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There are two items where volt drop can have a large impact, magnetic ballast fluorescent lamps, and refrigeration units, there are some other odd items like shrink rap machines, but most items today use switch mode power supplies so volt drop would need to be rather large before it becomes a problem.

However micro generation has resulted in tapping being changed in supply transformers to houses where for years the supply was 245 volt suddenly end up with 230 volt, so a on premises volt drop which has been there for years, now becomes apparent.

It is easy enough to measure the loop impedance of an incomer and loop impedance on a socket, put the results into software and see the volt drop, however with a tolerance of 0.02 ohms on both readings then to claim the volt drop is exceeded presents a problem.

OK if the volt drop is 20 volt one can be reasonably sure it's not a reading error, but at what point if ever would you highlight a large volt drop? And if a contractor has made alteration which cause a volt drop and you don't highlight it, if it causes a problem latter could the owner claim from you?
 
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davesparks

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How exactly are you using loop impedance measurements to establish the volt drop? How are you including the load current into your calculation?

Yes volt drop does matter even if the load can handle a lower input voltage, the volt drop also affects the energy lost through heating of the cable and the potential between N and CPC at the end of the circuit.
 

UNG

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However micro generation has resulted in tapping being changed in supply transformers to houses where for years the supply was 245 volt suddenly end up with 230 volt, so a on premises volt drop which has been there for years, now becomes apparent.
Not sure where you get your facts but the voltage reduction to 230v +10% / -6% was a result of a 1994 EU directive to harmonise voltages across the EU and not micro generation as you suggest. Due to network equipment costs the voltage reduction across the network is an ongoing project that will carry on for many years. Back in the 90's at a Manweb trade event, a presentation was made on the subject and I seem to recall they were looking at an engineering cycle of around 40 years to bring the voltage down to 230v with scheduled equipment updates and that was just the Manweb region
 

davesparks

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Due to network equipment costs the voltage reduction across the network is an ongoing project that will carry on for many years.
It's actually being done? I was under the impression that the change was only a paperwork exercise and never going to actually happen in the real world. I thought even the newest substations were still outputting 433/250?
 

UNG

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It's actually being done? I was under the impression that the change was only a paperwork exercise and never going to actually happen in the real world. I thought even the newest substations were still outputting 433/250?
As I said Manweb's policy back in the mid 90's was to do nothing immediately across the network but as equipment was replaced or newly installed then they would reduce the voltage that might have changed when SP Energy Networks took over . Over the last few years I have come across a few places that have had noticeable drops in voltage close to where work has been carried out on the network with area where the voltages were as low as 216v

The other reason for the gradual changeover was that the voltage harmonisation was to be in 2 parts initially it would drop to 230v and if I remember correctly in the late 90's / early 00's is was supposed to drop to 220v, the last I heard of the drop to 220v from a DNO engineer was that it was still under consideration and due for discussion in the next couple of years but that was back in 2012 and I have not seen or heard anything on the subject since
 
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As to measuring loop impedance if measured at DNO head and at central socket of a ring final, and subtract former from latter then you have impedance of local circuit, so ohms law will give volt drop.

As to micro generation, I am not saying the voltage tolerance was changed as a result, but the tapping often needs changing, the generator needs to cut out once the maximum volt is reached, so if set too high, the micro generators will end up for much of the time locked out, and there will be a complaint, so the DNO is being forced to drop voltage tapping as a result.
 

littlespark

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Forgive me for maybe being dumb at 7:30 in the morning, but where are you getting a current from for ohms law? I only see a resistance and a final voltage?
 

davesparks

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As to measuring loop impedance if measured at DNO head and at central socket of a ring final, and subtract former from latter then you have impedance of local circuit, so ohms law will give volt drop.
You have the impedance of the local circuit with the effects of parallel paths included.

I can see that in theory this method will work, but since its applicable to an existing installation and not design I think its easier just to switch the normal loads on and measure the voltage directly.
 

