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1 Introduction For a long time, the electrical control method has adopted the conventional manual control method. Large unit electrical control is characterized by: When the unit enters normal operation, the electrical operation is less; The electrical quantity changes very quickly, mostly in the order of milliseconds, the safety and reliability requirements are high; the electrical misoperation or refusal to move It will cause danger to the unit, or a large area of ​​failure and power outages. Therefore, at the same time that the current unit control room electrical enters the DCS, relay protection, AVR, synchronization, plant power switching, fault recording and other functions do not enter the DCS of the unit, and special devices are used, and a certain degree of rigidity is retained. Hand exercises.
As we all know, the reliability of electrical components is particularly high. For this reason, its own structure has spent a lot of design ideas on anti-misoperation or rejection. After long-term operation practice, the primary electrical equipment and secondary wiring have undergone continuous improvement and correction, and have accumulated rich experience. A stringent and standardized practice has been formed and established. However, after the electrical equipment enters the DCS, the conventional operating devices and some relays disappear. The wiring methods and ideas can only be corrected or re-conceived according to the characteristics of the computer system, or that will be a long-term accumulation of experience and a set of established The rigorous and normative approach must be implemented in computer systems and use computer technology to make the design more perfect. This is a major issue that needs to be considered in the current project. Indeed, how to better apply the advantages of computer systems to electrical control systems is also a new subject worthy of in-depth discussion.
How to Consider Security and Fastness in the Configuration of 2DCS System Hardware As mentioned above, the electrical system places great emphasis on safety and speed. The system features provided by several DCS bidders on I&C Island of Waigaoqiao Power Plant Phase II project are briefly described as follows.
(1) System and its features, see Table 1 
The number of I/O points of DCS in the second phase of Waigaoqiao Power Plant plus the amount of intermediate processes that may be generated during the processing process has many processing points, and the processing speed of the network is required quickly. Especially in the emergency of a fault, a large amount of information will be concentrated in a short period of time. If the network configuration is not properly configured or the equipment configuration is not high, bottlenecks will occur and even the system will crash.
Each DCS system has its own characteristics, and the adopted network structure and specifications are also different. In Table 1, TCP/IP, storage and forwarding basically belong to the network layer, transport layer and above protocols, Ethernet, Token Ring, FDDI belong to the physical layer protocol.
Store and forward: The communication content is temporarily stored in the buffer of a transfer station and then sent out.
TCP/IP. TransmissionControlProtocol/In-ternetProtocol Transmission Control Protocol/Internet Protocol. This is a protocol group that allows communication between different network systems and different computers. It is decomposed into sequential, connection-oriented protocols (TCP) and efficient, endpoint-to-endpoint connectionless protocols (IP). According to the address and the routing information table in the router, the IP data can be forwarded by the router to different destinations. It does not include flow control, receive reply, error check, and serialization to relieve traffic congestion. TCP is a connection-oriented protocol that requires a path establishment phase, a path interruption phase, a supervision phase, and flow control, response, serialization, checksum detection, and heavy communication. For reliability and efficiency, TCP and IP can be used simultaneously. TCP talks and responds on the system, and uses IP to transfer data between network nodes.
CSMA/CD: CarrierSenseMultipleAccessWithCollisionDetection Carrier sense multiple access protocol with collision detection. IEEE802.3 Ethernet (Ethernet) uses CSMA/CD as the media access control protocol. When two stations start to transmit data at the same time, a conflict occurs. When the CSMA/CD protocol is used and the detection mechanism detects the collision, the two stations each retreat for a random time before attempting transmission. The CSMA/CD method is effective when traffic on the Internet is light. As the amount of information increases, more conflicts will occur. Workstations have repeatedly evaded and retransmitted, and the network has been busy. If you continue this way, it will lead to a decrease in performance.
Fast Ethernet Switching: 100 Mbps throughput. All lines are connected to a central hub for point-to-point exchange of data. The communication protocol is still CSMA/CD. Due to the adoption of the fast exchange method, the drawbacks of CSMA/CD in large data volumes are greatly compensated.
FDDI: FiberDistributedDataInterface fiber distributed data interface. It is a fiber optic cable standard with a dual-ring topology with a transmission rate of 100 Mbps and a maximum length of 100 km, which was established by ANSI X3T9.5. The redundant double-ring has high fault-tolerance characteristics and is well guaranteed for security. Figure 1 shows the data flow status of a FDDI double ring network when a node fails.
