Switching Operations in the Automatic Transfer Switching Device for Sunny Island
Differences between automatic transfer switching devices for single-phase and three-phase battery-backup systems with Sunny Island
This section describes the operating principle of the automatic transfer switching device as exemplified by the single-phase Sunny Island battery-backup system with all-pole disconnection ( > Automatic Transfer Switching Device for Single-Phase Battery-Backup System with All-Pole Disconnection). When looking at the other automatic transfer switching devices, the following differences are important:
- The function of the tie switch and grounding device of a three-phase automatic transfer switching device is analogous to that of the single-phase automatic transfer switching device.
- In battery-backup systems without all-pole disconnection, no grounding device is required.
- Phase coupling is optional and is only suitable for battery-backup grids with single-phase PV inverters and single-phase loads.
Operating principle of the tie switch with all-pole disconnection
The tie switch disconnects the battery-backup grid from the utility grid in the event of grid failure or if the utility grid has breached the thresholds for voltage and frequency. The contactor Q2 is the tie switch with all-pole disconnection.
The control voltage of contactors 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 Q2. Contactors Q3 and Q2 are controlled by multifunction relay Relay1 of the Sunny Island inverter. If multifunction relay Relay1 is in non-operative mode, contactors Q2 and Q3 activate. If contactor Q3 is in non-operative mode, contactor Q2 will also go into non-operative mode and be locked.
In the event of a total grid failure, contactors Q2 and Q3 go into non-operative mode due to the 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 Q2 and Q3. When a deviation from country-specific voltage and frequency thresholds of the utility grid occurs, multifunction relay Relay 1 is activated. Contactors 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, multifunction relay Relay1 goes into non-operative mode and contactors Q2 and Q3 are activated. The battery-backup grid is again connected to the utility grid.
Operating principle of the tie switch without all-pole disconnection
The tie switch disconnects the battery-backup grid from the utility grid in the event of grid failure or if the utility grid has breached the thresholds for voltage and frequency. The contactor Q2 is the tie switch without all-pole disconnection.
The control voltage of contactor Q2 is the voltage at 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. If 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 the 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 with the same line conductor as the control voltage of contactor Q2. When a deviation from the country-specific voltage and frequency thresholds of the utility grid occurs, multifunction relay Relay 1 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, multifunction relay Relay1 goes into non-operative mode and contactor Q2 activates. The battery-backup grid is again connected to the utility grid.
Operating principle of the grounding device
Contactors Q3 and Q4 form the grounding device. Contactors Q3 and Q4 are controlled by both multifunction relays of the Sunny Island. Triggering of contactor Q3 occurs simultaneously with 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 multifunction relay Relay 2 to control contactor Q4. When multifunction relay Relay 2 is activated, contactor Q4 is activated and also connects the neutral conductor to the grounding conductor. This arrangement ensures that the neutral conductor of the battery-backup grid in battery-backup operation is always connected to ground.
Operating principle of phase coupling
Contactor Q6 forms the phase coupler. If 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 that is connected to the Sunny Island is not interrupted on connection to the utility grid.