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In the past ten years, foreign PLC technology has made a leap, its capacity has been expanded exponentially, the volume has been continuously reduced, and the function has been continuously enhanced. It not only has logic operation, timing, counting, and sequence control functions, but also has special control functions such as PID, which can be directly Perform A/D, D/A conversion, and develop integrated management and control. Make operation, use, and project development easy and convenient. At the same time, PLC technology has also been widely used in power plant coal conveying equipment. In addition to large-scale industrial and mining equipment such as dumpers, bucket wheel machines, and belt conveyor systems, PLC control has been implemented, and ring coal feeders and coal entering the plant have been sampled. Medium-sized equipment, such as machines, also implements PLC control. In addition, PLC is also used in small devices such as physical verification devices and coal sampling machines.
At present, the application of PLC in the coal transportation system is basically limited to the equipment level. Each equipment or system is under the control of its own PLC and is basically independent of each other. In the same way that the control of coal-producing equipment was originally concentrated from the ground, the PLC control of the coal-conveying system will also be developed from the equipment level to the workshop level or even to the factory level. This is the need for reducing the consumption and increasing the efficiency of the coal transportation system, and also the production management. And monitoring needs. Some domestic domestic power plants have made some explorations in this regard. For instance, the first-stage conveyor system PLC and the second-phase conveyor system PLC of Yuanbaoshan Power Plant have been successfully connected under the guidance of Tsinghua University.
2. Control methods and functional features of the coal conveying program control system With the rapid development of large-capacity, high-parameter thermal power generating units, in order to meet the requirements of large-scale thermal power generation enterprises, the fuel delivery systems of large thermal power plants have also undergone qualitative changes. From the past, the grab machine + pusher + tape transfer mechanism model has evolved into a fuel delivery system that combines organically combined, closely coordinated, large-scale dumping equipment, stacker and reclaimer equipment, and belt conveyor systems. The functions of the fuel delivery system mainly include unloading coal, storing coal, blending coal, putting coal, and rough processing of coal. The coal unloading and coal storage equipment mainly includes dumpers, bucket wheelers and corresponding belt conveyor systems. The coal blending equipment is mainly ring coal feeders and silos. The coal-up equipment is mainly plow coal hoppers and corresponding belt conveyor systems. The rough processing equipment mainly includes iron separators, roller screens, and coal crushers. Due to large-scale thermal power plants, the amount of coal varies greatly within a certain period of time. The amount of coal varies greatly, and the difference in coal quality may also be large. At the same time, in order to meet the requirements of coal blending and coal coarse processing, the fuel delivery system must have a variety of very flexible operating modes to meet the stability of the unit. The request made.
Coal control system control methods are computer control, console control and local control. Three control methods may be selected by the selection switch. The computer control method is that the operator selects and starts the coal conveying system through the computer keyboard and transmits the instructions to the PLC system. The PLC system starts the relevant equipment according to the ladder diagram program and transmits the relevant information to the computer. The control mode of the console is that the operator selects and controls through the switches and buttons on the console, and the related information is displayed through the simulation screen. The local control method is on-site control through the control box located next to the motor. The requirements for the coal handling control system are mainly based on the production process, paying attention to the order of starting and stopping of each motor in the chain and coal conveying system between the coal conveying sequences, and emergency shutdown in case of emergency.
Here we take Yangluo Power Plant's coal handling program control system as an example to illustrate.
3. Introduction to the existing coal transport program control system of the logic power plant The object of the control system is: 25 belt conveyors (two of which are two-way operation), four belt coal feeders, and four motor vibration feeders. 2 iron machines, 4 disc separators, 6 ring feeders, 2 bucket wheel reclaimers, 2 roller screens, 35 vibration blocking devices, and 2 tipper machines, a total of 102 devices .
There are six cylinder silos (one for each of the first and second phases), one for each ring feeder under each silo, and one low coal level sensor and four high coal level sensors for each silo. Each silo has 4 plows (only 2 tailings), and each plow has signals for lifting and landing. There are 16 coal bunkers (including 8 in each of the first and second phases). Each period has two (two) belts for coal, each coal bunker has a low coal level and two high coal level sensors, each coal bunker has two plow coal eliminators (except for tail stock), each plough The coal lifter has lifted into place and dropped into position switch.
Belt conveyor with speed, on-site emergency stop, light deviation, heavy deviation, heavy slipping, tearing, DL tripping, tripping and closing circuit loop disconnection, operation, coal flow signal, and other signals except coal flow signal are input to In the PC, where the light deviation and the tripping circuit are disconnected, the signal of each belt is connected in parallel and then input to the PC. The start slip signal is processed by the speed signal after being discriminated by the PC program.
