Application Status of Fieldbus in Thermal Power Station
Fieldbus technology was produced in the mid-1980s with the development of electronics, instrumentation, computer technology and network technology. Fieldbus technology quickly entered various fields with its distinctive characteristics and advantages. The major foreign control equipment manufacturers have also developed different field buses, but these field buses are difficult to form a unified standard, which has affected the promotion and application of field buses to a certain extent. In addition, the changes that the field bus brings to the industrial control field are impactful, because they change not only the equipment, system or technology, but also the way that people will do things and the tools they need to do things. Although fieldbus technology has been born for more than 20 years, their scope and depth of application are not commensurate with the advantages they possess. With the rapid growth of market demand and the emergence of fieldbus products including smart meters, fieldbus technology will play an increasingly important role in the field of industrial control.
1 Application status of fieldbus in thermal power station
1.1 Standardization of fieldbus
IEC started to formulate international standards for fieldbus as early as 1984, but for more than ten years, some large international companies have proceeded from their own interests and fought around the issue of international standards for fieldbus. . By the end of 1999, there were more than 12 kinds of international standard field buses, including: FF, ControlNet, Profibus, P-Net, Swift Net, Word FIP, Interbus, AS-i, Device Net, SDS, Seripplex and CAN. In addition, there are 3 European standards, various national standards and some large enterprise standards (such as CC-Link from Mitsubishi of Japan). Multiple standards means no standards. In this situation, instrument manufacturers are confused, and system integrators, design institutes, and users are inevitably at a loss, thus greatly affecting the promotion and application of fieldbus.
1.2 The application of fieldbus in domestic thermal power stations
At present, no field bus equipment manufacturer can provide all field bus products equipped with the entire thermal power plant. The FF slogan with a relatively large variety of products has the slogan 2002 as "free choice, drive collection", but it still lacks many products necessary for thermal power plants, such as test meters and vibrometers for steam turbines, and silicon for boiler water quality testing. Acid and phosphate measuring instruments, etc. Therefore, it is impossible to construct a complete fieldbus control system (FCS) that conforms to all fieldbus characteristics at the thermal power plant.
A small number of petrochemical and chemical plants in China have adopted FCS, which has played a small-scale demonstration role. Some devices of thermal power plants also have the conditions to adopt FCS, but it is more difficult to implement. First of all, the design of the power station is completely different from DCS and PLC. DCS and PLC are based on I / O and processor, while FCS is based on intelligent field instruments and equipment; DCS and PLC control The task is completely completed by the processor, and the control task of FCS is basically completed by the field instruments and equipment. Therefore, there will be great changes in the design ideas and methods. This is for power design that must strictly follow the design regulations. As far as the college is concerned, making such changes is not easy. Secondly, the application of FCS has a great impact on production and management. How to use FCS to raise the production and management of thermal power plants to a new level is a challenging topic in itself. Therefore, from design to production, from production to management, it is more difficult to introduce FCS into a thermal power plant (even if it is part of a thermal power plant) without being ready to face FCS.
Although as a complete fieldbus control system is still difficult to quickly apply to thermal power plants, but the fieldbus products as this technology has been increasingly used in thermal power plants. Because these field bus products with the advantages of field bus are in line with the goal of the thermal power plant to pursue high efficiency and reliability. The application of fieldbus products in thermal power plants adopts an integrated approach, including the integration of fieldbus and DCS, the integration of fieldbus and PLC, and the integration of fieldbus and information network.
DCS has been widely used in the control system of the main equipment of thermal power stations, and the application of fieldbus must rely on DCS. This not only enriches the functions of DCS, but also promotes the development of fieldbus and FCS. There are two ways to integrate fieldbus and DCS: fieldbus and DCS I / O bus integration; fieldbus and DCS network integration. The former is that field instruments or field devices communicate with the field bus interface unit through the field bus, and then the field bus interface unit communicates with the DCS processor through the I / O bus. The latter is that field instruments or field devices communicate with the field bus server through the field bus, and the field bus server is directly hung on the DCS network.
