Practice and Discussion on Electric Control System of Thermal Power Plant Entering Decentralized Control System

After more than 10 years of exploration and practice, the application of DCS in thermal control system of thermal power plants in China has made a qualitative leap in the monitoring appearance of unit units, which shows great superiority. With the further improvement of the unit control operation requirements of the unit, the problem of the thermal power plant's electrical control system entering the DCS has also been raised, and some projects have begun to try. However, the design origin of DCS is aimed at the thermal control object. There are no small differences in functions, performance and usage habits from the characteristics and control requirements of electrical objects. Therefore, the function of the electrical control system enters DCS and has its particularity and needs. Attention to the problem. This paper combines the practice of entering the DCS with the electrical control system of Units 1 and 2 of Yangcheng 6X350MW Power Plant, and analyzes and discusses some problems.

1 Yangcheng Power Plant and its unit control system 1.1 Yangcheng Power Plant Overview and Unit Control Level Yangcheng Power Plant is a Sino-foreign joint venture and a national West-East Power Transmission Project. The first phase of the project designed a unit capacity of 6X350MW burning anthracite. The whole unit control system adopts Siemens TELEPERM-XP DCS as the main control device, and is equipped with other special thermal control and electrical devices. The total amount of I/O processed by DCS is more than 6,400 points, and 13 pairs of redundant AP8PFs are used to complete different functions such as DAS, DEH, SCS, MCS, MEH, FSSS, BPS, SOE and electrical control of the electrical system. The operation mode of the unit is realized by a main attendant with a number of auxiliary attendants. In the unit control room, except for a number of emergency stop buttons, 2 industrial TVs, steam turbine speed, generator active power, grid frequency 3 digital meters, no thermal, electrical conventional instruments and backup hand-operated devices, the entire unit operation Surveillance is all implemented with CRT, and is equipped with two 4-screen combination rear projection large-screen displays. From the control function, it is only necessary for the operation personnel to select and confirm at several control selection points of the startup and operation processes, and the control system can complete the start and stop of the whole unit and the normal operation process control. The utility and other auxiliary systems of the power plant use PLC and other special devices to complete the control. The important information is transmitted to the DCS for display and archiving through communication or hard wiring. Therefore, Yangcheng Power Plant is a power plant that realized the DCS-body control of the unit unit earlier.

1.2 Electrical control system composition After comprehensive consideration of the overall automation level requirements of the unit, the characteristics of electrical control objects, the current status of DCS and electrical control devices, determine the electrical control system into the DCS program. The main system is structured as follows.

Volume 34 Fire Electrical Power Plant Electrical Control System Entering Decentralized Control System Practice and Discussion 2001 No. 12 Discussion T and Recommendations 1.2.1 Unit Self-Starting and Stopping Control System The logic function of the unit's self-starting and stopping control system is completed in DCS.

During the automatic start-up of the unit, it issues instructions to the electrical system according to the predetermined procedure: input AVR; start the synchronous system and the plant power switching system to switch the plant power; after the self-contained power supply, start the 500kV synchronous system, the unit Parallel with the power grid; when the machine is stopped, the load is reduced to the minimum, the reverse power protection action trips off the 500kV main switch and the grid is disconnected; the synchronous system and the plant power switching system are started, and the power consumption of the factory is reversed; the generator demagnetizes and locks the electrical system .

1.2.2 Protection of generator transformer group and plant power system These important protection functions are realized by special microcomputer protection devices. Directly take PT, CT and other power signals to protect the outlet from directly operating the corresponding circuit breaker. Each system works completely independent and is not affected by the DCS status. Only these protection devices and the operating status information of each system have more than 60 switching signals. They are hardwired to enter the DCS for display, alarm, and recording. This is a function that is based on the characteristics of the electrical control system for a long time. The function of the microprocessor-based electrical control device is more suitable for the fast, reliable and professional requirements of the electrical protection system. Because the DCS logic processing speed is second level, if DCS is to perform these functions, on the one hand, it must speed up the processing speed of the local process control station, which will inevitably lead to lower processing capacity and capacity, which will undoubtedly increase hardware and may affect other functions. The normal implementation; on the other hand, DCS can not meet the anti-interference and special technical processing requirements of electrical protection.

The same method also handles the fault recorder. In fact, this configuration method also realizes the principle of distributed control and centralized control of information collection from the overall control of the unit. The signal transmission of the electrical protection system and the DCS can be completely communicated, but whether the communication method is adopted requires a comprehensive economic comparison.