When a site on the Internet fails, the upper and lower sites isolate the failed site and reconstruct a ring network with other normal sites. Safety and reliability have greatly improved.
In addition, FDDI uses the IEEE 802.5 token ring transmission access method. A token frame goes from one station to another along the network. After a station acquires a token, it starts to transmit data, and puts the token back in the ring after the transfer. There is a time limit mechanism to prevent a station from occupying tokens for a long time. It can be divided into asynchronous, synchronous, and connection-based. Westinghouse's Ovation uses the redundancy of FDDI double ring network, synchronization determinism, and token advantages. Hitachi’s HITACS also uses FDDI network, real-time data transmission through the token to actual regulation, each station in the specified time to transmit data to other stations, any station can transmit data in the cycle time, its stable system load rate is also This is achieved through periodic storage transfers.
The FDDI network can achieve a stable load rate during normal operation and abnormal operation. When a fault occurs, traffic jams will not be caused by too many events. The Ethernet network detects bursts of collisions. When there are too many events, there are many problems, especially the load rate. Therefore, in the case of industrial and mining enterprises such as power plants, in the event of a failure, that is, when the amount of information is large, it is more important to guarantee the timeliness. In this case, the fixed and fixed information transmission method occupies a great advantage.
It can be seen from the above that the DCS system provided by some manufacturers also includes a network connected to a printer, etc. This approach can greatly reduce the load pressure of the real-time control system.
(2) In each DCS system, redundant controller configuration methods are adopted. There is no interference between the active and standby controllers. The controller configuration is shown in Table 2. 
(3) The design of I/O speed is shown in Table 3. 
Different from previous projects, this project adds a DCS system to each unit and a public DCS system. The electrical power generation and transformation group, the power plant and other power plants enter the DCS for monitoring, and the utility power system enters the public DCS for monitoring. Its public DCS also has the function of two-way communication with ash, water, oil, coal and other PLC systems. . This can ensure that when the unit DCS system is not commissioned and put into operation, or when the unit is out of service, the utility power system is monitored through the public DCS system. From the system point of view, dividing the monitoring of the power-supply system of the unit plant and the monitoring of the electricity-utility of the utility plant on two DCSs also has many advantages. In the past, there was discussion on whether the utility power system of the utility was entering the #1 unit DCS or the #2 unit DC$. As a result, if a certain DCS is entered, when the DCS is overhauled, the monitoring of the utility power system is switched to another DCS, resulting in a lot of trouble. If two DCSs are connected, the site must have two sets of signals, making the field wiring very complicated. If the public DCS is set, the system is clear and the operation is safe, which is more conducive to the common monitoring of many public auxiliary systems that can be accessed by the public DCS.
The current DCS control of the electrical system is limited to ON/OFF operations during normal operation. The time requirement is not too high, but the safety requirements are still high. As described above, the DCS manufacturers of the network, controller, etc., have adopted redundant configurations. Then, for I/O cards, due to the misoperation of circuit breakers and logic judgment errors, it will cause serious consequences. Therefore, in the second phase of Waigaoqiao Power Plant, the main circuit breakers will be controlled to open and close commands, and the open position will be input. Off, position input is redundantly configured. Incidentally, the thermal control professional made a 3 out of 2 configuration for the parameters that were of particular importance, and redundantly configured the general important parameters.
In view of the thermal control professional's design ideas for controllers and I/O cards, it is basically from the perspective of security and configured according to different system functions. However, according to the different systems and safety considerations, the electrical specialty is also systematically divided. Therefore, after discussions with various manufacturers, the electrical system was divided as follows in the hardware configuration. (1) Considering the convenience of overhaul, when the I&C equipment is overhauled, the electrical cannot be stopped, so the electrical system is in the power supply, the controller , Consider the independence of related communications, modules and group screens.
(2) The plant power is divided into A and B systems. In order to ensure that the system A does not affect the B system, the plant power supply is based on the A and B systems; consider the power supply, controller, related communication, module and group screen. Independence.
(3) When the unit is shut down, the power supply for the plant needs to continue to operate. Therefore, the power generation, power plant, controller, related communication, module and group screens are considered independently of each other.
