good thinking batman,
actually, SMA have their own design software on their site if you want to prove a point.
Cable Size
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actually, SMA have their own design software on their site if you want to prove a point.
Get the DNO to agree to have the G83/1 settings altered to account for the VD problems
If we went down this route,would the small size cable carry the ampage OK
---------- Post Auto-Merged at 17:31 ---------- Previous post was made at 17:30 ----------
If we went down this route,would the small size cable carry the ampage OK
---------- Post Auto-Merged at 17:31 ---------- Previous post was made at 17:30 ----------
Some good news at lasthttp://www.talk.electricianforum.co.uk/images/smilies/Angel.gif
First can we do one quick check with your inverter to check your on correct settings.
switch off both DC supplies wait 20 secs or so then disconnect AC supply to fully shut down inverter.
Wait until screen on inverter goes blank
Then re apply AC power to inverter,
Take note of the settings on start up, this will scroll along the bottom of the screen as the inverter does its start up procedure,
then switch both your DC isolators back on
Please post your findings..
Yes a bigger cable would reduce the resistance therefore maybe stop you pushing over the max permissible range and shutting down your inverter.
But the voltage at your property might be too high anyway and a cable change might not change anything
I hope this helps... DB
---------- Post Auto-Merged at 17:03 ---------- Previous post was made at 16:48 ----------
Sorry ,lost some of my reply in the originally posted quote from Newman, Silly me.
switch off both DC supplies wait 20 secs or so then disconnect AC supply to fully shut down inverter.
Wait until screen on inverter goes blank
Then re apply AC power to inverter,
Take note of the settings on start up, this will scroll along the bottom of the screen as the inverter does its start up procedure,
then switch both your DC isolators back on
Please post your findings..
MMM , thats a tough one to answer. I need more Info.
Yes a bigger cable would reduce the resistance therefore maybe stop you pushing over the max permissible range and shutting down your inverter.
But the voltage at your property might be too high anyway and a cable change might not change anything
I hope this helps... DB
---------- Post Auto-Merged at 17:03 ---------- Previous post was made at 16:48 ----------
Sorry ,lost some of my reply in the originally posted quote from Newman, Silly me.
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So this voltage discussion is getting interesting.
Let's summarise what we know:
On a "dull day" the OP has seen between 243 and 247V displayed, so it's reasonable to assume that under little, or no generation, that's the incoming supply voltage.
We have established that the submain cable has a resistance of 0.4 ohms theoretical and the installer measured something close to that, so he says.
So at 16A volt drop (increase) will be of the order of 6.5 volts. Yes it's outside the 1% "special" case for solar PV, but within the BS7671 5% limit for a "normal" final circuit.
On a sunny day, the OP has seen 263V displayed before the inverter tripped. That's a whole 13 volts more than the "range" of supply voltages deduced above. The volt rise attributed to generated power and the cable resistance cannot account for that much voltage rise.
EDIT: Canoeboy has confirmed in the following post that the maximum grid voltage is 264V so I think we have established beyond doubt now, that it IS tripping due to excessive grid voltage seen by the inverter.
My guess is the fault is a COMBINATION of the cable resistance, giving "excessive" voltage rise, AND the supply voltage going outside normal limits.
The OP says he's having a voltage monitor fitted for 14 days. It will be very interesting to see what range of voltages it records, and what the DNO's response is to that range of voltages.
My gut feeling is replacing the cable to get within the official "1%" volt drop (rise) might reduce the frequency of inverter trips, but won't completely eliminate the problem, because as already shown, the volt rise cannot be explained just by the resistance of the cable.
It seems again, we have a possible situation where our supply is "harmonised" but the DNO have not, as we all know, actually done anything to harmonise it, and virtually all of us have a supply voltage VERY close to the upper limit, but usually JUST within it. But that does not give much headroom for voltage rise when generating power.
What's needed (and is lacking so far in this discussion unless I have missed it) is a Zs reading of the solar PV circuit or Ze, so we can determine the impedance of the supply. If it's at the end of a long supply cable, then part, or all of the problem may be down to the DNO.
Just to help fully understand this, what are the pre set limits in the Sunny boy for maximum and minimum grid voltage?
Let's summarise what we know:
On a "dull day" the OP has seen between 243 and 247V displayed, so it's reasonable to assume that under little, or no generation, that's the incoming supply voltage.
We have established that the submain cable has a resistance of 0.4 ohms theoretical and the installer measured something close to that, so he says.
So at 16A volt drop (increase) will be of the order of 6.5 volts. Yes it's outside the 1% "special" case for solar PV, but within the BS7671 5% limit for a "normal" final circuit.
On a sunny day, the OP has seen 263V displayed before the inverter tripped. That's a whole 13 volts more than the "range" of supply voltages deduced above. The volt rise attributed to generated power and the cable resistance cannot account for that much voltage rise.
