Job Sheet 1 The SCADA System Network

Transcription

1 Job Sheet 1 The SCADA System Network The SCADA system communication network makes it possible for data to be transferred between the central host computer servers, remote terminal unit (RTU), and/or programmable logic controllers (PLCs). SCADA systems can be connected in a variety of ways, including leased telephone lines, very high-frequency radio, ultra high-frequency radio, point-to-point, multiple-address radio systems, spread-spectrum radio, or microwave radio. Each of these has advantages and disadvantages that include factors such as cost, licensing, maintenance, and capacity. While the use of cable is a good option for a factory or other similar small geographical area, ordinary telephone lines are more economical and practical for larger geographical areas. Remote control is required in locations where telephone lines are not available; however, radio systems are often the solution to economical data communication. Either a single computer or several networked computer servers can serve as the central host computer or master station. The information collected from and sent back to the RTUs and/ or PLCs is processed by the computer, and presented to the operator using HMI software. Operator access to the SCADA system data and information occurs through client computers networked to the central host computer server. One or more operator terminals may be available, depending on the structure and location of the components of the SCADA system. Initially, SCADA system vendors provided proprietary hardware, software, and operating systems. Today, SCADA systems can be easily integrated into networks that use an open system architecture (Figure 1-1). While some RTUs and PLCs still retain proprietary vendor protocols, the open system architecture makes it possible to distribute the functionality of a SCADA system across both wide area networks (WANs) and local area networks (LANs). A further advantage of the open system architecture is that it is now possible to add a wide variety of peripheral devices such as monitors, printers, etc. to the SCADA system network. central host computer activities. The ability to distribute tasks and functionality across a WAN provides the distinct advantage of disaster survivability. With processing distributed across more than one physical location, the SCADA system can generally survive the loss of one location. This is important, particularly where national security is an issue. Festo Didactic Inc

2 Figure 1-1. Sample SCADA Network. SCADA System Software Software for the SCADA system may be proprietary software that is custom-designed for a disadvantage of using proprietary software is its limited compatibility with a variety of hardware and software applications. Some SCADA systems use a combination of both proprietary and COTS software. SCADA system software is used for a variety of purposes. Operating system software provides central host computer and operator terminal hardware control. Application software allows transmittal and reception of data between RTUs, PLCs, and the central host computer. This same software also provides the graphical user interface that enables human access to mimic screens, alarm pages, control functions, etc. Communications protocol drivers control of the data communications network. Network management software monitors performance maintain RTU and/or PLC applications and data processing tasks. 2 Festo Didactic Inc

3 SCADA System Protocol In a SCADA system, the RTU or PLC accepts a variety of commands to operate control points, set analog output levels, and respond to requests. The SCADA master station receives correlates to a database in the SCADA master station. The master station is able to identify the source of the address through correlation with this database. The typical SCADA protocol is made up of two message sets or pairs. One message set contains valid statements for master station initiation or response, known as the master protocol. The other set contains the valid statements that the RTU or PLC can initiate or respond to. This is the RTU/PLC protocol. There are several protocol models used in SCADA systems today. A protocol is a set of Electrotechnical Commission (IEC) series and Distributed Network 3 (DNP3). uses serial communication to transmit data from point A to point B. Utility companies, such as the electric company, use the DNP3 protocol; but it can also be used in other industrial environments. Both of these sets of standards are based on the three-layer Enhanced Performance layer OSI model and is designed to provide optimum performance for telecontrol applications. As shown in Figure 1-2, the three layers are the application layer, data link layer, and physical layer. The four standard OSI layers that are omitted from the EPA model are the presentation layer, session layer, transport layer, and network layer. A fourth layer in the EPA model, called the user layer, is located above the application layer in order to represent the functions and processes that distinguish a fully operable telecontrol system from a data communication system. The EPA model is used for any continuously operating system that operates over a single network. OSI Model Layers EPA Model Layers 7. Application 3. Application 6. Presentation 5. Session 4. Transport 3. Network 2. Datalink 2. Datalink 1. Physical 1. Physical Figure 1-2. Seven-layer OSI Model vs. Three-layer EPA Model. Festo Didactic Inc

