Abstract: In thermal power plants, steam turbine protection system is very important. This article discusses the use of PLC control system for a variety of steam turbine protection, and discusses the main features of the system, structure and implementation.
Keywords: steam turbine; PLC; redundant system; man-machine interface; touch screen
steam turbine thermal monitoring and protection devices and their component signal from the alarm system and protection of the control system is important to protect the safe operation of steam turbine equipment. With the increase of unit capacity, security surveillance and protection of the turbine is even more important, at the same time security monitoring and protection of steam turbine equipment accuracy and reliability is also a higher demand. Original and early design of protection systems and the hardware logic mostly lap relay, and its poor reliability, maintenance was larger. Therefore, the use of programmable logic controller (PLC) on the steam turbine thermal control devices to monitor and protect the very important and necessary. Described below for the application of PLC-controlled turbine protection system.
1 Turbine Protection System Overview
turbine during normal operation, it is necessary to regulate power consumption based on user load, to prevent conditioning system failure due to malfunction, and the turbine speed caused when a sudden load rejection risk, to prepare the unit to have certain abnormal a rapid movement down to prevent accidents. Turbine must be set to speed, the rotor axial displacement, bearing vibration, the relative expansion tanks, steam turbine oil pressure and oil temperature of all bearings, vacuum condenser, generator and other parameters of the main protection action to protect, in these parameters of any one of the Yunxu value than when the Guiding, asked Zidongfachu signal Shi magnetic circuit throttle action, Anquan oil leaking out, cut into the steam to carry out a forced outage, Bingjutongshi sound and light alarm, record downtime Yuan Yin, Xiang DCS control systems and Send interlock signal conditioning systems, interlocking doors conditioning, generators and pumps, so that the whole system quickly back to a safe state, to protect the turbine purpose.
2 system components
turbine protection system consists of part of field devices, PLC control system parts, man-machine interface (touch screen) and the composition of the external communication systems. On-site equipment includes: Steam Turbine Monitoring System (checking of turbine speed, axial displacement, bearing tile vibration, the relative expansion of the cylinder, etc.), pressure monitoring system (test oil pressure, security hydraulic oil, condenser vacuum), oil Temperature Detection System (back testing the bearing oil temperature), magnetic oil circuit breaker shutdown system; PLC control system includes: redundant PLC controllers, signal isolation relays, drive relays and contactors; external communication systems, including: DCS control system, turbine speed load regulation system. System architecture shown in Figure 1. Overall system structure on-site data acquisition and processing, monitoring and control of field devices.
3 hardware design
the turbine protection system, the importance of the decision of the system at any time will not permit any malfunction or failure to actuate, so as the PLC logic control unit is generally used in domestic and foreign high quality and good stability products, such as AB-ControLogix series, GE-PAC7i series, Schneider Modicon QUANTUM products.
the following to choose AB-ControLogix series PLC as an example of the system description, system redundancy with hot standby configuration, control of the core components of (CPU) configuration sets were installed in two separate Rack, 2 rack CPU connected through fiber-optic synchronization module synchronization hot standby operation, the CPU and related components of any set of failure or error when no disturbance to switch to another CPU, to ensure reliable and stable operation of the system . PLC s IO IO module installed in a separate chassis, IO mode of communication with the CPU for the redundant ControlNet network. PLC s digital input output isolation relay points are used, the total interference signal to prevent the on-site adverse effects on the system to ensure the long-term reliable operation of the system.
human-computer interaction modules use Allen-Bradley company PV1000 color industrial touch screen products, the touch screen can be monitored, operation and operating parameters recorded, the touch screen system, operator station, man-machine dialogue simple, easy to modify and expand the system configuration, and the touch screen does not hang with the advantages of long term stable operation. Touch Screen and CPU means of communication is via redundant ControlNet network.
Turbine Protection System PLC structure diagram shown in Figure 2. Can be seen from the chart, in the protection system into normal operation, if a CPU failure or poor contact of a communication medium, will not affect the normal operation of the protection system.
4 software design
software design consists of two parts: PLC control and touch screen monitor protection logic, the operation records configuration screen. PLC control and protection logic using ladder prepared to protect the continuity of the logical process chosen to run the task in all the time, so that the protection logic program always running. Protection of logic programming includes some of the protection of investment return, alarm and display part, tripping action part of the event record and SOE records of several parts.
As a result of the touch screen to protect the investment return from a general protection switch, extending the protection settings for each independent protection switch, the sub-protect switch on the touch screen configuration to achieve. Investment return equivalent to the protection of turbine protection system running open-loop or closed loop operation selection key in the protection of exit, the turbine protection system is open-loop operation, this time to protect the operating parameters corresponding to abnormal, an alarm protection system only, not Council Action Trip; in the protection of investment, the turbine protection system is closed loop, this time to protect the operating parameters corresponding to abnormal, an alarm protection system, while Tripping, close the main valve. Sub-protection switch design, makes the protection system more flexible, on-site staff can put into operation some of the most important protection, the protection does not meet the conditions for the time being do not enter.
PLC collected on-site turbine alarm signal, tripping signal at the touch-screen alarm screen and the trip screen display, replacing the former with a large number optical plate alarm tripping means, greatly reducing the routine maintenance. Action signals the first trip trip record, the reasons for the analysis of steam turbine trip provided a good basis. PLC Protection of logic and the touch screen between the adoption of the corresponding CotrolNet protocol for real-time communication, thus ensuring the turbine operating parameters on the touch screen display and to the event log, the touch screen on the operation of real-time is PLC scan, and in the program execution.
SOE records requests to milliseconds, required to achieve through the program in the PLC, and PLC in the record, to record the results on the touch screen display.
5 Conclusion
the above ideas and methods of protection by the PLC control system has been successively turbine new North thermal power plant in Shenyang, Shouguang giant to thermal power plants, thermal power plant in Tongliao Shengfa dozens of user units of steam turbine equipment in operation , the results show that the system is reasonable in design, the system Zai reliable field operation, not only automate and improve the equipment running Shui Ping, Jian Qing-site personnel to maintain the volume, but also prolonged the turbine s operation Shouming There is a clear economic and social benefits .
References :
[1] Shi-Ping Zhou "300MW Thermal Power Unit testing techniques," China Electric Power Press 2002 ???
[2] Li Jiangang "turbine equipment and run" China Electric Power Press 2006 ???
[3] Rockwell Automation "ControlLogix Selection Guide"
[4] Allen-Bradley "system user manual ControlLogix"
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