SCADA and Its Application in Electrical Power Systems

Power systems have evolved according to the needs of investors, consumers, and operators over the past decades. Enterprise resource planning solutions has led power systems to automate. And so, power systems began to incorporate the SCADA system in the late twentieth century. Before we know what SCADA systems are, we need to consider the history first.

 

History of SCADA system

In the early years when electric power systems began developing, electricity generation plants were only associated with their respective local loads. If anything failed in the whole linearly connected system, which could include subsystems like generating plant, power lines, connections, then the lights would be out. Customers had not yet adapted to depend on electricity. Outages, whether routine or emergency, were taken as a matter of course. As reliance on electricity grew, so did the need to find ways to improve reliability.

Generating stations and power lines were interconnected to provide redundancy. As the system expanded and began to scale out in size, it became harder to manage. Solutions were needed to face the challenges of controlling equipment over long distances. To overcome this, operating personnel were often stationed at the important points in this grid system so that they could monitor and quickly respond to any problems that might arise due to any fault or failure. They would communicate with central electricity dispatchers, often employing telephone, to keep them informed about the condition of the system.

Many manufacturing floors, remote sites, and industrial plants relied on personnel to monitor equipment and manually control through mechanical push buttons and analog dials. As the demand for reliable electricity grew even more and as labor became a significant part of the cost of providing electricity, technologies such as SCADA were developed which allow remote monitoring and control of the system's key parameters.

What is SCADA?

SCADA stands for Supervisory Control And Data Acquisition. SCADA is a system of different hardware and software elements that come together to enable a plant or facility operator to supervise and control processes.

Supervisory control is a general term for a high-level of overall control of many individual controllers or multiple control loops. It gives the operations supervisor an overview of the plant process and permits integration of operation between low-level controllers.

Data acquisition is the process of sampling signals by measuring a physical property of the real world in the form of signals and converting it from analog waveform into digital numeric values so that it can be processed by computing machines.

 

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Key features

Some of the key features of the SCADA system are mentioned below.

 

Computers process the data and let personnel in charge to oversee and direct the status of the power system using the acquired data. Personnel in charge were often operators and engineers who monitor the information remotely or locally. Now, the master station is tasked to supervise most of the system.

Control

Control in SCADA refers to sending command messages to a device to operate the Instrumentation and Controls system (I&C) and power-system devices. Conventionally, SCADA relies on human managers to initiate command from an operator console on the master computer. Field personnel can also control machines using front panels.

Data collection

Instead of collecting data and filling datasheets by hand, SCADA automatically compiles information in real-time. SCADA gathers data from hundreds or even thousands of sensors at a given time. It also generates backlogs for later analysis.

• Data communication:

SCADA delivers information to a central hub. A communication network transport all the data gathered from sensors. Earlier systems had radio or modem. Today, SCADA data is transferred over internet protocol (IP) and Ethernet.

• Data presentation:

SCADA interacts with human operators through work-station computers that deploy the human-machine interface (HMI). The master station presents a widespread view of the whole system and alerts the operator by visual display or alarm sound.

Components and its functions

SCADA system comprises of the following components

• Sensors:

Field instruments are an array of transmitters, monitors, and sensors. Sensors are the transducers which detect changes in physical quantity. These sensors can be analog or digital, but ultimately their purpose is the same. Sensors help its users to measure and collect data from various locations. The more complex a system, the more sensors we may need in place.

• Conversion units:

Sensors are responsible for collecting data, but we also need something to be able to receive and interpret the data. This is where the conversion unit comes in. Conversion units are the computerized units deployed at a specific location in the field. These are connected to sensors. They convert the information they receive into digital format, which is then sent to the centralized system to display. The two most common types of conversion units used in a SCADA system are PLCs and RTUs. How do we determine which unit we need? that depends on what our specification is.

            Programmable logic controllers (PLCs)

Programmable logic controllers are good for situations where we want more localized control. The programmable logic controller is an industrial digital computer designed for output arrangements and multiple inputs. PLC is used sometimes in place of other conversion units due to their versatility, flexibility, affordability, and configuration. However, one may need good programming skills to make the most out of it.

            Remote terminal units (RTU)

Remote terminal units are microprocessor-controlled electronic devices. Their objective is to interface a SCADA system with a sensor or whatever object the RTU is connected to. Normally, they transmit information through wireless communication. Therefore, they are considered good for functions covering a broad area geographically.

The above conversion units assist as local collection points for gathering information from sensors and delivering commands to control and protection relays.

• Communication network:

SCADA system cannot exist without a properly designed communication network system. All the SCADA system aspects rely solely on the communication network. It provides a channel for the flow of data between the supervisory control, the data acquisition units, and any controller that is connected to the system. The main function of a communication network within a SCADA system is to connect the Conversion units with the SCADA master station. The data can be transmitted through various communication platforms such as ethernet, telephone line, power line carrier communication, optical fiber line, cellular, radio, satellite, Wi-Fi, microwave, or other wireless protocol. Most facilities have specialized integrated network connectivity field buses, wired or wireless, due to security reasons.

• Master unit:

Master units are larger computer consoles that act as the central processing hub for the entire SCADA system. The Master unit offers a human-machine interface to the system and automatically regulate the managed system based on the response of inputs created by sensors.

The master unit is considered to be the supervisory computer system because they serve as the SCADA system centralized processing unit. Although the units themselves are typically larger computer consoles, there are several other SCADA components, such as software programs and HMIs, which could be named under this category as well.

