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Topic Title: DNO voltage limits
Topic Summary: What is the maximum voltage permitted at the consumers terminals.
Created On: 08 October 2018 08:06 PM
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 08 October 2018 08:06 PM
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HarryJMacdonald

Posts: 494
Joined: 15 May 2002

A club I am a member of has just had solar PV panels fitted, the microinverter type.
On very sunny days several of the microinverters report that they are not generating as they have tripped on overvoltage - set to 264V.
(I note that this is 240V + 10%.). They usually start generating again quite soon.
Should I be asking the DNO to investigate? What is the UK limit for voltage these days?
 08 October 2018 10:07 PM
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mapj1

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Joined: 22 July 2004

when you are the load, so the voltage drop between the TX and you is downhill, 230V +/-10%, so 208 to 253 volts.
OF course when you are generating the voltage slope is reversed, so it may be 260 at the inverter and yet still just in spec at the DNO terminals, depending on the current and voltage drops involved.
How far are the inverters from the main terminals, what is the voltage there, and in turn how far is that from the substation?
It may be possible to get the substation turned down a tap or two, (2.5% or maybe 5%) but that depends how many volts the other users on the same feeders are getting.

-------------------------
regards Mike


Edited: 08 October 2018 at 10:31 PM by mapj1
 08 October 2018 10:08 PM
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daveparry1

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I seem to think the tolerance is -6% +10%, I might be wrong though!
 08 October 2018 10:40 PM
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mapj1

Posts: 11252
Joined: 22 July 2004

actually you may be right, we may never have finally ratified the last step in pan European harmonisation.
The upper limit I'm more sure of.
might be interesting

-------------------------
regards Mike
 08 October 2018 11:17 PM
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broadgage

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Originally posted by: daveparry1

I seem to think the tolerance is -6% +10%, I might be wrong though!


I agree.
 08 October 2018 11:58 PM
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alancapon

Posts: 7343
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Originally posted by: daveparry1
I seem to think the tolerance is -6% +10%, I might be wrong though!.

Correct.

The idea of a lower limit of -10% has been spoken of, but nobody has the bottle to propose it. The fear was trying to persuade 240V equipment to operate at 207V was a step too far.

Regards,

Alan.
 09 October 2018 08:56 AM
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gkenyon

Posts: 5193
Joined: 06 May 2002

Originally posted by: alancapon

Originally posted by: daveparry1

I seem to think the tolerance is -6% +10%, I might be wrong though!.


Correct.



The idea of a lower limit of -10% has been spoken of, but nobody has the bottle to propose it. The fear was trying to persuade 240V equipment to operate at 207V was a step too far.



Regards,



Alan.
Sorry for being a little picky here, but I just want to clear something up.

Whilst BS EN 50160:2010+A1:2015 Voltage characteristics of electricity supplied by public electricity networks specifies the nominal supply voltage and frequency, and permitted ranges of variation (for voltage this is usually +/- 10 %, but in some cases, may be + 10 % / - 15 % if I remember correctly), Regulation 27 of ESQCR specifies tighter limits that are within the range in BS EN 50160, i.e. +10 % / - 6 %.


However, the supply voltage is not the equipment utilization voltage. There is a further voltage drop within the installation - according to BS 7671, this 5 % (of nominal) voltage drop for circuits other than lighting, or 3 % voltage drop for lighting circuits.

Hence, at the point of use, equipment may see a utilization voltage of 230 V + 10 % / - 11 % (204.7 to 253 V), and lighting loads may see a utilization voltage of 230 V + 10 % / - 9 % (209.3 to 253 V).


Equipment manufacturers should use BS EN 60038 (IEC 60038) as their design standard in this respect, and reference is made to HD 60364-5-52 in EN 60038 (and IEC 60364-5-52 in IEC 60038), which have the same voltage drop as BS 7671.

