SCADA Supervisory Control and Data Acquisition
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SCADA stands Supervisory Control and Data Acquisition. As the name indicates, it is not a full control system, but rather focuses on the supervisory level. It is a computer system for gathering and analyzing real time data. SCADA systems are used to monitor and control a plant or equipment in industries such as telecommunications, water and waste control, energy, oil and gas refining and transportation. A SCADA system gathers information, such as where a leak on a pipeline has occurred, transfers the information back to a central site, alerting the home station that the leak has occurred, carrying out necessary analysis and control, such as determining if the leak is critical, and displaying the information in a logical and organized fashion. SCADA systems can be relatively simple, such as one that monitors environmental conditions of a small office building, or incredibly complex, such as a system that monitors all the activity in a nuclear power plant or the activity of a municipal water system. This paper describes the SCADA systems in terms of their architecture, their interface to the process hardware, the functionality and the application development facilities they provide
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SCADA (supervisory control and data acquisition) is a category of software application program for process control, the gathering of data in real time from remote locations in order to control equipment and conditions. SCADA is used in power plants as well as in oil and gas refining, telecommunications, transportation, and water and waste control. SCADA systems include hardware and software components. The hardware gathers and feeds data into a computer that has SCADA software installed. The computer then processes this data and presents it in a timely manner. SCADA also records and logs all events into a file stored on a hard disk or sends them to a printer. SCADA warns when conditions become hazardous by sounding alarms
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1.1 Supervisory Control and Data Acquisition System:
Supervisory control is nothing but the ability to exercise control over a specific device, and to confirm its performance in accordance with the directed action. Let us define a supervisory control system as a collection of equipment that will provide an operator at a remote location with enough information to determine the status of a unit and to cause actions or operations to take place at that facility without being physically present.
Contemporary SCADA systems exhibit predominantly open-loop control characteristics and utilize predominantly long distance communications, although some elements of closed-loop control may also be present. SCADA systems generally cover larger geographic areas, and rely on a variety of communications systems that are normally less reliable than a LAN. Closed loop control in this situation is less desirable. It is used to monitor and control plant or equipment. Scada is a combination of hardware and software. It needs a man machine inter phase like a personnel computer
1.2 Main Functions of SCADA
• DATA ACQUISITION
• SUPERVISORY CONTROL AND MONITORING
• INFORMATION STORAGE AND REPORTS
• DATA PROCESSING
• SECURITY ANALYSIS
1.2.1 Data Acquisition
The primary function of SCADA system is to automatically collect data from the field using various types of sensors. The data is acquired by means of Current Transformers, Potential Transformers, Transducers and various other methods.
There are two basic modes of capture of input data. These are:
• Scheduled Capture, whereby the local units are polled on a regular basis and all input data are transferred
• Change of state capture, whereby only input data which have changed are transferred.
1.2.2 Supervisory Control and Monitoring
One of the main functions of SCADA system is to allow the entire process to be monitored and controlled with graphical user interface. The operator can interact and supervise a process from the operator console. The continuous monitoring can also ensure that the system retains its smooth operation by taking protective action. It is up to the individual specifications set, that decides how much the SCADA controls and monitors.
All the data scanned by the Central monitoring station is processed so that the system detects the abnormal conditions and if present alerts the operator in the form of audio-visual indication thereby calling for the intervention.
1.2.4 Information Storage and Reports
Record-keeping has always been an important task in the operation of electric systems. Accurate records are necessary to satisfy legal and governmental requirements, for accounting purpose, for support and forecasting of future system operations, and for engineering planning purposes.
1.2.5 Data Processing
Data Processing means a conversion of data from raw form into the form that is useful for calculation and presentation. Data Processing is responsible for converting Analog values from raw data to engineering units. It is also responsible for converting digital status points to a system convention of device states (0-closed, 1-open).
1.2.6 Security Analysis
The system security of any process may be defined as the ability of the system to operate in normal state even with the occurrence of specified contingencies. System security analysis is generally broken down into following three functions:
• System monitoring: SCADA provides up to date information regarding the condition of the process.
• Contingency analysis: Sometimes abnormalities give the operator very less time to react. SCADA system provides contingency analysis, which consists of actions to be taken by the operator in advance. Thus it allows the system to operate defensively.
• Corrective action analysis: It allows the operator to take appropriate operating action in the event of contingency in order to ensure the smooth functioning of the process.
