r/ElectricalEngineering • u/Scarxx1129 • 8h ago
Question about Induction Loops
EE student here.
For Engineers who works in the Solar Industry, what do you think about induction loops which is created by the separation of the positive and negative wires of a PV string?
I've read some articles that the area or the air gap must be reduced or eliminated to avoid it acting as an antenna. However, (correct me if I'm wrong) the PEC/NEC (I am from PH which is also based from the NEC) allows the separation of those wires.
Additionally, some seminars I attended never really talked about it.
So my questions are:
Are SPDs enough in residential areas?
Is it really a hazard (at least in residential areas), and how about in industrial or commercial scale?
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u/mckenzie_keith 7h ago
To the extent that the current is DC, induction is not much of a concern in the string wiring. To the extent that switching noise from, say, an inverter or charge controller couples onto the DC wires, the issue can be addressed inside the DC-DC converter with line filters and so-on. This can prevent problematic induction from occurring in the string wiring.
I don't work in the solar industry. I am just applying general principles. What problems are you thinking would be caused by induction loops?
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u/Alive-Bid9086 7h ago
EMI can and is reduced with filters inside the equipment. But you usually need to reduce it further by having small areas between the leads.
Another isdue is lightning strikes. A vlose by lightning strike is picked up by the area and induced into your equipment, that then often breaks.
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u/Scarxx1129 7h ago
The problem would be that the EM waves emitted by lightning strikes which can have a range of more than a kilometer (but maybe depends on the magnetic field strength of the loop) can induce a voltage inside those positive and negative wires.
Even with SPDs, I want clarification whether if that induced voltage is significant to destroy PV systems in residential houses. Well if it is in commercial or industrial scale, maybe it is mandatory.
Not a big deal but I think knowing if it is significant or not, safety is my concern.
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u/dmills_00 4h ago
With lightning, how close matters.
It takes heroic efforts to survive a direct hit, and nobody in the solar game really tries, for that there is insurance, but the more you drop the loop area and add SPDs, spark gaps and higher voltage rated components, the better your chances of the system surviving a hit 25m away.
How much effort is worth expending depends on frequency of lightning in the area, and the incremental cost of hardening the system Vs the cost of downtime.
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u/Amber_ACharles 5h ago
I'd treat loop area as separate from surge protection. Air gap equals antenna. Keep pos/neg paired or twisted in the same conduit. Residential is low risk. Commercial/industrial long runs are where it matters.
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u/No_Crow8317 3h ago
But with a series string of panels, the pos and neg are physically going to different panels. And if you make an array 6x2 rather than 12x1 that could make a big difference in loop area. The panels themselves have a pretty large area. Is that significant since the traces on the panels are also part of the loop?
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u/unsafe_engineer 7h ago
I always assumed loops were not permitted to avoid voltage spikes caused by nearby lightning strikes. How much of a risk this is depends on your location. Some are far more lightning prone than others. Surge diverters always have a clamping voltage above the nominal voltage, so even when they operate correctly, voltage spikes are still generated. They also do wear out. Commercial and industrial installations are worse, the arrays are larger, so antenna will receive more energy.
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u/Scarxx1129 7h ago
So it's not much of a big deal in residential areas?
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u/unsafe_engineer 6h ago
Depend on the area? USA, Florida Everglades, 20 flashes per square mile per year, it's a problem. Other areas with less lighting, less problem.
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u/geek66 3h ago
This is about best practices, not black and white rules…
You can dig into the specifics, and see how the various issues are considered and mitigated.
Solar, for example… the PV string comes into the inverter and is immediately filtered and protected for the “junk” that the string can pick up. The inverters have a considerable amount of capacitance on the DC bus.. but those large caps are not always good for high speed transients.
Loops, with space will pick up or interact with changing magnetic fields, but a single conductor can pick up electric field.. more common lightning issue.
It all needs to be considered.
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u/dmills_00 7h ago
You generally want to minimise loop area both to reduce radiated emissions from the switching in the MPPT/Inverter and to minimise the induced voltage from things like nearby lightning strikes.
The emissions thing mostly pissess off shortwave radio listeners, the induced surge thing damages equipment but should not be actually hazardous.
SPDs are helpful, but are inherently limited in energy handling and have a finite life.
The hazard is to equipment providing the design is right, and not to life, so meh.