Does this choice have any impact on high energy fault damage?

[jaggedben]

...Can it make sense for them to require insurance endorsement to cover losses to other people's stuff and utility equipment in order to hook up solar without isolation for damage coming from solar asset that would have been avoided by a 10kV BIL isolation transformer?

I still don't get why you think that isolation of the DC current conductors matters whatsoever. Your primary contact is with grounded non-current-carrying metal parts. I'm not even the most knowledgeable person in this thread who has pointed that out.

Someone much smarter and experienced and I in risk science can decide if it's a worthy risk or if its along the line of same risk as getting abducted by flying monster from the outer space.

I suppose if the insurance companies ever have more than one or two major payouts then they will start to raise it as an issue with the solar industry. For what it's worth, I've never heard of anyone raising your concerns based on the results of a real-world incident rather than theory. Ultimately this isn't really any different from HV lines being potentially exposed to many other types of things, including HVAC systems on roofs, and building metal. Perhaps the greater surface area of solar systems is of meaning ... and perhaps it isn't.

 

[Electric-Light]

I still don't get why you think that isolation of the DC current conductors matters whatsoever. Your primary contact is with grounded non-current-carrying metal parts. I'm not even the most knowledgeable person in this thread who has pointed that out.

including HVAC systems on roofs, and building metal. Perhaps the greater surface area of solar systems is of meaning ... and perhaps it isn't.

A solar panel is like a film resistor with the element exposed to the element, but behind a protective coating or a glass plate. If the solar panel was encased behind a fine metal grill or in a metal box with, I agree wtih your point. Mivey pointed out that current can flow from paths other than across the transformer. So then its possible.

Does having isolation there matter in the magnitude of common mode fault current through L1 and L2? My guess is yes, but I don't have a way to test it.

 

[jaggedben]

A solar panel is like a film resistor with the element exposed to the element, but behind a protective coating or a glass plate. If the solar panel was encased behind a fine metal grill or in a metal box with, I agree wtih your point. Mivey pointed out that current can flow from paths other than across the transformer. So then its possible.

...
I would also expect the front glass of the panel to provide very effective insulation.
...

I guess we need to see some info on the inductance/capacitance of tempered glass, and some math. (Note that the glass also still makes major contact with the grounded frame.)

Not that this really affects any point of substance, in my opinion. This would be a freak occurrence, if it happened.

 

[Electric-Light]

I guess we need to see some info on the inductance/capacitance of tempered glass, and some math. (Note that the glass also still makes major contact with the grounded frame.)

Doesn't it shatter or pierce through quite easily when it involves hardware and wiring methods used for uninsulated poles falling down onto the panel from a pole height?

Not that this really affects any point of substance, in my opinion. This would be a freak occurrence, if it happened.

I would say a vehicle or weather vs a pole incident in the corner lot along a two lane highway causing a primary to fall somewhere on the lot is not a "freak" incident. It would sizzle and crackle on the ground or some structural metal with only ground connection. We hear of power outage due to stuff like this all the time and California gets its fair share of brush fires due to primary wire incidents during hot weather. The requisite for the latter is dry flammable materials near the point of fault.

If solar panels cover a large area of that lot, the probability of downed line or propelled by a falling pole doesn't seem like a wild imagination.

 

[jaggedben]

Doesn't it shatter or pierce through quite easily when it involves hardware and wiring methods used for uninsulated poles falling down onto the panel from a pole height?

No, not 'quite easily'. Not if you're just talking about the wire falling on it and not the entire pole. The modules are designed to withstand Texas hail. And if the pole falls on the house, I think the insurance companies have greater things to worry about.

I would say a vehicle or weather vs a pole incident in the corner lot along a two lane highway causing a primary to fall somewhere on the lot is not a "freak" incident. It would sizzle and crackle on the ground or some structural metal with only ground connection. We hear of power outage due to stuff like this all the time and California gets its fair share of brush fires due to primary wire incidents during hot weather. The requisite for the latter is dry flammable materials near the point of fault.

If solar panels cover a large area of that lot, the probability of downed line or propelled by a falling pole doesn't seem like a wild imagination.

