Utility Scale PV Arrays Located near HV Transmission Lines: Minimum Allowable Distance

[Fisherman199]

I was posed a question recently by a friend doing some planning work on a PV install near a swamp in nothern territories. He asked how close he could locate the PV site to their transmission lines. Apparently, they've never had this question internally.

I'll admit that this is not one I've heard in my years of transmission or generation planning. Usually the PV sites are located off an HV tap to the IC point and so can be thousands of feet or several miles from the transmission level voltages.

It's well-known, on very high voltage lines, even little birds won't land on them because the current density gives them a little "buzz". I've walked under 500kV lines during rain with an umbrella and felt the slight upward pull and have heard others tell of times they could see corona discharge in their umbrellas near 600kV+ lines during rainstorms and on muggy summer days.

He's said they're just going to move forward with ~350ft minimum from the corridor boundaries (115kV line) and be done with it (apparently very short timeline). That said, I'm not satisfied with the "meh, just use this" answer and so I'm curiously chasing down an answer with more veracity ("teeth", as it were). But... I'm having a difficult time finding anything in IEEE or IEC about this specific topic. I'm hoping I don't have to break out my emag studies but i will if forced.

Thoughts from the order?

P.S. I wish @jim_hardy were still with us. This would be a perfect question for him to address. @anorlunda has not posted in a while so he's probably off in his boat somewhere, otherwise I'd have sent him a message. he's sailing the world and the rest of us are still plugging away. i always knew he was the smartest of us.

 

[Baluncore]

https://cms.eirgrid.ie/sites/default/files/publications/Solar-Farm-Clearances-Report-Rev-A.PDF
See table 1, on page 1.

Since with 3PH, the three lines are usually mounted one above the other, the stray field will be a minimum towards the horizon, so 350 ft away might well be OK. A conductive ground grid below the array, with multiple grounds, would reduce differential voltages induced in the support structures and PV interconnects. The interconnects should be twisted, so arranged to have a minimum loop area.

The worst location is under the lowest conductor. That is where you would expect corona discharge and the greatest unbalanced magnetic field.

An EM analysis should not be of a balanced 3PH line, it should be of a momentary short of one wire, to tower or ground. That will generate the biggest induced current in nearby wire fences, or PV arrays. A short between two lines, having equal and opposite currents, will more likely cancel itself.

I once ran a seismic survey along the clearing under live 132 kV transmission lines. We used electric detonators, with twisted pair shot wires, and crossed our fingers that there would not be a line to tower short at a critical moment. The geophones did not suffer from 50Hz interference, the biggest problem was the mud, and frogs croaking into the geophones.

 

[Fisherman199]

https://cms.eirgrid.ie/sites/default/files/publications/Solar-Farm-Clearances-Report-Rev-A.PDF
See table 1, on page 1.

Since with 3PH, the three lines are usually mounted one above the other, the stray field will be a minimum towards the horizon, so 350 ft away might well be OK. A conductive ground grid below the array, with multiple grounds, would reduce differential voltages induced in the support structures and PV interconnects. The interconnects should be twisted, so arranged to have a minimum loop area.

The worst location is under the lowest conductor. That is where you would expect corona discharge and the greatest unbalanced magnetic field.

An EM analysis should not be of a balanced 3PH line, it should be of a momentary short of one wire, to tower or ground. That will generate the biggest induced current in nearby wire fences, or PV arrays. A short between two lines, having equal and opposite currents, will more likely cancel itself.

I once ran a seismic survey along the clearing under live 132 kV transmission lines. We used electric detonators, with twisted pair shot wires, and crossed our fingers that there would not be a line to tower short at a critical moment. The geophones did not suffer from 50Hz interference, the biggest problem was the mud, and frogs croaking into the geophones.

I don't know much about the specifics of his install but I'll assume he intends a grounding field and twisted cables. I don't know why one wouldn't. my experience with substations says that often how things should be done is replaced with what budget allows. my experience with solar/battery/wind is that planning is often poor on the part of generation builders and contracts are often renegotiated 2-3 times higher than originally signed. I don't envy his tasks.

The paper you cite, as i read it, suggests ordinary clearances are sufficient; so, essentially, up to the corridor boundary. that seems very close to me but I won't argue what I haven't studied.

i spoke with him again. apparently they've not even done an IC study. Typically there would be some powerflow, transient, and EMT studies with large solar plants desiring interconnection. it seems there's some rush to get approval for ITCs before EOY.

to your point on faults occurring while near HV electrical equipment... I can confirm it's quite the heart racer.