Connecting Load-Shedding Contactors
Qualified person
Load shedding prevents battery deep discharge and controls the supply of energy to the loads. Load shedding provides the option of disconnecting specific loads from the system.
Load shedding is necessary for an off-grid system that is exclusively supplied with PV energy or wind energy.
The Sunny Island controls up to two load-shedding contactors depending on the state of charge of the battery. You can install two types of load shedding:
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One-level load shedding
If the battery state of charge limit has been reached, one load-shedding contactor disconnects all loads at the same time. Depending on the configuration, the load-shedding contactor closes when the battery has been sufficiently charged or when the stand-alone grid has been switched to an external energy source. -
Two-level load shedding
In two-level load shedding, there are two thresholds for the state of charge of the battery in order to control two load-shedding contactors. When the first threshold for the state of charge of the battery is reached, the first load-shedding contactor disconnects a group of loads. When the second threshold for the state of charge of the battery is reached, the second load-shedding contactor disconnects the remaining loads.
Connection of control cable for one-stage load shedding (example)
Load shedding in a multicluster system
One-level load shedding is integrated into the Multicluster-Box. The load-shedding contactor is controlled directly by the master of the main cluster via communication with the Multicluster-Box. If you install an additional load-shedding contactor in a multicluster system, it is controlled with a multifunction relay in the master of extension cluster 1. Additional load-shedding contactors cannot be controlled by the main cluster.
Load-shedding contactors in a cluster
If you connect load-shedding contactors to the master, limited operation is possible in the event of a disturbance. Slaves can control the load-shedding contactors less reliably in the event of a fault. In the event of a disturbance, the slave may wait for confirmation from the master.
Specifications for load-shedding configuration:
The following values are stored in the user interface of the Sunny Island for setting the load-shedding system. If you connect load-shedding contactors, consider the effects in the system and comply with the instructions for use.
Value | System effects | Application |
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One-stage load-shedding scheme (Load shedding 1) | If the Sunny Island has activated the load-shedding system and then an external energy source is connected, the load-shedding process is terminated immediately (regardless of the battery's state of charge). The external energy source is then supplying the loads. The battery is only charged with the excess energy. |
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One‑stage load-shedding scheme or first stage in terms of two-stage load-shedding schemes (Load shedding 1) | Setting for a one-stage load-shedding scheme or the first stage of a two-stage load-shedding scheme. Load shedding is only stopped when the battery has been sufficiently charged. This setting affects the system behavior regardless of whether an external energy source is present. |
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Second stage in terms of two-stage load-shedding scheme (Load shedding 2) | Settings for second load-shedding contactor in terms of a two-stage load-shedding scheme. Load shedding is only stopped when the battery has been sufficiently charged. |
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Load shedding in multicluster system (Load shedding 1) | In a multicluster system, this setting is intended for additional one-stage load-shedding. When the battery state of charge of a cluster falls below a set value, the load-shedding process begins. The load shedding only ends when the batteries of all clusters have reached the set value of the battery state of charge. How long it takes to reach this value depends on the battery technology used and the selected battery capacity. If different battery technologies and different battery capacities are combined in the clusters of a multicluster system, the display values for the individual clusters may vary. |
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Requirements:
- The technical requirements of the multifunction relay must be met ( > Technical Data).
Cable requirements:
- Copper wire
- Conductor cross-section: 0.2 mm² to 2.5 mm²
Procedure:
- Ensure that the load-shedding contactor only disconnects loads from the system. This ensures that the battery can be recharged from AC sources in the system.
- When connecting the load shedding, preferably use the multifunction relay Relay2. Since the default setting of Sunny Island uses the multifunction relay Relay2 for load shedding. Carry out the following steps:
Connect the insulated conductor for coil connection A1 of the load-shedding contactor on the Sunny Island to terminal Relay2 NO ( > Connecting Relay 1 and Relay 2).
Connect the insulated conductor for coil connection A2 to terminal BatVtgOut− ( > Connecting BatVtgOut, DigIn, BatTMP and BatCur).
Connect terminal BatVtgOut + to terminal Relay2 C. Use the same conductor cross-section as that of the cable for the load-shedding contactor.
- If the multifunction relay Relay2 for load shedding is not available, use the multifunction relay Relay1 when connecting the load shedding. Carry out the following steps:
Connect the insulated conductor for coil connection A1 of the load-shedding contactor on the Sunny Island to terminal Relay1 NO ( > Connecting Relay 1 and Relay 2).
Connect the insulated conductor for coil connection A2 to terminal BatVtgOut− ( > Connecting BatVtgOut, DigIn, BatTMP and BatCur).
Connect terminal BatVtgOut + to terminal Relay1 C. Use the same conductor cross-section as that of the cable for the load-shedding contactor.
- Repeat steps 1 to 3 for two-stage load shedding. Connect the second load-shedding contactor to an unused multifunction relay.
- Write down the terminal assignment of the load shedding terminal for setting the multifunction relays. Tip: Use the table provided in this document ( > Setting the Functions of the Multifunction Relays):