1.2.3 Synchronous system and plant power switching system The components of the synchronizing system and the plant power switching system of the unit unit of Yangcheng Power Plant are considered together. The system structure is more complicated. The DCS and the electrical relay form a double logic, and the same synchronizing device is switched to complete the detection of different synchronizing points. These functions are realized by the adjustment of DEH and AVR.

When the unit starts, the power supply is provided by Shanxi Power Grid. After the unit starts and stops the control system until the fixed speed of the steam turbine, the plant power switching system in the DCS is started. Firstly, the 6-point working line switch of the 6kV power system is automatically selected. Check that the switching point condition is met and issue a command to start the synchronizing device. At the same time, the factory power switching circuit composed of relays is also subjected to the same inspection, and the synchronizing device is allowed to start. According to the detection situation, the synchronous device sends the adjustment of the turbine speed and the generator terminal voltage to DEH and AVR respectively, and then sends the closing command to the 6kV working inlet switch of the A section after the synchronization requirement is met, and the 6kV standby incoming line switch of the A section is connected. In the DCS, it is confirmed that the power switching of the A-segment factory is completed, and the B-segment is automatically selected to perform the above-mentioned switching work.

After the unit comes with the factory power, the DCS will switch the synchronous device to the 500kV synchronization point by the network control manual pre-selection of the parallel switch). After checking the synchronization conditions, the synchronous device will be started to perform the corresponding work, and the Jiangsu power grid will be automatically juxtaposed. If the unit's start-stop control system is not put into operation, the above work can be done manually by the CRT. When the machine is shut down, the generator is disconnected from the power grid. The electrical protection system starts the plant power switching system and the synchronous system to perform the reverse switching of the plant power. The switching ends and the electrical system is blocked.

1.2.4 Generator Excitation System This system is equipped with 2 sets of redundant microcomputer automatic voltage regulating device AVR. Through the operation keyboard installed on the local control cabinet panel, the device can be debugged, set, retired, switched, operated and so on. The device communicates with the DCS via the communication interface for nearly 60 signals, and sends all the information to the DCS for display, recording, alarm and other comprehensive use. Through the CRT, all functions of the AVR are remotely set, retired, switched, and operated. The AVR accepts other relevant status information of the unit in the DCS, executes the command from the start and stop system, and completes the corresponding operation. At the same time, the DCS sends clock information to the AVR, so that the two systems keep the clock synchronized. Therefore, the AVR is an independent working system for the excitation function, and it is a functional control station for the entire control system of the unit.

1.2.5 Auxiliary electrical system security power supply, diesel generator, DC power supply system and all power equipment operation, control and status parameter display, recording, alarm, etc. all enter the DCS. At the same time, each power device still serves as the execution terminal of the thermal control sequence control system.

The 24 auxiliary transformers such as coal, ash and chemical water only retain the operating status and parameter monitoring in the DCS. The independent protection devices and the control of the injection and retreat are set in the local control cabinet. Block switch control panel and partial cable. In fact, for this type of system, two redundant PLCs can be set up in the distribution room, the operation control logic and status signals are set in it, two-way communication is established with the DCS through the twisted pair, and the line selection operation block is configured in the DCS. The status display point window), issuing commands and accepting status information to achieve the purpose of CRT monitoring, is more economical and reasonable.

1.2.6 Boost station control The monitoring of the 220kV power supply substation and the 500kV booster station of Yangcheng Power Plant did not enter the DCS. In order to let the value of the network control know the operation status of each unit, the DCS of each unit of the original design separately sets a CRT terminal in the network control through the remote bus, and can view all the information of each unit. However, from the use of Units 1 and 2, this type of preparation is neither economical nor operational. In this regard, after all units are put into production, it is planned to transmit the main information of each of the six units to a server through communication, and then connect one CRT to complete the information display of the six units in the network control. This information can also be connected to the plant-level MIS in the future.