I'm not saying it couldn't happen, I'm saying that the number of events where all of this comes together is likely very small. How often does an HV line along a 2-lane hit highway actually hit a house and not "somewhere [else] on the lot"? And then, supposing it does hit a house, there's still a less than 50% chance it hits a solar array. What is the likelihood that the HV line comes in contact with an LV line that may be running from lower down on the same pole? Surely that must happen occasionally, too. How often and what are the typical consequences?

There are other safety advantages to the new inverters for the people who actually work with them and live under them. The general life and safety advantages of these inverters are likely to outweigh the issue you have raised, in my estimation.

 

[Electric-Light]

No, not 'quite easily'. Not if you're just talking about the wire falling on it and not the entire pole. The modules are designed to withstand Texas hail. And if the pole falls on the house, I think the insurance companies have greater things to worry about.

You're emphasizing damage to the house where solar asset is located. Have you seen what medium voltage fuse holders look like? It wouldn't be just an 8AWG wire falling on it. It would be like throwing a five pound steel block on it tethered to a cable attached to 7,200v. The primary discussion is about possible damage to other households sharing the same pole pig.

My understanding is that solidly grounded wye is common for primary serving residential/rural areas. In other words, I'm positing that if you chuck a porcelain and steel rod(common material on pole components) attached to a 7200v primary into a glass panel solar panel that is a part of transformerless PV system with biggest inverters/circuit size that has been known to be used for this application, the series of let through current from several automatic reset could plausibly damage stuff that is fed from the same distro xfmr. The transformer may or may not be attached depending on what happens first.

I'm also positing that various paths allows different amounts of current to pass through line conductors and neutral regardless of inverter design but the isolation transformer can make a significant difference in the magnitude.

http://www.cooperindustries.com/con...es/library/201_1phTransformers/TC202001EN.pdf
http://www.netaworld.org/sites/default/files/public/neta-journals/NWsp09-Hartman.pdf

I'm not saying it couldn't happen, I'm saying that the number of events where all of this comes together is likely very small. How often does an HV line along a 2-lane hit highway actually hit a house and not "somewhere [else] on the lot"?

That's exactly my point. The probability of things coming together increases with popularization of filling more roof area and other parts of the lot with solar panels thus the validity of assessing the effect of omitting isolation transformer to the magnitude of discretionary PV distributed generation to exposing other utility customers in harm's way. Prescriptive policy on risk mitigation and harm reduction is essential.

It became necessary to address tail pipe emissions as more cars filled the same area. Comparatively speaking this is analogous to more restrictive policy on power quality and interference concerns caused by inverters, LED ballasts and so on in mixed use and residential zones.

And then, supposing it does hit a house, there's still a less than 50% chance it hits a solar array. What is the likelihood that the HV line comes in contact with an LV line that may be running from lower down on the same pole? Surely that must happen occasionally, too. How often and what are the typical consequences?

The increased quantity of cars inevitably raised the probability and absolute frequency of crashes and then it became important to prescribe policies to reduce the magnitude of damaging effects of crashes regardless of who's at fault. One such example is the barrier on back of semi trailers to lessen injuries to car drives who dives/gets pushed into the back of them.

At the time when only a few elites had a car, cars still ran into trees, but talk of requiring insurance, rush hour pollution and pile up would have been perceived with the same ire. vehicle-to-vehicle fiery crash were things that only happened on racing events at the time.

There are other safety advantages to the new inverters for the people who actually work with them and live under them. The general life and safety advantages of these inverters are likely to outweigh the issue you have raised, in my estimation.

The safety and impact on those around them trumps it.

 

[mivey]

http://www.netaworld.org/sites/default/files/public/neta-journals/NWsp09-Hartman.pdf

I hope they checked the equipment withstand rating. Removing arrestors on equipment rated for a grounded system could also cause a catastrophy. The arrestors are there to hold the voltage across the equipment to a maximum voltage.

The article should have made it clear just removing arrestors is not a go-to solution.

 

[mivey]

You are putting a lot into a freak scenario.

I'm trying to tell you that unless you insulate the other stuff around your equipment and wiring, putting insulation on one end of your wiring is not likely to stop the fault from traveling on part of your equipment and wiring and reaching L1L2.

It may not travel across the isolation winding but that is only a fraction of the path you have provided.

