SUPERVISORY CONTROL AND DATA ACQUISITION

ABSTRACT
”The Energy is neither created nor destroyed” and the energy is generated, transmitted, distributed and finally utilized. At every stage certain supervision, control and protection is necessary. This paper deals with basic SCADA system, its components, basic block diagram, functions, applications and advantages of SCADA.
SCADA helps in monitoring the system and have alarm generation facility incase of faults, which helps in real time analysis. This paper deals with the data logging ability of SCADA enabling off line analysis. Thus remote control over power system is achieved by SCADA, which is effectively depicted in this paper.
This paper is an attempt to highlight the features of SCADA, which is a revolutionary development in automotive monitoring and control of process. The need for SCADA as well as its hierarchical structure has also been mentioned in the paper. The component of SCADA, which is divided into two parts hardware and software, has also been taken in detail. Features of the SCADA such as simulation options, data import and export function has also been taken into account. A criterion for economic operation of grid as well as states in which it operates has also been considered. Security and reliability which is a prime factor for automated systems has been explained to us..

INTRODUCTION:
These days sophisticated working environment has become a need of the hour. Analysis of the following problem would make the need more specific. For example: Central Railways cover a large and extensive area and efficient operation of such large network is must. Consider that circuit breaker near remote place has tripped and the supply has been cutoff. The power supply has to be restored as early as possible so that the route is cleared for the other trains and the smooth flow of trains is possible.
Hence the question of centralized monitoring and control arises. If the person back in control room knows the position of circuit breakers and could control it from there itself, the power is restored quickly and hence disruption of train route is avoided. To achieve this control data is to be acquired precisely and accurately. Thus the above problem shows us that there is need of centralized control and monitoring system, which in this age is achieved by using the SCADA system.
Automation eliminates human errors, while achieving better productivity and optimum utilization of resources with lesser requirement of time. SCADA is a revolutionary development in automatic monitoring and control of processes. 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 distribution systems, generation of electricity, customer information system and engineering analysis.
WHAT IS SCADA AND ITS NEED?

SUPERVISORY CONTROL AND DATA ACQUISITION –we more frequently call it as SCADA. As the name implies SCADA system supervises, acquires and control data received from a distant data source from the control center. SCADA system is located in the control center and is operated in the scanning mode, communicating between the CONTROL CENTER and the REMOTE STATION by means of two-way communication channels. Such a supervisory control and data acquisition system is intended to facilitate the work of operator by acquiring and compiling information as well as locating, identifying and reporting faults. On the basis of information received, the operator makes necessary decisions via the control system he can then perform different control operations in power stations or influence the processing of the information acquired. The main task of a modern day power system is to ensure quality and reliable power at an economic rate. Hence the system is to be updated at a very fast rate (real time mode/management), which helps to control the complex system effectively without any loss of time.
FUNCTIONS OF SCADA:
DATA ACQUSITION- Furnishes status information & measurands data to operator
CONTROL - Allows the operator to control the devices e.g. ckt breakers, Xmer, tap changer etc from a remote centralised location.
DATA PROCESSING - Includes data quality & integrity check, limit check, analog value processing etc.
TAGGING - Operator identifies any specific device & subjects to specific operating restrictions to prevent from unauthorized operation
ALARMS - Alerts the operator of unplanned events & undesirable operating conditions in the order their severity & criticality
LOGGING- Logs all operator entries, alarms &selected entries
TRENDING- Plots measurements on selected scale to give information on the trends e.g. one minute, one hour etc.
HISTORICAL REPORTING - To save & analyze the historical data for reporting, typically for a period of 2 or more years & to archive.

FUNCTIONAL UNITS OF SCADA:
Following equipments perform the above functions;




The figure shown below represents the simplest SCADA configuration employing single computer;
Computer receives data from RTUs via the communication interface. Operators control base one or more CRT terminals for display. With this, terminal it is possible to execute supervisory control commands and request the display of data in alpha numerical formats arranged by geographical location and of type.
The programming input/output is used for modifying the supervisory software. In the basic SCADA system, all the programs and the data is stored in the main memory. The more sophisticated version of SCADA has additional auxiliary memories in the form of magnetic disc units.
TWO-WAY COMMUNICATION CHANNELS BETWEEN THE MASTER CONTROL CENTRE AND REMOTE CONTROL CENTRE

Traditionally, the SCADA systems were used for scanning mode, providing data regarding generating stations, generating units, transformer sub-stations etc. Traditional hard wired SCADA systems were arranged to perform several functions to supplement Automatic Control and Protection Systems.
Now a day’s protective relays, control relays and control systems are used for automatic control of generating stations and transmission systems along with SCADA. Only initiating devices may be different or omitted with fully automatic SCADA control. For example, tap changing may be initiated either by the sub-section control room operator or by the automatic voltage control relays connected in the protection panel of the transformer.
Controls systems were arranged to keep the values of controlled quantities within target limits. Protection equipments were arranged for sounding alarms and for tripping circuit-breakers. With the recent revolution in microprocessor technology, the size, performance and cost of digital automation systems have become acceptable in commercial installation. SCADA provides integrated approach to power system protection, operation control and monitoring, automatically with least intervention of the control room operator.
The microprocessors located in the master station, generating stations, transmission sub-stations and distribution sub-stations provide control and protection decisions locally where the data is located. The action is reported to the operator "by exception". The operator retains the option of taking intervening action of overriding or initiating of his own. All these microprocessor based systems are connected through the GLOBAL POSITIONING SYSTEM. The functions and architecture of SCADA system is selected in accordance with the functional requirements and size of the power system.
HEIRARCHICAL STRUCTURE OF SCADA.





