ct clamps too close together?

[jouleflow]

Hi,

I have a 16kW array fed to my cu via 3 - 5kW solis inverters. I have a 4kW export limit so each inverter has a ct clamp. The 3 clamps are together on my main incoming cable.

Is it ok to have these 3 clamps touching each other?
How is it decided which inverter to shut down?

We have a lot of tripping issues, the system was installed incorrectly & still doesn't work properly. Could there be interference between the clamps & would them constantly turning on and off randomly be causing the tripping.

Thanks in advance

Greg Webb

 

[UKMeterman]

Well,
Each one will be indepently deciding, I am pushing out too much, need to to turn down the wick. Depending on the control loop and the nature of the local load this could cause instablitlies. You might also want to check the local supply voltage to see if you are tripping on over voltage.

 

[Wilko]

Hi - just trying to understand how the 3 invertors can be limited to achieve 4kW total system output. Are you saying that each of the 3 invertors has their own CT and is independently trying to limit to 4kW? (likely result today being 12kW ...). Or if not, how does each know what the other is doing? If you've a circuit diagram and pics it might help .

 

[jouleflow]

Hi - just trying to understand how the 3 invertors can be limited to achieve 4kW total system output. Are you saying that each of the 3 invertors has their own CT and is independently trying to limit to 4kW? (likely result today being 12kW ...). Or if not, how does each know what the other is doing? If you've a circuit diagram and pics it might help .

Thanks for the reply, I'm not an electrician so I can't say how each one is set up. I strongly believe that each one is set to 4kW so once this is reached one of them will turn down or off, if it still is over 4kW then another will turn down or off. I am positive they are all set up the same.

 

[jouleflow]

here is a pic of all 3 ct clamps in a row on the incoming main cable.

 

[UKMeterman]

Ok a picture paints 1000 words, they need to be clamped round 1 of the 4 cables going into the bottom of the electricty meter!

 

[jouleflow]

Ok a picture paints 1000 words, they need to be clamped round 1 of the 4 cables going into the bottom of the electricty meter!

Thanks, I will try that, it just seems that the clamps will then simply be the other side of the main incoming fuse. Wouldn't they still be sensing the reverse flow to the grid in either position? I am thinking of using the brown cable from the bottom of the fuse to the meter. See pic attached.

 

[UKMeterman]

Yep, that would be the one, if you clamp round the black cable the magnetic field of the flow and return cancel each other out so there is no signal to measure.

 

[jouleflow]

Of course!!, brilliant deduction. Thank you so much, things are never quite what they initially seem. If it is ok I will post again after a few days to let you know how it is working.

 

[sean_ork]

Was this a DIY installation ?

 

[jouleflow]

Was this a DIY installation ?

No a local company put it in last September and I had loads of problems far too many to list here but included no drip loops - ct clamps on the wrong cable - meter frying - loads of "spare" holes in roof, new supply cable from grid - earthing problems etccccccc.

p.s just tripped again!

 

[sean_ork]

Is your supply single or three phase ?

 

[UKMeterman]

Is your supply single or three phase ?

You can see the meter and supply fuse, count the fuses / cables

 

[jouleflow]

single phase.

 

[jouleflow]

If it helps I have an Iboost clamp on the same cable that was removed for the earlier pics. This is the current set up, the Iboost has the white wire.

 

[UKMeterman]

You didn't mention the I boost, lets get one inverter working first!

 

[sean_ork]

Given that the installer appears to have been unable to install the CTs correctly, I very much doubt that they'll have been able to configure those inverters in cascade configuration (If indeed that's even possible with those inverters)

Given the usual SEG limit, did you receive permission to connect that capacity by your DNO, and did they ask to witness test the means of export limitation ?

You might want to start looking for a proven competent installer to have a look over that install.

 

[davesparks]

If each inverter is separately measuring the current to limit itself to 4kW then they will surely all be fighting against each other.

Each inverter would be measuring the combined output of all three inverters but trying to regulate that output as though it is the only inverter on the system.

 

[Gary K]

What are you doing with the rest of the power produced?
Are you heating a swimming pool or do you have another way to absorb the additional power if and when you can control the export to 4KW?