Therefore, for the most part, equipment intended for use in the EU should be able to cope with a utilization voltage range of at least 195.5 to 253.0 V, and lighting loads should be able to cope with a utilization voltage range of 200.1 to 253.0 V.

In the UK, however, the utilization voltage range will be well within this, 204.7 to 253.0 V, and lighting loads 209.3 to 253.0 V.

Before anyone asks, I suspect the UK considered that there was a lot of equipment in use prior to supply voltage harmonization, that might be damaged, if the supply voltage were lowered to the full 230 - 10 %.

-------------------------
EUR ING Graham Kenyon CEng MIET TechIOSH
G Kenyon Technology Ltd

Web-Site: www.gkenyontech.com

Edited: 09 October 2018 at 09:07 AM by gkenyon
 09 October 2018 09:13 AM
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gkenyon

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Incidentally, if we take the view going forward, that we should complete harmonization (perhaps to save energy by lowering the supply voltage, so ESQCR permits the lower end of the range to be 230 - 10 %), as only a small amount of "pre-harmonization" equipment will be in use today, that is likely to impact BS 7671 design criteria.

In particular, it may be necessary to lower::
- Cmin down to 0.9 from 0.95
- maximum EFLI tables in Chapter 41 by an amount equating to Cmin moving from 0.95 to 0.9.

... and this would therefore have an impact on whether we considered some installations with circuits near the limits to continue to meet safety requirements of BS 7671 going forward ...

-------------------------
EUR ING Graham Kenyon CEng MIET TechIOSH
G Kenyon Technology Ltd

Web-Site: www.gkenyontech.com
 09 October 2018 09:37 AM
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arg

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Originally posted by: gkenyon
(perhaps to save energy by lowering the supply voltage, so ESQCR permits the lower end of the range to be 230 - 10 %),


Why would lowering the supply voltage save energy?

Is this the old "voltage optimiser" canard that only works with the kind of unregulated simple loads that are rare with modern equipment (and makes things worse with loads that draw more current to compensate)?

Or something else that I've missed?
 09 October 2018 10:55 AM
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mapj1

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no, it is exactly that.
In a hard science world, we would be looking at increasing the voltage to make the distribution more efficient, not lowering it so that everyone's motors ran the risk of stalling anbd the cable losses were worse.

Actually I suspect if tthe LV boundary was at 1.2kV rather than 1.0, we'd see more 690/1k2
three phase installed on large area industrial estates and things, rather as we already see 400/690 to augment the 230/400 where distance and voltage drops are a problem.
Actually I've only seen 690 single phase once, and that was at a Siemens plant in Germany, but that was the sort of place you really wanted a bike to save time walking from one end to the other, and they were quite capable of re-writing their own rules and having a transformer at each end would not worry anyone. (they may have called it 660/1K1 but some thing like that)

-------------------------
regards Mike
 09 October 2018 11:35 AM
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gkenyon

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Originally posted by: arg

Originally posted by: gkenyon

(perhaps to save energy by lowering the supply voltage, so ESQCR permits the lower end of the range to be 230 - 10 %),




Why would lowering the supply voltage save energy?



Is this the old "voltage optimiser" canard that only works with the kind of unregulated simple loads that are rare with modern equipment (and makes things worse with loads that draw more current to compensate)?



Or something else that I've missed?
http://www.energynetworks.org/...lts-working-group.html

If you look through the consultation papers, you'll see the supposed rationale in terms of energy savings, however, as Mike pointed out, and as attested by the relevant comments received, it's perhaps not all that simple!

-------------------------
EUR ING Graham Kenyon CEng MIET TechIOSH
G Kenyon Technology Ltd

Web-Site: www.gkenyontech.com
 09 October 2018 12:11 PM
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mapj1

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It is of course cheaper for the DNOs to widen the permitted voltage limits than to put more transformers in, and the full range is not being used as it is.
The price is the end users equipment reliability. A few things, filament lamps come to mind, last much longer on underspec voltages, but nearly everything electronic nowadays (less than 10 yeasr old say) draws more current to compansate when the voltage falls. Series wound moters just run faster or slower, and induction motors start-up times vary.

allowing the option to supply at pre-agreed other voltages might be more use.

