Due to complex nature of bulk power handling, critical installations like electrical sub-stations are always been closely monitored. Traditionally, this has been achieved by maintain operating & maintenance staff at every substation. However, with increasing number of sub-station & pressure to decrease operational expenses it is no longer possible to man every new substation. On the other hand at the data gathered in the sub-stations is gaining strategic importance in planning & operations.

In such situation therefore, it is desirable to have quick data acquisition and instant response to any event, with minimum human intervention. The concept of SCADA is ideally suited for such situations.

General Definition of SCADA (supervisory control and data acquisition) :
An industrial measurement and control system consisting of a central host or master (usually called a master station, master terminal unit or MTU) ; one or more field data gathering and control units or remotes (traditionally called remote stations, remote terminal units, or RTU's); and a collection of standard and/or custom software used to monitor and control remotely located field data elements. Contemporary SCADA systems exhibit predominantly open-loop control characteristics and utilise predominantly long distance communications although some elements of closed-loop control and/or short distance communications may also be present. Systems similar to SCADA systems are routinely seen in factories, treatment plants etc. These are often referred to as Distributed Control Systems (DCS). They have similar functions to SCADA systems, but the field data gathering or control units are usually located within a more confined area. Communications may be via a local area network (LAN), and will normally be reliable and high speed. A DCS system usually employs significant amounts of closed loop control. SCADA systems on the other hand generally cover larger geographic areas, and rely on a variety of communications systems that are normally less reliable than a LAN. Closed loop control in this situation is less desirable & basically not needed as it is primarily taken of by protection gear.

What it all means to you :
In the field of electrical transmission /distribution network, SCADA is used for monitoring/ controlling of multiple substations or possibly a generating station from a central control room. The communication link between the two ends could be a dedicated cable, a telephone connection, a satellite channel, Power Line Communication (PLCC), or even a fiber-optic link. In the simplest case, this would be a dial-up or leased P&T line, with modems on both the sub-station & control room. Using industry standard RS-485 protocol, a single modem could possibly connect to several monitoring units in a sub-station. At the central control station the data could then be acquired & stored in a suitable format. A Computer equipped with hi-resolution visual display capability is ideally suited for this. Thus an operator/ incharge siting at the central room can monitor multiple sub-stations at a time. A mimic diagram, for each sub-station can summarize the status of whole of the sub-station in one single display. Any event occurring in any of the sub-station will be immediately notified with audiovisual alarm & corresponding control can be initiated if required. The data acquired by the system can be used for analysis, reporting, fault-diagnostics, etc.

Some of the advantages of such type of system would be

• Central control room for a group of sub-stations.
• Accurate & timely data for fault analysis.
• Instant actions can be taken in case of emergencies.
• All sub-station reports available for the management to take quick decision.
• Better management of available resources.