UK Mains distributors propose reducing the voltage by five volts

[paul cotter]

Crash syncing a generator normally takes out the rotating diode assembly but in theory can be much more destructive with the possibility of mechanical damage. I have seen an MCCB with a 20kA breaking capacity welded shut on a 1MVA genset after an ACB developed a delay and missed the sync point. I once crash synced an 800kVA set, due to a wiring error but nothing happened other than a series of breakers tripping.

[Randy222]

goto fix_power_issue

fix_power_issue()
  ukmains.lowerVoltage(-5)
  return

If volts=0 then {printf "problem solved"; exit}
else {goto fix_power_issue}


 

[johansen]

Crash syncing a generator normally takes out the rotating diode assembly but in theory can be much more destructive with the possibility of mechanical damage. I have seen an MCCB with a 20kA breaking capacity welded shut on a 1MVA genset after an ACB developed a delay and missed the sync point. I once crash synced an 800kVA set, due to a wiring error but nothing happened other than a series of breakers tripping.

the washington state ferry system has some boats with 3 diesel generators to drive the electric final propulsion drive, they bring them into synchronization to parallel them.

To save fuel and money they shut 1 generator down and start it up with each crossing, using it only for the final stopping and going power (somehow this is by law, so they don't crash the dock, but they do that occasionally anyways) (i would hope they alternate which generator gets shut down and starts up to save thermal cycling wear and tear, but i don't know)

well the switching elements they built on the Tacoma wasn't rated for 24 operations a day for years (because the engineers didn't know it would be used like this).. so one day it blew up..


motors are funny things, the bigger they get the more inductive as well.. but, the efficiency and internal energy stored also continues to grow with size. at a certain point, maybe 10MVA or so, an electrical short in the stator results in liquid copper faster than you can shut off the exciton to the rotor.

[paul cotter]

Rotating electrical machines sure do store a lot of energy. When doing grid-parallel commissionings I always have had to have a figure for the sub-transient reactance of the alternator/motor to calculate the maximum short circuit current under fault conditions.

[5U4GB]

well the antenna losses would go down despite the IR losses going up

i wonder what the economic costs and chaos would be if they changed the nominal from 50 to 48

A new Netflix show, "The fall of UK by 2 Hertz"
 

"The Fall and Rise of UK Mains Voltages".

[5U4GB]

The UK formally switched from a nominal 240V to 230V on 1 January 1995 to align with European standards.  Users have had over 30 years to adapt.

This happens in other countries as well.  NZ had a major egg shortage in 2022-23 because the battery-hen ban introduced in 2012 alongside the EU and other countries was due to take effect then and factory farmers suddenly realised they had to make some changes after ten years of watching the cutoff date slowly approaching them.

[BradC]

NZ had a major egg shortage in 2022-23 because the battery-hen ban introduced in 2012 alongside the EU and other countries was due to take effect then and factory farmers suddenly realised they had to make some changes after ten years of watching the cutoff date slowly approaching them.

I assume they had to switch from battery hens to mains powered hens..

[soldar]

The UK formally switched from a nominal 240V to 230V on 1 January 1995 to align with European standards.  Users have had over 30 years to adapt.

This happens in other countries as well.  NZ had a major egg shortage in 2022-23 because the battery-hen ban introduced in 2012 alongside the EU and other countries was due to take effect then and factory farmers suddenly realised they had to make some changes after ten years of watching the cutoff date slowly approaching them.

In Spain, and I suspect it was the same in the rest of Europe, they just gradually raised the voltage from 220 to 230 as they replaced transformers. There might have been some problems here and there but I never heard of any. In fact a lot fo people just kept saying "220V" long after the change over and many still do. I have had arguments over the years because many people still believe it is nominally 220V.

I do not understand why in the UK they are making such a huge deal about lowering 5V from 240 to 235V.  The way I see it the distributing network could just announce it and do it and I doubt there would be any problems but if there were they would be totally on the customer.

IMHO they are enlarging this disproportionately.

[5U4GB]

IMHO they are enlarging this disproportionately.

It's the UK, they nearly had civil war break out when they changed the name Finisterre to FitzRoy in the shipping forecast.

[soldar]

It's the UK, they nearly had civil war break out when they changed the name Finisterre to FitzRoy in the shipping forecast.

I am generally against change so I share the feeling. I am all for tradition, pomp, circumstance and a lovely cuppa tea.