Program control system uses Siemens S5, 15U (CPU942) type PC as the control host, PC all switch signals, all field input and output signals are isolated by relays, in order to improve the system's anti-jamming capability and protect the PC module to make With higher reliability, while controlling indoor and outdoor self-contained systems for maintenance and inspection, all field signals are transmitted with DC 110V. After entering the control room via 110V DC relay, the contacts are connected with DC24V voltage and enter PC for processing; PC The DC24V signal output by the output module drives the DC24V relay, and its contacts send the DC110V signal to the site to start and stop various types of control equipment.
The system can be divided into two relatively independent sub-systems. First, the coal system refers to the former equipment of the cylinder warehouse; and the coal blending system refers to the equipment after the cylinder warehouse. Each sub-system includes a belt system and The storage system can be independently controlled except for the program selection and test light. The system has two short-circuit belts (12PA/B). The coal source of the coal blending system can be directly from the coal source of the coal system instead of the cylindrical bin. .
The control method of the coal handling system and the coal blending system is the same. According to the specific conditions listed above, the control method of the belt system of each system is divided into two types: "program control" and "disarm protection"; the distribution system of each system is divided into For the "programme" and "hands" in two ways. Among them, the first three methods can all be controlled by a PC-programmed program, while the “hands-on†system does not participate in the control, and the one-to-one operation is performed through the button switches on the console. This method is not used as a normal operation method. Use in debugging or emergency situations.
4. The design and implementation of the existing coal transportation program control system transformation plan for Yangluo Power Plant First of all, the entire coal handling program control system should have the following new features:
1. After the improvement, a workshop-level PLC control network is formed. The control object of the original coal transport program control system of Yangluo Power Plant is only the belt conveyor system and its attached equipment. It can only be considered as an equipment-level PLC control system, and other large-scale equipment such as Bucket machines, dumpers, etc. are not included in the control range of this system. The primary task of the new system after the renovation is to establish a workshop-level PLC control system, which will include all coal conveying system equipment in the monitoring range of this system. This requires the establishment of a PLC. Controller network. The network includes two rollover PLC controllers, two bucket wheel PLC controllers, and six ring-type coal feeder PLC controllers. The network should also have the ability to network with the factory's Mis system.
2. The upgraded new system should have powerful monitoring functions. The new system not only has a switch control, but also an analog control. At the same time, it provides a lot of timely information for the operators. The system itself also carries out automatic adjustment and control of some of the devices through the integration of relevant information. , Such as ring-type coal feeder ratio adjustment.
3, the transformation of the system should have a wealth of operating information management capabilities This includes a variety of report management, defect management, work ticket management and equipment, regular rotation management, the amount of coal in the cylinder and coal quality query.
4. The new system should have high operational reliability. The operating environment of the coal conveying equipment is very bad. Most of the electric control cabinets are placed below the horizon, and the damp heat and dust environment greatly increase the faults in electrical connection and relay pull-in. The grounding of the control cable is also a fault that often occurs. At the same time, due to the long-distance transmission of the control cable and the high-voltage power cable in a cable trench, a higher induced voltage is generated, resulting in accidental false signals. The new system should minimize cable runs and use cables as little as possible.
The following detailed description of the specific implementation.
First, the hardware configuration comprehensive analysis of OMRON, MODICON, SIMENS three brands of PLC components and software functions, from the development of a simple, easy to use, flexible configuration, powerful considerations This system selected the SIMENS SIMATIC S7 series PLC components.
1. Host computer monitoring system This system adopts the upper computer monitoring method to replace the original analog disk control method. The operation and monitoring of the entire coal conveying system are realized on the upper computer. In the upper computer, not only the operating status, process parameters, fault alarms, etc. of the system equipment should be displayed, but also the collection, collation and archive management of various related information related to the operation. The host computer should also have the ability to network with the Mis system.
The system is configured with two upper computers, one as an engineer station and one as an operator station, and the two units are used as backups. The upper computer is connected to the main PLC through a PROFIBUS-DP network. The upper computer selects two PG760 IPCs and the monitoring software selects WinCCV4.02 from SIMENS.
2. Programmable controller system The main PLC of this system adopts two SIMATIC S7-400 series machines. The two main engines are hot standby each other. They are responsible for the control of the lower-level PLC controller and the control of the conveyor belt conveyor system. There are also five PLCs that use the SIMATIC S7-300, which are responsible for the control of the dumper system, the ring coal feeder system, the #1 bucket wheeler system, the #2 bucket wheeler system, and the belt conveyor system.
