Connecting 3-phase inverters to corner-grounded delta transformer

lyapunov00

Member
Location
Madrid, Spain
We are designing a storage system with a 3-phase inverter, to be connected to the grid via a transformer. I just got the schematics from the utility company, and they said that one of the phases of the transformer is grounded on the primary side (I guess it's a case of a corner-grounded delta transformation). My understanding is that normal inverters would not work in such a setup, am I right? Could someone point me to some reference where I can read about issues that might occur? Tried to google but couldnt find anything of use.

Pic of schematic:

https://imgur.com/PGBjZrA

Thank you all for your time

 

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pv_n00b

Senior Member
Location
CA, USA
It's the configuration on the inverter side that counts. If they are corner grounding their distribution system on the HV side that will not affect the inverter.
 

lyapunov00

Member
Location
Madrid, Spain
Thank you, so if I understand your reply properly, what needs to be done is to also corner ground the transformer close to the inverter at the HV side (that transformer comes from us, so we get to pick its configuration). It would only be an issue if there would be no transformer in the middle

Thank you again
 
Thank you, so if I understand your reply properly, what needs to be done is to also corner ground the transformer close to the inverter at the HV side (that transformer comes from us, so we get to pick its configuration). It would only be an issue if there would be no transformer in the middle

Thank you again
No. The utility side of the transformer doesnt get grounded again. The transformer doesnt care that it is fed with one phase that is grounded. The inverter side would be grounded because it is a separately derived system and the grounding configuration would have to match what the inverters want, which for 99% of installs these days would be grounded Wye.
 

lyapunov00

Member
Location
Madrid, Spain
Sorry about that, the real schematic might be confidential so I drew something quick.

There's just one thing that I didn't quite get, I understand how the transformer should be set on the inverter side (grounded Wye or whatever the inverter manufacturer requires), but not sure what to do on the utility side.

Thank you for your help, as you can see I'm a newbie on this
 

GoldDigger

Moderator
Staff member
Sorry about that, the real schematic might be confidential so I drew something quick.

There's just one thing that I didn't quite get, I understand how the transformer should be set on the inverter side (grounded Wye or whatever the inverter manufacturer requires), but not sure what to do on the utility side.

Thank you for your help, as you can see I'm a newbie on this
On the utility side, the transformer can either be
1. a delta winding, with the corner ground not causing any difference to actual operation unless the higher voltage from tap to ground is a specification issue, or
2. A wye winding, with the wye point left unconnected, since there is nothing to connect it to. Again, the windings need to be rated for the maximum voltage to ground that they will see.
Just be careful to get the right transformer winding turns ratio for the configuration (wye or delta) that is used.
 
Sorry about that, the real schematic might be confidential so I drew something quick.

There's just one thing that I didn't quite get, I understand how the transformer should be set on the inverter side (grounded Wye or whatever the inverter manufacturer requires), but not sure what to do on the utility side.

Thank you for your help, as you can see I'm a newbie on this
Basically, in the low voltage world, the utility side of a transformer is fed just like it is any other device, with the the exception that if there is a neutral terminal, it is not used. The primary and secondary are isolated, so the transformer erases the grounding configuration of the utility and you start over at the secondary.
 

pv_n00b

Senior Member
Location
CA, USA
Thank you, so if I understand your reply properly, what needs to be done is to also corner ground the transformer close to the inverter at the HV side (that transformer comes from us, so we get to pick its configuration). It would only be an issue if there would be no transformer in the middle

Thank you again

Your schematic might be leaving out some important points, such as where the service disconnect is. Your schematic shows what looks like a utility distribution transformer directly feeding your PV transformer with no intervening disconnect or protection. Assuming a usual service there would be a main service entrance switchboard where one leg of the 3 phases is grounded to give a corner grounded delta service. That feeds the delta side of your PV transformer and as with any load on the load side of a grounded service entrance, it does not get grounded again.
 
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