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Topic Title: voltage variations
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Created On: 03 February 2017 12:52 AM
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 03 February 2017 12:52 AM
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kellyselectric

Posts: 186
Joined: 22 July 2016

Today around 5pm ish we suffered a series of voltage dips very noticeable and prolonged dips and then return to normal it happened many times over the next hour or so then just settled back to normal now why would this be we have no overhead wiring here apart from the 400Kv grid I live in Weymouth Dorset if that helps
 03 February 2017 12:51 PM
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broadgage

Posts: 2448
Joined: 07 August 2007

Was not something very similar reported a week or two ago ?

Brief dips or even brief interruptions can of course be caused by wind, perhaps at a considerable distance away, Auto reclosing grid circuit breakers generally restore normality in a second or so.

However prolonged dips in the voltage suggest something else.
Are we perhaps seeing the early signs of grid instability caused by lack of traditional rotating alternators on the system, and an excess of capacity connected via static converting plant.

Any such instability would be worsened by the present prevalence of switched mode power supplies.
In the past, if a nominal 240 volt supply dropped briefly to about 120 volts, most loads would draw less amps and thereby assist in restoring normality.
These days many SMPS would continue to operate at half the normal input voltage and would draw twice the nominal current thus further depressing the voltage.
Remember that electronic lamp ballasts and variable speed motor drives are species of SMPS.
 03 February 2017 01:13 PM
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rocknroll

Posts: 9549
Joined: 03 October 2005

Well it has been extremely windy in the S and SW for a week now, coming along the 35 and 354 heading Blandford this morning the car was taking a fair old buffering in open spaces.

Regards

-------------------------
"Take nothing but a picture,
leave nothing but footprints!"
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"Oh! The drama of it all."
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"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"
-------------------------
 03 February 2017 01:18 PM
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potential

Posts: 1641
Joined: 01 February 2007

I think the voltage drops were being caused by the result of wind on wires and trees for the most part.
Wind was generating about 27% of demand last night, its dropped since then.
I don't think the capacity of the grid is being stretched but may be weak in some areas.
 03 February 2017 08:14 PM
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kellyselectric

Posts: 186
Joined: 22 July 2016

Thankfor all for your replies I found out the cause of the dips this morning. SSE rocked up about 11am and dug a big hole right were they did a previouse repair a few months ago they removed a section of cable and a joint leaving just the 2 ends in in the hole. We didn't have any powercuts so presumably were off the same tx just from a different direction
 03 February 2017 08:29 PM
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acsinuk

Posts: 210
Joined: 30 June 2007

If the grid is near overload then Natgrid control might consider locking the tap changers and reduce the voltages which will result in lower voltage but will save the system from collapsing. Just be patient please. You might consider running a DC battery backup system for lights and telecoms.
 03 February 2017 09:28 PM
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broadgage

Posts: 2448
Joined: 07 August 2007

Yes voltage reductions are possible at times of high load, but the load was an entirely normal about 40GW at the time.
About 8GW from wind and only about 15GW from gas with about another 10GW available from gas if needed.

So no shortage of generating capacity last night. That is why I wondered about instability caused by an excessive proportion of that capacity being from static converters rather than rotating machinery.
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