-------------------------
regards Mike
 09 October 2018 11:57 PM
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alancapon

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Indeed, and with the upper limit still in excess of 250V, the ESI standard transformer still has a 433V secondary at nominal tap, just like it always did. What it will do, is allow alternate DNO network configurations for faults / maintenance that wer previously regarded as borderline / poor, to be regarded as acceptable. With the increased loading of the DNO distribution network, particularly with the predicted increase of EVs (electric vehicles) there is unlikely to be an appetite for reducing the voltage under normal circumstances.

Regards,

Alan.
 10 October 2018 09:58 AM
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arg

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Originally posted by: gkenyon
http://www.energynetworks.org/...lts-working-group.html


If you look through the consultation papers, you'll see the supposed rationale in terms of energy savings, however, as Mike pointed out, and as attested by the relevant comments received, it's perhaps not all that simple!


An interesting read, thanks.

The main thrust of their work seems to be the issue of allowing more distributed generation (rooftop solar) without exceeding the upper limit - if the lower limit is dropped, then the 'typical' voltage can drop, leaving more headroom for distributed generation to push the voltage up without tripping out on overvoltage.

However, the paper does report an experiment where they dropped the supply voltage by 0.88% and got a "statistically significant" reduction of total energy consumed by 1.16%. If the loads were pure resistive and unregulated (ie. no thermostatic controls to make the loads run longer at lower power), you'd expect 1.55%. So this result suggests a surprisingly high level of these crude resistive loads.

There was apparently no further work to understand how this result came about, and the rest of the paper makes the assumption that this will happen in general - that a reduction in voltage will result in a significant reduction in demand, which they rely on for stability after fault or excess demand events (where the reducing voltage could cause the distributed generation to stop on undervoltage trip, adding to the problem).

It's not particularly surprising that a short-term reduction in voltage will reduce demand - there are a lot of resistive heating loads which will simply run for longer to deliver the same energy. Whether that will continue forever seems questionable - if people switch resistive heating for heat pumps, those will typically draw more current at the reduced voltage.

And even with the present day mix of loads, it does seem very surprising that a long term energy saving can be made. Are there really that many heating loads running flat-out (no thermostat, or never managing to hit the set temperature?). Obviously there will be some, but those will be offset by the electronic loads that take more current and therefore use more total energy due to voltage drop in wiring.

Obviously my armchair analysis has to bow to the report's measured results, but it seems hard to explain.
 10 October 2018 02:09 PM
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HarryJMacdonald

Posts: 494
Joined: 15 May 2002

Back to the original question!
The club has a fairly large single phase load so the panels are all on this phase to maximise the amount used on site.
This phase is measured by my (uncalibrated) meter at about 264V which is also what the microinverters say they trip at. The other two phases, which have no generation connected, are also above 260V on my meter.
I intend to get hold of a calibrated meter, but can I take it that the voltage limit (with no generation, should not be above 253V?
 10 October 2018 02:51 PM
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mapj1

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At the DNO connection yes.
And if I were you I'd try and get contact info of an area engineer, rather than be fobbed off by the "have a nice day" office team, as it may well be possible to get it wound down a click or two, but it needs someone who understnads the local substion and the layout of users

-------------------------
regards Mike
 10 October 2018 03:12 PM
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gkenyon

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Originally posted by: mapj1

At the DNO connection yes.

And if I were you I'd try and get contact info of an area engineer, rather than be fobbed off by the "have a nice day" office team, as it may well be possible to get it wound down a click or two, but it needs someone who understnads the local substion and the layout of users
Good advice Mike.

-------------------------
EUR ING Graham Kenyon CEng MIET TechIOSH
G Kenyon Technology Ltd

Web-Site: www.gkenyontech.com
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