Solar inverter over voltage reports.

JKenH

1961Nick said:

JKenH said:

I forgot that my plug in energy meter shows voltage. It is quite variable and goes up and down with the sun but the house voltage is around 3v lower than what I am seeing at the inverters.

That still puts the peak over 253v.

However, plug in energy monitors are typically accurate to +/- 3% & many of them only have a range upto 250v. 

I have just tested the mains with my multimeter and am seeing 254/255 when my plug in meter is showing 251.5v. 

I am seeing 254.5 and 255.8 at the inverters. The sun is shining, I am generating 4.3kw and using 3.9kw.

Heedtheadvice

Surely that higher voltage at the inverter is accounted for by the extra three volts or so that the inverter generates to give the potential difference to drive the current to the grid? (Assumption here that you are not measuring at identical moments)

Now if at identical moments (and the meter and inverter are accurate....a big assumption as both will not be necessarily currently calibrated and possibly not that accurate!) then the voltage must be dropped accross the connections between measuring points (connectors, cables switches and fuses etc) inverter to your grid connection owing to the summed resistance of them all and the current flowing from generation.......or a similar or additional voltage drop between grid and where you have your meter connected if on a circuit drawing power such as a ring main.

I would suggest a more in depth analysis  to exclude possible measurement errors ought to be a first step and once excluded a more comprehensive set of measurements and checks.

Heedtheadvice

Note : (I seem unable to edit above post at the moment, no doubt finger trouble!!)

Consider meter (DMM) accuracy. A fairly decent meter such as a Fluke 115 for the AC 600V range specifies an accuracy (up to a period of 1 year after calibration!) of 1% plus three counts. Ignoring counts, 1% of 250v is 2.5, so even that alone could account for most of the reading differences. Then there is the accuracy of the inverter measurement plus any voltage drops here and there. If your meter is a poorer one then it's accuracy is probably worse.

A similar but cheaper Duratool DMM is specified at plus/minus 2% on it's 500V range !!!

JKenH

Heedtheadvice said:

Note : (I seem unable to edit above post at the moment, no doubt finger trouble!!)

Consider meter (DMM) accuracy. A fairly decent meter such as a Fluke 115 for the AC 600V range specifies an accuracy (up to a period of 1 year after calibration!) of 1% plus three counts. Ignoring counts, 1% of 250v is 2.5, so even that alone could account for most of the reading differences. Then there is the accuracy of the inverter measurement plus any voltage drops here and there. If your meter is a poorer one then it's accuracy is probably worse.

A similar but cheaper Duratool DMM is specified at plus/minus 2% on it's 500V range !!!

My meter is indeed a cheap £10 one so I take your point about accuracy as indeed I do Nick9s comments about my plug in meter. Also as you point out the inverter readings I see on the app may not be at the very same moment in time as the other readings. When NPG came to measure the voltage at my meter it was lower by around 3v than my inverter readings so if that difference is maintained when I am seeing 259v the grid voltage is going to be around 256v. 

After the sun has set the voltage measured on my plug in meter drops to around 243/244 volts. At the moment there is a thin veil of cloud, and I am using 1.5kw, generating 3kw and seeing 247.5v on my plug in meter. Turning the panels off dropped the voltage by 3v. 

I have just done a test. With 1.5kw load which is what I was just using, as the sky brightened, (not full sun) I saw 248.5. I then turned on both ovens and two immersion heaters and the voltage dropped to 237.5. I then turned everything off that I was using so my consumption was 300w and the voltage shot back up to 250.5v. In full sun a minute or two later (4.5v generation) I saw 252v. As my problems mainly occur in the afternoon I intend to switch my panels off when the grid voltage is high and see what happens then. 

There is something amiss as in previous years I have not had an issue with the inverter shutting down and it is is always when the sun is shining so I don’t think it is as simple as all 3 of my measuring devices all over reading. 

However I very much appreciate your input. I don’t have any electrical engineering background and every comment I receive adds a little more to my understanding.

NPG emailed me yesterday as follows.

Thank you for your recent enquiry regarding the quality of electricity supply to your premise.

We have not, following immediate investigation, identified a fault on our system that could be impacting the quality of supply to your premises.

The next step is for us to carry out a more detailed investigation. If during this investigation we identify a fault that we can resolve we will let you know. If we do not find a fault we may need to install electricity supply monitoring equipment at your premises and at our local substation.