 

[jouleflow]

We have no gas so our electricity usage is high. We do have a pool heater & the iboost use a lot of the power. I try to use enough so the ct's don't limit the inverters. I don't think the concept is correct & maybe one large inverter with one ct should have been the way to go. I can understand the inverters fighting against each other & they are certainly not intelligently linked.

Regarding the dno accepting the install, I left this to the installer & I believe that the ct clamps have to be hard wired to the inverters, which they are, so they are reasonably tamperproof ?

I have been considering asking one of the trade organisations to look over the system. Is this a good idea.

 

[sean_ork]

Good luck getting anyone in a suit looking at it.

Do you get any errors displayed when they fault ?

 

[jouleflow]

The problem is that when it trips, it is in the main house but the inverters are in an outbuilding & often when I get to the inverters they are functioning again. So I haven't see any particular messages but the alarm light has been on occasionally.

Can I assume the trade organisations aren't be too bothered to check on their members work.

 

[sean_ork]

What actually "trips" ?

If you turn two of the inverters off will the remaining one function without issue ?

 

[jouleflow]

We have a split cu in the house & the rcd to on one side trips. None of the mcb's trip. This main cu controls the house plus feeds, one cable to the outbuilding via a 32A mcb. The outbuilding has the inverters which feed back to a garage style cu in the house that has a 100A main switch plus a 63A mcb. From this the + & - cables feed into two henley blocks below the meter.

I haven't tried switching off individual inverters, I am not confident that I could do everything in the correct order or know how to interpret the results.

I did consider disconnecting one of the ct clamps so only two would fight it out, This would give a theoretical maximum feedback of 5kW with the disconnected one running at 100% & the other two turned off by their ct signals. I'm sure this is not the done thing but just something to consider.

The rcd was off this morning, I assume this was due to the inverters start up load.

The rcd that controls the inverter side of the main cu is 80A and 30ms & seems to be the most sensitive part of the whole system. Due to the high startup demands, could this be changed for an 80A 100ms rcd?

 

[sean_ork]

If each inverter has it's own individual AC isolator just turn two off, removing CTs will not do anything helpful.

Has this system ever worked for any extended period of time without faulting ?

 

[Wilko]

Hi - Some invertor manufacturers advise using 100mA RCD on them. If you've the details we might be able to check. Also please confirm if you mean 30mA where you've said 30ms in #24 .
Changing the consumer unit RCD from 30mA to 100mA may not be possible here as the 30mA RCD may still be required for the other circuits.

 

[jouleflow]

If each inverter has it's own individual AC isolator just turn two off, removing CTs will not do anything helpful.

Has this system ever worked for any extended period of time without faulting ?

I will try that when I get home. Is it ac off first then dc off? to turn on is it ac on then dc on?

 

[jouleflow]

Hi - Some invertor manufacturers advise using 100mA RCD on them. If you've the details we might be able to check. Also please confirm if you mean 30mA where you've said 30ms in #24 .
Changing the consumer unit RCD from 30mA to 100mA may not be possible here as the 30mA RCD may still be required for the other circuits.

Sorry I meant mA. The feed from the inverters goes via the garage unit to the Henley blocks so dosen't go through the cu where the rcd trips. I believe the inverters use power from the grid to start up and although this does not go through the rcd could the brief startup cause an imbalance & still trip the rcd?

The inverter is a Solis 4G 5kW single phase.

 

[Wilko]

Hi - thanks - do you know the installation earthing type and any test results?
Ok, what is attached to the RCD that trips?

 

[jouleflow]

Hi - thanks - do you know the installation earthing type and any test results?
Ok, what is attached to the RCD that trips?

The incoming cable was increased to 135mm sq and I think is called tt. It was supposed to increase the available power and the main fuse was increased to 80A. This was also supposed to help with earthing. We are on the end of a line. There are a couple of earth rods that were put in to help years ago, should these be removed now so we just use the grid earth. I believe our earth is atached to the neutral anyway. They tested the ohms to see if the main fuse could be increased and the reading was ok to do so. It was 60A.

Attached to the rcd that trips? I am at work at the moment & I will post when I get home.

