Cable Size

[steptoe]

Have just checked system on PV-sol, which would suggest that 16 250w Suntechs won't work with the SMA 4000TL inverter, in that the system will output 16A for an inverter capable of taking 15.3A (assuming 2 strings of 8 panels)This might explain why inveretr keeps tripping out on sunny days - it's protecting itself from being overpowered. Could you do me a favour and double check exact panel and inverter models to make sure I have modelled the right stuff.

good thinking batman,

actually, SMA have their own design software on their site if you want to prove a point.

 

[newman]

Have just checked system on PV-sol, which would suggest that 16 250w Suntechs won't work with the SMA 4000TL inverter, in that the system will output 16A for an inverter capable of taking 15.3A (assuming 2 strings of 8 panels)This might explain why inveretr keeps tripping out on sunny days - it's protecting itself from being overpowered. Could you do me a favour and double check exact panel and inverter models to make sure I have modelled the right stuff.

Just checked, Inverter is Sunny Boy 4000TL-20, Panels are Sun Tec STP250S-20/Wd+

 

[newman]

No problem with 16 of the Suntech Panels over two strings on a 4000TL inverter according to Sunny DesignSee attached

View attachment 3346

@Newman: How many strings have you got - i.e. how many DC cables (small black ones on LH said of inverter) are there ?

There are 4 ,2 sets of two, I think they are 4 mm

 

[newman]

In that case so long as the strings are equal 8/8 or max of 10/6 then the panels and inverter are perfectly compatible - You should be able to see this as the SMA inverter display flashes between the 2 strings it will show DC volts for each string in turnGrid Fault is Grid Voltage / Freq Problems, in your case cause by the long supply run and associated VD - all a problem associated with the muppet installer

Sorry but the only way round this is

1. Get the installer to install the correct cable for the correct VD as per MCS rules

2. Get the DNO to agree to have the G83/1 settings altered to account for the VD problems

Note - 2 is not the best route and to do this your installer would need to have an SMA grid guard code along with DNO approval to be able to alter the SMA voltage limits

Do you know if your supply is TT, TNS or TNCS ?

Pretty sure its 16mm TN-S

 

[newman]

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 ----------

At least it's not TT then :slap as that would have presented more problems on a TL inverter

Some good news at lasthttp://www.talk.electricianforum.co.uk/images/smilies/Angel.gif

 

[dbicket]

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..

Hi the inverter shutts down for a few mins then trys to reconnect ,only happends on a sunny day, the error code on sunny explorer is Grid Fault 1, the mains supply stays on. It does say on the inverter that the incoming voltage to high(I think} I am at the moment getting the DNO to suply me with a moniter for 14 days to chece the incoming voltageGrid fault 1 on a 4000tl is

The grid voltage has exceeded the permissible range. this error can have the following causes :

The grid voltage at the point of connection of the inverter is too high

or

Grid impedance at the connection point of the inverter is too high

Now you say that the DNO are going to supply you with a meter to monitor the grid voltage? have you been having problems before with overvoltage before for them to to supply this.

Are you close to your local DNO transformer? sometimes this can explain overvoltage if your property is right next to the transformer

As i said before it is possible for the DNO to turn down the voltage going to your property, if you can prove that your supply is outside their regulations.

This is all very simple stuff for your installer or local electrician to check and help you resolve this issue.

Ask your installer to check the fault list from the inverter. This will give a good pattern of when and exactly at what times these faults are happening. This can be done with a laptop with bluetooth, or any of the sma communication range ie sunnybeam.

I can understand where you are coming from,but will not the inverter assume the correct cable will have been fitted in the first place, so, say grid voltage too high

The inverter does not Know what size of cable is fitted it only looks for the correct ranges for its transmission back to the Grid

The max input size for cable on the 4000tl is 10mm

---------- Post Auto-Merged at 15:16 ---------- Previous post was made at 15:08 ----------

Hi are you saying if I find another reason for the inverter triping ,say inverter is set at the wrong settings for a high DNO voltage supply,then I have no need to replace the cable.

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.

 

[ProDave]

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?

 

[steptoe]

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.

 

[ProDave]

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.

 

[newman]

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..

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.

The readings are FW PACK 320 HP 310 SN 2100547258 G83/1 LANGUAGE ENGLISH

 

[steptoe]

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

 

[ProDave]

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.

 

[steptoe]

The readings on any cert could be fictional or real....

just like his competence.....

 

[dbicket]

The readings are FW PACK 320 HP 310 SN 2100547258 G83/1 LANGUAGE ENGLISH

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

 

[dbicket]

The inverter cannot push the voltage up, the grid voltage is fixed, it's like a crowbar and cannot be altered by a small inverter, the only reason current flows from the solar to the DNOs side is due to the dc levels within the inverter, pushing the current one way, it's nothing to do with AC voltage levels.Taking a reading every hour with a volt meter will tell little, it needs a monitor put on the mains for a couple of weeks, the DNO will do this if pushed or you can find a proper firm who have one or hire one.

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]

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.

 

[kme]

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

 

[Manator]

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.

 

[batty]

Don't mention kermit your wake Mrs Streetwalker.

 

[newman]

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