New to transformers with solar, can you help me out?
System Specs: 300 kW of PV with 9 String inverters operating at 480/277 Wye combined with an AC combiner. Combined inverter output power is run through a transformer to step down the combined inverter outputs from 480/277 Wye to a 240 Delta (high leg) and then it will make a supply side connection at the main building service (allowed by AHJ & Utility). The utility service is a 240 Delta High-leg. There are no loads in the inverter combiner, only utility interactive power production sources (solar inverters).
Question: DO WE NEED TO INSTALL A NEUTRAL CONDUCTOR ON THE 240 DELTA SIDE OF THE TRANSFORMER? (BETWEEN THE TRANSFORMER AND THE UTILITY INTERCONNECTION)
I have confirmed with the inverter manufacturer that the inverters only use the neutral for instrumentation & voltage referencing (not a current carrying conductor). Note: We will have a neutral installed on the 480/277 side (solar inverter side) of the transformer and this neutral is bonded to ground in the transformer. The inverter manufacturer has stated that this is sufficient for the instrumentation needs of the inverters and the inverters don't need to have a neutral on the 240 Delta side of the transformer.
The electrical engineer we had review the design is telling us that we need a neutral on the 240 Delta side of the transformer to handle the 120 V (& 208 V High-leg) loads in the building.
Our master electrician feels that because this is only a utility interactive power production source with a true 240 Delta output from the transformer we don't need the neutral conductor between the transformer and the supply-side connection to the utility. It is purely a power production source that will never run when the utility is down. Therefore we should let any 120 V loads (or high-leg loads) be handled by the utility. Why introduce neutral currents onto our transformer when we don't have to.
I'm curious to see what you all think. Install the neutral between the transformer and the utility interconnection or leave it out?
System Specs: 300 kW of PV with 9 String inverters operating at 480/277 Wye combined with an AC combiner. Combined inverter output power is run through a transformer to step down the combined inverter outputs from 480/277 Wye to a 240 Delta (high leg) and then it will make a supply side connection at the main building service (allowed by AHJ & Utility). The utility service is a 240 Delta High-leg. There are no loads in the inverter combiner, only utility interactive power production sources (solar inverters).
Question: DO WE NEED TO INSTALL A NEUTRAL CONDUCTOR ON THE 240 DELTA SIDE OF THE TRANSFORMER? (BETWEEN THE TRANSFORMER AND THE UTILITY INTERCONNECTION)
I have confirmed with the inverter manufacturer that the inverters only use the neutral for instrumentation & voltage referencing (not a current carrying conductor). Note: We will have a neutral installed on the 480/277 side (solar inverter side) of the transformer and this neutral is bonded to ground in the transformer. The inverter manufacturer has stated that this is sufficient for the instrumentation needs of the inverters and the inverters don't need to have a neutral on the 240 Delta side of the transformer.
The electrical engineer we had review the design is telling us that we need a neutral on the 240 Delta side of the transformer to handle the 120 V (& 208 V High-leg) loads in the building.
Our master electrician feels that because this is only a utility interactive power production source with a true 240 Delta output from the transformer we don't need the neutral conductor between the transformer and the supply-side connection to the utility. It is purely a power production source that will never run when the utility is down. Therefore we should let any 120 V loads (or high-leg loads) be handled by the utility. Why introduce neutral currents onto our transformer when we don't have to.
I'm curious to see what you all think. Install the neutral between the transformer and the utility interconnection or leave it out?