DCS system in power

Abstract: After a brief introduction on the basis of the DCS system, discusses the need for power plant DCS system used, and a 600MW unit as an example on the current DCS system in power plant applications.
 Keywords: DCS system, power plant generators

 With the implementation of national energy conservation strategy, from the small generator sets to supercritical and ultra supercritical units and other large development at the same time, distributed control system DCS is also widely used in the operation of thermal power control. DCS strong guarantee safe and stable operation of power plant.
 1 DCS System Overview
 System is a distributed control system DCS (Distributed Control System) the title, it is a computer technology, control technology, network technology and CRT display technology, high-tech products, with control functions and easy operation and high reliability [ 1], has been widely used in industries including power plants, including the entire control system. Especially since the 1990s, DCS hardware widely used technical indicators of more advanced high-end industrial grade PC, and some even use a RISC workstation; software into a common commercial software packages, the system interconnect apply international standards of common network, step by step direction to information integration.
 2 DCS system, the need for power plant
 China's first manufacturers to introduce the DCS system is Wangting power plant, 300MW in 1985 was the introduction of the U.S. unit Westinghouse DCS system for the pilot to try. After 20 years of development, DCS was limited from the steam turbine, boiler and other thermal power plants and to monitor the development of the whole production process, both the boiler furnace safety supervisory system, there are steam turbine digital electro-hydraulic control system, etc. [2]. The author believes that the demand for power plant DCS system depends primarily on two reasons:
 (1) energy saving requirements. 100MW, 300MW and 600MW supercritical thermal power set of standard coal consumption of approximately 400,320 and 300g/kwh, energy-saving effect is obvious. Achieve such a large-scale energy-ho must be achieved through the DCS.
 (2) unit stability and safety requirements. For large unit power plant, DCS central plant system as a whole, to improve unit stability and security is extremely important. Currently, in addition to maintaining a small number for emergency shutdown, shutdown of the backup manual operation button, all the control, protection and monitoring functions all set in the DCS.
 Therefore, a large multi-unit power plant control objects and complex, nonlinear, large delay, the control parameters influence each other, interference sources and multiple features, only by adopting a strong DCS system to ensure security and stability of the entire power plant, to achieve national emissions-reduction targets.
 3 DCS system in power plant applications
 The current mainstream models are mostly new power plants of 600MW supercritical unit, a 600MW unit in the following paper [3], for example explore the DCS system in power plant applications.
 (1) goals. DCS should be used in power plant power plant safety, economic, and optimal operation of the target, it must work closely with the actual production process of the plant to function and charged devices targeted by the stratification and distribution of hardware and software design, unified data management and data formats as well as human-machine interfaces to achieve optimal control and operation strategies.
 (2) subsystem. DCS system hardware and software in addition to setting up the distribution of DAS (Data Acquisition System), MCS (analog control system), SCS (sequential control system) and the FSSS (flame safety monitoring system) and other essential subsystems outside, but also to be control objects and functional areas to set up other subsystems, such as electrical control systems, turbine bypass control system, water supply system, combustion system, Wind and Smoke systems.
 (3) the basic performance requirements. In addition to the DCS system to meet the high reliability and safety requirements, but also must have the following basic functions:
 A. System real-time. Call time must be guaranteed, including the screen, the parameter refresh time, response time and signal operating instructions scan the system, including real-time requirements.
 B. analog channel accuracy. The entire operating temperature range, analog input signal high and low to meet the ± 0.1% and ± 0.2%, the output signal is ± 0.25%.
 C. SOE point resolution of the accident sequence. SOE resolution of the input signal should not exceed 1 ms.
 D. History station capacity and acquisition cycle. Historical data collection points can not be less than 60GB, acquisition time can not exceed 0.5s.
 E. anti-jamming capability. All input and output modules to be resistant to common mode interference voltage 250V, differential-mode interference voltage 60V.
 F. System fault tolerance. Controller including the network of local interruption or failure of the system under various types of self-healing capabilities, fault tolerance of illegal input device power to restore the normal ability.
 G. System time synchronization accuracy. DCS system should have the GPS function of time.
 H. controller loading rate and margin. In a variety of conditions, each controller of the CPU load is not more than 60% CPU load operator station not more than 40%.
 I. network communication load rate. General data communication bus load rate should not exceed 40% for Ethernet should not exceed 20%.
 J. system power margin. System should accept the dual power supply, and capable of dual bumpless.
 K. other features. Include: report printing function; alarm; system configuration and online download function; channel and network modules and self-diagnostic function; output channel self-holding function; redundant controller and network switching equipment; power switching function; all loss of electricity and some loss of power system response.
 L. system availability. Field trials of the DCS system reliability test mainly availability (SAT). Availability features that a device or system restore can be completed within the stipulated time the probability of its specified functions. Through the availability test, validate continuous and reliable operation of the unit capacity of DCS. General requirements for system availability of 99.9% or more.
 4 Conclusion
 At present, China's thermal power of the machine, oven, electric inconsistent level of control, auxiliary system is not high level of automation, large centralized control room, cable quantity, duty and more. Improve the level of plant automation applications, especially in larger over 600MW supercritical unit and the application, to improve safety and reliability of the DCS, DCS improved results, so that the application of DCS in power plant reached a new level is still current and future longer need to walk a section of road.
 References
 [1] Zhang Xueshen, Ye Ning. Distributed Control System and Its Application [M]. Beijing: Mechanical Industry Press, 2006.
 [2] even plums. Domestically distributed control system for 600MW unit of analysis [J]. China Electric Power, 2003 (2) :46-48.
 [3] Xu Chong. Pannan 600MW power plant safety design of the study unit DCS [D]. Shanghai: Shanghai Jiaotong University, 2007.

