SMA SI 3.0-11 Quick Reference Guide V.3.0 - Manual (Page 18)

3 Information and System Description SMA Solar Technology AG
18 Ersatzstrom-IS-en-30 Installation - Quick Reference Guide
Circuit description of the tie switch with all-pole disconnection*
The tie switch with all-pole disconnection consists of contactors Q1 and Q2. The tie switch disconnects the battery backup
grid from the utility grid in the event of a grid failure or if the utility grid is outside the limiting values for voltage and
frequency.
The control voltage of contactors Q1, Q2, and Q3 is equal to the voltage of a line conductor of the utility grid. This means
that the tie switch can only be activated when grid voltage is present. An auxiliary contact of contactor Q3 locks contactor
Q1. Contactors Q3 and Q2 are controlled by the multifunction relay Relay1 of the Sunny Island inverter. If the
multifunction relay Relay1 is in non-operative mode, contactors Q2 and Q3 activate. If contactor Q3 is in non-operative
mode, contactor Q1 will also go into non-operative mode and be locked.
In the event of a total grid failure, contactors Q1, Q2, and Q3 go into non-operative mode due to lack of control voltage
and they disconnect the battery backup grid with all poles from the utility grid. The Sunny Island also measures the voltage
of the utility grid. For this, the Sunny Island is connected with the same line conductor as the control voltage of contactors
Q1, Q2, and Q3. If there is a deviation from country-specific limiting values for voltage and frequency of the utility grid,
the multifunction relay Relay1 is activated. The contactors Q1, Q2, and Q3 remain in non-operative mode or go into
non-operative mode.
When the utility grid is available again, the Sunny Island detects this. The Sunny Island synchronizes the battery backup
grid with the utility grid. Following successful synchronization, the multifunction relay Relay1 goes into non-operative
mode and contactors Q2 and Q3 are activated. Contactor Q3 unlocks contactor Q1 and Q1 is activated. The battery
backup grid is again connected to the utility grid.
Circuit description of the tie switch without all-pole disconnection**
The tie switch without all-pole disconnection consists of contactor Q2 (see Section 5.1.1 "Schematic Diagram of the
Automatic Transfer Switch", page 30). The tie switch disconnects the battery backup grid from the utility grid in the event
of a grid failure or if the utility grid is outside the limiting values for voltage and frequency.
The control voltage of contactor Q2 is equal to the voltage at the line conductor L1 of the utility grid. This means that the
tie switch can only be activated when grid voltage is present. Contactor Q2 is controlled by the multifunction relay
Relay1 of the Sunny Island inverter. If the multifunction relay Relay1 is in non-operative mode, contactor Q2 activates.
In the event of a total grid failure, contactor Q2 goes into non-operative mode due to lack of control voltage and
disconnects the battery backup grid from the line conductors of the utility grid. The Sunny Island also measures the voltage
of the utility grid. For this, the Sunny Island is connected to the same line conductor as the control voltage of contactor
Q2. If there is a deviation from country-specific limiting values for voltage and frequency of the utility grid, the
multifunction relay Relay1 is activated. Contactor Q2 remains in non-operative mode or goes into non-operative mode.
When the utility grid is available again, the Sunny Island detects this. The Sunny Island synchronizes the battery backup
grid with the utility grid. Following successful synchronization, the multifunction relay Relay1 goes into non-operative
mode and contactor Q2 activates. The battery backup grid is again connected to the utility grid.
3.4.3 Grounding Device for the Battery Backup Grid
With TN and TT systems, the neutral conductor must be grounded for protection in the case of indirect contact with live
components. Grounding in the utility grid is usually achieved at the local grid transformer.
In automatic transfer switches with all-pole disconnection, all poles of the battery backup grid are disconnected from the
utility grid in the event of grid failure. As a result of the disconnection, the neutral conductor in the battery backup grid is
not grounded. Therefore, in automatic transfer switches with all-pole disconnection, a grounding device must ground the
neutral conductor in the event of grid failure. The grounding device enables the required protection in the event of indirect
contact with live components. The grounding device is set up for fail-safe operation.
If the neutral conductor of the battery backup grid is connected to the utility grid, there must be no further grounding in
the battery backup grid. The grounding device therefore disconnects the connection between the neutral conductor and
ground if the automatic transfer switch connects the battery backup grid to the utility grid.
* The explanation is based on a single-phase battery backup system with one Sunny Island. Three-phase battery backup systems behave in the
same way.
** The explanation is based on a single-phase battery backup system with one Sunny Island. Three-phase battery backup systems behave in the
same way.