Transformer compatibility

M

Mian Usama

Member
Location
Pakistan
Occupation
Engineer
Hoymiles microinverters operate at 120/208V and need to interconnect with a 480/277V utility transformer. To achieve this, we plan to install a step-up transformer, where the primary Wye side will be connected to 120/208V, and the secondary side will be connected to the utility’s 480/277V system.

My question is: Do we need to run a neutral from the step-up transformer secondary to the utility’s 480/277V connection, or can we connect using only the three phases?
 
Typically the utility side of the transformer is the primary, even in your situation where the power flow is from the PV system to the utility. This is because the utility side gets energized and where you want taps to adjust voltage.

So you actually want a step down transformer with a 480V primary and 208/120 V wye secondary.

Typically you will have a delta primary, and will not bring the 480V neutral to the transformer. However sometimes the utility will require a wye primary for what they call 'effective grounding'. If you have a wye:wye transformer, then you must bring the neutral to the transformer.

Jonathan
 
winnie said:
Typically the utility side of the transformer is the primary, even in your situation where the power flow is from the PV system to the utility. This is because the utility side gets energized and where you want taps to adjust voltage.

So you actually want a step down transformer with a 480V primary and 208/120 V wye secondary.

Typically you will have a delta primary, and will not bring the 480V neutral to the transformer. However sometimes the utility will require a wye primary for what they call 'effective grounding'. If you have a wye:wye transformer, then you must bring the neutral to the transformer.

Jonathan
Click to expand...
Thank you for the detailed explanation. We have not purchased a transformer yet. The building already has a transformer that provides 480/277V, and we would like to tap our solar system into that service.

For the step-up transformer we are planning to install, should we use a Delta configuration on the primary and simply connect the three phases to the conductors coming from the utility transformer?

Also, will this configuration cause any issues, such as phase imbalance or other operational problems?
 
winnie said:
If you have a wye:wye transformer, then you must bring the neutral to the transformer.
Click to expand...
No, you don't. You can use a transformer with a wye primary (480V side) and leave the neutral floating. I have done it and it works fine. WHY I had to do it is because the PV contractor I was consulting with bought the wrong transformer and installed it before I knew anything was awry.
 
ggunn said:
No, you don't. You can use a transformer with a wye primary (480V side) and leave the neutral floating. I have done it and it works fine. WHY I had to do it is because the PV contractor I was consulting with bought the wrong transformer and installed it before I knew anything was awry.
Click to expand...
Thank you for the clarification. So just to confirm, are you recommending using a Wye configuration on both sides of the step-down transformer?and leave the neutral floating
 
Mian Usama said:
Thank you for the clarification. So just to confirm, are you recommending using a Wye configuration on both sides of the step-down transformer?and leave the neutral floating
Click to expand...
No. I did what I did when I had no choice; the wrong transformer was purchased and installed in spite of what I had specified so I had to make do. You should have a delta on the primary side (the side connected to the service) and a wye on the secondary side.
 
You must log in or register to reply here.
Top