The term supervisory control and data acquisition (SCADA) refers to the network of computer processors that provide control and monitoring of remote electrical or mechanical operation e.g. management of power distribution grid or the control of mechanical processes in a manufacturing plant.
Typical the old SCADA systems would encompass computers and network links that manage the remote operation via a set of field located programmable logic controllers (PLCs) and remote telemetry units (RTUs). These PLCs or RTUs would be connected to field transmitters and actuators and would convert analogue field data into digital form for transmission over the network.
In modern SCADA systems, with respect to high voltage substations or even medium voltage substations, the substations control devices aren’t necessarily RTUs or PLCs but intelligent electronic devices that serve the purpose of protection, local and remote control. These intelligent electronic devices provide means to acquire and transmit the analogue and binary input data to the control system via communication links.
SCADA systems are in essence a real-time operating database that represents both the current and past values of status of the field input/output points (tags) used to monitor and control the operation.
Relationships can be set up within the database to enable functional or computed elements to be represented which provide operators with a logical representation of the remote operation. This representation enables the whole operation to be monitored and controlled through a central point of command whereby concise information is available in a clear schematic and textual form typically or graphics workstations.
Related: Types of Busbar Arrangements in Grid Stations and Substations
The supervisory functions of SCADA system present plant operators with a representation of the current and historical states by means of graphic schematics, event logs and summaries. These screens also identify all abnormal conditions and equipment failures which require operator acknowledgement and remedial actions. The control functions enables specified items of plant to be controlled by issuing direct commands by instigating predetermined control sequences or by automatically making programmed response to a particular event or status change.
