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 Post subject: HVDC Transmission line arcs and arc flash
PostPosted: Sat Jul 10, 2010 3:01 pm 
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I've a particular interest in HVDC transmission line incidents of arcing and arc flash.
A HVDC underground transmission line, operating at 500MW, +/-200Kv with an estimated current rating of 1400 to 2000Amps is scheduled to connect between the UK and Ireland. The majority of the cable will be below the sea bed, but some 46Km will transverse underground form landfall to a VSC Converter station using IGBT technology, the cables (2 cables and fibre optic line, operating in bi-polar mode) are buried to a depth of approximately 990mm.

The question that I have is, what would happen if there was a breach of the cable(s) following an accidental dig in? Would there be an arc flash incident? If so, to what extent?
I've searched extensively for topics relating to HVDC arc and arc flash tests, but it seems very little information is available for some reason?


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PostPosted: Thu Jul 22, 2010 6:48 am 
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Would anyone have information or opinions on this topic?


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PostPosted: Thu Jul 22, 2010 8:23 am 
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I would say that you are probably pretty much on your own with this one. I am not aware of any testing/info at that level of DC.

990mm seems to me to be very shallow for a 200 kV line. I would want to protect it from dig ins.


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PostPosted: Thu Jul 22, 2010 11:27 am 
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The 2012 version of NFPA 70E (though it doesn't apply to these types of lines) has formulas for calculating DC arc flash. These are the only formulas right now. Kinectrics, Steve Cress and I worked with a large Canadian Hydro to get a study on DC arc flash. Dan Doan has an excellent paper on DC arc flash and these two papers are the basis of the DC taskforce's annex in the new NFPA 70E. The ROP is online at [url="http://www.nfpa.org"]www.nfpa.org[/url] and you can download for free.


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PostPosted: Thu Jul 22, 2010 3:31 pm 
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elihuiv wrote:
The 2012 version of NFPA 70E (though it doesn't apply to these types of lines) has formulas for calculating DC arc flash. These are the only formulas right now.


Unfortunatly this answer does not address the High Voltage DC transmission system which is completely different than the systems that NFPA presently addresses. HV DC operates at voltages in the hundreds of thousands of volts and the above mentioned equation will not work well. The equation in NFPA reminds me of Ralph Lee's work in that it is heavily based on voltage which will severly skew the results into the stratosphere at higher voltages - Similar to previous concerns that have been expressed about using Lee equations above 15 kV in the forum.

There actually are many other more precise equations and much research that has been conducted regarding DC - I guess these just never made it into NFPA. These other equations are what I base my [url="http://www.brainfiller.com/documents/HowtoPerformanArcFlashStudy.pdf"]DC arc flash training[/url]on.

The NFPA link mentioned just goes to the the NFPA site. Here is a link as previously posted on the forum that gets you directly to the ROC for the 2012 NFPA 70E

[url="http://www.arcflashforum.com/showthread.php?p=5807#post5807"]Link to NFPA 70E ROC info[/url]

If you have any questions, feel free to contact me at the email address listed on the welcome message of the forum.

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PostPosted: Fri Jul 23, 2010 4:36 am 
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brainfiller wrote:
There actually are many other more precise equations and much research that has been conducted regarding DC - I guess these just never made it into NFPA.


Who did it and where are these equations?

Thanks Jim


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PostPosted: Fri Jul 23, 2010 5:55 am 
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DC Arc Flash and 2012 NFPA 70E

Thanks Jim. I wasn't trying to say the equations were adequate. Just pointing out something has been done with data. I didn't know you had a DC arc flash class. Just pointing out there is some data. The only data I know has been done at Kinectrics and Dan Doan's equations work with the data BUT they are only good to 600V. This is pointed out in the accepted proposal from the DC taskforce. If anyone else has equations, they are not based on supporting data to my knowledge.

On Lee, you have to have theoretical before anyone can do the experiments to verify. I have seen the results of a HVDC arc in an aluminum plant in Brazil which burned a guy second degree burns 7 meters away so they can be nasty. It was estimated at around 300 cal/cm2 at 18 inches away but it could have still been plasma really.


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PostPosted: Fri Jul 23, 2010 6:04 am 
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Papers on DC Arc Flash

The best paper is not published. It is owned by IEEE/NFPA and Bruce Hydro. Bruce might share it but IEEE has it as part of the supporting data for the new models. I don't know if the majority will ever see it.

DC ARC MODELS AND INCIDENT ENERGY CALCULATIONS, IEEE Paper No. PCIC-2009-7, Ammerman, Gammon, et. al. is a good survey of the historical research.

Arc Flash Calculations for Exposures to DC Systems, IEEE Paper No. ESW2007-19, Dan Doan is the only other paper I know of.


Dan's calcs are for up to 600V. I'm pretty sure we could use the AC calcs from ArcPro and use multipliers for the HVDC and get pretty close.


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PostPosted: Sun Jul 25, 2010 8:53 am 
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I decided to add DC arc flash calculations to my Arc Flash Calculation Study class when I had to say “there is nothing in the standards about DC arc flash” one time too many. I recognized there has been a lot of great research resulting in many very good papers.

The Ammerman, Gammon, Sen, Nelson paper was one of the better resources that I use. This paper refers to a significant amount of past research and testing which includes important elements such as V/I characteristics, arc resistance, gap distance, box vs. air etc.

When developing the material and worksheets for the DC portion of my training class, I mention Dan’s equations from 2007 but focus on the details of the many sources in the Ammerman et. al. paper. I was able to create a few practical example problems along with a pretty easy to use process for the DC calculations.

Much of the rest of this was previously discussed in the May 2010 thread below.

[url="http://www.arcflashforum.com/showthread.php?t=1105"]DC Arc Flash Thread[/url]

Thanks for everyone’s input on this.

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PostPosted: Wed Jul 28, 2010 11:31 am 
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My understanding after touring Celilo, is that the converters shut down quickly during a fault, and very little current flows for a very short time.

What do you mean by "arc flash incident"? I generally think of these as occurring during intentional live line work, and back hoe accidents don't qualify. Shall we dress all excavation crews in arc rated clothing in case they forget to call for locates?


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