SPD protections in 37KWp installation out of LPS

josealjim
josealjim Solar Expert Posts: 33 ✭
in General Solar Power Topics #1


Some SPD manufacturers suggest to install SPD type 2 at both side of the dc cable when distance is longer than 10m. They always mention IEC normative but everything i have read from IEC is based on lighting strike PROBABILITIES, so it seems that electrical companies are a bit bloodsuckers.

For a 37kw system where the distance between inverters and panels is about 60m (20m underground outside the building + 40 inside the building. 100 people working in ),
what would you recommend? The solar parking will be install in Thailand.

- SPD class2 at both sides of the DC cable + SPD right near the ac output
- Only SPD right before the inverters DC input + SPD right near the ac output

Thanks in advance
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  • jcheil
    jcheil Solar Expert Posts: 722 ✭✭✭
    #2
    Re: SPD protections in 37KWp installation out of LPS
    josealjim wrote: »


    Some SPD manufacturers suggest to install SPD type 2 at both side of the dc cable when distance is longer than 10m. They always mention IEC normative but everything i have read from IEC is based on lighting strike PROBABILITIES, so it seems that electrical companies are a bit bloodsuckers.

    For a 37kw system where the distance between inverters and panels is about 60m (20m underground outside the building + 40 inside the building. 100 people working in ),
    what would you recommend? The solar parking will be install in Thailand.

    - SPD class2 at both sides of the DC cable + SPD right near the ac output
    - Only SPD right before the inverters DC input + SPD right near the ac output

    Thanks in advance

    I heard that too, and did the same. I guess I figured and extra $80 for the additional SPD at the array end (in addition to the 2 at the epanel) was extra (cheap) insurance.
    Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #3
    Re: SPD protections in 37KWp installation out of LPS

    Lightning usually does not strike inside buildings or underground: it hits wiring outside buildings that act as antennae to pick up the stray Voltage charge surrounding areas of strikes.

    So the most likely case is for grid lines and outside PV runs to get hit. The first place protection gets put is usually where these wires enter the building to send any Voltage spikes safely to ground. When the wire runs on PV are long then a second SPD at the array is helpful to keep the Voltage from damaging the PV because wire resistance comes in to play: the short path to ground may no longer be through the SPD at the entrance but rather through the PV and frames. Note that wire in conduit, even if it is metal and grounded, still counts as an outdoor run.

    Depending on how frequent, concentrated, and intense your lightning strikes are and extra SPD at the 'other end' of the wire is cheap insurance. Having one or more such devices is not, however, a 100% guarantee against damage from lightning: it pretty much does as it pleases. You can only reduce risk, you can't eliminate it.
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  • josealjim
    josealjim Solar Expert Posts: 33 ✭
    #4
    Re: SPD protections in 37KWp installation out of LPS

    Thanks.

    We are not going for an insurance. The dc cable will run throughout the lab where many people work and i was a bit concerned about high inducted voltages. The inverters come out with SPD type 3 so, as u said, ill install the SPD2 right before entering into the building.

    PS: I love this forum
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  • josealjim
    josealjim Solar Expert Posts: 33 ✭
    #5
    Re: SPD protections in 37KWp installation out of LPS

    There are many opinions regarding grounding and earth equipotential rods in PV systems installations. I hope you could help me with this topic guys.
    The installer and inverter company gave me some ideas about earthing pv systems but following Cariboocoo's advice and installing SPD protections right before entering into the building I though that 3 independent rodS in triangle right near the solar array to connect PV and SPDs would be a better idea that running any EGC throughout the building or bonding GEC to the building rods. Im a bit worried about voltage induction between isolated earth rods and also about closed loops if we equipotential them.

    WHAT DO YOU THINK ABOUT THE CONFIGURATION? I NEED YOUR HELP.

    Attachment not found.

    The SPDs will be installed outside with IP65 box, they will be connected by EGC to the PV electrodes bar (as you guys can see on the pic). To ground that box, can I use the same EGC or should I run another wire for it?

    Looking forward to hearing from you,

    thank in advance
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
    Re: SPD protections in 37KWp installation out of LPS

    I would run the ground for the box the SPD's are in inside and connect it to the rest of the ESG system. It is highly unlikely the box itself is going to pick up any Voltage from lightning strikes; it isn't a good 'target'.

    Mostly it is a question of which is the shorter run to the Earth grounding rod: under the road to the PV array or into the house to the other rods (and aren't they actually outside?).
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #7
    Re: SPD protections in 37KWp installation out of LPS

    BTW you may have an inadvertent ground loop formed by the inverter if the ground bus bar is in fact connected to the (case) ground terminal (as it probably is).
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  • josealjim
    josealjim Solar Expert Posts: 33 ✭
    #8
    Re: SPD protections in 37KWp installation out of LPS
    Cariboocoot wrote: »
    BTW you may have an inadvertent ground loop formed by the inverter if the ground bus bar is in fact connected to the (case) ground terminal (as it probably is).

    How could I avoid that?

    Thanks
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  • josealjim
    josealjim Solar Expert Posts: 33 ✭
    #9
    Re: SPD protections in 37KWp installation out of LPS

    Following your indications I have made another config.
    - SPDs right near the PV earth rods
    - Metallic conduit grounded at both ends
    - Bare cooper grounding electrode bonding jumper

    Attachment not found.