3. Remote I/O Station The system is equipped with two remote I/O stations, one for the coal pulverizer I/O control of the plow. The other is responsible for the I/O control of the pulverized coal blender in the original coal bunker. The remote station uses optical cables for the communication cables. Setting up a remote station greatly reduces the number and length of control cables. Will greatly reduce the fault caused by the cable grounding or wiring failure, the use of fiber optic cable as a communication cable will eliminate the voltage and current signal interference.
4. Once the meter has cancelled all the meters, the on-site measurement signal is sent directly to the main PLC after being sent by the transmitter and displayed on the upper computer. When the value exceeds the fixed value, the alarm information is displayed or the control is stopped directly.
Second, the software configuration 1, the host computer monitoring system The system host monitoring software selected SIMENS WinccV4.02 as a development platform. Using the software's variable archive editor and report designer, you can easily generate user archives for running user process data and configure them as reports.
2. PLC control software PLC control software selects SIMATIC STEP7 as the control software development platform. STEP7 programming software is a fully integrated, standard unified, configuration tool using a global relational database. It uses a modern software architecture to manage, process, archive, and document projects.
Third, the formation of the PLC network In order to improve the control performance, it is often necessary to connect PLCs and PLCs, or PLCs and computers, or PLCs and smart devices that are geographically located in different places through a transmission medium to realize communication so as to form stronger functions. Better performance control system. After the PLC is connected to the network, the network and the network can also be connected to form a more complex system. The PLC network can also be associated with a computer and become one of its subnets.
The purpose of PLC networking is:
1. Improve control range and control scale The PLC is installed at the industrial site for local control. However, if you are connected to the network, you can achieve remote control. The distance can be several tens, several hundred meters, several kilometers, or more, which can greatly increase the control range of the PLC. After networking, you can increase the number of I/O points that the PLC can control.
2. Realize integrated and coordinated control It is very convenient to use PLC to control a single device. However, if there are several devices to coordinate work, use PLC control. A better approach is networking, where each device is controlled by a single PLC, and these PLCs are then networked. The individual work of the equipment is controlled by each PLC, and the coordination of work between equipments is resolved by the data exchange between PLCs after networking to achieve the purpose of coordinated control.
For a production line consisting of a number of devices and devices, after the PLC is connected to the network, comprehensive control can be performed to increase the control of the device level to the control of the production line.
3. To achieve computer monitoring and management As the computer has a powerful information processing and information display capabilities, industrial control systems have increasingly used computers to monitor and manage the system, but to achieve this function, the computer must make PLC and computer networking.
PLC and computer networking, can achieve the following functions:
1 Read the working status of the PLC and the status of the I/O points controlled by the PLC and display it on the screen of the computer so that people can understand the working status of the PLC and the devices it controls.
2 Change the PLC working status and write data to the PLC. This can change the working condition of the equipment controlled by the PLC, or change the working mode of the PLC, and play the role of human intervention control.
3 Read the data collected by the PLC, and process, store, display, and print.
4. To achieve computer networking programming If you use computers and PLC networking, and then use the appropriate programming software, you can use ladder diagrams or flowchart programming, so that you can use other high-level language programming, more convenient.
5. It can simplify system wiring and maintenance and improve the reliability of its work.
6. On-site intelligent devices (including smart devices, smart meters, smart sensors, etc.) can be managed, and the benefits of these devices can be fully utilized to promote production automation and intelligence.
7. The sharing rate of resources is greatly improved, and reliable capacity can be achieved through corresponding configuration.
8. It is easy to realize the networking control under the stratification and stratification under self-construction.
Second, the SiemensPLC network's complex network topology PLC network layering and production pyramid structure layer is not a one-to-one relationship, several layers of functionality can be combined by a layer of subnet to achieve, as long as the layers of function transmitted The information requirements for communications are basically the same. Adopting a composite structure not only makes communications adaptable, but also has good scalability.
The following figure shows the three-dimensional network structure of a typical factory automation system. Based on the fieldbus PROFIBUS-DP/PA control system is located in the bottom layer of the factory automation system, namely the field level and the workshop level. Fieldbus PROFIBUS is a field-oriented and plant-level digital communication network.
1) Field device layer: The main function is to connect field devices, such as distributed I/O, sensors, actuators, switchgears, etc., to complete field device control and link between devices; such as a processing equipment control, an assembly line or Chain control between field devices on a production line. The master station (PLC, PC or other controller) is responsible for bus communication management and communication of all slave stations. All equipment on the bus production process control program is stored in the master station and executed by the master station.
