Switching is the process of rerouting the path that power takes through an electric transmission or distribution system by opening or closing switches in the grid. In some cases, switches can be operated remotely by control signals sent from the transmission or distribution operations center via SCADA or other communications systems. In other cases, switches are automated and operate automatically with local intelligence based on system conditions. But it is still common in the distribution system for switches to be operated manually by a field crew following directions communicated from the distribution operations center.
Reasons for switching on a distribution grid include:
- Disturbances such as a fault on a line requiring isolation of the section with the fault and reconfiguration to redistribute loads
- A clearance, which is a purposeful isolation of a line or line section for maintenance or equipment replacement while reconfiguring the system to maintain service to as many customers as possible
- Service restoration following an outage
- Managing line or substation overloads by shifting certain loads to a different circuit
- Redistributing loads to maintain load balances on equipment such as transformers or three-phase lines
Switching is much more common on distribution systems than transmission systems because transmission systems tend to be networked and there are less frequent outages.