1.3 Features of SCADA
• SIMULATION OPTION
• DATA IMPORT/EXPORT OPTION
• JOB MANAGEMENT
1.3.1 Simulation Option
SCADA system contains the simulator option which allows the operator to have a hand-on experience in dealing with the day to day problems occurring in the plant by creating the environs similar to that of the main process The operators are trained in this environment which depicts the same behavior of the plant and helps them, in understanding the plant operation in better version. The simulation method included in SCADA allows the testing of new control sequences before they are taken into operation.
1.3.2 Data Import/Export Option
In case of future expansion of the existing SCADA system or for acquiring data from another SCADA database the import feature allows the transfer of all the point configuration data via a ‘comma separated variable’ files.
Management of such data is possible using applications such as Microsoft excel Microsoft access, a text editor, or a database report writer.
For optimization of any pre-existing system it is very important to possess tools by which an existing system could be tailored according to the changes taking place. SCADA has a unique feature which allows the user to mould the system according to the demands thus making it more flexible. This ensures the plant optimization. Also while installing a new SCADA system these tools can help in properly meeting the requirements of the process.
Forecasting is the ability to predict the future state of a system by studying the previously collected data. Forecasting feature of SCADA systems allows the operator to visualize the state of the system well in advance, hence the operator has enough time to manage the system properly.
1.3.5 Job Management
The SCADA system can be programmed to do all the functions in the plant in a proper order. Also the tasks can be properly sequenced and executed to allow the most efficient task scheduling for proper utilization of man and machinery of the plant. Thus ensuring the most optimum utilization of the resources. Through proper job management and thus the conformance to international standards the safety and security of the plant and the personnel is also ensured.
1.4 Need Of SCADA In Our Project:
In a any power plant the turbine rotates and it gives mechanical power. That mechanical power is converted into electrical power through generator by faradays law of electromagnetic induction at Indian standard frequency. That is 50HZ.
The voltage of electrical output is maintained constant in power system for any load demand. But load is continuously varies with rising (or) falling trends. Consequently the voltage also varies with the load and similar to frequency also.
1.5 Problems Caused By Change in Voltage and Frequency & Its Remedies:
1. The change in voltage levels may cause severe damage to the load equipments at that instant the load equipment cannot be able to work efficiently.
2. Load output also varies with variation in input voltage levels.
3. The change in the frequency causes change in speed of consumers and also affects the plant production process.
4. The change in frequency damages the sensitive parts in the plant.
To minimize these problems must maintain the constant voltage & frequency in the power plant. In this project and implimentation we implemented an control strategy of voltage stabilization for excitation voltage in the alternator, why because? ,whenever the excitation voltage varies the output voltage of the alternator also varies. So to meet the load fluctuations we need to control the excitation voltage of the alternator.
In this project and implimentation, we also monitor the fluctuations in the frequency, due to non-linear loads the source frequency varies. We achieve these control and monitoring techniques of voltage and frequency by using SCADA technology.
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18-03-2011, 02:40 PM
Mohd Abdul Aziz
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SUPERVISORY CONTROL AND DATA ACQUISITION
System based control for HVDC links
Scada system has been used successfully to address some of the practical control problems. This paper introduces a practical control for a point to point HVDC link, based on the above system. The SCADA system is used to monitor the faults and to clear the faults. A ladder logic program has been dumping into a PLC. The simulation results presented in this paper prove the advantage of the proposed control scheme. This paper is an attempt to highlight the features of SCADA on hvdc links, which is a revolutionary development in automotive monitoring and control of process © 1999 Elsevier Science S.A. All rights reserved.
Keywords: SCADA; PLC; HVDC link.
SCADA’s powerful tools are being increasingly used for centralized control of remote processes to optimize operation of really complex systems such as automation of energy transmission, and generation of electricity. The inherent non-linearity involved in an HVDC link operation makes it difficult to design appropriate controllers under different normal and abnormal situations. The rate of change of the DC link current is highly sensitive to the firing angles on either side, due to the non-linear relationship between them. This leads to severe oscillations in DC link current and voltage waveforms as soon as a fault is cleared or the link is energized. These excursions impose a great deal of constraints in designing the converter valves, circuit breakers, reactors and filter banks. Sometimes the high value of di/dt can damage the associated equipment, especially the thyristor valves. Literature available in the DC adaptive control  is inconclusive of it’s practical application under large signal conditions. Several authors propose gain scheduling
controllers for HVDC links for these conditions. Recently Reeve et al. has tried a gain scheduling adaptive
Control strategy for HVDC links [2,3]. Hammedet al. has developed a coordinated control scheme based on optimal control strategy for parallel AC–DC
In this paper a new simplified control strategy based on the scada system approach has been developed. This system has been used to control the firing angle for the converter valves. In the end, the simulation carried out using programming logic controller (PLC).
