Supervisory control and data acquisition (SCADA) systems are used for real-time control and monitoring of electrical networks and power systems from a remote location. They operate with coded signals over communication channels to enable control of remote equipment. They may be combined with data acquisition systems to enable the use of such signals to acquire information about the performance of power plant equipment, operational performance data of a plant, and overall health of plant equipment.
Applications of SCADA in power plants
The use of programmable logic controller (PLC) hardware and powerful bus communication links along with SCADA helps in delivering an optimal solution for every process operation in a power plant. It equips the power plant operator with advanced control structures that help in undertaking flexible operations. In the power generation segment, SCADA helps in fault location and isolation as well as quick restoration of operations. SCADA can also be used in power plants for load balancing purposes. The demand for power varies with seasons and from month to month. In order to bridge the gap between demand and generation, load shedding is carried out on a rotational basis so as to provide power to all consumers. Other applications of SCADA in the power generation segment include continuous monitoring of speed and frequency; geographical monitoring of coal delivery and water treatment processes; supervising the status of circuit breakers, protective relays and other safety-related operations; generation operations planning; active and reactive power control; turbine protection; and load scheduling.
Overall, a SCADA system provides access to real-time data, thereby allowing the operator to make decisions faster. It also reduces human error, resulting in efficient and reliable plant operations. SCADA provides a facility for storing large amounts of data, which can be utilised by plant operators as and when required. It provides an interface to connect thousands of sensors across a wide region for various monitoring and controlling operations. Many types of data can be gathered from remote terminal units (RTUs) connected to the master unit. The data can be displayed in various formats as per user requirements. Besides, with advanced protocols and application software, power plant data can be monitored from anywhere and not just from the local site.
Automation of power plant control systems
In manual process control, the temperature gauge is monitored continuously and the valve is operated manually to control the firing rate as per the desired temperature. Controlling temperature manually is a lengthy and laborious process. With automatic process control, the temperature gauge is replaced with a transmitter and the manual valve is replaced with a pneumatic control valve. With the introduction of a controller, the operator has to enter just the desired value of temperature, and the controller will adjust the pneumatic value according to the process temperature. The operator can also monitor the process temperature from any remote location. This is a low-cost and high efficiency system. It is a short process, with high production efficiency, and is suitable for large-scale production. Under this, optimal operation is possible through atomisation, that is, by running at exact boiler and turbine efficiencies, and taking immediate action when they drop.
In a centralised control system, all the input signals from the field are sent to the central processing units, which accordingly send output signals to the field. One of the major drawbacks of central control systems is that all the inputs are given to a single processor, all the corresponding set points are also fed to the same processor, and all the outputs are derived from the same processor. If the processor fails, all the loops get affected. Furthermore, since a single processor processes a huge amount of data, the response time is comparatively slower. These drawbacks of a centralised control system can be overcome with a distributed control system (DCS). With DCS, control is distributed among different processors and so, even if one processor fails, the loops connected to other processors will not be affected. Further, if more control loops are required, more microprocessors can be added. With DCS, it is much easier to make software changes, and a wide range of algorithms can be selected.
Control systems may also be classified into analogue and digital. In an analogue control system, the control device makes control computations with analog signals (such as voltage) using an operational amplifier, while in a digital control system, the control device makes control computations with digital values using a processor (CPU). There are several advantages of digital controls over analogue controls. In a digital control system, after the signal detection system, all processing manipulations are done by software and as such, accuracy is limited only by the mathematical techniques used. Further, since no components and electronic circuits are involved, signal variations and component failures are fewer in number. Subsequently, fault analysis and troubleshooting are made easy. With an advanced control system, maintenance and replacement costs can be avoided and various processing accidents can be averted.
The digital revolution in the power sector has gained momentum. The adoption of automation solutions in power generation is gaining traction, to make plants smarter and more efficient in dealing with the challenges of the future. Digital technologies and solutions not only help in improving the operational performance of TPPs at minimum expenditure, they also enable practical upgrades.
The deployment of various information technologies such as SCADA in power plant operations is useful for allowing plants to undertake flexible operations and maintain high operational efficiency. With the power sector’s landscape changing rapidly due to the increasing share of renewables in the energy mix, ageing conventional power plants, growth of distributed generation and expansion of e-mobility, the deployment of new-age IT solutions in power plants is essential. In order to derive the full benefits of advanced technology solutions for power plants, developers must utilise plant performance data in every possible way to predict future scenarios, enhance efficiency and minimise unexpected downtime.
That said, with the growing interconnectedness of power systems, there is a higher risk of cyber attacks. Thus, utilities need to proactively manage the risks facing data and physical assets, and adopt best practices to keep systems secure and up to date. Further, for the successful implementation of SCADA and other automation solutions at power plants, it is essential to undertake change management, provide adequate training to the workforce, and carry out organisational reviews. n
With inputs from a presentation by Patteti Prasad, Executive Engineer, Andhra Pradesh Power Generation Corporation, at a recent Power Line conference.