SPST Switch (Three-Phase)
Three-phase single-pole single-throw switch
Libraries:
Simscape /
Electrical /
Switches & Breakers
Description
The SPST Switch (Three-Phase) block models a three-phase single-throw switch that uses an external signal to connect each phase of port ~1 with the corresponding phase of port ~2 via internal resistance.
The table shows how the external signal vT controls the block behavior.
| Condition | Block Behavior | Resistance Parameter Used |
|---|---|---|
| vT ≤Threshold | The switch is open. Each phase in the composite three-phase port ~1 connects to the corresponding phase in the port ~2 via large internal resistance. | Open conductance |
| vT >Threshold | The switch is closed. Each phase in the composite three-phase port ~1 connects to the corresponding phase in the port ~2 via small internal resistance. | Closed resistance |
Examples
Three-Phase Asynchronous Machine Starting
Model a wye-delta starting circuit for an induction machine. After one second, the Controller subsystem closes the switch labeled S1. Closing this switch connects the supply to the machine. Initially, the machine connects to the supply in a wye configuration because the switch labeled S2 connects each phase of the ~1 port to the corresponding phase of the ~2 port and leaves the ~3 port unconnected. Once the machine is at 80% of the synchronous speed, S2 reconnects the machine in a delta configuration by disconnecting each phase of ~2 and connecting each phase of ~1 to the corresponding phase of ~3. The motor then operates in a delta configuration regardless of rotor speed. The supply sees a higher impedance when the motor is in wye configuration, reducing the starting current and causing less disruption to other connected loads.
