Supervisory Control and Data Acquisition Essay Example

the past, cables and wired communication were used, but this was limited to small areas. SCADA is used in power plants to monitor transmission and uses wireless communication when LAN is not possible. SCADA is used in various areas such as power systems and water and sewerage systems for monitoring and control. The functionality of SCADA includes alarm detection, data acquisition, real-time control, database logging, and report generation. SCADA systems are categorized into RTUs, communications, and HMIs, which are operated by a master station, MMI/HMI, and RTUs or PLCs. RTUs or PLCs are data interface devices that connect to field sensing devices.The text describes computerized units located in distant countries that gather data and control information. These units are connected to detectors and switches, and their purpose is to convert electric signals to digital signals. The detectors and control relays are simple electric devices that cannot transmit information on their own. The remote telemetry unit (RTU) acts as an interface between the detectors and the SCADA web. The RTU and PLCs are responsible for most of the controlling in the SCADA system.

The text also mentions a communication network used to transfer information between monitoring devices, controlling units, servers, and central computers in the SCADA system. This network can be wireless, telephone lines, cables, satellites, or a combination of these.

Furthermore, there is a master station that serves as the main processing unit for the SCADA system. It is also referred to as a SCADA Center, master station, or Master Terminal Unit (MTU). The master station includes various modules such as Historical Management System, Trend Management System, Log Management System, and Alarm Management System.

MTU utilizes sensor inputs

to predict and automate the management of a system. The Human Machine Interface (HMI) or Man Machine Interface (MMI) acts as an intermediary between the SCADA system and the operator. It processes and presents information to the operator for supervision and control. SCADA system functionality can be divided into four maps: data acquisition, data communication, data presentation, and control. Data acquisition involves aggregating real-time data from hundreds of sensors to monitor the entire system. It digitizes and processes electric signals from detectors or gauges, and collects data from remote sites for processing on a centralized computer.

Data acquisition systems are commonly used for retrieving, analyzing, and displaying information. These systems can also be integrated into a process control system, utilizing software that allows for direct digital control of various processes. They typically include signals, detectors, actuators, signal conditioning, data acquisition devices, and application software. Data acquisition software is used for a range of functions, from simple data collection to advanced programs for measuring and controlling processes. In real-time, the software captures device data from scales, gauges, and barcode scanners.

Data acquisition package is responsible for reading device information from TCP/IP protocol. It has the capability to control various procedures such as starting or stopping a counter, sending control commands to an analog-to-digital converter, and collecting data points at regular intervals from sensors or switches. Some advanced data acquisition packages also provide graphical and pictorial representations, such as graphs or 3-dimensional graphics, to display the gathered information. The monitored data is then stored in a database.

The SCADA system's human-machine interface (HMI) is where the processed information is presented for monitoring by a human operator.

In order to monitor multiple

systems from a central location, a communication network is required to transfer all the collected data from remote areas to the central station and vice versa for processed data from the central station to the HMI/MMI. Previously, SCADA networks used wireless telephone lines, modems, or dedicated serial lines for communication.

Now we are using Ethernet, IP, and wireless communication in industrial works. SCADA information is encoded and transferred securely using these protocols. The SCADA protocols are designed to be very compact. RTU, or Remote Telemetry Unit, converts the electrical signals from equipment such as sensors and relays into digital values. The RTU acts as an interface between the sensors in a remote location and the SCADA system. Distant telemetry units, or RTUs, are used to transmit data from remote areas to a central station. The RTU receives command orders in protocol format from the central station, converts electrical signals, and transfers them to the appropriate control relays.

Data Presentation: The information received from RTU's or PLC's will be displayed to the web operator over a computer system in the central station. The human-machine interface (HMI) in the central station monitors the whole system, including detectors. It provides the operator with graphical or pictorial representations of the system's operation. It also alerts the operator with alarms when there is a malfunction in the system.

Control: The information gathered from a remote site is mostly controlled automatically by Remote Terminal Units (RTUs) or Programmable Logic Controllers (PLCs) with predefined values. An operator using the Human Machine Interface (HMI) monitors the situation and issues control commands as needed.

SCADA system allows operators to modify predefined parameter values for flow, circuit breaker operation,

starting and stopping of a counter, and enable alarm conditions, such as high temperature, to be displayed and recorded. The entire control can be achieved from a central location without any risk. The performance of the system is monitored after executing the control commands.

SCADA APPLICATION IN POWER SYSTEM: By using SCADA system, a large network consisting of multiple generating stations, substations, and large load centers is controlled from a centralized dispatch. SCADA system focuses on remotely monitoring, coordinating, controlling transmission and distribution components and devices in real time from a remote area, with data acquisition for analysis and planning from one control area.

Most SCADA systems operate on either a UNIX platform or VMS.
Operation:
In this system, the existing real-time data from the power system is collected using transducers. These transducers convert the alternating current (a.c.) signals from the current and power transducers into direct current (dc) signals proportional to the measured values for various parameters. The converted data is then transmitted to a remote terminal unit (RTU) located at generating stations or substations. The information is subsequently transmitted to the load control center through power line carrier systems (PLCC), fiber optic communication, and microwave channels. This allows for effective data acquisition.

The information processed by computer systems using energy management software enables automatic and remote control of the network at the load control center. The load control center then transmits instructions to the control rooms of the substation and generating station to carry out the necessary actions. Digital computers and microprocessors installed in the control rooms of large substations, generating stations, and load control centers are used for data collection, data monitoring, and automatic control. Therefore, by

utilizing a SCADA system for power distribution networks, a comprehensive approach to power system protection, operational control, and automated monitoring is achieved with minimal intervention from the control room operator.

