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Thread: 700 Volt surges reported from a commercial site

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    700 Volt surges reported from a commercial site

    Although I joined sometime ago and have read afew threads, this is my first post on the forum.

    I've just had a call from a client reporting that they're getting sustained surges of 700V in an industrial type plant. This is blowing various VFDs they are using, apparently. Most time the voltage sits at about 400V.

    They have a 315KVA mini-sub, council supplied, on the property which then feeds a 450-amp/400V possible load. A typical council supply to commercial properties.

    I haven't been to site so the fault they're reporting is second-hand knowledge. They have, however, told me that their neighbours are experiencing the same problem, which leads me to believe it's a supply problem on the HV/MV side. I'd assume this is a council problem and is also outside my skill set. I don't know whether HV fluctuations are handled by the mini-sub or not.

    My question is how to fix? They'll contact the council but is there something I can install inside the property to stop the damage?

    Is there some sort of large surge arrstor/capacitor I can install on the incoming supply to remove these surges, even if they are for long periods of time?

    This is uncharted water for me but I need a solution and am hoping you guys can help.

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    There are maybe 2 ways for protection , depending on the application or physical size, as this will have a bearing on cost.
    Voltage Monitor
    This is a voltage monitor which checks the incoming voltage and if with in the window switches a contactor on, and allows the load to be connected.
    Constant voltage transformer
    This is a special transformer that maintains the output to the load at a constant voltage. But as any piece of equipment there are limits.
    Victor - Knowledge is a blessing or a curse, your current circumstances make you decide!
    Solar and LED lighting solutions - www.microsolve.co.za

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    Please contact me . I have a client who is an experienced & qualified electrical contractor.
    anitag@mweb.co.za

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    Hi

    I would stick a voltage recorder on the LT side and see what is actually happening before making a decision - If the voltage spike is short you may get away with good quality surge arrestors - If not then go with the above suggestion of contactors and voltage monitors - Problem is that it causes chaos with production .

    I have used auto tap transformers on a small scale , 5Kva , but a quick spike still gets through before the change - There are a number of systems available but on 315Kva will start at R600K to purchase

    I would also check that the earthing , mainly earth to neutral from the star point is still intact and has no loose connections . You will get an elevated voltage between earth and neutral.
    My theory is that when something funny happens that cannot be explained , check the neutrals .

    With the neighbours also experiencing problems it could be MV side but then again somebody could have gone through the area and stolen all the earth to neutral bridge points or the earthing in the area has become a problem.

    We recently had the neutral conductors and earth wires stolen from multiply sub stations in the area over a period of a week or two at random intervals.

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    Thanks for the replies.

    I've spoken with the clinet and we'll start with the voltage recording and take things from there.

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    Quote Originally Posted by Cracker View Post
    Although I joined sometime ago and have read afew threads, this is my first post on the forum.

    I've just had a call from a client reporting that they're getting sustained surges of 700V in an industrial type plant. This is blowing various VFDs they are using, apparently. Most time the voltage sits at about 400V.

    They have a 315KVA mini-sub, council supplied, on the property which then feeds a 450-amp/400V possible load. A typical council supply to commercial properties.

    I haven't been to site so the fault they're reporting is second-hand knowledge. They have, however, told me that their neighbours are experiencing the same problem, which leads me to believe it's a supply problem on the HV/MV side. I'd assume this is a council problem and is also outside my skill set. I don't know whether HV fluctuations are handled by the mini-sub or not.

    My question is how to fix? They'll contact the council but is there something I can install inside the property to stop the damage?

    Is there some sort of large surge arrstor/capacitor I can install on the incoming supply to remove these surges, even if they are for long periods of time?

    This is uncharted water for me but I need a solution and am hoping you guys can help.
    This is very strange and interesting. I wonder if that surge is not from a sensitive earth fault. This can only be possible if it's an underground cable network where sensitive earth fault protection on Mv networks is not activated. It can only be a feed from the primary side of the MV trfr because I don't see it coming from the secondary windings.
    Please share your findings.

    Regards
    S.Mjali (Pr Techni Eng)


    Sent from my SM-G955F using Tapatalk

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    Put an online ups on the control circuits (it gets expensive...but so does replacing VFD's)...it will regulate the voltage on the control side (the part that blows) ...install a 3 phase trip connect...this device will monitor the voltage and drop out the contactor if a surge voltage is detected...very handy in locations where they steal the neutral cable which causes the voltage to spike...which could be the problem...a loose neutral connection

    Surge protection is not designed for over voltage.

    You need to install a logger...without recorded data you have no idea what is actually going on.

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