(4) According to the requirements of dualization, dualization shall also be considered on the power supply, controller, related communication, module and group screen.
4 Outlook and Suggestions The general unit DCS system has a large number of thermal processing professional network processing points, and there is a gradual upward trend. Its conventional I/O modules are also designed based on the characteristics of thermal parameters. In view of the existing conventional DCS equipment, the scale of the electrical access unit DCS can only be limited to the simple operation during monitoring and normal operation, that is, only by moving the original hard disk to the computer system. Other functions such as: fault recorder, protection, AVR, synchronous device, factory power switching device, etc., still use special devices.
In terms of computer monitoring of electrical systems, computer monitoring systems at substations and boost stations of power plants have taken the first step. It is designed and manufactured based on the characteristics of electrical systems. Under normal circumstances, the substation or booster station computer monitoring system has a limited number of network points and a small network size, but the network level is complete and the equipment is available in a variety of ways. Usually adopts distributed structure, intelligent I/O station, plus operator station, engineer station, network printer, front-end machine (according to the needs of the project), etc., can achieve AC sampling, the same period, locking, harmonic analysis , CRT operations, recording, archiving, open operations and other functions. With protection devices, etc., communication can also be used for communication. Due to the adoption of AC sampling, mathematical conversion can be used to define waveforms, conduct harmonic analysis and other series of work that is of great value to the electrical profession; it is also possible to perform simultaneous verification within the intelligent I/O station.
Therefore, if the unit control room electrical access to the unit DCS system, because the thermal DCS itself a lot of processing points, in addition to the simple scale of the electrical system in its inherent scale, of course, is feasible. At the same time, on the basis of the unified consideration of equipment selection, it is possible to attach the wave recorder, protection, and automatic devices to the network as a dedicated stand-alone station, and then to other stations or operator stations, engineer stations, etc. on the Internet. Communication contact. However, if you want to enhance the electrical characteristics of a thermal DCS system, you must further improve its controllers and I/O modules. If you choose the electrical DCS solution, you can follow the experience of the computer monitoring system in the substation or power station booster station to coordinate the various functions of the electrical system and further develop the expert system. In the status analysis, fault analysis, status processing, and faults Handling, preventing mistakes, training, simulation, etc., truly people-oriented, truly realize the perfect function of electrical automation system.
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Preliminary Study on Computer Monitoring Model of Power Plant Electric
Abstract : The gas enters the DCS system for monitoring. The considerations of safety, rapidity, and network and hardware configuration, combined with the DCS monitoring of the electric system of the 900 MW unit of Waigaoqiao Power Plant, introduce the characteristics of the DCS system implemented by foreign suppliers in China. Several of the controllers provided by several DCS manufacturers adopt multi-CPU mode, use dedicated interface cards, and special master/slave switch tracking hardware configuration, which allows the main CPU to process engineering data in a centralized manner without spending time processing. Things on a computer system. For a solution with a lower controller hardware configuration, this approach can appropriately compensate for the low efficiency of the controller's main CPU. From Table 3, it can be seen that in the configuration of a general DCS, the scanning period of AI and DI is relatively long. If you want to analyze harmonics or display waveforms for electrical parameters, or try to make simultaneous judgments, it is obviously not acceptable. Unless special modules and controllers are used. With regard to the current parameters of some fault recorders and substation monitoring systems (using AC sampling), it is necessary to achieve 12-bit or more analog-to-digital conversion, 9th harmonic analysis capability, and 0.5% or more waveform sampling accuracy. The frequency is at least lkHz, and 1ms is sampled once, and the weekly wave is sampled at 20 points. 3 The second phase of Waigaoqiao Power Plant's electric DCS monitoring mode is now outside the second phase of Gaoqiao Power Plant as an example. It briefly describes the general characteristics of DCS systems that are currently being implemented by several DCS manufacturers in China. In the second phase of Waigaoqiao Power Plant, considering the electrical safety and rapidity, the current general DCS system does not aim at the electrical characteristics to design its system and various components and modules suitable for electrical systems. The protection, AVR, automatic synchronization devices, and plant power switching devices all use specialized devices. In addition, the generators, generators, motors, etc. all entered the DCS monitoring.