Interconnection question

[sketchy]

Can a 480y-120/208y transformer back feed to the utility if it is a 3 phase y-delta service (high leg delta)? We are having islanding issues with a delta-delta transformer.

 

[Hv&Lv]

Can a 480y-120/208y transformer back feed to the utility if it is a 3 phase y-delta service (high leg delta)? We are having islanding issues with a delta-delta transformer.

Shouldn't your anti-islanding devices stop this issue? What type of device do you have in place now?
480 High leg?

 

[sketchy]

It's a SEL 547 relay. I'm just getting involved with the problem. It is my understanding that any delta service will fail the islanding test, unless it is fed with a y transformer. That doesn't seem right to me, but like I said I'm new to this game.

 

[Hv&Lv]

It's a SEL 547 relay. I'm just getting involved with the problem. It is my understanding that any delta service will fail the islanding test, unless it is fed with a y transformer. That doesn't seem right to me, but like I said I'm new to this game.

Doesn't sound right to me either, but I'm not an expert by no means. I would still think that your under/over voltage relays would disconnect the system no matter what the service configuration. Perhaps the boundaries are set too high?

Y-Y padmount are what we use for interconnection.

 

[sketchy]

3 phase y-delta comes to the property, ct's on the pole, then 2 single phase lines go to out buildings and 1 three phase line goes to a shed with motors hooked up. I was told that with those motors, an islanding test will never pass because of back feeding. I wonder if that section of the service with the motors is shut down will then the islanding test pass?

 

[sketchy]

Disconnecting the residence did not solve our issues. The SEL relay needs to see a 10 volt difference when the POCO loses a line. But with this service that doesn't happen.

 

[Hv&Lv]

Disconnecting the residence did not solve our issues. The SEL relay needs to see a 10 volt difference when the POCO loses a line. But with this service that doesn't happen.

I would think this would all depend on where the anti islanding device is connected. If it is connected at or very near the inverters before they export to the rest of the facility, the motors shouldn't make a difference. It is extremely hard to visualize the circumstances you desribe. A picture or sketch would be a tremendoues help.
I think you could also tighten the bandwidth up on these Schweitzer controls, you just need the program.