Generally speaking, Human Machine Interface (HMI) is a user interface or dashboard that connects a person to a machine, system, or device. In a SCADA system, it allows the operator to view and interact with collected and processed data. This interface is usually used to perform tasks like collecting data, creating maps, diagrams, sending out notifications, and making reports.

• Remote communication server (RCS):

After processing and analyzing the data gathered in the SCADA system, one needs a digitally and physically secure place to store this vast database. The human-computer interface (HCI) or HMI commonly requests data from a server responsible for data acquisition, a component of hardware that is used to connect software services to the conversion units out in the field. The server makes data acquisition from these local units possible.

Applications of SCADA

Commonly SCADA systems are used when a need arises to automate complex processes where human control is not feasible. In power system specifically, this can include

1.  The system needs an uninterrupted power supply and a protected environment
2.  We would need to know the status of a complex power system in real-time
3.  We would need to monitor and control system that are in remote areas

The power generation, transmission and distribution sectors, supervision, monitoring, and control are the main aspects in all these areas. Therefore, the SCADA implementation of power system improves the overall efficiency of the system for optimizing, supervising, and controlling the generation, transmission & distribution systems. SCADA function in the power system network offers greater system reliability and stability for integrated grid operation.

• SCADA for power generating stations:

Bringing an optimal solution for each process to involve in power generation operation is flexible with advanced control structures. With the use of PLCs and powerful bus communication links along with SCADA software and hardware in generating stations, it supervises several operations including protection, monitoring, and controlling. To provide reliable energy, to minimize operational costs, and to preserve capital investment, the SCADA system is taken as seriously in generating stations.

The highlighted functions of SCADA in power plants include:

• Continuous monitoring of speed and frequency of electrical machines
• Geographical monitoring of coal delivery and water treatment processes
• Electricity generation operations planning
• Control of active and reactive power
• Boiler and turbine protection and their condition in case of thermal plant
• Monitoring of renewable energy farms and load dispatch planning
• Load scheduling
• Historical data processing of all generation related parameters
• Supervising the status of circuit breakers, protective relays, and other safety equipment
• Power apparatus health monitor
• The sequence of events recording

• SCADA for power transmission system:

Transmission line corresponding circuit model parameters are often in error as compared to values measured by the SCADA system. Without a SCADA system, these errors cause the economic dispatch to be erroneous, and hence, lead to increased costs or incorrect billing. These errors could also affect state estimator analysis, contingency analysis, short circuit analysis, distance relaying, machine stability calculations, and transmission planning in case of expansion. Therefore, SCADA integration into the transmission system is significantly considered.

Some main functions of SCADA in electric transmission system are as follows:

• Re-routing services for station maintenance
• Service restoration
• Protective relay interface/interaction
• Voltage regulation management
• Load tap changer control
• Transformer management
• Real-time modeling
• Automatic circuit isolation control and interactive switch control display
• Interface real-time single-line displays
• On-line operation and maintenance logs
• Automatic system diagnostics by using system-defined controller alarms (alarm management)

• SCADA for power distribution system:

The power distribution system deals with the dispersal of electricity from distribution substations to the loads. Many utility companies depend on manual labor to perform the distribution tasks like interrupting the power to loads, hourly checking of key metrics, fault diagnosis, etc. SCADA implementation to the power distribution not only reduces the manual labor operation and its cost but facilitates smooth processes by reducing disruptions.

SCADA system gathers the data from various electrical substations and correspondingly process it. PLCs in substations continuously monitor the substation components and corresponding transmits that to the central system.

It is in charge of:

• Improving efficiency by maintaining a tolerable range of power factor
• Limiting peak power demand
• Trending and alarming the operators by identifying the problem spot
• Historian data and viewing that from remote and barely inaccessible locations
• Quick response to customer service interruptions
• Feeder automation and Load Sectionalizer
• Provide the ability to over-ride automatic control of capacitor banks
• Automated meter reading
• Circuit breaker control, lockout, and interlocking
• Continuous monitoring and controlling of various electrical parameters in both normal and abnormal conditions which may affect the quality like harmonic distortions

Advantages of SCADA

SCADA systems are an extremely advantageous way to run and monitor processes. They are great for small applications, such as climate control. They can also be effectively used in large applications such as monitoring and controlling a nuclear power plant or mass transit system.

• Optimizing performance:

SCADA systems minimize errors by accurately measuring data and increasing the overall efficiency of the system.

• Reliability and robustness:

The specific development of SCADA is performed within a well-established framework that enhances reliability and robustness where power requirement is crucial.

• Maximize productivity:

The specific development of SCADA is performed within a well-established framework that enhances reliability and robustness where power requirement is crucial.

• Improve quality:

Analyzes and controls the quality of the produced electric energy profile using standard SCADA functionality.

• Reduce operating and maintenance costs:

Less personnel and trips are required to monitor field gear in remote locations, this reduces maintenance and training costs.

• Integrate with business systems:

A SCADA system can be easily integrated with the business systems, leading to increased production and profitability.

Conclusion

SCADA system can be implemented on a large scale in power systems so as to increase their performance, reliability, and durability. Data acquisition and monitoring can be very convenient and accurate if power systems are upgraded to SCADA. Now, electrical systems are extremely efficient and intelligent to monitor and control all of the involved operations and procedures and it has become possible only because of technological advancements. So we can conclude that it's essential for the power sector to optimize their systems as per the requirements of the technical changes.