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.