Maybe they could have renamed it to "Ceremonial Maritime County of Finisterre, Fitzroy, Waterloo and Blenheim". That would avoid all confusion with the only issue that by the time you finish reciting the name the weather had probably changed already.

[themadhippy]

I do not understand why in the UK they are making such a huge deal about lowering 5V from 240 to 235V.

so much wrong here.The uk is 230V and has been for  about 30 years,there not lowering the voltage, there proposing  to move the lower limit from -6% to -10%

[soldar]

I do not understand why in the UK they are making such a huge deal about lowering 5V from 240 to 235V.

so much wrong here.The uk is 230V and has been for  about 30 years,there not lowering the voltage, there proposing  to move the lower limit from -6% to -10% 

The only thing wrong is that you haven't read the thread and you have not informed yourself of what's going on in the news. That's the only thing wrong.

[themadhippy]

The only thing wrong is that you haven't read the thread and you have not informed yourself of what's going on in the news

Wrong yet again,iv'e read this thread ,and am fully aware of whats going on in the news,i was in fact aware of the proposed change sevral weeks before it even graced the pages of this forum.Even the title of the tread is wrong there is no plan to reduce the supply voltage by 5V.

[Monkeh]

there is no plan to reduce the supply voltage by 5V.

The proposal is to then implement a 1% voltage reduction in the first year and then monitor and assess the impact (including the potential issues outlined in this report). This will be followed by a further reduction of 1% in the second year where acceptable.
This would result in a 2% voltage reduction overall (generally applied on the 11 kV network, therefore impacting both the 11 kV network and the downstream LV network). Currently, customers receive an average voltage of 243 V. Therefore, this proposal would reduce the average voltage to 238 V (an average reduction of 5 V).

[soldar]

The only thing wrong is that you haven't read the thread and you have not informed yourself of what's going on in the news

Wrong yet again,iv'e read this thread ,and am fully aware of whats going on in the news,i was in fact aware of the proposed change sevral weeks before it even graced the pages of this forum.Even the title of the tread is wrong there is no plan to reduce the supply voltage by 5V.

You have not even read the OP:

UK uses 230V -6% +10% giving a working range of 216 to 253 volts
EU uses 230V -10% +10% giving a working range of 207 to 253 volts

UK distribution tends to run closer to 240V which is too close to the upper limit. Now with users also dumping power on to the grid sometimes the voltage exceeds the upper limit and devices like EV chargers trip and disconnect.

So distributors propose reducing the voltage to about 235V and also reducing the lower admissible voltage to align with EU tolerance.

https://www.efixx.co.uk/Articles/Proposed-Changes-to-UK-Mains-Voltage-Limits-Explained

[richard.cs]

reducing the voltage 5% at the consumer 240v range won't affect the efficiency much, its just changing the taps on the upstream regulators. actual I^2R losses at the distribution level of neighborhoods i've been told is negligible.

I agree with the rest but I am not so sure on that last bit. The final distribution is where the currents are highest, and in the UK often where the cables are oldest. Domestic supply impedances in urban areas vary 5:1 or more depending largely on distance to the transformer (0.1-0.5 Ohms is pretty typical), which implies the cable impedance (which is mostly resistive) dominates over both the transformer impedance and the transformed upstream impedance.

That said, the effect of changing taps on efficiency is not going to be that significant. If the voltage drops 5% and the loads are of a type where the current comes up 5%, then the losses will go up 10%, but actually, most loads aren't like that, and even if they were 10% more loss is only 10% of an already small number. Besides, the whole point is not to drop everyone's voltages to the lower limit all the time, but to allow the a tap change that will bring the sunny-day voltage down from 253 V (which might be 260 V if inverters weren't limiting) to maybe 245 V, allowing more solar export, when under current rules that tapping would be disallowed because of the half hour at teatime when the voltage falls under 216 V.

[ejeffrey]

reducing the voltage 5% at the consumer 240v range won't affect the efficiency much, its just changing the taps on the upstream regulators. actual I^2R losses at the distribution level of neighborhoods i've been told is negligible.

I agree with the rest but I am not so sure on that last bit. The final distribution is where the currents are highest, and in the UK often where the cables are oldest. Domestic supply impedances in urban areas vary 5:1 or more depending largely on distance to the transformer (0.1-0.5 Ohms is pretty typical), which implies the cable impedance (which is mostly resistive) dominates over both the transformer impedance and the transformed upstream impedance.

I don't think this follows.

For a single customer the last mile determines the impedance.  But the upstream links are shared by more customers.  Because the losses are I^2R, those aren't independent. 

