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Phase loss

Kelly Marie Angel

I remember back when I worked In Newbury  we frequently suffered from flickering lights low mains voltage and more often than you'd expect loss of a phase for maybe a half a second or thereabouts. The oddest effect was that the voltage would dip and return to normal several times in succession I could see on a voltmeter on my bench and of course it was noticable on the workshop lights. This effect was noticable over a wide area so not an LV problem. Why didn't the DNO sort it out ? What would cause this effect it must of been something at 11 or 33Kv  rather than LV

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    Humm, difficult to say for certain. The HV system can open on faults and then auto re-close (to cope with things like tree branches or birds briefly shorting out bare HV overhead lines) - and they can re-try a number of times before giving up if the fault persists - but usually the operate on all three lines simultaneously as far as I know and you'd usually see close to zero volts during the open periods. Loosing one phase can give very odd results like much reduced voltage on two of the three LV phases - but that's usually the result of single phase protective devices opening - i.e. fuses - and when they open they stay open, so that wouldn't account for dip and return either. The only other things I can think of are intermittent faults - like a loose connection (blowing in the wind) or something like an auto tap changer that's past its best.

       - Andy.

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