Supervisory control and data acquisition (SCADA)-based automation systems are among the most commonly used technologies in gas pipeline systems, which have increased vastly in size over the years. SCADA is a computer-based data acquisition system which gathers operating data from remote field locations and transmits it through communication links to control centre locations for display and reporting. The data is monitored by control centre operators.
A centralised monitoring pipeline system allows the gas pipeline company to effectively manage its gas transportation services. SCADA accomplishes the task of monitoring and controlling the natural gas flow through the pipeline by supplying the necessary data to centralised gas control stations. These centralised stations then assimilate and manage the data provided by SCADA and the compressor stations. The data, which mainly comprises the flow rate through the pipeline, operational status, and pressure and temperature readings, can be used to assess the status of the entire pipeline network at any point of time.
Pipeline systems can also be controlled through microwave, radio, dedicated landlines or intranet networks using a mix of copper, fibre optics and wireless technologies. The four components crucial for any SCADA network are field instruments and devices, station control using programmable logic controllers (PLCs) and remote terminal units (RTUs), master terminal units, and the control centre.
A centralised SCADA system enables gas pipeline operators to perform operating tasks more effectively by providing accurate and real-time information. It also helps monitor and control product movements accurately and allows for safe oper-ations of the pipeline system, including the pump and compressor stations. Monitoring gas flows is essential for gauging the pressure of the gas being transported through the pipelines.
A typical SCADA system comprises various subsystems, which are the local monitoring and controlling stations.
Functioning of the SCADA system
The SCADA system is connected with the pipeline network through various components. The pipeline network is further connected to digital/analog sensors, which gather data regarding gas flow, temperature and pressure. These sensors are, in turn, connected to RTUs or PLCs situated at various input locations, including the pipeline, compressor station or a gas storage facility. Each PLC and RTU is operated by a supervisor to control these units, and takes corrective steps in case of any disruption in gas flows.
Data from these remote devices then flows through the communication network to the master station of SCADA, which displays it through the HMI. The SCADA master station continuously monitors all the sensors and alerts the operator in case of any deviations from the normal functions. The operator at the master station has the ability to access both historical and real-time data on the system functioning, thereby being capable of controlling the system more efficiently.
SCADA helps to gauge unusual activity, including higher or lower than optimum gas flow pressure or temperature, at the time of its occurrence which allows the operator to take corrective measures.
In case a signal is received via the SCADA system indicating an emergency situation, an emergency shutdown system ensures that the pipeline is closed down.
At all its stages of implementation, the main objective of a SCADA system is to check pipeline integrity in order to enable effective and efficient monitoring and control of the network.
Master control stations: These are designed to enable effective and efficient monitoring, safe operation and control of the station control centres (SCCs) or the RTUs for the entire pipeline network. It is equipped with self-diagnostic facilities that check the health of the entire system. The data is acquired from SCCs/RTUs in real time through the communication circuits.
SCCs: These aim at ensuring safe operation and control of the local station and block valves. They acquire data from the local PLC and block valve RTUs under their control in real time and transmit it to the master control station. They display and record data in graphic and text formats for the local station and block valves under their control.
Web-enabled SCADA systems
A web-enabled SCADA system provides access and control for a plant from anywhere in the world through the web. This system acquires data from the operational SCADA system master stations or local control stations through the use of proxy servers. This data is then transported to the web pages via an appropriate communication medium.
These systems can connect with multiple servers and clients within the organisation, as well as at remote locations, to control and monitor the process. The systems are secured in a manner that allows only authorised users to control the process. Web-enabled systems are capable of sending maintenance reports and breakdown reports through automated emails. These systems are economical, since they eliminate the need for a telephone and leased line remote access.
SCADA usage in India and globally
Gas companies in India such as GAIL (India) Limited, Adani Gas Limited, Gujarat State Petronet Limited and Assam Gas Company Limited have been implementing SCADA systems. Globally too, SCADA is being used by various companies in their operations. Russian gas major Gazprom, the largest producer of gas in the world, uses this technology to supervise over 200,000 km of pipeline network in the country. In Turkey, the implementation of a SCADA system by the country’s largest gas distribution firm, iGDAS, has helped it detect gas failures in the system in real time, so that they can be rectified immediately.
The adoption of SCADA in the city gas distribution segment is poised for growth, as it offers real-time information to provide uninterrupted monitoring and control. SCADA has proved helpful for utilities such as GAIL Gas Limited, Indraprastha Gas Limited and Mahanagar Gas Limited by combining the monitored data with demand, environmental, physical and gas composition data across the enterprise for business decision support. With gas utilities increasingly adopting the related technology solutions, the efficiency of the CGD segment is expected to improve in the near future.