2. HVDC system model
A two-pole point-to-point 6-pulse HVDC system has been simulated with the help scada system
The filters and transformers on either side of the DC link and the transmission line are represented in detail. The system shown in Fig. 1 is divided into four subsystems:
2.1. Subsystem 1
The rectifier side subsystem consists of a constant voltage and constant frequency source behind an impedance that comprises inductance and resistance to * Corresponding author. represent a simplified AC system. The short circuit
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Supervisory Control and Data Acquisition
Where we may require
• Industrial- manufacturing ,production ,power generation ,fabrication and refining.
• Infrastructure process may include like water treatment and distribution ,electrical power transmission and distribution systems.
• Facility based systems.
• Human Machine Interface
• Supervisory computer system
• Remote Terminal Units or Programmable Logic Controller
• Communication infrastructure
• Sensors measures Inputs and Outputs to the system.
• Sensors called DI/DO measures the direct digital ON/OFF values.
• There may be some analog sensors for some exact readings for example values of temperature
• Earlier–Radio, Modem or dedicated serial lines.
• Today-Ethernet and IP.
• For security reasons data is send in closed LAN/WAN’s not in open internet.
• GSM antennas and CDMA systems are installed at the physical locations.
• Data Presentation
• Computer stations variously called as master station.
• Humane Machine Interface.
• Full computerized control of SCADA master unit.
• Operator just need some mouse clicks to control any unit which are in turn controlled be the receiving RTU’s.
• Sophisticated master unit controls can run completely automatically.
• Another example from my summer training
• First Generation-Monolithic
• Second Generation-Distributed
• Third Generation-Networked
• Computing done by mainframe systems.
• No network’s existed therefore SCADA systems were independent systems with no connectivity to other systems.
• Communication protocols often proprietary.
• Redundant as a backup mainframe has to be used.
• Multiple stations were connected through LAN
• Task specific stations thus reducing costs and size .
• Communication still proprietary based.
• Security was a big problem.
• Open architecture rather vendor-controlled proprietary based.
• Internet Protocols used for communication.
• GSM and CDMA’s are installed.
• PID control continues even if communications to the main computer lost.
• System compatible with any further installation.
• Provide on board statistical and mathematical processing.
Area of concern
• The security and the vulnerability of the whole system through cyber-crime is the priority area of concern and the work in this direction is being considered.
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Supervisory Control and Data Acquisition (SCADA)
SCADA systems are used for monitoring and controlling chemical or transport processes and can be used in a factory environment such as electric power generation, water supply systems, gas and oil pipelines or any other distributed processes. In the field of electrical engg. SCADA is used in Distribution Automation.
• What we get out of distribution automation by SCADA systems??
SCADA principles of operation
• Master station and HMI
• Master station - The term "Master Station" refers to the servers and software responsible for communicating with the field equipment (RTUs, PLCs, etc)
• HMI(Human Machine Interface) - The HMI of a SCADA system is where data is processed and presented to be viewed and monitored by a human operator. This interface usually includes controls where the individual can interface with the SCADA system.
Interface with physical studies
• Programmable Logic Controllers(PLC)
• Intelligent Electronics Devices(IED)
• Remote Terminal Units (RTU)
• Fiber optics
• Low power radio
• Communications by fiber optics
• SCADA Functionalities
• Monitoring and control of EHV and HV network
• Distribution network power flow - To execute real-time power flow studies for optimal switching
• Fault location, isolation and service restoration
• Switching procedure management – execute switching orders
• Outage management systems – keeps records of forced and planned outages
• Load shedding and restoration
• Short term load forecasting
• Alarming facilities on fault detection
Future of SCADA in Distribution Automation
• The future SCADA systems are expected to centralize all the aspects of distribution i.e., supervisory, monitoring and controlling.
