Supervisory Control and Data Acquisition (SCADA)

1. INTRODUCTION

SCADA stands for Supervisory Control and Data Acquisition. The need of SCADA industry was born out essentially for easy and manageable front-end to a PLC (programmable logic controllers) system. SCADA systems are considered as the backbone of modern industries. This system is used by both private and public sector industrial companies and organizations. Their configuration ranges from simple to large complex installations. A wide variety of devices in industry like gas and water pumps, traffic signals and track switches are monitored and controlled remotely, and their efficiency is maintained through this system.

The entire system is monitored in real time which is the main process of the SCADA. This is done through data acquisition like meter reading and for checking the sensors’ status. SCADA system has several data elements which are called points. Each point on system is a sensor or a monitor, and they can be either hard or soft. A soft data point can be seen as software calculate or an application whereas hard point can actually be a monitor. From these soft and hard points, the data elements are stored usually and recorded to create a history or time stamp. The data points, depending on a system communicate at standard intervals. The data is displayed to human besides of being used by RTU. Humans can interface with the system to make changes or override settings when needed.

OBJECTIVES

In today’s world, some SCADA system always runs behind the control setup of any industry or company. It can be seen a significant saving of money and time by using the effective SCADA systems. The main purposes and objectives of this system are:

REGULATORY COMPLIANCE:  SCADA system ensures that the regulation standards which are set by the industry are followed by the processes by monitoring and controlling them to meet those industry regulations.

SAFETY: Faults in the systems are detected early by the SCADA to make the operations suspicious in any situations. Possible risks, necessary precautions in the control process and its management and repair are also considered thus providing the safety of the personnel. Reaching the risks at the critical level is also limited by the system which can cause devastation the industry.

OPERATING EFFICIENCY: It also facilitates the unattended operations efficiently in control process. The processes are optimized as a result input value is reduced, and output value is maximized.

DATA RECORD: SCADA can record and store the data of control process. Various devices are processed and analyzed over the time. Also, it keeps the records of all the working detail of the various field areas. Strategy and initiatives of future plans are enabled for the betterment of the specific area. 

2.   FUNCTIONS OF SCADA

SCADA system performs below four functions:

a.    Data Acquisition

Measuring a physical or an electrical phenomenon like current, voltage, etc. using the computer is the process of data acquisition. It consists of sensors, data acquisition hardware, and programmable computer software. SCADA system has the master terminal unit (MTU) which acquire data periodically from a remote terminal unit (RTU). The remote terminal unit respond as a request from MTU or transfer the data continuously when the state of parameter changes or in the case of exceeding in the limits of the parameter. In this process the internal database of RTU is scanned internally, periodic polling of RTU by MTU, data transmission from the RTU to the MTU, data scaling in engineering units and also previous state or value can be updated in the database.

b.    Networked Data Communication

In a communication system, the data is transferred between the interface devices at the field and the control units and computers in SCADA central unit. The System of communication can be a radio, cable, telephone, satellite, etc. or it can be the combination of any of these. To communicate with different devices, machines, and the software products the SCADA system master in technologies. It starts with the simple serial connection through the system of field bus to the complex network constructions. This system is operated often in combination with human machine interface applications and the production level reporting.

General Layout of SCADA System 

    c.     Data Presentation/Display

SCADA system presents information on the multiple screens including both synoptic diagrams and texts. It provides the facility of monitoring the human operations continuously and interference when needed. HMI software of SCADA consists of graphical symbols library which associates tag names for particular parameter or device such as level information of tank or the ON/OFF switch status etc. Its display structure is mostly organized in the form of tree structure where using the cursor, trackball, keyboard or positioning techniques of touch-screen allows the human operator to choose various displays on index pages.

    d.    Control Applications

Switches are used in SCADA system to operate devices at control area. By using the switches, any process can be turned ON or OFF at any level from control station. SCADA system works automatically, but in the critical situations, it is handled by human power. Below figure represents the implementation of SCADA structure in the power generation where several operations are supervised including monitoring, protection and controlling.

SCADA in Power Generation 

3. FEATURES OF SCADA

The features of SCADA that are taken into account are:

    a.    Alarm Handaling

Most of the SCADA systems have an in-built alarm feature. Many plants are monitored and controlled using automation systems which provide rich data to SCADA system. Using this data almost every aspect of operating plant can be monitored. It provides different options like event loggings historical alarms and generation of the alarm reports. In modern automation system alarms can easily be added to the screen without any expense which provides many benefits. But alarm fatigue can be created for the operator if there are too many alarm points.

     b.    Trend Curve Pattern

Trends are the industrial process data which is displayed in real time in the form of charts. These files can be saved and viewed later if needed. There are two types of trends: real-time trend which provides information about any event in the real time so updated continuously. It is possible to configure down the trends in real time to milliseconds and also provide the details of the current condition of process. Whereas historical trends are the past event trend patterns which are configured down in days. Through this feature, data is displayed and exported or archived the historical events.