PLC has been widely used in the control system of auxiliary equipment of thermal power stations, and the application of field bus must also rely on PLC. In the field bus, like Contr01. Net, ProfiBus, etc. are themselves supported by the major PLC suppliers, and these fieldbus technologies and products have been integrated into the PLC system, becoming part of the PLC system or becoming an extension of the PLC system. Taking ControlNet as an example, ContmlNet was first proposed by Rockwell AutomaTIon of the United States in October 1995. It is a high-speed, highly deterministic, and repeatable network, and is particularly suitable for information transmission in complex applications that have strict requirements on time. ControlLogix, one of the widely used PLC systems in thermal power plants, uses ContmlNet to build a distributed I / O network system. As an extension of the PLC system, ControlNet is also used as an auxiliary system for the plant-level control network to connect the entire thermal power plant, including ash and slag removal systems, coal transportation systems, water treatment systems, etc. Through ControlNet, centralized monitoring of auxiliary systems throughout the plant And data sharing.
The characteristics of the fieldbus in terms of network make it very natural to integrate with the information network. Industrial Ethernet is a typical example. Although Industrial Ethernet does not belong to the 12 international standards of fieldbus, with its rapid development, Industrial Ethernet has become the de facto industrial standard. With the continuous improvement of the communication rate of Ethernet and the birth of full-duplex switched Ethernet, the non-deterministic problem of Ethernet has been solved. At present, almost all the plant-level information network systems of thermal power plants use Ethernet, and the integration of fieldbus and information network can be realized through industrial Ethernet.
At present, in thermal power stations, pressure transmitters and other instruments are generally selected to be intelligent and support HART communication protocol. However, these instruments do not constitute a HART communication network, HART communication is only used to set the instrument through the handheld communicator. This aspect shows that the thermal power station has provided some conditions for the application of fieldbus technology in terms of smart instruments. On the other hand, it also shows that the application of fieldbus in thermal power stations does have certain resistance. Investment.
2 Fieldbus application prospects in thermal power stations
The main factors affecting the popularization and application of fieldbus in thermal power stations are:
â‘ In the case of non-uniform standards, a large number of fieldbus applications has certain risks;
â‘¡ The selection range of fieldbus products is too narrow to meet the needs of thermal power stations;
â‘¢ The field bus has not achieved true interoperability;
â‘£ Lack of large-scale demonstration projects;
⑤ Lack of research on the impact of fieldbus on the design, installation, commissioning, production and management of thermal power stations;
â‘¥In the case of domestic emphasis on hardware and software, and equipment and services, it is difficult for fieldbus to show superiority in engineering investment;
⑦In the absence of demonstration projects, the economic benefits are not convincing.
The field bus is relatively clear in terms of the advanced technology of the network and beneficial to improve the reliability of the system. Therefore, despite all the difficulties, the field bus can be gradually applied in thermal power plants, and this application will become more and more extensive and Deeper and deeper. The main reasons are:
â‘ Because some fieldbus supporters are also manufacturers of DCS and PLC, in order to continuously improve the performance of their DCS and PLC products, they will continue to use and integrate the fieldbus. So accompanied. DCS and PLC, fieldbus will be applied in thermal power stations.
â‘¡The emergence of a large number of smart instruments supporting multiple fieldbuses instead of just one HART protocol and their application in thermal power stations have promoted the application of fieldbuses. This kind of application began to be small-scale and localized. Reducing control cables and obtaining more instrument information, the application of this field bus appears in the form of I / 0 bus integration with DCS or PLC.
â‘¢ With the wide application of frequency converters and smart switches that support multiple field buses in thermal power stations, the field bus connecting these smart devices will also be practically applied. This application has only begun to be small-scale and local. The starting point is In order to reduce the control cables and obtain more device information, the application of this fieldbus is in the form of network integration with DCS or PLC.
Under the influence of some demonstration projects in the petrochemical industry and chemical industry, and with certain preparations in design, installation, commissioning, production and management, the thermal power plant is adopted on some systems: FCS will certainly become a reality and can The driving force behind this trend comes mainly from the requirements of the thermal power plant's own interests. Whether FCS can be used in the entire thermal power plant depends on the development of fieldbus technology, products and services.
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