2 Commissioning and commissioning Due to the electrical control system entering the DCS, the unit DCS 2001 12th China Power Vol. 34 Discussion T and the commissioning of the proposed one brought new problems, especially the power plant receiving power and DCS The contradiction of electrification is most prominent in Unit 1. In the 2 months before the power consumption of the plant, the Yangcheng Power Plant Unit 1 was specially prepared for the electrification of the DCS. Firstly, clean the electronic room where the DCS control cabinet is installed, and ensure the DCS's live environment. The engineer station and the CRT are temporarily placed in the electronic room. The UPS system is qualified by the construction power supply and can supply power to the DCS. After these conditions are basically satisfied, start the engineer station and three DCS control cabinets related to the plant power system, perform system recovery and debugging, and make some temporary settings to ensure the operation of the plant power system. At the same time, the functions of other thermal control systems in the three cabinets should be debugged. After the power consumption of the plant is received, the other cabinets are gradually started with the end of the installation work, and the DCS is debugged according to the traditional method, and the unit is trial-operated. The trial operation of the branch and the installation of the DCS are all completed. The power supply for the factory is powered off for 3~5 days. The DCS parts are designed according to the design, and the wiring of the thermal control system in the three cabinets is improved. Restart DCS for system debugging. Unit 1 has improved and improved the electric control system of DCS four times, so that the control system of the whole DCS and the unit has reached a good state, and all the functions of the original design have been realized.

After the electrical control system enters the DCS, there are new problems in the division and cooperation of the electrical and thermal control 2 professional debugging work. In principle, the thermal controller should be responsible for the debugging of the DCS device and all electrical information processing functions. The electrical control, interlocking, and protection logic functions should be completed by electrical personnel. All electrical control functions should be tested by electrical personnel.

Part of the information of the electrical system is entered into the DCS through communication, which is a technical difficulty in system debugging. It must be debugged and optimized by two-way configuration. The communication period, period, rate, transmission amount and interrupt mode and information priority level of each subsystem are allocated from the perspective of the overall system; otherwise, information loss, congestion, and crash will be caused. Adverse consequences.

3 Discussion of several problems 3.1 Advantages of electrical control entering DCS Through the practice and adjustment and improvement of the No.1 unit of Yangcheng Power Plant, it can be seen that the control of large thermal power unit is covered by DCS with all systems including electrical system. The superiority: the whole generator set adopts modern tools and means to achieve high level and perfect monitoring; improve the reliability of electrical control; unit unit control information to achieve maximum sharing, more conducive to the realization of the integrated automation of the entire generator set And improve the management level, and the unit unit has truly reached the full centralized control operation.

3.2 About coverage and configuration mode From the use of Units 1 and 2, the electrical control system can fully enter the DCS, but the incoming will increase the I/O point and internal configuration capacity, and expand the DCS scale. DCS prices are usually based on I/O points, which obviously increases DCS investment. And because DCS can't directly accept signals such as PT and CT, the current and voltage will increase the conversion cost. Therefore, the decision of DCS to cover electrical control should include economic considerations. Depending on the specific conditions of DCS, electrical control devices, power plant characteristics, etc., it is possible to pursue the feasibility, reliability, and rationality of the overall system. There is no need to force everything to be realized by DCS.

3.3 Design coordination and function distribution The traditional DCS application design is completed by the thermal control professional, and after the electrical control enters the DCS, which functions and what forms are entered, the logic function design and the incoming information are processed and the division of the electrical special device, Contact, DCS and independent electrical control device data communication protocol establishment, etc., should be completed by the electrical professional planning and with the thermal control professional, which is extremely important for a reliable and economical integrated system.

The control logic and parameter settings of the electrical system are generally completed once, and rarely change once the debugging is appropriate. And after a system is powered up, it may not be allowed to exit for a long time or for many years. However, the thermal control logic and design parameters are usually determined by trial and error, and there are many changes. Any one function or any modification of the tuning parameters must be transmitted by the engineering station to the process control station. Most DCSs do not have an online transmission function. The output status of the station may be in any state during the offline operation of the control station. As long as the electrical control and thermal control items are located in the same process station, modifications to the thermal control functions or parameters may cause the electrical system to malfunction, so this must be noted when assigning process stations for electrical control functions in the DCS. On the other hand, for the new unit, the power consumption of the plant is often earlier than the normal recovery and charging of the DCS. Therefore, when the process station is assigned to the electrical control function, it is also convenient to locally electrify in advance to meet the power consumption of the plant.

3.4 Device clock coordination problem The control unit of the whole unit is composed of DCS and several independent microprocessors and digital devices, each with its own clock. In the engineering design, the system synchronization clock protocol should be considered uniformly, otherwise the information with time stamps in the system will be disordered.

Responsible Editor Lu Ling) The development of power in the western region should be the first