API 570 Standard PDF

API  570Revision / Edition: 3RD     Chg:      Date: 11/00/09PIPING INSPECTION CODE: IN-SERVICE INSPECTION, RATING, REPAIR, ANDALTERATION OF PIPING SYSTEMSDocument AbstractCoverage API 570 covers inspection, rating, repair, and alteration procedures for metallic and fiberglass reinforced plastic (FRP) piping systems and their associated pressure relieving devices that have been placed inservice.IntentThe intent of this code is to specify the in-service inspection and condition-monitoring program that is needed to determine the integrity of piping. That program should provide reasonably accurate and timely assessments to determine if any changes in the condition of piping could possibly compromise continued safe operation. It is also the intent of this code that owner-users shall respond to any inspection results that require corrective actions to assure the continued safe operation of piping.API 570 was developed for the petroleum refining and chemical process industries but may be used, where practical, for any piping system. It is intended for use by organizations that maintain or have access to an authorized inspection agency, a repair organization, and technically qualified piping engineers, inspectors, and examiners, all as defined in Section 3.LimitationsAPI 570 shall not be used as a substitute for the original construction requirements governing a piping system before it is placed inservice; nor shall it be used in conflict with any prevailing regulatory requirements. If the requirements of this code are more stringent than the regulatory requirements, then the requirements of this code shall govern.Specific ApplicationThe term non metallics has a broad definition but in this code refers to the fiber reinforced plastic groups encompassed by the generic acronyms FRP (fiberglass-reinforced plastic) and GRP (glass-reinforced plastic). The extruded, generally homogenous nonmetallics, such as high and low-density polyethylene are excluded. Refer to API 574 for guidance on degradation and inspection issues associated with FRP piping.Included Fluid ServicesExcept as provided in 1.2.2, API 570 applies to piping systems for process fluids, hydrocarbons, and similar flammable or toxic fluid services, such as the following:a) raw, intermediate, and finished petroleum products;b) raw, intermediate, and finished chemical products;c) catalyst lines;d) hydrogen, natural gas, fuel gas, and flare systems;e) sour water and hazardous waste streams above threshold limits, as defined by jurisdictional regulations;f) hazardous chemicals above threshold limits, as defined by jurisdictional regulations;g) cryogenic fluids such as: LN2, LH2, LOX, and liquid air;h) high-pressure gases greater than 150 psig such as: GHe, GH2, GOX, GN2, and HPA.Optional Piping Systems and Fluid ServicesThe fluid services and classes of piping systems listed below are optional with regard to the requirements of API 570.a) Fluid services that are optional include the following:1) hazardous fluid services below threshold limits, as defined by jurisdictional regulations;2) water (including fire protection systems), steam, steam-condensate, boiler feed water, and Category D fluid services, as defined in ASME B31.3.b) Other classes of piping systems that are optional are those that are exempted from the applicable process piping construction code.Fitness-For-Service and Risk-Based Inspection (RBI)This inspection code recognizes Fitness-For-Service concepts for evaluating in-service damage of pressure-containing components. API 579 provides detailed assessment procedures for specific types of damage that are referenced in this code. This inspection code recognizes RBI concepts for determining inspection intervals. API 580 provides guidelines for conducting a risk-based assessment.