Low voltage on mains - what causes this?

[Rollerball]

Due to high winds, just had a brief blip on the power followed by the lights dimming and staying dimmed and some mains powered devices failing to work (or failing to work as the voltage dipped ever lower).

Phoned the electricity company, they advised to power off all mains devices and only leave on a few (dim!) lights as needed.

After about an hour the power went off completely and a few seconds later came back on at full power (hence me being able to type this).

I'm curious though - what causes such a prolonged running at low voltage (slowly getting lower over time)? I've experienced plenty of power cuts in my time, but never running on low voltage for such a prolonged period.

Feel free to be as technical as you like.

 

[Spark123]

Probably one of the phases in an overhead HV line had popped a fuse, the blackout was when the DNO pulled the fuses to change the blown one.

 

[Chri5]

Nature.

It sometimes looks so innocent

Blame 70mph winds, load of ran and various network issues.

 

[Rollerball]

Probably one of the phases in an overhead HV line had popped a fuse, the blackout was when the DNO pulled the fuses to change the blown one.

Ah ha, that's what I said to my wife (well, to be exact: "I guess a fuse has blown").

However, why was there still power at a low voltage? Is it a safety feature at the sub-station (or whatever) so that all of the power isn't going down one line instead of being more evenly distributed?

 

[Spark123]

It isn't a safety feature. Transmission lines from the power station to the local substation (and probably up the road to infront of your house) are 3 phase.
If we lose a phase on a transmission line the other two phases will continue to send power to the downstream transformer, the result being a lower than normal voltage being apparent on the 3 phase output of the transformer.
The phases in the front street are made up of a mixture of the phases in the transmission lines, this being made up from the Delta-Star transformer at the local sub hence all 3 phases in the street will appear to have some voltage on them but not necesserily in the correct phase.

 

[Rollerball]

Thanks for the explanation.

 

[maguire]

Chri5 is that your gaff down there
DM

 

[Rollerball]

That's his holiday home.

 

[Chri5]

I wish, unfortunately my wife has some form of xenaphobia- she won't leave London...... So i'm unlikely to ever get the chance for such a dreamscape

 

[Steve]

Out of interest, your computer and anthing with a SMPS was probably ok to be left on as long as the voltage was >100 volts.

 

[dingbat]

... my wife has some form of xenaphobia- she won't leave London....

I would have thought the last place a xenophobic would want to live would be London!

 

[plugwash]

Another thing that can cause big problems is a neutral break on the low voltage side. With the neutral broken the phase-neutral voltages beyond the break will depend on how different phases are loaded swinging anywhere from nothing up to 400V.

If the power is behaving in dodgy ways disconnecting anything of value is a bloody good idea to reduce the risk of it getting fried.

 

[Rollerball]

Disconnecting as in pulling out all plugs from their sockets, or just switching off at the wall sockets?

 

[RF Lighting]

You'd be best off to completely unplug them just to be sure.

 

[Rollerball]

Thanks. And how about the lights?