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HV Safety - Legislation on underrated HV Switchgear - 6.6kV Switchgear on 11kV Network

Tony Duffy

Hi,

I have come across HV switchgear in a recent audit that is underrated for the supply voltage. The switchgear is on a UK 11kV network, the switchgear itself is 11kV rated, as is one of the five outgoing circuit breakers. However, four of the five circuit breakers are 6.6kV rated. I am reporting these findings (along with others) and I am struggling to demonstrate the lack of compliance of this switchgear. I argue that using 6.6kV switchgear in an 11kV network is a breach in law but I can't back it with specific legislation. I can find guidance from the HSE on "overstressed" switchgear but I don't think this is really applicable (that's switchgear underrated for current fault levels, right?). I'd like to back up my statements in my report with some HSE guidance or H&S law but I am struggling.

Does anyone know of any specific legislation covering underrated HV switchgear/circuit breakers?

For more information, this switchgear is circa 1950s, oil filled and DMO (dependent manually operated).

Thanks,

Tony

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  • +1

    I am a mere engineer, not a lawyer but I would start with Electricity At Work Regulations: Regulation 5

    No electrical equipment shall be put into use where its strength and capability may be exceeded in such a way as may give rise to danger.

    In support of this, HSE HSR25 (my emphasis)

    82 The term ‘strength and capability’ of electrical equipment refers to the ability of the equipment to withstand the thermal, electromagnetic, electrochemical or other effects of the electrical currents which might be expected to flow when the equipment is part of a system. These currents include, for example, load currents, transient overloads, fault currents, pulses of current and, for alternating current circuits, currents at various power factors and frequencies. Insulation must be effective to enable the equipment to withstand the applied voltage and any likely transient over-voltages.

    See also HSE HSG230, but I suspect that's what you're already referring to.

    That said, to have survived that long in service so underrated without being either damaged or noticed is quite a feat. Are you sure the rating given isn't phase to earth?

  • 0 in reply to Jam

    Hi Jam,

    Thanks for the reply. I think the section 5 quote andHSR25 will work well thanks.

    Yeah I was looking at HSG230, I had used it in other places to justify the replacement needs of the other old oil filled DMO gear. It talks about "overstressed":

    "Switchgear is described as being ‘overstressed’ when it is operated beyond its design rating"

    but reading their actions for overstressed it felt like it was referring to switches that now have higher loads or fault currents. It was more along the lines of limit access to it, reduce the load etc. I felt the actions for underrated switchgear should be a little more urgent. I wrote it up like it was overstressed but I'm worried I'm muddying the water/going off on an incorrect tangent with it.

    The plate on the breakers just says "service voltage 6.6kV". There's one breaker in the switchgear that is identically to look at but says "service voltage `11kV". I get what you mean about it being in services for so long without failure. I suspect it has been bought secondhand and not been in service on 11kV for the whole 60ish years. It will have been at least 20 though. As for not noticing, the switchgear itself is stamped to 11kV and the breaker plate is a little out of the way. I can see how it has been missed.

    As to why there is one at 11kV and 4 at 6.6kV.... That's a proper mystery!

    Cheers,

    Tony

Reply
  • 0 in reply to Jam

    Hi Jam,

    Thanks for the reply. I think the section 5 quote andHSR25 will work well thanks.

    Yeah I was looking at HSG230, I had used it in other places to justify the replacement needs of the other old oil filled DMO gear. It talks about "overstressed":

    "Switchgear is described as being ‘overstressed’ when it is operated beyond its design rating"

    but reading their actions for overstressed it felt like it was referring to switches that now have higher loads or fault currents. It was more along the lines of limit access to it, reduce the load etc. I felt the actions for underrated switchgear should be a little more urgent. I wrote it up like it was overstressed but I'm worried I'm muddying the water/going off on an incorrect tangent with it.

    The plate on the breakers just says "service voltage 6.6kV". There's one breaker in the switchgear that is identically to look at but says "service voltage `11kV". I get what you mean about it being in services for so long without failure. I suspect it has been bought secondhand and not been in service on 11kV for the whole 60ish years. It will have been at least 20 though. As for not noticing, the switchgear itself is stamped to 11kV and the breaker plate is a little out of the way. I can see how it has been missed.

    As to why there is one at 11kV and 4 at 6.6kV.... That's a proper mystery!

    Cheers,

    Tony

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