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Loss of Neutral can cause damage to mains conencted devices...how avoid damage?

Z

zenerbjt

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Hi,
As you know, all electricity from your national grid is ultimately three phase in origin. If the neutral gets disconnected somewhere in the supply, then the Line-Neutral voltage becomes the Line-Line voltage, and any connected devices may well get overvoltaged and blow up.

For a 10kW installation, supplied with three phase, how can we ensure that the Line-Neutral voltage does not rise up to the line-line voltage if there is a loss of neutral connection?
 

KlausST

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Hi,

Not clear how the setup is.
Do a simulation and show us the results.

Klaus
 
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betwixt

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This actually happened near my home a few years ago. I'm in a very rural location with ancient and unreliable power distribution. Our electricity arrives as true three phase (only three wires) 11.5KV then gets dropped to 240V TP&N at the transformer which then heads off along four core cables to several small distribution boxes. Each of the small boxes feeds between four and six properties as single phase plus neutral.

The incoming neutral wire corroded and burned out at one of the distribution boxes, leaving six houses sitting across the phases. I was called out to investigate and called at one of the houses. It was quite funny in a tragic kind of way, the owner showed how they could switch their electric kettle on and make the lights in the house across the road turn on instead!

Thankfully there wasn't much damage and repairing the neutral restored some normality. Other than big varistors across the supply to protect each phase there isn't much you can do. At least its an obvious fault when you see the symptoms.

Brian.
 

FvM

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Varistors aren't selective enough to protect in this situation. You can install overvoltage circuit breakers in the switchboard.
 

Easy peasy

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You can install a transformer in your home that is designed to provide and augment the neutral - unfortunately it will do the same for anyone on the same 3ph + N supply, best bet is some very large MOV's from each phase to N, and a trip circuit - or fuses - that will disconnect the mains if significant current ever flows in the MOV's
 

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