FEATURES OF SCADA
Tracker Option: This feature provides collection and storage of variety pertaining to the serialized items such as time stamps, quality measurements, temperature, humidity, pressure, sub- assembly part number etc through various automated sensors and readers like bar code readers, radio frequency tags, mechanical tag based system. This information is used for over viewing the flow of serialized items and the location of materials through the system which helps in isolating the defective items from the perfect ones. For example boxes or containers over a specified weight limit may be routed to different storage area
Simulator option: SCADA system contains in it the simulator option, which allows the operator to have a hand-on experience in dealing with the day-to-day problem occurring in the plant by creating the environs similar to that of the main process. The operators can be trained in this artificial fault environment, which helps in understanding the plant operation in better version.
Data import/export function: This feature allows the transfer of all the point configuration data via a ‘comma separated variable’ file. Points are the representation of actual field parameters; these are the variables in which the actual incoming data is stored. Similarly point configuration can be sent to other SCADA system for their use over their. This is made possible through data import/export facility. Data management is possible using MS EXCEL, MS ACCESS etc.
Flexibility: This feature provides tools by which an existing system could be tailored according to the changes taking place. Thus the user can mould the system according to the demands thus making it more flexible.
Forecasting: Forecasting is the ability to predict future state of the system by studying previously collected data. Forecasting feature of SCADA system allows the operator to visualize the state of the system well in advance, hence the operator has enough time to manage the system properly. This feature of SCADA finds a huge application in Energy Management System.
Job Management: Using SCADA all the tasks can be properly sequenced and executed to allow the most efficient task scheduling for proper utilization of man and machinery of plant. Thus ensuring the most optimum utilization of the resources. And hence, the conformance to international standards of safety and security of the plant and personnel is also ensured.
STATE ESTIMATION:
The prime interest of the power system managers is the economic way of operating the grid, which is economic load dispatch. For economic operation of grid we must fulfill the following criteria’s:
• Optimize the low cost/unit generation and minimize the high cost generation
• Optimal loading of all EHV lines within permissible limits
• Cost evaluation of generation on penalty factor base
It is the foremost duty of the load dispatcher to run the grid in steady state which is normal and healthy state of the grid through which easy monitoring and security of the grid is achieved. This evaluation is only possible with specialized software packages which need the real time data.
SECURITY OF SYSTEM OFFERED BY SCADA:
In the age of automated systems, security, reliability and availability of data is top priority of any computer based automated system. Small loss of data in such system can cause havoc and may bring a system to a standstill.
SCADA ensures a high degree of security. 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. The system shall by all means remain in the state of normal operation by means of fast acting control systems following a contingency and without having a system to go into an emergency state. Continuous monitoring of security and appropriate corrective action for improving security is called security control. System security analysis is generally broken down into following three functions:
• System monitoring: SCADA provides up to date information regarding the condition of the processes.
• Contingency analysis: Sometimes abnormalities give the operator very less time to react. SCADA System provides contingency analysis, which consists of action 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 corrective action in the event of contingency in order to ensure the smooth functioning of the process.
CONCLUSION:
From the above paper, we can summarize that the SCADA supplements the control and protection system to form an integrated system, which is compact, economical and versatile…. In short we can say that it acts under the GLOBAL POSITIONING SYSTEM, so that whole system works in same time domain.
Today the buzzword in any industry is “Optimal Performance at Maximum Economy”. SCADA has provided the industry with the perfect “Man Machine Interface” which has solved many or to be precise, most of the problems related to monitoring, supervision, data acquisition and controlling. The most significant contribution of SCADA is probably having an easy-to-use graphical interface, which has made the tedious job of operators very easy. SCADA has manifold applications like Distribution Management, Energy Management, Power Plant Management & Oil and Gas Distribution System. SCADA has also enabled Grid monitoring by virtue of which power can by shared on national basis. So the bottom line is that SCADA is a boon to Indian power sector.
Advantages of SCADA system:

Flexible, simple, reliable, Efficient with fewer work forces, Security,
Self-checking and readability, Portable and cost efficient.
Applications of SCADA system:
The SCADA systems can be applied in the following areas -Inside power plant, On power plant, Industrial establishment. Load dispatch center, Railways.
REFERENCES:
1. Torsten cegrell,”power systems control technology “.
2. Sunil S. Rao, “Switchgear Protection and Power Systems”
3. A.K. Sawhney, “Electrical Measurements & Measuring Instruments”