The electric utility SA system uses a variety of devices integrated into a functional package by a communications technology for the purpose of monitoring and controlling the substation. S
Systems incorporate microprocessor-based intelligent electronic devices (IEDs), which provide inputs and outputs to the system. Common IEDs are protective relays, load survey and operator indicating meters, revenue meters, programmable logic controllers (PLC), and power equipment controllers of various descriptions.
Other devices may also be present, dedicated to specific functions within the SA system. These may include transducers, position monitors, and clusters of interposing relays. Dedicated devices may use a controller (SA controller) or interface equipment such as a conventional remote terminal unit as a means of integration into the SA system.
The SA system typically has one or more communications connections to the outside world. Common communications connections include utility operations centers, maintenance offices, and engineering centers.
Most SA systems connect to a traditional SCADA (supervisory control and data acquisition) system master station serving the real-time needs for operating the utility network from an operations center.
SA systems may also incorporate a variation of the SCADA remote terminal unit (RTU) for this purpose, or the RTU function may appear in an SA controller or host computer.
Communications for other utility users is usually through a bridge, gateway, or network processor.