Will do then.
Where to start diagnosing high voltage spikes?
- Thread starter von555
- Start date
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The high voltage is one problem and should be solved by a tap change at the sub station.
The large range of changes is a separate problem and suggests that the network as set up cannot cope with the variations in load that occur from a local heavy user of electricity. Setting supply voltage high enough to ensure voltage drop on the cable to the heavy user does not drop that user below 230 volt may be the reason your supply is so high.
If this is a new problem have there been any changes in the area.
An example was a pumping station that was upgraded but still fed from the local 230/415 cable that supplied a cluster of houses. Before the upgrade the low power pumps ran for long periods of time. The affect on supply voltage was noticable but excessive. After the up-grade the more powerful pumps ran for much shorter periods of time. The effect on changes in voltage was then very noticable and a new 11Kv supply for the pumping station had to be install.
Another possible cause . Are you anywhere near a railway line with overhead ( 25 kv ) traction supply and do the peaks and troughs of voltage match to passing trains. The 25 kv overhead system uses ground return for its "neutral" and voltage gradients in the earth can be high when a train passes, ( not dangerously high thanks to linked rails spreading the ground contact area ) but still high enough to affect ground rods used for earthing nearby property and communication systems. It is possible these could also affect domestic supply network Neutrals if those Neutral have multiple connections to ground rods close to the track. The traction currents prefering to take the low impedance route along the network Neutrals and thus creating voltage differences alaong the Neutral which would affect the voltage at the domestic consumers.
It would help to add the start and end times to the graphs to relate peaks and troughs to events such as tea time kettles etc.
The large range of changes is a separate problem and suggests that the network as set up cannot cope with the variations in load that occur from a local heavy user of electricity. Setting supply voltage high enough to ensure voltage drop on the cable to the heavy user does not drop that user below 230 volt may be the reason your supply is so high.
If this is a new problem have there been any changes in the area.
An example was a pumping station that was upgraded but still fed from the local 230/415 cable that supplied a cluster of houses. Before the upgrade the low power pumps ran for long periods of time. The affect on supply voltage was noticable but excessive. After the up-grade the more powerful pumps ran for much shorter periods of time. The effect on changes in voltage was then very noticable and a new 11Kv supply for the pumping station had to be install.
Another possible cause . Are you anywhere near a railway line with overhead ( 25 kv ) traction supply and do the peaks and troughs of voltage match to passing trains. The 25 kv overhead system uses ground return for its "neutral" and voltage gradients in the earth can be high when a train passes, ( not dangerously high thanks to linked rails spreading the ground contact area ) but still high enough to affect ground rods used for earthing nearby property and communication systems. It is possible these could also affect domestic supply network Neutrals if those Neutral have multiple connections to ground rods close to the track. The traction currents prefering to take the low impedance route along the network Neutrals and thus creating voltage differences alaong the Neutral which would affect the voltage at the domestic consumers.
It would help to add the start and end times to the graphs to relate peaks and troughs to events such as tea time kettles etc.
Updated graph with annotations. Hope it is clear:
I don't have a lot of ideas about the cause. We are somewhat near a railway line. We are also near Scotland's largest construction project: the new Forth road crossing. I asked the DNO engineer if that could be the source of the problem and he didn't think so.
I'm still planning to ask them to install a voltage recorder. It was suggested by the DNO engineer, who then decided to dig up the street instead.
I don't have a lot of ideas about the cause. We are somewhat near a railway line. We are also near Scotland's largest construction project: the new Forth road crossing. I asked the DNO engineer if that could be the source of the problem and he didn't think so.
I'm still planning to ask them to install a voltage recorder. It was suggested by the DNO engineer, who then decided to dig up the street instead.
The shape of the graph is fairly typical of what I see on a regular basis, just a bit on the high side, if the substation was showing similar voltages as I;ve said I would adjust it down by 2.5% (6V) which would put the voltage within optimum limits (don't for get it can go down to 216, but we avoid going below 220 if at all possible)
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Is it likely the UPS is not reporting the line voltage accurately? I do have a plug in meter https://energenie4u.co.uk/index.php/catalogue/product/ENER007 but without logging can't check on the variability. I've been noting values every time I go past, but can't overnight etc?
In some respects it's up to the DNO to show you are getting the correct volts, if the UPS was out by a large margin it would be suspect.