SCADA FUNCTIONALITY IN POWER SYSTEMS

• Data acquisition: SCADA provides measurements and status information to operators.
• Visualization: SCADA represents diagrams and measurements on selected time intervals.
• Supervisory control: SCADA enables operators to remotely control devices such as circuit breakers and relays.

SCADA uses web operators to remotely control circuit breakers, disconnect switches, transformer taps, and tap changer positions. It allows operators to monitor the generation and high voltage transmission system to predict overload conditions or abnormal voltages. SCADA monitors the position of all switch gear, substation loads and voltages, capacitor banks, tie line flows, and interchange schedules. It utilizes telemetry to detect failures and errors in the bidirectional communication links between the computer and remote equipment. These functions are continuously scanned. SCADA provides status and measurements for distribution feeders at substations.

The use of SCADA (Supervisory Control and Data Acquisition) system helps improve the functionality of distribution control centers, as it allows for real-time monitoring of client metering, pricing, and equipment exchange. It also aids in the management of distribution systems by collecting and analyzing extensive data, thus minimizing human errors and ensuring efficient operations. The system generates periodic reports that facilitate the analysis of power system performance. Additionally, SCADA includes distribution network monitoring capabilities with geographical mapping and error detection features.

The introduction of 'distributed control' has reduced the cost of cabling within

the works and has the potential to replace control suites with distributed CRT/keyboard Stations. Data Acquisition collects information from specific points in the power system and converts them into engineering units. These inputs are then brought through cables to terminals. This information is used for various functions, including:

• Display on CRT screen.
• Graphic display of works sub-systems.
• Data logging.
• Alarm generation.
• Event logging.
• Trending of parallel variables.
• Performance calculation.
• Generating control signals.

The CRTs in the control room allow operators to display alarms and works variables.

The information of works, including existent clip variables and position information, can be viewed. The bounds of all variables are checked to ensure that no variable is out of scope. If a variable is out of scope, an error message is displayed. The position modifications and clip of events are accurately maintained in order to ensure efficient quality analysis. To achieve this, all the equipment is periodically calculated.

AUTOMATIC SUB-STATION CONTROL

Electrical energy is transferred from large generating stations to distant load centers through various sub-stations. These sub-stations require certain monitoring, control, and protection functions.

Every substation is equipped with a control room where the relay and protection panels, as well as control panels, are installed. The control-relay panels are responsible for controlling various devices such as circuit surfs and pat modifiers. In smaller independent substations,

the operator can supervise and operate normal service with the help of parallel and digital control systems.

The surfs can be remotely operated from the control room using a remote control. In cases of errors or abnormal conditions, the surfs are automatically operated by protective relays. Therefore, the primary control in the sub-station can be categorized into two classes: normal everyday operation by operators' commands and automatic operation by the action of protective relays and control systems.

SUB STATION CONTROL FUNCTION ARRANGED THROUGH SCADA SYSTEM

Alarm Functions: The alarm functions are designed to sound an alarm or provide annunciation signals in case of unsafe or unusual events such as abnormal values of process parameters, fire, illegal entry in premises, over temperatures, low voltage of subsidiary supply, and unusual occurrences. These alarms are obtained from a data logger and are meant to alert the operator in the control room.

Control and Indication:
- Control of two-position devices such as circuit-breakers, isolators, earthing-switches, starting motors. The ON/OFF state of these devices is indicated on the control board/mimic diagrams.
- Control of devices with variable positions (e.g., closed, middle open) including setting values, input scenes, and indication of position on control panels.
- Control of multi-position devices (e.g., pat modifier) and indication of position on control panels.
- Indication without control.
- Control without indication, such as adjusting the generator load by automatic load frequency control.

Data aggregation, entry, and display. Devices operate consecutively based on preset timing and conditions, including:

• Auto-reclosing operation of circuit-breakers, with opening-closing time intervals
• Sequential operation of circuit-breaker, isolator, and earthing switch during circuit interruption
  

and closing.

Through the SCADA system, the operator in the control center can perform various operations at a distant sub-station, such as:

• Opening and closing of switching devices I
• Tap-changing of transformers for voltage control
• Switching of capacitance banks for voltage control
• Load shedding for load frequency control

Some of these operations can be automated by a computer-based system without human intervention, including network islanding and backup protection. The automatic control functions are divided into:

• Interconnection functions
• Transmission line automatic functions
• Distribution system automatic functions

Therefore, the use of SCADA system increases capacity utilization in power generation.ii. The SCADA system is responsible for monitoring and controlling the power grid, ensuring operational efficiency and system security. It allows for remote monitoring and control via wireless networks.

Advantages of the SCADA system include real-time data monitoring, time synchronization with GPS, supervisory control, communication for power system coordination and control, alarms for abnormal conditions, surveys, optimal power utilization through computers, electrical power plant planning, reduction in manpower, monitoring of power theft, cost savings, faster restoration of normal operations, equipment outage minimization, user-friendly report generation, web integration, and energy management.

References:
1. http://en.wikipedia.org/wiki/SCADA
2. D.P.KOTHARI, MODERN POWER SYSTEM ANALYSIS
3. http://www.dpstele.com/pdfs/white_papers/scada.pdf