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Terminology confusion

Kelly Marie Angel
Hi all the term medium voltage has as far as I know been out of favour for a good few years i think I'm right that any thing up to 999 volts is LV and anything above that is HV is this still the situation? I ask because I've seen a few videos and Web pages recently describing  medium voltage switch gear and equipment these are mostly pages that keep coming up now following my searches on power factor correction. Which in turn were a result of my post on large cotton reels in substation you now how it is a few mouse clicks and your into something else
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    Depends a bit where you are on the planet.


    Here in BSI and the Euronorm  ISO land, you are quite correct the phrase 'medium voltage' has no definition, we go from LV below 1000V RMS or 1500VDC to HV above that. (it is the higher of the phase to phase and phase to neutral voltage, so 690/1k2 3 phase is also considered HV but a single phase of 690 to earth would not be - not that I've ever seen that used in the UK, only in Germany. Here we seem to have LV as 230/400 3phase and occasional flights of LV at 400/690 or jump to  full blown HV and run at 3k3, 6k6  or 11k or something.)


    However in the US and places that adopt their standards, you will find MV referring to the layer between about 1kV and 30-50kV.

    So our 11kV and 33kV lines, that are HV in the UK would be called MV in other places. As the makers of insulators and switches for these voltages sell similar parts to both regions, you will find literature that uses 'the wrong words' is also in circulation


    Mike.
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    Depends a bit where you are on the planet.


    Here in BSI and the Euronorm  ISO land, you are quite correct the phrase 'medium voltage' has no definition, we go from LV below 1000V RMS or 1500VDC to HV above that. (it is the higher of the phase to phase and phase to neutral voltage, so 690/1k2 3 phase is also considered HV but a single phase of 690 to earth would not be - not that I've ever seen that used in the UK, only in Germany. Here we seem to have LV as 230/400 3phase and occasional flights of LV at 400/690 or jump to  full blown HV and run at 3k3, 6k6  or 11k or something.)


    However in the US and places that adopt their standards, you will find MV referring to the layer between about 1kV and 30-50kV.

    So our 11kV and 33kV lines, that are HV in the UK would be called MV in other places. As the makers of insulators and switches for these voltages sell similar parts to both regions, you will find literature that uses 'the wrong words' is also in circulation


    Mike.
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