EDIT: Canoeboy has confirmed in the following post that the maximum grid voltage is 264V so I think we have established beyond doubt now, that it IS tripping due to excessive grid voltage seen by the inverter.
My guess is the fault is a COMBINATION of the cable resistance, giving "excessive" voltage rise, AND the supply voltage going outside normal limits.
The OP says he's having a voltage monitor fitted for 14 days. It will be very interesting to see what range of voltages it records, and what the DNO's response is to that range of voltages.
My gut feeling is replacing the cable to get within the official "1%" volt drop (rise) might reduce the frequency of inverter trips, but won't completely eliminate the problem, because as already shown, the volt rise cannot be explained just by the resistance of the cable.
It seems again, we have a possible situation where our supply is "harmonised" but the DNO have not, as we all know, actually done anything to harmonise it, and virtually all of us have a supply voltage VERY close to the upper limit, but usually JUST within it. But that does not give much headroom for voltage rise when generating power.
What's needed (and is lacking so far in this discussion unless I have missed it) is a Zs reading of the solar PV circuit or Ze, so we can determine the impedance of the supply. If it's at the end of a long supply cable, then part, or all of the problem may be down to the DNO.
Just to help fully understand this, what are the pre set limits in the Sunny boy for maximum and minimum grid voltage?
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thinking out loud,
does this mean the resistance of the supply cable is forcing the inverter to overload trying to push its 16A down the cable due to the high resistance?
the DNO really need to fit a voltage monitor at the inverter end as well as the supply end to get some true relative readings imo.
could this possibly lie in the realms of as the inverter 'pushes' its power out at a fractionally higher voltage than the grid, when it gets half way down the cable the grid is now at the same voltage so it hits a 'wall' and cant shift the current anymore?
as I said, just thinking aloud, I dont think this is going to be easy to solve or understand with the limited info we are privy to so far.
does this mean the resistance of the supply cable is forcing the inverter to overload trying to push its 16A down the cable due to the high resistance?
the DNO really need to fit a voltage monitor at the inverter end as well as the supply end to get some true relative readings imo.
could this possibly lie in the realms of as the inverter 'pushes' its power out at a fractionally higher voltage than the grid, when it gets half way down the cable the grid is now at the same voltage so it hits a 'wall' and cant shift the current anymore?
as I said, just thinking aloud, I dont think this is going to be easy to solve or understand with the limited info we are privy to so far.
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It's simple ohms law steps.
the cable is reported to be 0.4 ohms. so if 16A flows, there will be a voltage drop (between source and load) of 6.4V
So when generating, the sunnyboy is the source and the grid is the load. So as the grid is pegged at a (pretty) constant voltage, the inverter must increase it's output voltage in order to drive that current down that resitance to that load.
What's happening is the inverter increases it's voltage, until it hit's it's pre set limit of 264V, then it trips.
As I said a couple of posts back, if the nominal supply voltage is only 247V max, then the volt drop along the cable would not be high enough for the inverter to hit that limit. Somehow we are seeing 13V rise, not the expected 6.4V
So EITHER the cable resistance is in fact a lot higher than calculated and measured, OR the Ze is very high, OR for some other reason, the supply voltage is on occasions going even higher than 247V (or of course a combination of those factors)
I think this thread will go quiet for 2 weeks now until the result of the 14 day supply voltage monitoring test is known.
I think the OP needs to demand the installer comes back to actually measure again and confirm to us what Ze for the supply is and what Zs for the PV circuit is. I'm thinking that Zs may be a whole lot higher than expected, and in fact this circuit may not even be meeting the 5% volt drop of 7671. Make sure he actually measures both of those, not just makes a guess at them.
the cable is reported to be 0.4 ohms. so if 16A flows, there will be a voltage drop (between source and load) of 6.4V
So when generating, the sunnyboy is the source and the grid is the load. So as the grid is pegged at a (pretty) constant voltage, the inverter must increase it's output voltage in order to drive that current down that resitance to that load.
What's happening is the inverter increases it's voltage, until it hit's it's pre set limit of 264V, then it trips.
As I said a couple of posts back, if the nominal supply voltage is only 247V max, then the volt drop along the cable would not be high enough for the inverter to hit that limit. Somehow we are seeing 13V rise, not the expected 6.4V
So EITHER the cable resistance is in fact a lot higher than calculated and measured, OR the Ze is very high, OR for some other reason, the supply voltage is on occasions going even higher than 247V (or of course a combination of those factors)
I think this thread will go quiet for 2 weeks now until the result of the 14 day supply voltage monitoring test is known.
I think the OP needs to demand the installer comes back to actually measure again and confirm to us what Ze for the supply is and what Zs for the PV circuit is. I'm thinking that Zs may be a whole lot higher than expected, and in fact this circuit may not even be meeting the 5% volt drop of 7671. Make sure he actually measures both of those, not just makes a guess at them.