    - What do you all guys think about this one?
    - The distance between array and building is about 20m. I worried about lighting strikes induced voltages into the dc wires along the metallic conduit, I dont want any high voltage entering into the building. By grounding both ends of the conduit will they be avoid?
    - What kind of EGC and GEC wire should I use (section,etc)

    Attachment not found.

    We dont want to break the asphalt to much in order to set the wires. Could i place the bare cooper bonding jumper as indicated in the picture?

    Thanks
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #10
    Re: SPD protections in 37KWp installation out of LPS
    josealjim wrote: »
    How could I avoid that?

    Thanks

    The inverter indicates a ground bus bar and also a grounding terminal. You show the ground terminal going to the first ground rod and the ground bus bar connected to the second via the AC distribution box. Then the two rods are tied underground.

    If the ground bus bar in the inverter is connected to the ground terminal on it then there is a loop: inverter bus bar to AC box to second rod to first rod to inverter terminal to bus bar.

    The first thing to check is if the inverter ground bus bar and ground terminal are bonded. If so, eliminate the wire from the terminal to the ground rod. There will be one ground wire coming from the inverter and connecting to the AC box and then the ground rod. You may not need that second ground rod at all (you usually don't unless soil conditions warrant it). The two are very close together.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #11
    Re: SPD protections in 37KWp installation out of LPS
    josealjim wrote: »
    Following your indications I have made another config.
    - SPDs right near the PV earth rods
    - Metallic conduit grounded at both ends
    - Bare cooper grounding electrode bonding jumper

    Attachment not found.

    - What do you all guys think about this one?
    - The distance between array and building is about 20m. I worried about lighting strikes induced voltages into the dc wires along the metallic conduit, I dont want any high voltage entering into the building. By grounding both ends of the conduit will they be avoid?
    - What kind of EGC and GEC wire should I use (section,etc)

    This diagram is, in my opinion, much better save two things:
    1). There appears to be a ground wire going in to the conduit at the PV side which does not come out. This wire is unnecessary. The conduit should be attached to ground at both ends. The house end connects to the grounding system there. This should negate (as much as possible) and problems from lightning strikes.
    2). There is still the loop potential as described in my previous post although you've switched the inverter ground wiring around.

    Wire used for ground has to please the local AHJ but it's going to be 6 AWG minimum.
    Attachment not found.

    We dont want to break the asphalt to much in order to set the wires. Could i place the bare cooper bonding jumper as indicated in the picture?

    Thanks

    I am not understanding the reason for this. Two conduits? Normally the positive and negative can be run in the same tube. Since it is metal the ground connection is at each end. If you bury the contacts to the conduit and connect to the ground rods at each end no additional grounding conductor between the two should be required.

    That doesn't mean someone one say otherwise. If it is the inspector, you must comply with their demands even if it doesn't make any sense.
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  • josealjim
    josealjim Solar Expert Posts: 33 ✭
    #12
    Re: SPD protections in 37KWp installation out of LPS
    Cariboocoot wrote: »
    This diagram is, in my opinion, much better save two things:
    1). There appears to be a ground wire going in to the conduit at the PV side which does not come out. This wire is unnecessary. The conduit should be attached to ground at both ends. The house end connects to the grounding system there. This should negate (as much as possible) and problems from lightning strikes.
    2). There is still the loop potential as described in my previous post although you've switched the inverter ground wiring around.

    Wire used for ground has to please the local AHJ but it's going to be 6 AWG minimum.



    I am not understanding the reason for this. Two conduits? Normally the positive and negative can be run in the same tube. Since it is metal the ground connection is at each end. If you bury the contacts to the conduit and connect to the ground rods at each end no additional grounding conductor between the two should be required.

    That doesn't mean someone one say otherwise. If it is the inspector, you must comply with their demands even if it doesn't make any sense.


    I dont want to attach the end house conduit to the earth house system by running a wire throughout the house, I do want that the only connection between both earth systems (pv array and house) is made by the GEC bonding jumper.
    Attachment not found.
    Attachment not found.

    What do you think about this new configs?
    How can I bond the conduit to the grounding electrode bonding jumper?

    Im working in thailand and i dont trust installers here so Id like arrange everything following NEC

    I will check any possibility of electrical loop at the inverter anyway.


    The two conduits config was given to me by the installer, so lets make it one:
    Attachment not found.

    Should the connection between conduit and array earth be made by bonding the array end of the conduit by EGC to the array bus bar and the house end of the conduit by bonding to the electrodes bonding jumper as attached?
    The house end of the conduit should be bonded by GEC or EGC?

    THANKS A LOT
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #13
    Re: SPD protections in 37KWp installation out of LPS

    Simplification usually makes things better.

    Your metal conduit (now one; better) can be connected at each end to the ground rods. There doesn't need to be a separate wire between them. It will act as grounding conductor and additional grounding for both safeties. If the conduit terminates at the array box that counts as a ground connection at that end. At the other end if you don't want to bring it in to the house (and there is little chance of a problem at that point) you can clamp wire on to it and run that to the house ground rod.

    The inverter bus bar and ground terminal, if not already bonded, can be connected to the house ground rod above ground.

    Since you are in Thailand you probably haven't got any code to worry about. As such the idea is to go for what gives you the most electrical protection for both safety (no hot-to-touch casings) and lightning protection. You may have noticed that there is a lot of on-going discussion about what is best for this and that has caused our own regulations to change over the years. In some cases back and forth.

    Attaching basic ground diagram, although I see for this I'd have to do a more detail work.
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