As a rough example.  Let's assume your local supply resistance is 0.1 ohm and your upstream distribution resistance is 0.01 ohm.  Turn on your kettle that draws 10 amps and you will see a 1.1 volt drop and 11 W losses, 90% of which is in the local loop.

Now imagine 100 neighbors all turn on their kettles.  Your impedance stays the same but the open circuit voltage drops 10 volts. Now when you turn on your kettle, there is the same 10W loss in your local distribution but an extra 100 watts in the upstream network as your 10 amps flows over that 10 volt drop..

[richard.cs]

reducing the voltage 5% at the consumer 240v range won't affect the efficiency much, its just changing the taps on the upstream regulators. actual I^2R losses at the distribution level of neighborhoods i've been told is negligible.

I agree with the rest but I am not so sure on that last bit. The final distribution is where the currents are highest, and in the UK often where the cables are oldest. Domestic supply impedances in urban areas vary 5:1 or more depending largely on distance to the transformer (0.1-0.5 Ohms is pretty typical), which implies the cable impedance (which is mostly resistive) dominates over both the transformer impedance and the transformed upstream impedance.

I don't think this follows.

For a single customer the last mile determines the impedance.  But the upstream links are shared by more customers.  Because the losses are I^2R, those aren't independent. 

As a rough example.  Let's assume your local supply resistance is 0.1 ohm and your upstream distribution resistance is 0.01 ohm.  Turn on your kettle that draws 10 amps and you will see a 1.1 volt drop and 11 W losses, 90% of which is in the local loop.

Now imagine 100 neighbors all turn on their kettles.  Your impedance stays the same but the open circuit voltage drops 10 volts. Now when you turn on your kettle, there is the same 10W loss in your local distribution but an extra 100 watts in the upstream network as your 10 amps flows over that 10 volt drop..

I think I agree, in that yes there is an element of voltage drop further upstream that I add current to without significantly changing the magnitude of it, and therefore does not look to me like impedance but rather a fixed voltage drop. My current then adds to that quasi-fixed drop producing losses higher than I would expect from my measured source impedance alone.

To some extent we are talking different levels of local (in the UK most of my nearest 100 neighbours will likely be on the same transformer as me, in the USA they wouldn't), but I don't think that changes to conclusion: what I observe/measure as a 250 V source with 0.2 Ohms in series, is potentially (when mapped across transformers, etc.) something more like a 270V source, with a very low impedance shared with a lot of load, plus 0.2 Ohms shared with just me and my neighbours. My assumption you could map measured source impedance measurements onto loss distribution was flawed.

[soldar]

I do not want to get into all this nitpicking about increased power loss in the last mile because I think it is very minor and, in any case, the moment to consider it was 30 years ago and not now. It was 30 years ago when the UK decided it was worth changing from 240V to 230V because the advantage of having a voltage in common with the rest of Europe outweighed the disadvantages.

30 years ago UK decided to change to 230V  but then did not do it in practice and stayed at 240V. Now this creates problems. This would have been avoided if the voltage drop had been done long time ago.

[richard.cs]

30 years ago UK decided to change to 230V  but then did not do it in practice and stayed at 240V. Now this creates problems. This would have been avoided if the voltage drop had been done long time ago.

I am yet to be convinced that there are any real problems, 30 years ago there may have been a few, but there was also no particular reason to change anything other than product specifications until embedded generation grew towards current levels. Some places at +10/-6% and others at +6/-10% is fine when all your product standards require them to accept +/-10%. I agree that a few percent on the last mile losses is pretty insignificant.

30 years ago we had tungsten lamps and small electronics commonly used unregulated supplies. Neither is true today, modern loads are generally more tolerant.

[Monkeh]

30 years ago UK decided to change to 230V  but then did not do it in practice and stayed at 240V. Now this creates problems. This would have been avoided if the voltage drop had been done long time ago.

I am yet to be convinced that there are any real problems

Microgeneration being unable to generate due to high grid voltages is a problem. One which can be heavily mitigated without requiring massive changes to infrastructure if the supply voltage is adjusted.

[richard.cs]

I am yet to be convinced that there are any real problems

Microgeneration being unable to generate due to high grid voltages is a problem. One which can be heavily mitigated without requiring massive changes to infrastructure if the supply voltage is adjusted.

Let me clarify, I don't believe lowering the voltage causes any real problems. It clearly solves a real microgeneration problem. It's therefore a sensible thing to do.