If this is necessary we will contact you to arrange an appointment to install the equipment. This will enable us to analyse the data collected at your premises and at the local substation and establish if an issue exists

In the meantime please reply to this email or contact us on 0800 011 3332 if you need further information.

Edit: would you consider it normal to get a voltage swing of over 10v (measured on a separate circuit from the cooker and immersion ring mains) when a load of around 11kw is added?

Edit 2: I have just looked at the voltage showing on my Zappi car charger 
and it is approximately 2-3v higher than the plug in meter I am using when the house load is 200w. The Zappi is fed from the Henley block on a separate circuit to the house consumer unit.

The maximum voltage seen by the Zappi is 258.3v.

1961Nick

Multi meters are generally pretty accurate. I've just tested my old cheap analogue one against the more expensive newer digital one & both read 238v. The battery inverter is showing 239.2v (live) & the solar inverter 238.8v (from the app 5min delayed - it's in the loft).

All 4 devices seem to be pretty accurate but I'd be very confident with the multi meter readings.

It's abundantly clear that you have an over voltage issue & the DNO needs to move your tap & reduce the supply voltage by 10v.

A friend in Leicestershire recently had the same problem after a new solar installation (255v) which also caused his inverter to trip. His DNO sorted the problem out the following morning. It shows that there is no need to make a meal out of it! 

1961Nick

Just another thought, it might be worth trying to capture some minimum voltages on your multi meter to see how much the tap can be reduced without breaching 216.2v.

JKenH

1961Nick said:

Just another thought, it might be worth trying to capture some minimum voltages on your multi meter to see how much the tap can be reduced without breaching 216.2v.

Thanks Nick. The Zappi has captured min and max voltages, with the min being 229.5v (max 258.3v). I haven’t seen that high a max today so presumably it is over a long period.

Heedtheadvice

Whilst I might take issue with Nick's assumption that his measurements are pretty accurate because of the closeness of all the readings -they could all be in error- it is a good indication of consistency so that one can be compared with another. I also feel my meter is fairly accurate, but I know it is not calibrated to national standards so cannot be relied upon to measure the absolute voltage rather than a good indication.

 It is still the best way to measure a voltage drop by measuring between the two points on both live and neutral legs rather than reading from separate points in circuits with several unknown error sources, meters inverter measuremnets, circuit position, variations in loads and time. However it is really only for those who know what to do in a safe manner is measurement of mains voltages or between point on such circuits.

I do agree with Nick that the best approach is to let the DNO progress the investigation. They will use known accurate calibrated equipment (or at least they should do!) and they are the only ones who can make any necessary changes to supply voltage. If after that there is still a problem then that is another matter to be tackled.

Plus the idea to look for the min voltage and it does seem that the DNO has the lattitude to reduce voltage to your property but they will also take into consideration, especially in rural areas, voltages at other properties fed from the same transformer.

When I have had a similar problem I have logged voltage against time to see the variation and an indication rather than absolute voltage.

Martyn1981

1961Nick said:

Multi meters are generally pretty accurate. I've just tested my old cheap analogue one against the more expensive newer digital one & both read 238v. The battery inverter is showing 239.2v (live) & the solar inverter 238.8v (from the app 5min delayed - it's in the loft).

All 4 devices seem to be pretty accurate but I'd be very confident with the multi meter readings.

It's abundantly clear that you have an over voltage issue & the DNO needs to move your tap & reduce the supply voltage by 10v.

A friend in Leicestershire recently had the same problem after a new solar installation (255v) which also caused his inverter to trip. His DNO sorted the problem out the following morning. It shows that there is no need to make a meal out of it! 

My earlier post:

So in short (too late), you notify your DNO that you have concerns, and PV shutdowns, they try to fob you off, you stand firm, they fit a monitoring device for a few weeks/months, then they admit there's a problem, change the tappings (whatever that means) and fix the problem.

It's incredible that for some areas, 10yrs on, the same old song and dance routine is necessary.

[Deleted User]

Talk to your DNO. If you have a smart meter, they can milk it for 30 minute voltage data. I was getting 256 volts at night and on the basis of my smart meter data they agreed to fit a voltage recorder. They then tapped my local transformer down to a notional 240volts. I still get voltages as high as 246volts.

For any Powerwall owners, a voltage in excess of 256volts results in a 5 minute disconnection from the Grid.