2) Workshop monitoring layer: The workshop level monitoring is used to complete the connection between the main workshop production equipment, such as the connection between the main controllers of three production lines in a workshop, to complete plant level equipment monitoring. Workshop level monitoring includes on-line monitoring of production equipment status, equipment failure alarms, and maintenance. Usually also has plant level production management functions such as production statistics, production commissioning and so on. Workshop level monitoring usually requires a workshop monitoring room, an operator workstation and printing equipment. The workshop level monitoring network can adopt PROFIBUS-FMS, it is a multi- main network, this level of data transmission speed is not the most important, but must be able to convey a large amount of information.
3) Factory management: The workshop operator workstations can be connected to the workshop office management network through a hub to send workshop production data to the workshop management. The workshop management network is a subnet of the factory's main network. Subnets are connected to the plant backbone through exchanges, bridges, or routes to integrate plant data into plant management. Workshop management adopts what is commonly referred to as Ethernet, that is, IEC802.3, TCP/IP communication protocol standards.
The plant backbone network can use networks such as FDDI or ATM according to actual plant conditions.
The configuration of the entire coal transport program control network is as above:
I. The whole set of networks adopts SIEMENS equipment, so that fieldbus technology can be used to achieve a complete distributed structure and the benefits brought by this advanced technology can be fully obtained;
II. The uppermost layer of the network is Ethernet. Two PLCs are directly connected to the Internet to implement hot standby so that the status and parameters of the coal transmission system can be reliably transmitted to the entire plant MIS. At the same time, the information of laboratory stations, furnace measurement and belts are also sent to MIS via Ethernet;
III. The second layer of the network is the PROFIBUS-DP network, and the five PLCs are respectively the conveyor subsystem, the dumper subsystem, the bucket wheel subsystem, the loop subsystem, and the bucket turbine subsystem 2. They are running simultaneously with this subsystem. The PROFIBUS-DP network communicates with PLC1 and PLC2 to receive parameters or send status. The operator station and the engineer station are connected on the PROFIBUS bus as a monitoring station, which can perform remote programming, modification of parameters and online monitoring functions;
IV. The third layer of the network is the remote I/O link: AS-i interface layer, some actuators, sensors or small modules (LOGO!) on the remote site communicate via DP/AS-I linker and PROFIBUS-DP network. To receive parameters or send status;
V. The specific configuration is as follows:
PLC1, PLC2: Adopt S7-400 series CPU415-2DP, plus Ethernet communication module CP342-1;
PLC3, PLC4, PLC5, PLC6, PLC7: Adopt S7-300 series CPU315.
Operator station and engineer station: Use PG760. The PG760 is a powerful desktop computer that is compatible with regular AT/MicroDOS/Windows PCs. The PG760 has an integrated MPI interface. Select the CP5411 network card to connect to PROFIBUS-DP. The configuration STEP 7 programming package can be used as a programming device. Use PG760 Usually do not configure software packages such as WINCC to use as a monitoring station.
5. Summary Although the program was officially put into use at the end of the year, the initial commissioning of the program in practice proved that the entire system is safe and reliable, with high stability, and the relatively backward coal handling program control system has been upgraded to a new level. With the advancement of computer control equipment, most of the current thermal power generating units use distributed control systems (DCS) or fieldbus control systems, such as coal handling coal blending control systems, chemical water treatment control systems, and ash removal control systems, due to their independence. Distributed, and far from the main plant, most have not yet been incorporated into the DCS control system, still based on programmable logic controllers (PLCs), plus some operations, displays, interlocks, and alarms to form an independent control system. In addition, the microcomputer monitoring system and the industrial television monitoring system are coordinated with the control level of the main equipment, which greatly improves the reliability and automation level of the whole plant operation. It is believed that with the development of China's electric power industry, program control as the main control method for coal conveying systems will be applied more widely in thermal power plants.
Application of PLC in Transformation of Coal Handling Program Control System in Power Plant
1. Introduction Coal-conveying system is a common system in petrochemical power plants. With the rapid development of China's power industry, the installed capacity and stand-alone capacity of thermal power plants are increasingly increasing, and the scale of coal transportation systems has also increased substantially. The requirements for its control methods and operating levels are also increasing. The coal conveying program control system is mainly based on programmable controllers and realizes automatic control of the coal conveying system. Compared with the control of strong electric power concentration, it has technically strong control function, simple programming, convenient process interlocking, and can save a large number of hard wiring, easy maintenance, and online modification. PLC can not only complete the complex relay control logic, but also can achieve analog control, and even intelligent control; and can achieve remote communication, networking and host computer monitoring. It can create conditions for computer control and management in the whole plant. Create conditions for computerized control and management of geographical distribution. For geographically distributed systems, remote control stations and closed-circuit television monitoring systems can also be added.