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well we know he has set it for UK setting with the G83/1 bit,
to change that to a bespoke setting requires a code from SMA and permission from the DNO
to change that to a bespoke setting requires a code from SMA and permission from the DNO
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Just one more question to the OP:
Did the installer leave you an EIC (electrical installation certificate) or MWC (minor works certificate) for the electrical work.
They will (should) show the test results and Ze and Zs readings.
If he didn't leave you any paperwork, then that is yet another duty he has failed to honour, and grounds on it's own to get him back to produce the required paperwork. If he has to come back to do any testing in order to do that, be the customer from hell, and follow him around and watch what he does. He should be using a tester to take and record some readings at the incoming supply and at the load as a very minimum. Make sure he takes some readings and records them, don't let him work alone, judging by what he's done so far, he's very likely just to make something up.
Did the installer leave you an EIC (electrical installation certificate) or MWC (minor works certificate) for the electrical work.
They will (should) show the test results and Ze and Zs readings.
If he didn't leave you any paperwork, then that is yet another duty he has failed to honour, and grounds on it's own to get him back to produce the required paperwork. If he has to come back to do any testing in order to do that, be the customer from hell, and follow him around and watch what he does. He should be using a tester to take and record some readings at the incoming supply and at the load as a very minimum. Make sure he takes some readings and records them, don't let him work alone, judging by what he's done so far, he's very likely just to make something up.
just like his competence.....
Everything looks to be set up fine, the G83/1 being the important bit.
I think your next step is to get your incoming voltage checked either with your monitor from DNO or get your pv installer to check this with a fully calibrated test meter.
Get them to test the voltage with the inverter switched both off and on over say maybe a day taking readings every hour.
This will prove if the voltage incoming is too high or if its the inverter itself pushing the voltage up!
Have you had any other electrical problems in the house ie light bulbs popping more frequently than normal or any appliances breaking down shorter than their lifespan.Computer equipment also suffers more from high incoming voltage, any laptop power supplys failing.
cheers DB
Hi Canoeboy,
Sorry dont agree with you there, The inverter must push the voltage up by a few volts to push the current back down the grid. If the voltage remained the same you would not feedback anything.
Voltage drives the current right( or have i finally gone mad)
One of the first things i do when i go into a property is to plug my fluke in and monitor it as i start my remedial work to see if i may have problems with high voltage within the property.Only do this as we have encountered this a few times now in properties when installing pv Especially with the sma range of inverters as they seem to be more temperamental with overvoltage than other makes of inverter.
ivor dispatch
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http://files.sma.de/dl/7418/Netzanschluss-UEN083010.pdf
Hello
Grid impedance is very important, the link shows a graph to show grid impedance, voltage and inverter size.
Have had a couple of installations effected by high voltage low limit trips on G59 settings. The DNO,s do all they can to help, tap change on local transformer but local network will be investigated.
Ask the installer to do a grid impedance test at the intake meter point between L & N and record voltage then the same at the inverter terminals, this might point towards the problem using the graph.
Good luck.
Hello
Grid impedance is very important, the link shows a graph to show grid impedance, voltage and inverter size.
Have had a couple of installations effected by high voltage low limit trips on G59 settings. The DNO,s do all they can to help, tap change on local transformer but local network will be investigated.
Ask the installer to do a grid impedance test at the intake meter point between L & N and record voltage then the same at the inverter terminals, this might point towards the problem using the graph.
Good luck.
Here we go - the old "inverters raise the voltage a bit" argument.
Think about it - its nonsense.
If two systems were installed on the same property, on the same phase, each inverter would have to "push the voltage up" more than the other one for it to work; which it blatantly doesn`t do.
There IS a training company, who are using this description in their notes - but its complete & utter rubbish. Sorry - I`m in canoey`s boat :slap
Think about it - its nonsense.
If two systems were installed on the same property, on the same phase, each inverter would have to "push the voltage up" more than the other one for it to work; which it blatantly doesn`t do.
There IS a training company, who are using this description in their notes - but its complete & utter rubbish. Sorry - I`m in canoey`s boat :slap
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I have never done any PV installations, and to be honest have never been drawn into the foray. I can say though that I am very interested in this thread and the direction it is taking. All I know it that electrical science never changes, and it amazes me sometimes that some would treat DC just as they do AC, there is a defined difference. It does look like some mistakes were made in the initial install and the installer, whilst fully aware of the AC side of the install had little grasp of the DC side. As I am ignorant of this type of install as previously stated I stand to be corrected.
Well done on a very useful debate.
Well done on a very useful debate.
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Don't mention kermit your wake Mrs Streetwalker.
So just to summarize, getting the DNO to moniter the incomming supply is the correct thing to do. The readings on the Electrical Certificate may be false (I think they will be) if anybody needs any readings I will get them.I am contacting NAPIT on Tuesday to complaine. Is there anything else I should do
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