Trend Curve Pattern

   c.     Data Access

Despite the large scale integrated system the data is always uniform no matter where and how it is accessed through monitoring system. The data is accessible in real time and to any third parties and network user. This reduces not only cost but the personnel efforts through remotely monitoring with the increasing efficiency thereby providing the benefits of early detection of the faults, adjustment of devices remotely and running of operations smoothly.

   d.    Networking And Processing

This aspect of SCADA involves the supporting of all the compatible protocols and networks. It also made possible the availability of data in network from anywhere and processes the reports and trends. One of the important features of networking and processing is the real time operation of the open design architecture of the SCADA.
4.   CLASSIFICATION OF POWER SYSTEM AUTOMATION

Power system automation is classified into substation automation and distribution automation system discussing them one by one.

1.  Substation Automation

In substation automation system, frequency, bus voltage, power factor, line loading, etc. are the basic variables. In substation there are two operations involved which are classified as:

1.Routine operations: Operator gives commands to carry out these operations.

2.Automated Operations: these are carried out by using the control system and relays.

An automated substation is the combination of following two systems:

a.      Control System:

Control system functions are collecting and scanning of data, reporting, controlling variables like voltage, power, etc.  Also, it controls the switching actions for example closure of the circuit breakers automatically, changing tap, transferring of loads etc.

b.      Protective System:

In protective system, abnormal conditions are detected for example automatic tripping, alarms etc. and also the faults are minimized within substation.

For automating the substation these two systems co-operate with one another. Automated functions are mostly integrated in a modular nature of software, which provides the facility to integrate with the other systems.

2.    Distribution automation

Fault detection was carried out in distribution system by the manual labour, which required increased effort and time to resolve the issues in this system. Distribution system is inefficient as it has various elements. Because of this automation is required for running the distribution system efficiently and to minimize the faults occurring in it.

For the automation process of the distribution system, following equipment are required which are classified as:

 1. Data collecting equipment

2. Data transmitting equipment

3. Monitoring equipment

4. Processing equipment

5. HMI (human-machine interface)

Integration of all of above equipment is done by using the distribution SCADA system. And for the installation of the distribution SCADA system following units is required.

a.      Data Acquisition Unit:

To control and monitor the distribution system data is required such as frequency, voltage, current, power factor, time, reactive power and real power. Among the other transducers, CT’s and PT’s are employed to collect data. The data is amplified and conditioned before transmitting to control room and then it is processed there.

b.      Remote Terminal Units:

Signals are recorded and checked before transmission to control room by using the RTU’s. These are used for setting values and sending commands to the devices.

c.       Communication Unit:

To transmit data and commands over long distance, efficient communication system is required. UHF MARS, power line carrier communication etc. are the technologies used for this purpose.

5.   ADVANTAGES OF DISTRIBUTION AUTOMATION

Because of high electricity generation and maintenance cost and not so good customer service, the electric utilities consider the distribution automation as a solution. Other than these economic challenges the other advantages of distribution automation are:

a.    Reduction in Line loss:

The role of substation is the hub of distribution network. Distribution feeders, electrical equipment and other components of the distribution system complement and work in tandem in this hub thereby increasing the reliability of the whole distribution network. To address the VAR/Volt control expert algorithms are used which controls and monitor the voltage devices in substation with the coordination of down-line voltage devices which increases the throughput of line and reduces the line losses.

Distribution Optimization

b.    Reduction In Energy Coast

Monitoring in real time uses power with the help of which monitoring equipment along with distribution feeder helps the customer to keep tracks of their respective patterns of energy consumption and provides the facility to assign accountability to the operating staff and first line supervisor to perform responsibly. This helps the utilities and customers in the reduction of their cost.

c.     Economic Benefits

As far as the investment is concerned there are so many benefits of the effective distribution automation system. Benefits related to investment can be achieved by adding the deferring generation and releasing the transmission capacity and by replacing the equipment of distribution substation. Features that contribute to the capital deferring benefits are data logging and monitoring, voltage or VAR control and load management.

Automation system work very closely with the distribution networks and push them at the height of their physical limits and thus reduce the investment by a significant margin. This is possible because the automated system gather the data accurately of the distribution network as compared to conventional system. Due to this, electrical utility are allowed to have quality engineering, better planning and maintenance prevention in place.

d.    Reliability

Qualitatively the reliability is enhanced and complaints are reduced. The features of the distribution automation include load shedding, minimum operating cost and various automation control functions that offer the benefits regarding interruption and the customer service.

e.     Compatibility

Distribution automation extends too many product and functional areas including application software, computer systems, communication systems, RTU’s and the metering products. So in order to supply utility with complete integrated system, it is necessary for supplier to have agreements and the alliances with the other vendors.