Strange mains electricity issue

[karma mechanic]

Earlier in the week there was a thunderstorm during the night and the power went off. Then on for a while, off again and was eventually restored late in the morning. (Chandler's Ford, Hampshire).
Having reset the clock on the microwave, oven and water softener we then went out leaving the NAS to sort itself out.

Coming back to the house in the early afternoon I popped into the downstairs loo and noticed that the light and fan didn't come on. Checking round the house I discovered that no lights actually worked (all CFL, LED or halogen on electronic transformers). However, the microwave display still showed the correct time, the Tivo and the Sky box still had power lights, the computer was still blinking its standby light and the router was running. It looked like the lighting ring had no power, but checking the consumer unit showed nothing that had tripped.

So I put the kettle on so I could ponder this - the blue LED lit but no water heating occurred. The display on the front of the oven was off, but the NAS was still busy re-syncing its drives connected to the same ring.

Then I went into the garage to get a multimeter, and the mains halogen light in there managed to provide about as much illumination as an electric fire.

Very odd.

Measuring the mains voltage showed 70 volts RMS.

At this point the lady next door knocked and asked if our electricity was ok, since the solar panel controller in their garage was making a lot of disturbing noises and was showing a message 'grid imbalance'. No panels on our house.

After a while I heard a few local house alarms going off as the normal mains voltage was restored, and everything went back to normal. Nothing seems to have been damaged, and I doubt whether anything is likely to be damaged by too low a voltage anyway. Maybe running halogen bulbs orange rather than white would spoil the normal way they maintain the filament, but probably not in a few minutes.

So, any ideas about what was happening? Could we have been running on next-door's solar feed-in?

[JimbobVFR]

Although by no means a hard and fast rule I'd normally expect 2 neighbouring houses to be on different phases of the supply, does sound very odd though.

[Martin4x4]

Brownout

http://en.wikipedia.org/wiki/Brownout_%28electrici...

[karma mechanic]

I understand the brownout idea, but I wouldn't have expected a voltage right down at 70. I've now found a report from Southern Electric that says: 'there had been some quite significant damage to the electricity network following an electrical storm last night.' The failure mode of a substation could be quite interesting when the smoke comes out...

[Morningside]

I have had our voltage drop down to 100 volts before. I only really noticed it because the lights seemed so dull. Computers TV etc normally just about struggle due to being 100v-240v switchmode PSUs.

Has it happened before? Is so, I think they place a box on your supply for a while.

I would be surprised if the Solar panels managed to run other peoples houses and I thought there MUST be some safeguard if total power fail not to try and supply the whole town.

Unless your wires are underground have a look to see who else is on your phase. I have had it before where our side is out and the other side of the street is still on. Have they also had problems.

[tapkaJohnD]

I understand that AC has a waveform to the voltage.
And that that wave form is single for domestic, but may be 'three-phae' for industrial purposes, I thought to provide more power.
And that in a substation, power transmitted as three pahes might be separated into single pahse to supply more homes.
But why would the supply to adjacent houses on the same road be on different phases?.

I've seen our house and our neighbours cut off, and the houses opposite not, but mine is hundred yeras old and those less than twenty, so a new supply.

Just curious.
JOhn

[anonymous-user]

tapkaJohnD said:

But why would the supply to adjacent houses on the same road be on different phases?.

JOhn

Because the power company needs to try to load each phase the same! To do this, they will measure the load on each phase, and split up the loads to try to even out that consumption.

[tapkaJohnD]

Thank you, Max! I can understand that too, even if I can't spell phase. Just trying to understand more.

I live in an estate of houses, about one hundred of them, from a hundred years old to twenty. I have an example of each on either side on my home. There is an electricity sub-station - small brick shed with transformers etc. - that I presume is the supply for all the houses. And I presume that the splitting of three phase (got it right!)from the high voltage mains supply to single phase and sharing those out to the houses occurs there. Would the three phase supply be split to single phases each going down one one of three roads? Simplifying, obviously. Or are there three wires down each road with a feed to 'alternate' houses?

If you can 'alternate' from three alternatives.

JOhn

[spikeyhead]

I've seen both cases, where each phase went to "alternate" houses and where each phase was sent to each street in a development. I think I've seen a case where separate phases were used for either side of the street.

I've no idea how common it is for just one phase to fail, unless it's from localized damage then I suspect it's quite rare.

[Hooli]

Morningside said:

I would be surprised if the Solar panels managed to run other peoples houses and I thought there MUST be some safeguard if total power fail not to try and supply the whole town.

They should be connected so they are isolated from the grid. Otherwise when the power company turn the power off to work on it they could still get electrocuted.

[897sma]

Hooli said:

Morningside said:

I would be surprised if the Solar panels managed to run other peoples houses and I thought there MUST be some safeguard if total power fail not to try and supply the whole town.

They should be connected so they are isolated from the grid. Otherwise when the power company turn the power off to work on it they could still get electrocuted.

It a requirement of the electricity supply regulations (G83 for small domestic) that they disconnect within .4 seconds to stop that scenario. They cannot reconnect until they have measured the grid to ensure its stable.

[trashbat]

I didn't see this at the time but the same thing happened to me, probably around the same date but only briefly and during the day - near Winchester, Hants. The power went off and most stuff shut down, but the microwave, cooker clocks etc didn't lose their times, which they do immediately on switching off the supply, so obviously it was supplying some voltage. Never seen that before.

[PRTVR]

897sma said:

Hooli said:

Morningside said:

I would be surprised if the Solar panels managed to run other peoples houses and I thought there MUST be some safeguard if total power fail not to try and supply the whole town.

They should be connected so they are isolated from the grid. Otherwise when the power company turn the power off to work on it they could still get electrocuted.

It a requirement of the electricity supply regulations (G83 for small domestic) that they disconnect within .4 seconds to stop that scenario. They cannot reconnect until they have measured the grid to ensure its stable.

What would happen if the supply did not fail but was just reduced ? Could you have a situation where power was still being feed back into the grid.

[Hooli]

PRTVR said:

897sma said:

Hooli said:

Morningside said:

I would be surprised if the Solar panels managed to run other peoples houses and I thought there MUST be some safeguard if total power fail not to try and supply the whole town.

They should be connected so they are isolated from the grid. Otherwise when the power company turn the power off to work on it they could still get electrocuted.

It a requirement of the electricity supply regulations (G83 for small domestic) that they disconnect within .4 seconds to stop that scenario. They cannot reconnect until they have measured the grid to ensure its stable.

What would happen if the supply did not fail but was just reduced ? Could you have a situation where power was still being feed back into the grid.

Sounds plausible, I'm not actually sure how the system works though.

[897sma]

It would still disconnect if 6% below or 10% above 230v or if .05% out on frequency

Edited by 897sma on Friday 31st October 11:15