480V DC fault to water - size of danger zone?

[mm007hm]

Situation:
A large PV solar array, installed over water in a lake or pond.
We have been retained to advised on shock hazard / corrosion issues.
System has multiple 480 ~ 600V DC (not AC) 150 amp armored feeder cables running from the array, to shoreside DC > AC inverter. The client wants to know how big an area they need to enclose around the array to prevent trespassing / unauthorized personnel from entering an area that may be subject lethal voltage gradients if a worst-case fault to water were to occur.
Can anyone help calculate what the size the 'Danger Zone' would be with a full fault at 480V 150A into fresh water?
None of us in the Marine Industry have any data to calculate size / strength of the field around a fault from DC+ to water.
Deaths from 120 / 240 V AC faults to water are well known, any voltage gradients that subject a swimmer to over 30mA can kill, but we have found little or no data on hazards from high voltage DC, other than one expert who commented that based on a Coast Guard study, it take approx 3x the DC current to be lethal as AC. We are of the opinion that there is no way to define the danger zone to to infinite variables with salinity, conductivity, etc, but we need some sort of ruling or opinion from a higher authority to bolster our case.
Any help appreciated.

 

[mcclary's electrical]

Situation:
A large PV solar array, installed over water in a lake or pond.
We have been retained to advised on shock hazard / corrosion issues.
System has multiple 480 ~ 600V DC (not AC) 150 amp armored feeder cables running from the array, to shoreside DC > AC inverter. The client wants to know how big an area they need to enclose around the array to prevent trespassing / unauthorized personnel from entering an area that may be subject lethal voltage gradients if a worst-case fault to water were to occur.
Can anyone help calculate what the size the 'Danger Zone' would be with a full fault at 480V 150A into fresh water?
None of us in the Marine Industry have any data to calculate size / strength of the field around a fault from DC+ to water.
Deaths from 120 / 240 V AC faults to water are well known, any voltage gradients that subject a swimmer to over 30mA can kill, but we have found little or no data on hazards from high voltage DC, other than one expert who commented that based on a Coast Guard study, it take approx 3x the DC current to be lethal as AC. We are of the opinion that there is no way to define the danger zone to to infinite variables with salinity, conductivity, etc, but we need some sort of ruling or opinion from a higher authority to bolster our case.
Any help appreciated.

I read about it being debated when they were building the electric chair as to which one would be more effective. I remeber the article comparing it taking twice as much DC power to do the same "job:roll:",,,on a person. I'll see if I can find that again. I don't think there were any "hard numbers" other than what I just said

 

[benaround]

Is this a grounded or ungrounded system ? Either way, ground fault protection is required.

An ungrounded system, would not allow metal armor cables to be used, 690.35

 

[dbuckley]

Can anyone help calculate what the size the 'Danger Zone' would be with a full fault at 480V 150A into fresh water?

You're not going to get a 150A fault, as your resistance wont be low enough.

You can calculate the approximate voltage gradient across the water by assuming the water is of of uniform resistance, which wont be true where the depth varies, but its a start. Take any two points where you can get energization, put 480V across them, and theres your linear relationship.

Except for the fact that electricity will take all possible paths, and thus you'll get something like a oval between two points rather than a line, and the oval may extend for a significant distance.

I'd start by figuring out what fault modes you have so you can work out where you can get a potential differece for people to be shocked. If you can solidly bond the metalwork of the array and the conduits to one side of the arrays so that there is no point for the electricity to escape (ie the +ve conductor is entirely surrounded by -ve metalwork) then that will reduce the scope of the possibility of shock to approaching zero, and then fences and the like become aesthetic and security issues, rather than a saafety issue.

 

[cadpoint]

Well besides what's been said, I think one needs to get a seaonal water test.
Just to know what's in the water and how the construction will change the of pond.

Second, I think one should have a owner supplied boat on site. Fiberglass and no aluminum stringers or bummer rails, wood paddles, life preservers and the works. Besides all that one standard safety practice is to not stand up in
a small boat...

IMO, it sounds like such a future scarey story!

 

[zog]

Situation:
A large PV solar array, installed over water in a lake or pond.
We have been retained to advised on shock hazard / corrosion issues.
System has multiple 480 ~ 600V DC (not AC) 150 amp armored feeder cables running from the array, to shoreside DC > AC inverter. The client wants to know how big an area they need to enclose around the array to prevent trespassing / unauthorized personnel from entering an area that may be subject lethal voltage gradients if a worst-case fault to water were to occur.
Can anyone help calculate what the size the 'Danger Zone' would be with a full fault at 480V 150A into fresh water?
None of us in the Marine Industry have any data to calculate size / strength of the field around a fault from DC+ to water.
Deaths from 120 / 240 V AC faults to water are well known, any voltage gradients that subject a swimmer to over 30mA can kill, but we have found little or no data on hazards from high voltage DC, other than one expert who commented that based on a Coast Guard study, it take approx 3x the DC current to be lethal as AC. We are of the opinion that there is no way to define the danger zone to to infinite variables with salinity, conductivity, etc, but we need some sort of ruling or opinion from a higher authority to bolster our case.
Any help appreciated.

There are companies that specilize in this sort of analysis, was my job many years ago. This is not simple enough to get answered in a forum like this, you may want to sub contract this one out. Lot's of liability on the line here.