splash/slag protection. And yes FR is the correct terminology here since the hazard is fire, not arcs. So using arc rated PPE it starts with a bare minimum of 4 cal/cm2. The lowest rating I've seen is for a cotton treated long sleeve knit tee shirt that was rated 6.5 cal/cm2. U.S. regulations (and IEEE C2) do not currently require face protection for this rating either. So based on the minimum requirements the "standard" work uniform would exceed 4 cal/cm2. Thus the reason the chart doesn't go down below that point is because it's already at the minimum required regardless of the incident energy. But with the low incident energies that previous poster calculated even that is not really necessary.


Top
 Profile Send private message  
Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 10 posts ] 

All times are UTC - 7 hours


Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Jump to:  
© 2017 Arcflash Forum / Brainfiller, Inc. | P.O. Box 12024 | Scottsdale, AZ 85267 USA | 800-874-8883