zog
Senior Member
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- Charlotte, NC
Anyone know of any formulas for Arc Flash calcs on DC systems? How about any info at all on DC Arcs?
Arc Flash on DC Systems
- Thread starter zog
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zog
Senior Member
- Location
- Charlotte, NC
Re: Arc Flash on DC Systems
Well nobody has responded to my question and I know why, there have not been any studies on DC arc flashes. IEEE 1584 plans on conducting these studies in the future, until then, the NFPA 70E recommends using the AC equations.FYI.
Well nobody has responded to my question and I know why, there have not been any studies on DC arc flashes. IEEE 1584 plans on conducting these studies in the future, until then, the NFPA 70E recommends using the AC equations.FYI.
rcwilson
Senior Member
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- Redmond, WA
Re: Arc Flash on DC Systems
zog - from my work in the aluminum industry where we had high power DC busses (850 VDC, 80,000 Amps) I know that the DC arc is dangeraous, can burn a long time and is difficult to calculate. We had large rectifiers feeding the system (75 MVA)so the short circuit currents were very high. Most systems will not have that high short circuit current. The rectifier impedance keeps the current low.
Our basic rule of thumb was the DC leakage current is about 3 times "safer" (it takes 3 x the DC current to stop your heart as the 60 Hz)and teh arcs were twice as destructive.
I never found any calculations to back up those rules that came from expereince of WW-II engineers and electricians.
There are some good references on how to calculate a DC fault current, but I have found nothing on how to estimate the resulting arc energy.
zog - from my work in the aluminum industry where we had high power DC busses (850 VDC, 80,000 Amps) I know that the DC arc is dangeraous, can burn a long time and is difficult to calculate. We had large rectifiers feeding the system (75 MVA)so the short circuit currents were very high. Most systems will not have that high short circuit current. The rectifier impedance keeps the current low.
Our basic rule of thumb was the DC leakage current is about 3 times "safer" (it takes 3 x the DC current to stop your heart as the 60 Hz)and teh arcs were twice as destructive.
I never found any calculations to back up those rules that came from expereince of WW-II engineers and electricians.
There are some good references on how to calculate a DC fault current, but I have found nothing on how to estimate the resulting arc energy.
zog
Senior Member
- Location
- Charlotte, NC
Re: Arc Flash on DC Systems
The SKM software has a DC module for DC short circuits but there have not yet been any studies for a DC arc flash.
Ralph lees studies say your thumbrules are about right, he found that about 15mA AC will cause a loss of muscle control while it takes about 75mA DC to cause the same effect.
The SKM software has a DC module for DC short circuits but there have not yet been any studies for a DC arc flash.
Ralph lees studies say your thumbrules are about right, he found that about 15mA AC will cause a loss of muscle control while it takes about 75mA DC to cause the same effect.
rcwilson
Senior Member
- Location
- Redmond, WA
Re: Arc Flash on DC Systems
zog - I lost my Ralph Lee articles. I'm glad you were able to confirm my poor memory. I had the privelege of taking some IEEE safety classes from Ralph Lee early in my career. I believe his work in electrical safety has saved lives and will save many more.
zog - I lost my Ralph Lee articles. I'm glad you were able to confirm my poor memory. I had the privelege of taking some IEEE safety classes from Ralph Lee early in my career. I believe his work in electrical safety has saved lives and will save many more.
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