 

[jaggedben]

You're emphasizing damage to the house where solar asset is located. Have you seen what medium voltage fuse holders look like? It wouldn't be just an 8AWG wire falling on it. It would be like throwing a five pound steel block on it tethered to a cable attached to 7,200v. The primary discussion is about possible damage to other households sharing the same pole pig.

You posited a vehicle crashing into the pole. The hardware is on the pole right? How likely is it that one of these fuseholders hits the house and the rest of the pole does not? Not very, it seems to me.

My understanding is that solidly grounded wye is common for primary serving residential/rural areas. In other words, I'm positing that if you chuck a porcelain and steel rod(common material on pole components) attached to a 7200v primary into a glass panel solar panel that is a part of transformerless PV system with biggest inverters/circuit size that has been known to be used for this application, the series of let through current from several automatic reset could plausibly damage stuff that is fed from the same distro xfmr.

I fully get your scenario. Yes, electricity can cause damage to things. But again, is your scenario really more likely to happen than the HV lines directly impacting LV lines lower down on the same pole?

...

The safety and impact on those around them trumps it.

Seriously?!? That's MY safety you're dismissing. And if you're suggesting that the residential solar industry should pack up its backs over this imagined scenario you can't point to a real world instance of, and I should fire all my guy's because of this... that's offensive too.

 

[jaggedben]

You are putting a lot into a freak scenario.

I'm trying to tell you that unless you insulate the other stuff around your equipment and wiring, putting insulation on one end of your wiring is not likely to stop the fault from traveling on part of your equipment and wiring and reaching L1L2.

It may not travel across the isolation winding but that is only a fraction of the path you have provided.

Thanks.

 

[Electric-Light]

I'm trying to tell you that unless you insulate the other stuff around your equipment and wiring, putting insulation on one end of your wiring is not likely to stop the fault from traveling on part of your equipment and wiring and reaching L1L2.
It may not travel across the isolation winding but that is only a fraction of the path you have provided.

I agree with you.

Put 5 ohm, 3 ohm, and 1 ohm across a voltage source and we know the current is voltage divided by 1.9 ohm + whatever the source impedance is. My drawing did suggest it was whatever the shorted resistance of inverter vs infinity.

So provided that the contact is with voltage less than the 10kV BIL of the typical low voltage xfrmr:

transformerless: current to L1/L2 divided between shorted out inverter and the other peripherary path you talked about. This = Zx
transformer isolated: the path is only the peripherary. This = Zy

is Zx low enough compared to Zy to have substantial impact? That is beyond my knowledge. Your view?

shorted resistance of inverter combined with other path.

for isolated, it is just the other path provided that the contacted line is below the 10kV BIL rating of the transformer.

It could be a big difference, it could be practically the same.

You posited a vehicle crashing into the pole. The hardware is on the pole right? How likely is it that one of these fuseholders hits the house and the rest of the pole does not? Not very, it seems to me.

I fully get your scenario. Yes, electricity can cause damage to things. But again, is your scenario really more likely to happen than the HV lines directly impacting LV lines lower down on the same pole?

...

Seriously?!? That's MY safety you're dismissing. And if you're suggesting that the residential solar industry should pack up its backs over this imagined scenario you can't point to a real world instance of, and I should fire all my guy's because of this... that's offensive too.

It's common enough for trees (conductive) to fall into lines which would bridge between whatever wires already there. I would hope that proper measures are taken. Electricity is bare necessity that everyone depends on. It adds risk, but generally everyone enjoys benefits of having electrified living. If solar adds risk to other utility users at all, do those who face the risk see any benefit whatever or are they merely exposed to risk for a project that exists solely to benefit the finances of those banking on distributed generation money?

I would also take the same position that safety of existing people in homes and businesses takes priority over that of private aircraft passenger/pilot's in a proposed private runway. I didn't say they're unimportant but the latter group do so by choice. The people in adjacent areas have no choice but to be exposed to increased risk. Although is there any reasoning why unisolated system is safer that could not also be added to isolated system?

The added protection required to protect workers from the new dangers created by unisolated system could also make isolated system safer.
Supposing seatbelts made people safer in a small bus compared to large bus without seatbelts, would seatbelts in the large bus make it even safer?

