Main Breaker tripping constantly, what is the problem?

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zach.bes

Member
Location
Porterville
Hello All,

The main 400A breaker (with 300A shunt) keeps tripping at a newly commissioned 215KW solar site. We can't for the life of us figure out what is causing it. I'm starting to suspect that since we didn't pull a neutral conductor between the step up and down transformers that it is causing the constant tripping. Would you mind looking over the attached spec to see if maybe this could be the reason for the problem?

505deec12f537e5f360b183a0d72b2ac.jpg


Thanks

Zach


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GoldDigger

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Staff member
Location
Placerville, CA, USA
Occupation
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Not running a neutral to the inverters (what make and model) could cause problems with errors from the inverters, but it is hard to see why that might cause the AC main to trip.

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jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
Can you elaborate on 'constantly tripping?' If the tripping has no relation to when the sun is shining and the system is generating output, then it would stand to reason it is more likely an installation or manufacturer defect, and not a design issue.
 

iwire

Moderator
Staff member
Location
Massachusetts
Just food for thought.

Could it be mischief by someone?

We would put a recording meter on the circuit to help troubleshoot this.
 

Sahib

Senior Member
Location
India
Zac.bes: Have you meggared the electrical installation prior to commisioning? What are the insulation resistance values?
 

kwired

Electron manager
Location
NE Nebraska
We would put a recording meter on the circuit to help troubleshoot this.

I agree, one needs to know what the current is and if it is too high then the next step is finding out why it is too high.

If it is not too high it might be a malfunctioning breaker or some adjustable component is set wrong.
 

zach.bes

Member
Location
Porterville
Can you elaborate on 'constantly tripping?' If the tripping has no relation to when the sun is shining and the system is generating output, then it would stand to reason it is more likely an installation or manufacturer defect, and not a design issue.

I'm thinking it must be a faulty breaker.


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zach.bes

Member
Location
Porterville
Just food for thought.

Could it be mischief by someone?

We would put a recording meter on the circuit to help troubleshoot this.

I've thought of hooking up a data logger to see what's going one. I guess this is the next step.


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pv_n00b

Senior Member
Location
CA, USA
Maybe a bad CB. Maybe a ground loop because you have every neutral grounded, which significantly increases the possibility of ground loops.
 
I wish I could help with your question. However, I do have one of my own. What is the reason your step up and step down transformers are Y-Y rather than Y-Delta? The absence of a neutral and non-compliant bonding seem to be an issue. Won't the system produce unbalanced currents which will be forced to use the 6 Thhhn as a current carrying conductor? In the event of the ground wire bieng compromised it appears the bonding at the step down transformer would produce voltage gradients and a risk of electrocution.
 

zach.bes

Member
Location
Porterville
I wish I could help with your question. However, I do have one of my own. What is the reason your step up and step down transformers are Y-Y rather than Y-Delta? The absence of a neutral and non-compliant bonding seem to be an issue. Won't the system produce unbalanced currents which will be forced to use the 6 Thhhn as a current carrying conductor? In the event of the ground wire bieng compromised it appears the bonding at the step down transformer would produce voltage gradients and a risk of electrocution.

I had the same question for the designer. Seems odd to go y-y on both ends of the transformers. But I'm not an engineer, I just install per spec, with the occasional question here and there.


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zach.bes

Member
Location
Porterville
I wish I could help with your question. However, I do have one of my own. What is the reason your step up and step down transformers are Y-Y rather than Y-Delta? The absence of a neutral and non-compliant bonding seem to be an issue. Won't the system produce unbalanced currents which will be forced to use the 6 Thhhn as a current carrying conductor? In the event of the ground wire bieng compromised it appears the bonding at the step down transformer would produce voltage gradients and a risk of electrocution.

Also, since the inverters operate on 277v with a neutral, whatever current they pull does indeed have to travel on the #8 ground wire.


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GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Also, since the inverters operate on 277v with a neutral, whatever current they pull does indeed have to travel on the #8 ground wire.


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And individual single phase inverters cannot be counted on to provide balanced current since they are driven by separate sub arrays. A unified three phase inverter is more likely to have low net neutral current.

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zog

Senior Member
Location
Charlotte, NC
I'm thinking it must be a faulty breaker.


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Not sure what you mean by 400A breaker with 300A shunt? (300A trip setting maybe?) Did you do any commissioning tests on the breaker? What type of breaker and trip unit do you have?
 
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