UNG

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As to micro generation, I am not saying the voltage tolerance was changed as a result, but the tapping often needs changing, the generator needs to cut out once the maximum volt is reached, so if set too high, the micro generators will end up for much of the time locked out, and there will be a complaint, so the DNO is being forced to drop voltage tapping as a result.
I think you are a bit deluded if you think the DNO is being forced to alter tappings to suit micro generation

Pre EU directive 240v +/- 6% gives a voltage range of 225.6v to 254.4v
Post EU directive 230v - 6% + 10% gives a voltage range of 216.2v to 253v as you can see the upper voltage limit changed very little post EU directive

If the supply voltage falls within the limits detailed above the DNO certainly won't be forced to do anything and will do little or nothing unless equipment is being changed within it's normal engineering cycle

There is a bit more to the electricity network than you seem to understand and while micro generation can be a good thing it can also contribute to the local voltage problem you are highlighting if there is a significant amount of localised micro generation which is beyond the DNO's control
 
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Forgive me for maybe being dumb at 7:30 in the morning, but where are you getting a current from for ohms law? I only see a resistance and a final voltage?
On the IET lectures it was stated that for a final ring, you calculate at 20 amp centre and 12 amp even spread, so design current for circuit Ib = 26 amp, although no hard and fast rule, that is how the 106 meters for a ring final is calculated.

This is also why the ring final works so well when compared with a 2.5 mm sq radial, as you still have that 20 amp at end of radial, so only 32 meters with 20 amp radial.

With other circuits the item it supplies will give current, so an immersion heater on a 16A radial will still be calculated at 13A rating for immersion heater. Cooker not so cut and dried, since load can be higher than the MCB size, could be size of MCB or size of appliance, or use diversity.

My question in early years was can it come back and bite us? Could some one measure the impedance of the circuit and claim it has always been too high, so as the installer or the author of the inspection report could we be asked to pay for the correction costs?

However once I built the software (using Java script) to convert loop impedance measured into volt drop, I realised the error of being +/- 0.02 ohms at both incomer and end of circuit means unless the volt drop was really excessive it would be near impossible to prove over the limit, and of course if asked to fit a socket to supply a cooker extractor for example the design current for circuit Ib is the size of the cooker extractor not 13A. So it would be near impossible to prove not to UK spec.
 

Simon47

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If the supply voltage falls within the limits detailed above the DNO certainly won't be forced to do anything and will do little or nothing unless equipment is being changed within it's normal engineering cycle

There is a bit more to the electricity network than you seem to understand and while micro generation can be a good thing it can also contribute to the local voltage problem you are highlighting if there is a significant amount of localised micro generation which is beyond the DNO's control
Indeed, they aren't going to drop the voltage unless they have to. In the main, they have less I^2R losses in their network if they keep the voltagecas high as they can - thus getting to supply more if what they are given to customers instead of heating up their cables !
But as said, where they get complaints, or monitoring flags it up, they will change tappings where embedded generation (which reduces or can reverse the normal "voltage always reduces as you get further down the network" rule that the networks were originally designed for) causes terminal voltages above the upper limit. They will still aim to stay near the upper bounds though to keep their losses down as stated above.
 
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This would mean micro generation can't put power into the grid, they can reduce the power used in the local circuit only, and where you have multiple generators on one transformer those will the higher limits will win.

So if you have 20 houses in a street only one or two can export power to the other houses, the rest will spend most of their time locked out with over voltage.
 

Simon47

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Arms
No, it means that the DNO would get complaints and have to reduce the voltage on that street - or rather, the area served by that transformer. Reduce it enough and the street could feed the grid without inverters tripping - but when the sun went down, the voltage would be lower.
The DNO won't reduce the voltage more than they have to for the previously mentioned reasons.
 
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No, it means that the DNO would get complaints and have to reduce the voltage on that street - or rather, the area served by that transformer. Reduce it enough and the street could feed the grid without inverters tripping - but when the sun went down, the voltage would be lower.
The DNO won't reduce the voltage more than they have to for the previously mentioned reasons.
In other words what I had said about micro generation causing the voltage to be dropped is true?

