Configuring single phase GT Residential inverters for small commercial 3-phase systems
It is a regulatory mandate that all UL1741-2005 inverters be attached to a neutral connection for phase to neutral sensing purposes. The output voltage of the GT single phase inverters is 240VAC or 208VAC Line to Line (120VAC Line to Neutral), therefore, it is required that the distribution system be a 240V:120V split phase, for single phase configuration, or a 208V:120V WYE for three-phase configuration. GT single phase inverters can also be connected to a three-phase Delta 240V center tap transformer, however, only the 240V:120V phase can be used, resulting in an un-balanced system.
Xantrex GT single phase inverters can be configured in multiples of three for a three-phase balanced system. Different models can be combined to meet the PV power requirements, and since the form factor is identical among all models, installation is easy and clean. Each inverter should be connected to a phase of the 208V:120V WYE transformer, where Line to Line voltage is 208V and Line to Neutral 120V.
The resulting power for a three-phase configuration is the sum of the output rated power of each inverter. The GT single phase series inverters comes equipped with 2 RJ-11 ports that allow the interconnection of multiple inverters for three-phase configurations where the requirement is to avoid high un-balanced generating conditions on the transformer. Any inverter disconnecting from the grid will force the remaining inverters offline as well. This conditions remains until grid parameters for all inverters are within operating conditions.
If a strict balanced system is required, daisy chain the inverters via the RJ-11 ports. Note that the wire that is required is a 4-wire straight through cord. The terminals are the 4P4C type commonly used on telephone handsets. A handset cord cannot be used as it crosses over. More than likely, these cords will need to be fabricated. No terminators are required as RJ-11 is not a network port. Additionally, 2 RJ-45 Xanbus ports are available to allow information about each inverter and its associated PV array to be communicated between all of the inverters in the system. System information can be displayed on any inverter LCD in the system. To enable communication between inverters, daisy chain each inverter in the network via the RJ-45 Xanbus ports using a standard Category 5 (CAT 5 or CAT5e) available from any computer supply store. The network terminator supplied with each GT inverter is required at each end of the network to ensure the communication signal quality on the network Knockouts on each side of the inverter facilitate wiring of the signal and communication cables between devices.
Three-phase System: Power Configuration (assuming same inverter model) GT single phase inverters: 8.1 kW3 x GT2.8 9.3 kW3 x GT3.3N 11.4 kW3 x GT4.0N 13.5 kW3 x GT5.0 16.2 KW6 x GT2.8 18.6 kW6 x GT3.3N 22.8 kW6 x GT4.0N 27.0 kW6 x GT5.0