Hmm, these guys obviously have never seen your supply!
http://www.bbc.co.uk/news/science-environment-20629671
http://www.bbc.co.uk/news/science-environment-20629671
DNO engineer just visited. Again. I showed him my graph and he checked out the supply. Says it dropped from 251 to 240 which he said is odd. He's recommending a voltage recorder. So hopefully we'll find out if it is as variable as the UPS is suggesting.
Thought I would post an update. Things went quiet over the festive period, but the DNO did say they would be back to install a voltage recorder. I had to keep phoning them, and they said they'd get onto it. Anyway they were supposed to be here on Tuesday, but instead ended up digging up a street away from me. Apparently it is a problem with the area and they're now not going to install a voltage recorder as they're installing new towers (or something like that). I've been assured that it will be sorted after this!
Bit of a palaver, but that's life.
Bit of a palaver, but that's life.
Time to sort out those voltage sensitive electrical items that have recently packed in!! 
**
Would the DNO be liable if they've been supplying over voltage for a significant time?
If so, it would appear to be fortunate for them that 99.9% of households haven't the gear/ wouldn't know how to monitor their incoming supply.
** I've a couple of t.v's you can have!!!
**Would the DNO be liable if they've been supplying over voltage for a significant time?
If so, it would appear to be fortunate for them that 99.9% of households haven't the gear/ wouldn't know how to monitor their incoming supply.
** I've a couple of t.v's you can have!!!
Yeah, I was thinking of charging them for all the bulbs and computers that have blown. Who knows how long it was dodgy for? My old UPS did used to do funny things, and I just put it down to being cheap.
But seriously, I'm just glad they're not digging up my next door neighbours' drive again!
But seriously, I'm just glad they're not digging up my next door neighbours' drive again!
or yours!
Funnily enough my brother was saying they are getting a lot more over-volts complaints now that embedded generation is increasing. Apparently management aren't keen on lowering the voltage a bit generally as that increases their losses*.
* In case anyone is wondering why ...
Reduce the system voltage, and with the amount of switch mode stuff running these days you don't reduce the current in proportion. Hence the I^2R losses in the distribution system increase as a proportion of power supplied to customers.
It's not that. As you go along the cable from supply to load, voltage reduces due to the resistance - Ohms law (V=IR), though there are slight complications in AC systems. Also there are losses in the transformers. Normally, all this is adjusted for at substations with "tap changers". There are multiple taps on the transformer so the output voltage can be adjusted, with changes being made by special make-before-break switches called tap changers (yes, this does momentarily short a few turns in the transformer during operation). I believe most of the tap changers are manual and will be set and left unless there's a problem.
Now, daily load, and hence volt drop, changes during the day, and typically results in the sort of voltage changes seen by the OP. In the early hours, load is lightest and the voltage rises. During the day load increases and voltage reduces. The exact pattern varies (ours is slightly different at work because we are in an area with large commercial loads and not a lot of residential load). Also, in a small hamlet, on the end of a long line, where several houses have night storage heaters you can get significant effects as they turn on and off.
But consider what happens as embedded generation increases - solar PV being the most significant in a domestic setting, but there are also wind turbines and small hydro. One of my customers at work has an 80-something kW hydro turbine connected to the 415V supply in the middle of nowhere - I bet that has an impact on supply voltage, especially if for some reason it trips when running at full load.
Instead of voltage decreasing between supply and load, it would (in theory at least) be possible for it to increase if the generation is more than the load. The aforementioned hydro plant will most definitely produce more than the farm and handful of surrounding houses use.
So that's the first issue - the supplier can no longer rely on a certain amount of volt drop.
But it gets worse. Renewables are highly variable - Solar PV drops to 0% output at least once per day. So the overall variation in current, and hence volt drop, in the supply chain is even more variable.
Looks very much like the graphs I do from our UPS. Except that we have a number of steps superimposed on the daily up and down which I suspect are tap changes at the grid substation round the corner.Updated graph with annotations. Hope it is clear:
Generally the automatic tap-changers are on the 33kV to lower HV voltage level with the tap-changers at the 400/230V transformers being manual and off circuit (dead).
We are experimenting with auto tap-changers at this voltage level to take account of local generation & the expected load changes as the gas runs out (whenever that will be).
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