Before we had any solar panels in the area the voltage at my house was around 245 volt, and the 65 watt fluorescent fitting in the kitchen with a 58 watt tube worked fine.

Now with solar panels fitted voltage around 230 volt and that 15 volt drop is enough to stop the fluorescent light starting so had to replace with a LED tube.

Most things in a house don't really have a problem with volt drop, often they are designed to work with 100 to 250 volt using a switch mode power supply, some old stuff may have a problem, but today all ballasts are electronic, so only remaining new item which is a problem with volt drop is refrigeration units, except for the inverter drive type.

The problem is they have an over load so if the pressure is high when it tries to restart it will trip, then cool and reset by which time the pressure will have dropped, however with a volt drop the over load can trip far more than normal then fail, so refrigeration units can be damaged with excessive volt drop.

There are other odd items, I know we had problems with a shrink rap machine, but in the home fluorescent lamps, and fridge/freezers are the main problem.

However as an electrician we have no idea where an AC, fridge/freezer, or wine chiller will be used in the house. And the main point is can it return to bite us? I would say unless a massive error, no, as to measure volt drop in some way we need to measure the resistance or impedance of the installation, we can measure impedance at the appliance and at incomer then work out volt drop at a set load. However two problems, one is our meters only good to 2 decimal places, so we need to allow for 0.05 ohms error in measuring. And the second is what is the design current of the circuit, often this is not the size of the MCB, although rule of thumb is to use 26 amp design current for calculations with a 32 amp ring final, it is not written in stone.
 

Strima

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Had it on a farm recently which has a shop, cafe and restaurant. Put some temp power in for a sound stage, voltage was right on the cusp at 217 volts at my end of the run, 220 volts in the barn. Switch mode power supplies were happy enough with that.

The whole lot runs off a three 100 amp supply and they have struggled in recent years due to additions with no supply upgrade. I told them we would struggle for power but no one listened.

First band comes on, strikes a chord and the restaurant ovens went into under volt... :D

This has finally got the farmer to contact his supplier to get an upgrade so not all bad.
 

Simon47

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Arms
Eric, I think we are violently in agreement - just discussing different aspects of the topic :rolleyes:
There's two subthreads here - one about harmonisation of voltage limits, one about embedded generation.
Harmonisation isn't changing anything - it was a paper exercise to bring the UK and EU into the same definition but without actually changing anything in the real world. The DNOs aren't going to embrace 220V as the norm because it would increase their I^2R losses (by around 15 to 20% o_O) for no gain.
Where embedded generation is involved, then yes, they will change the taps locally and as little as they can get away with to keep supplies within limits. And I'll bet this will be done on a "when customers complain their inverters trip out" basis*. The downside to doing this is that when the embedded generation isn't producing full output, customers will see lower voltages and potentially problems with some devices - as you've observed.

* Went to a public talk recently given by a chap I've heard talk before on the same subject - smart metering. I did comment that in the 10 years since his previous talk, he had become "rather less positive" about them.
He did say that one of the elements of the business case was that DNOs could use them for widespread voltage monitoring at consumer premises. But, like several other features used in the business case, the meter spec wasn't accurate enough (people writing the spec didn't consult those who'd use the feature) and so they are useless to the DNOs for that purpose :rolleyes: Just one, of many, "cost savings" in the business case that just won't happen.

BTW - I disagree that all ballasts are electronic these days. IME there are still plenty of magnetic ballast/switch start flouro fittings on sale and being installed. I wouldn't pay extra for electronic ballasts for places like lofts etc that are rarely used - for those I really don't care if it takes a few seconds longer and a few "plinks" for them to come on.
 

Simon47

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Arms
I suppose that in extreme, if we keep adding more embedded generation then the DNOs will have to fit automatic tap changers on local distribution transformers. Won't that be fun - and expensive :rolleyes:
Or we just widen the allowed voltage range and accept brownouts as a "normal" thing like some of our friends across the pond do.
 

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