4 The IEC series and DNP3 protocols have many similarities, but are not 100% compatible, and there is no clear consensus as to which of these protocols is the best. Currently, a new SCADA protocol, intended to replace both of these, has been published by IEEE and has been submitted for review to the IEC. Called UCA 2.0, it was developed by the Electric Power Research Institute. Organizations that have contributed and that continue to contribute to the standardization of SCADA systems include the Institute of Electrical and Electronics Engineers (IEEE), American National Standards Institute (ANSI), Electric Power Research Institute (EPRI), International Electrotechnical Commission (IEC), and the DNP3 Users Group. SCADA System Data temperature transmitters, and pressure meters. These and other similar devices are often considered the eyes and ears of the SCADA system. Systems that automate a process such as electric valve actuators, motor control switchboards, or electronic chemical addition equipment can be said to form the hands of a SCADA system. Where equipment is spread out over a large geographical area, local site control occurs through the use of remote telemetry units (RTUs) or programmable logic controllers (PLCs). Input and output to and from these devices is monitored and controlled through the supervisory control part of the SCADA system. Data from RTUs and PLCs is collected and stored in a database. The data collected can be meter readings, equipment status, etc. The collected data must then be translated into a format or language that the SCADA system understands. RTUs do this by converting the electrical the data to be transmitted. The data can be monitored and/or analyzed by the computer using a software program, or by an individual who can adjust parameters or take required actions based on the data analysis. For example, if a liquid attains a preset maximum height in a vessel, the PLC directs the inlet The SCADA system database is a distributed database, or tag database. Data elements are referred to as tags or points. A point is a single value monitored and controlled by the system and can be either an input value or an output value. A hard point is an actual value, while a 4 Festo Didactic Inc

5 soft point is the result of a logic and/or math operation applied to a hard point. These values the value was recorded or calculated. The history of a point is the collection of all the valuetimestamp information in the database for that particular point. Other information is frequently register and/or alarm information. These tags and metadata are used to identify the devices, inputs, outputs, etc. that are of interest in reports and/or alarm situations. SCADA System Security While newer SCADA systems are easier to implement, integrate diverse devices into, and maintain because they use open standards, and COTS hardware and software, they are now a concerns: 1. As standardized technologies have been adopted, their vulnerabilities are more widely known. 2. Control systems are now frequently connected to other networks. 3. The use of security technologies and practices has sometimes been constrained, remote connections may not be secure, and technical information about control systems is easily obtained from a variety of sources. 4. SCADA systems can be attacked by viruses or the system can be hijacked. 5. Use of leased telephone lines, twisted-pair cable, microwave radio, and spread spectrum techniques also make SCADA systems vulnerable to security threats. It is important to remember that wherever a SCADA system is part of a larger corporate network, once the corporate network is compromised, the SCADA system is at a high risk for a security breech unless other safeguards are implemented. To develop an effective security strategy, it is necessary to analyze both the corporate network and the SCADA application system layers, communications, and policies and procedures. There are many tools and techniques that can be designed into the system, depending on the goals of the industry and the cost effectiveness of the solution(s). SCADA and the Wind Turbine Just as in other industries, the SCADA system can be considered the nerve center of the wind turbine and/or wind farm facility. A central computer is connected to substations, meteorological stations, and individual turbines. An operator can monitor, and if necessary, affect the behavior of each wind turbine and/or the entire wind farm. The SCADA communications system Festo Didactic Inc

6 records data on a regularly scheduled basis for such characteristics as energy output, energy availability, and error signals. The communications network for a wind turbine SCADA system is generally connected with Figure 1-3. SCADA System Network: Wind Farm. While SCADA systems are available from independent suppliers, whoever supplies the wind turbine generally also supplies the SCADA system. An independent supplier for a SCADA system is generally used if a wind farm is to be constructed over a period of time using turbines from more than one manufacturer. In this instance, the SCADA system from an independent supplier has a greater likelihood of compatibility with several turbine manufacturers models. SCADA and the Electrical Pitch Hub Trainer The electrical pitch hub trainer does not include a complete SCADA system; however, it does contain some key components. As you complete the job sheets in the balance of this course, you will use the key components included to become familiar with the characteristics of SCADA control. You will also practice some of the important monitoring and control tasks that are an essential part of a wind turbine operator s job description. 6 Festo Didactic Inc

7 OBJECTIVES In this job, you will identify typical SCADA system network components for a wind turbine farm. PROCEDURE Identify the wind turbine farm SCADA system network components in the diagram below. Identify where your trainer should be placed in this diagram if it were part of a wind turbine farm network. Festo Didactic Inc

8 Review Questions 1. Which of the following components of the SCADA system makes it possible for data to be transferred between the central host computer servers, and the RTUs and/or PLCs? a. Communication network b. Network software c. Network hardware d. Graphical interface 2. COTS, when used in reference to SCADA system software, is the acronym for a. b. complete organizational turbine software. c. commercial organizational turbine software. d. commercial off-the-shelf. 3. SCADA system software provides a graphical user interface that enables human access to a. mimic screens. b. alarm pages. c. control functions. d. All of the above are correct. 4. IEEE, ANSI, EPRI, IEC, and the DNP3 Users Group all contribute to the a. mechanical design of nacelles. b. c. standardization of SCADA systems. d. advancement of circuit board technology. 8 Festo Didactic Inc

9 5. In order to monitor and store data, compare data to preset values, and apply logic or mathematical operations to collected data, SCADA systems use a. input and output values. b. hard and soft points. c. either proprietary or COTS software. d. a nacelle operator. 6. What are some of the security risks of newer SCADA system software? Name: Date: Instructor approval: Festo Didactic Inc