 

[jaggedben]

... If solar adds risk to other utility users at all, do those who face the risk see any benefit whatever or are they merely exposed to risk for a project that exists solely to benefit the finances of those banking on distributed generation money? ...

I think "at all" needs to amended to "by a non-negligible amount." At this point it is entirely conjectural that there is a non-neglible, statistically meaningful likelihood that a solar system adds any measurable risk regarding the kind of incident you're talking about, let alone one that is specific to inverter topology. I thinking there are more important things to worry about.

 

[Electric-Light]

I think "at all" needs to amended to "by a non-negligible amount." At this point it is entirely conjectural that there is a non-neglible, statistically meaningful likelihood that a solar system adds any measurable risk regarding the kind of incident you're talking about, let alone one that is specific to inverter topology. I thinking there are more important things to worry about.

Downed lines happen with enough real relevance that there's an awareness campaign about what to do in case you come across one. Some people might never see a live downed primary wire in their life but that doesn't mean it doesn't happen. Proving a negative is less practical than a combination of speculating plausible sufficient combined causes.

I suppose it would have to wait until a notable incident happens to build enough interest to get research grant and support to experimentally drop a primary on a large solar system many times and observe damage in loads sharing the same utility transformer.

You supposed that unisolated systems are safer. Can you explain how and do you have statistically meaningful data?

 

[iwire]

Can you explain how and do you have statistically meaningful data?

I think it's funny you are asking for 'statistically meaningful data' when you have provided absolutely nothing but conjecture to substantiate your worries.

 

[mivey]

I agree with you.

Then that should be the end.

This = Zx
...
This = Zy
...
is Zx low enough compared to Zy to have substantial impact? That is beyond my knowledge. Your view?

The path around the isolation transformer may be of very little withstand so the protection the iso xfmr provides may be practically useless.

Unless you do something about the path around the isolation transformer you have netted very little protection.

 

[mivey]

Although is there any reasoning why unisolated system is safer that could not also be added to isolated system?

Adding the isolation transformer does not guarantee that the L1L2 system stays isolated from the HV currents resulting from the HV line contacting the PV panels.

 

[jaggedben]

Downed lines happen with enough real relevance that there's an awareness campaign about what to do in case you come across one.

Do they happen often enough that insurance companies charge higher homeowner insurance premiums to people who live in closer proximity to HV power lines? Just wondering.

... Proving a negative is less practical than a combination of speculating plausible sufficient combined causes.

LOL. Neither sounds practical to me.

I suppose it would have to wait until a notable incident happens to build enough interest to get research grant and support to experimentally drop a primary on a large solar system many times and observe damage in loads sharing the same utility transformer.

That's pretty much what I said at the end of post #21, although I think insurance companies would probably find another way to assess the comparative risks. By the way, large solar systems generally don't share a transformer with other customers, depending on what you mean by large. It think it's small systems you're really concerned about.

You supposed that unisolated systems are safer. Can you explain how and do you have statistically meaningful data?

First, I'll grant you that the isolation or lack thereof has little to do with safety. That's for efficiency, which I'll get to below. The safety improvement comes from very much improved ground-fault detection that was mandated for the UL standard for non-isolated inverters. The new ones will trip off with mA of ground fault current, whereas the old ones with fuse protection could allow a ground-fault of several amps one the grounded side to keep flowing until a second ground fault on the ungrounded side creates a serious uncontrollable arc. At least one notable fire happened due to the old system. (Bakersfield Fire, look it up.) Safety is also increased for workers when neither DC conductor is grounded: you no longer have a shock harzard between one half of the system and the racking. I can vouch from personal experience that since these improvements were made, the number of times me or my guys have inadvertently caused DC arcing on unfinished wiring or mismatched polarities has dropped from a few to zero. That's as much data as I have to provide.

As far as the value of that extra 1-2 percent energy production gained from non-isolation... Back of the envelope, the value of that energy generated in one day in the US is probably around a million dollars, and going up all the time. I'm going to go out on a limb and suggest that over the course of a year that adds up to a lot of money compared to any payouts that might ever be needed to cover your hypothetical type of accident, if it can even ever be proven that inverter topology contributed to additional damage.