To be able to manage and control a power system, the network engineer requires reliable and current information about the state of the network. He obtains this information from power flows, bus voltages, frequency and load levels along with the position of circuit breakers and isolators, the source of these data being in the power stations and substations of the network. As these are spread over a wide geographical area, the information must be transmitted over long distances. Therefore, the electrical parameters and switch states must be converted into a suitable form of transmission to the control center. A Telecontrol system is also required to transmit these data using communication channels.
The modern communication is based on fiber optics or wireless communication networks, which provide a powerful broad band communication technology. The classical powerline carrier communication technology has also been enhanced with the use of digital technology. It is almost a requirement that all the new HV and EHV lines be laid with fiber optical core in the ground wire as the incremental cost is relatively low. The trunk routes may have dedicated logical links for speech, data and protection signal besides the data and voice network for telecommunication purposes.
The Telecontrol system consists of a master station communicating over communication channels with remote terminal units (RTUs) located in the power stations and switching stations. Normally, the RTUs are quiescent, that is, they only send data after a direct interrogation from the master station; thus more than one RTU can be connected to a transmission channel as the channel can be time shared.
Related: Supervisory Control and Data Acquisition in Power Systems
A Telecontrol network can be configured as a point to point, star (radial) or multi-point (part line) system as shown in the figure below:
The transmission can be duplex, half-duplex or simplex (in the case where data traffic is unidirectional). The modern generation of RTUs can remain quiescent and can report the data on their own initiative using slave and master communication protocols. The use of standard protocols is also encouraged to facilitate, the use of equipment from different suppliers. Modern RTUs can communicate over data communication networks providing a large bandwidth with good reliability.
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