SMA SI 3.0-11 Quick Reference Guide V.3.0 - Manual (Page 19)

SMA Solar Technology AG 3 Information and System Description
Installation - Quick Reference Guide Ersatzstrom-IS-en-30 19
Circuit Description of the Grounding Device
Contactors Q3 and Q4 form the grounding device (see Section 4.1 "Single-Phase Battery Backup System", page 20).
Contactors Q3 and Q4 are controlled by the two multifunction relays of the Sunny Island inverter. Contactor Q3 is
activated in parallel to contactor Q2 of the tie switch. If contactor Q2 deactivates and the tie switch opens, contactor
Q3 connects the neutral conductor in the battery backup grid to the grounding conductor. In addition, the Sunny Island
uses the multifunction relay Relay2 to control contactor Q4. If the multifunction relay Relay2 activates, contactor Q4
activates and also connects the neutral conductor to the grounding conductor. This arrangement ensures that the neutral
conductor of the battery backup grid is always connected to ground.
3.4.4 Phase Coupling for Single-Phase Battery Backup Systems
In single-phase battery backup systems, in the event of grid failure, the battery backup grid is single-phase. If the
installation of the battery backup grid is three-phase, only one part of the loads can continue to be supplied.
Phase coupling enables combination of the line conductors in the battery backup grid. As a result, the other two line
conductors are also supplied with voltage. This means that, in the event of grid failure, a three-phase battery backup grid
becomes a single-phase distribution grid.
Phase coupling can be switched on independently for the other line conductors. Phase coupling is only suitable for battery
backup grids with single-phase PV inverters and single-phase loads.
Circuit description of the phase coupling
Contactor Q6 is the phase coupler. If the multifunction relay Relay2 activates on the Sunny Island, contactor Q6
activates and connects the unsupplied line conductors via circuit breakers F3 and F4 with the supplied line conductor.
In the event of grid failure, the line conductor that is connected with the Sunny Island is supplied with voltage first. Then
the phase coupling combines the two other line conductors. When the utility grid is available again, the phase coupling
disconnects the combined line conductors. Only the line conductor which is connected to the Sunny Island is not
interrupted on connection to the utility grid.