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Loss of neutral

lyledunn
I have just been involved in a situation where temporary loss of neutral on a TNCS system caused thousands of pounds worth of damage. It seems this loss of neutral situation, either within or outside the installation, is occurring more frequently. SPDs are now commonly fitted but at DBS  and generally with a Up in the order of 860v, so giving no protection on loss of neutral in a three-phase and neutral system. Cost benefit analysis across the national spectrum might not support a compulsion but is it time designers should be raising the issue with clients and at least offering a solution. On the other hand, is there a packaged solution?
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    From memory capacitance was  ~ 1k j ohms so an uF or three- the sort of thing in a small lamp ballast. in normal use there is no NE voltage so no current flows in it - by the time VNE is > 20-30 volts something needs double checking urgently I think we'd have set to trip 30mA below 50V AC .  There was other stuff in the box to indicate phase rotation as well, and a few other credible fault conditions besides.

    torch bulbs as fuses either 12V or 6V in the MES style, both are higher than a well behaved NE offset. At a push a 24V vehicle lamp might do either. 

    I realise something far more sophisticated is possible, probably with a PIC or an arduino we could log to fractions of a volt and have it calling in its readings to a central computer system every few seconds.

    But I suspect that neutral faults are all or nothing, so it is either less than 6V, or a large fraction of 230 and a go /no-go indicator is good enough.


    M.
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  • 0
    From memory capacitance was  ~ 1k j ohms so an uF or three- the sort of thing in a small lamp ballast. in normal use there is no NE voltage so no current flows in it - by the time VNE is > 20-30 volts something needs double checking urgently I think we'd have set to trip 30mA below 50V AC .  There was other stuff in the box to indicate phase rotation as well, and a few other credible fault conditions besides.

    torch bulbs as fuses either 12V or 6V in the MES style, both are higher than a well behaved NE offset. At a push a 24V vehicle lamp might do either. 

    I realise something far more sophisticated is possible, probably with a PIC or an arduino we could log to fractions of a volt and have it calling in its readings to a central computer system every few seconds.

    But I suspect that neutral faults are all or nothing, so it is either less than 6V, or a large fraction of 230 and a go /no-go indicator is good enough.


    M.
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