• Degree of automation and control is being improved which are to be used in future “Smart power grids”
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SCADA stands for supervisory control and data acquisition. It generally refers to industrial control systems: computer systems that monitor and control industrial, infrastructure, or facility-based processes, as described below:
• Industrial processes include those of manufacturing, production, power generation, fabrication, and refining, and may run in continuous, batch, repetitive, or discrete modes.
• Infrastructure processes may be public or private, and include water treatment and distribution, wastewater collection and treatment, oil and gas pipelines, electrical power transmission and distribution, Wind farms, civil defense siren systems, and large communication systems.
• Facility processes occur both in public facilities and private ones, including buildings, airports, ships, and space stations. They monitor and control HVAC, access, and energy consumption.
A SCADA System usually consists of the following subsystems:
• A Human-Machine Interface or HMI is the apparatus which presents process data to a human operator, and through this, the human operator monitors and controls the process.
• A supervisory (computer) system, gathering (acquiring) data on the process and sending commands (control) to the process.
• Remote Terminal Units (RTUs) connecting to sensors in the process, converting sensor signals to digital data and sending digital data to the supervisory system.
• Programmable Logic Controller (PLCs) used as field devices because they are more economical, versatile, flexible, and configurable than special-purpose RTUs.
• Communication infrastructure connecting the supervisory system to the Remote Terminal Units.
Industrial Use of SCADA System
This article describes the function of SCADA, its application in oil and gas flowing, waste water management, power and electricity surges.
WHAT DOES SCADA DO?
From a central reading location a SCADA system can track a number of remote sites equipped with Remote Terminal Units (RTUs) or Programmable Logic Controllers (PLCs). The RTUs can measure an array of conditions and a wider variety of parameters, including temperature, current, voltage flow, and tank levels.. The following types of sensors can be included in RTUs:
BLOCK DIAGRAM ::
Fig 1 :: Basic Block Diagram Of SCADA
The components we are using in PC based SCADA ie Sensors, Analog to Digital convertors, MAX 232, Desktop,crystal oscillator, ULN driver, relays.
In this PC based SCADA we are controlling temperature automatically of respective machine and monitoring voltage and current of that machine by using temperature,voltage and current sensors which are connected to respective machines.The temperature sensor we are using is LM35 whose specifications is -55ºc to 135ºc.where as thermistor can withstand low temperature and monitoring the readings of voltage and current for that we are using variable resistance pots.and the output of voltage,current and temperature sensors are analog but the micro controller supports only digital data.so this analog data is converted to digital data using ADC.and in this project and implimentation we are using AD0809 IC,in which the technique involved is successive approximation to convert analog to digital.and sensors are communicated to micro controller in this we are using is AT89S52 micro controller which is advanced version of 8051 which has xtra feature i.e.,it supports serial communication UART.and it has watch dog timer which is used to set when the program is stuck.and this micro controller send the data serially from ADC to desktop through MAX232.here max 232 is used to provide communication between micro controller and th pc,because directly micro controller and pc cannot communicate each other,the reason behind this is the language used in micro controller is TTL.
The specification of TTL is for logic’1’=5.v and for logic’0’=0.v.where as RS232 language is used in desktop,the specification of reserved standarad 232 logic is for logic’1’= -3 to -25.v and for logic’0’ = -3 to 25.v. so to convert TTL logic RS232 logic or from RS232 logic to TTL logic.,we have to use MAX232 which consists of inverting amplifiers.The clock frequency given to the micro controller is through crystal oscillator in that we are using quartz oscillator to provide very constant frequency,the clock frequency given ADC is from IC555 TIMER is astable multi-vibrator
To drive the loads we are using ULN drivers,which amplifies the current to 500m,amp and the supply given to this ULN drive is +12.v and the IC we are using is ULN2003A , which consists of darlington pair arrays acts as inverters.and this ULN driver has 7 i/p pins of that we are using only 1 pin to drive only one relay.
The power supply provided to all sections are given through circuit which includes step down transformer,rectifier,filter and regulator.The available power supply is 230.v AC.But the required voltage is 5.v and 12.v Dc.To step the voltage we use step down transformer.and it is 12v AC.This 12vAc is given to bridge rectifier which gives 11v pulsated DC and this is given to capacitive filter circuits.To get 11v Dc which is given to ULN driver and also to regulator 7805 to get 5.v DC with 500m amp current.
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18-02-2012, 04:11 PM
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