To try to solve the initial issues when the solar was installed was that it was originally connected to an existing new upstairs cu in the outbuilding. This cu was designed to have the lights - ring main etc of the upstairs part of the outbuilding. This cu had it's own armoured cable back to the house cu & the downstairs also had it's own cu that also had it's own armoured cable back to the house cu. To try to solve the issue all the upstairs cables were routed downstairs leaving the upstairs cu empty & purely for the solar input.

 

[sean_ork]

I will try that when I get home. Is it ac off first then dc off? to turn on is it ac on then dc on?

Yes, those inverters do have inbuilt export limitation.

If you could confirm how the panels are configured (how many to each inverter) you should be able to get at least one working - don't forget the CTs are directional.

Again, has the system ever worked without faulting for any lengthy period of time ?

 

[jouleflow]

If each inverter has it's own individual AC isolator just turn two off, removing CTs will not do anything helpful.

Has this system ever worked for any extended period of time without faulting ?

Yes it has worked ok but never perfect, the bright weather could be affecting it as the inverters are being capped more than usual.

 

[sean_ork]

It would interesting to view the inverters log files, they should show what grid voltage the inverters are seeing - I suspect it's going above it's expected range.

 

[jouleflow]

If each inverter has it's own individual AC isolator just turn two off, removing CTs will not do anything helpful.

Has this system ever worked for any extended period of time without faulting ?

Yes it has worked ok but never perfect, the bright weather could be affecting it as the inverters are being

Yes, those inverters do have inbuilt export limitation.

If you could confirm how the panels are configured (how many to each inverter) you should be able to get at least one working - don't forget the CTs are directional.

Again, has the system ever worked without faulting for any lengthy period of time ?

I have double checked the cts & the arrow points towards the grid which is the direction of flow it is monitoring.

There are 54 260W panels and split into 18 panels per inverter.
They are all working at the moment, but still unsure if the 3 individual cts are affecting one another adversely.

 

[jouleflow]

It would interesting to view the inverters log files, they should show what grid voltage the inverters are seeing - I suspect it's going above it's expected range.

I did get the installer to make sure the voltage from the inverters was above the grid voltage to make sure it was used in preference to the grid. I don't know how to check the log files I'm afraid.

 

[sean_ork]

I did get the installer to make sure the voltage from the inverters was above the grid voltage to make sure it was used in preference to the grid. I don't know how to check the log files I'm afraid.

That's not quite how it works, but let's hope they've not altered any grid parameters.

You should quite easily be able to figure out how to access the statistics and logs, there's likely to be a Bluetooth connected app.

That'll likely be the second thing on the to do list of anyone you got to site.

 

[jouleflow]

That's not quite how it works, but let's hope they've not altered any grid parameters.

You should quite easily be able to figure out how to access the statistics and logs, there's likely to be a Bluetooth connected app.

That'll likely be the second thing on the to do list of anyone you got to site.

Thanks I will mention this check, I don't do apps etc and the only access I have to any data will be through the display & even then I may need a password to access some stuff.

I remember the output voltage was set to uk & when checked with a meter it was 260V. This was automatically set by the inverter when selecting uk.

 

[sean_ork]

If 260 was indeed your mains grid voltage, you'd probably be best advised to turn all inverters off, and get someone out to site.

That's way outside of the allowable range.

 

[jouleflow]

If 260 was indeed your mains grid voltage, you'd probably be best advised to turn all inverters off, and get someone out to site.

That's way outside of the allowable range.

Sorry Sean, the voltage that was measured was the output voltage from the inverter so automatically set to that when selecting uk. The mains incoming voltage was not checked as I recall at the time but when the subsequent new mains cable was installed by the dno it would have been checked then so should be around 240v.

 

[sean_ork]

Perhaps you've misunderstood what was done during the commissioning, at no point should there have been 260v measurable at the inverters output - the Country code is selected, and its that that defines the grid parameters.

A single, export limiting inverter, on a single phase, is a fairly conventional installation. Cascading, a number of inverters, on a single phase certainly isnt conventional, and given the apparent inability of the installer to correctly fit the CTs I very much doubt they'll have configured the export limiting correctly.

Given what you'll have already invested in your system, I really think you'd be best finding a Solis distributor or support and asking for a site visit - yours isn't a conventional installation so the average PV installer will have a lot of head scratching to do, you need to find someone who knows those inverters.