The practice and discussion of entering the decentralized control system of thermal control system of thermal power plant

After more than 10 years of exploration and practice, the application of DCS thermal control systems in thermal power plants in China has resulted in a qualitative leap in the monitoring of the unit units, which represents a great advantage. With the further improvement of the centralized control and operation requirements of the unit units, the problem of the thermal control system entering the DCS has also been raised, and some projects have begun to try. However, the design origin of DCS is for thermal control objects. There is not a small difference in function, performance, and usage habits from the characteristics and control requirements of electrical objects. Therefore, the function of the electrical control system enters DCS also has its own particularities and needs. Attention problem. In this paper, the practical situation of entering the DCS in the electrical control system of No. 1 and No. 2 units of Yangcheng 6X350MW power plant is analyzed and discussed.

1 Yangcheng Power Plant and its unit control system 1.1 Overview of Yangcheng Power Plant and unit control level Yangcheng Power Plant is a Sino-foreign joint venture, and the national West Electric Power Transmission and Transmission Co., Ltd. is a power transmission project. The first-phase project design capacity is 6X350MW unit combusted with anthracite. The entire unit control system uses the Siemens TELEPERM-XP type DCS as the main control device, together with other dedicated thermal control and electrical devices. The number of I/Os handled by the DCS totals more than 6400 points, and a total of 13 pairs of redundant AP8PFs are used to complete the DAS, DEH, SCS, MCS, MEH, FSSS, BPS, SOE, and logic control functions of the electrical system. The operation mode of the unit operation is provided by a main watchman with a number of auxiliary watchers. In the unit control room, except for several emergency stop buttons, two industrial televisions, steam turbine speed, generator active power, and grid frequency three digital meters, no thermal engineering, electrical conventional instruments and backup manual operation devices are provided, and the entire unit operation is operated. All monitors are implemented using CRTs and are equipped with two 4-screen rear projection large screen displays. From the control function, it only needs to run the personnel to select and confirm several control selection points in the process of starting and running. The control system can complete the entire unit startup and shutdown and normal operation process control. The utility and other auxiliary systems of the power plant are controlled by special devices such as PLCs. 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 has earlier realized DCS-unitized control of unit units in China.

1.2 The composition of the electrical control system After comprehensive consideration of the unit's overall level of automation requirements, the characteristics of the electrical control object, the status of the DCS and the electrical control device functions, the electrical control system is determined to enter the DCS program. The main system is specifically structured as follows.

The 34th volume of thermal power plant electrical control system into the decentralized control system of the practice and discussion of the first 12 years of 2001 T discussion and recommendations 1.2.1 unit start-stop control system from the unit start-stop control system logic function completed in the DCS.

During the automatic start-up of the unit, it commands the electrical system separately according to a predetermined procedure: input AVR; start the simultaneous system and plant power switch system, switch the plant power; start the 500kV synchronous system after the power is supplied from the factory, the unit Parallel to the power grid; when the machine stops, the load is reduced to the minimum; the reverse power protection action trips off the 500kV main switch and the power grid is disconnected; the start-up system and the plant power switch system are used in the same period; the power consumption of the factory is deducted; and the generator is de-excitation and lockout electrical system. .

1.2.2 Protection of Generator Transformer Units and Plant Power Systems These important protection functions are implemented using dedicated microprocessor protection devices. Directly take PT, CT, and other power signals to protect the circuit breakers that directly act on the outlet. Each system works completely independently and is not affected by the DCS state. Only these protection devices and the working status information of each system total more than 60 digital signals. Use hard wiring to enter the DCS for display, alarm, and recording. This is in consideration of the characteristics of electrical control systems that have been developed for a long time. The functions of electrical control devices with microprocessors as their core are more suitable for the requirements of fast, reliable and professional electrical protection systems. Because the DCS logic processing speed is in seconds, if you want DCS to complete these functions, you must speed up the processing speed of the local process control station on the one hand, which will result in a decrease in processing capacity and capacity, which will undoubtedly increase the hardware, and may also affect other functions. The normal realization; On the other hand, DCS can not meet the electrical protection of anti-jamming and special technical processing requirements.

The same method deals with the fault recorder. In fact, from the perspective of the overall control of the unit, this constitution method also realizes the principle of distributed control and information centralized control. The signal transmission of the electrical protection system and the DCS can completely use the communication method, but whether to use the communication method requires comprehensive economic comparison.

1.2.3 System and plant electricity switching system in the same period The composition of the unit system and plant electricity switching system of Yangcheng Power Plant is considered together. The system configuration is more complex. The DCS and the electrical relay form a double logic, and the same synchronous device is switched to complete the detection of different synchronization points. These functions are achieved by the adjustment of DEH and AVR.

When the unit is started, Shanxi Power Grid will provide the starting power. After the unit starts and stops the control system until the turbine is set to speed, the plant's electricity switching system in the DCS is started. First, the A-section work switch of the 6kV factory power system is automatically selected at the same time.) Check that the conditions of the switching point are satisfied and issue an instruction to start the synchronization device. At the same time, the factory electrical switching circuit consisting of relays is also subjected to the same inspection, allowing the simultaneous start of the device. During the same period, according to the detection conditions, the DEH and AVR shall issue adjustments to the turbine rotation speed and the generator terminal voltage respectively, and then issue a closing command to the A section 6kV working line switch after the requirements of the same period are satisfied. The joint jumps section A 6kV standby line switch. In the DCS, it is confirmed that the A-plant power switchover is completed and the B-section is automatically selected to perform the above-mentioned switching work.

After the unit has used its own power, the DCS will switch the same period to the 500kV point of the same period by the network control manual pre-selection parallel switch), check the conditions of the same period to meet, start the corresponding device to carry out the corresponding work, and Jiangsu Power Grid automatically side by side. If the unit is not put into operation from the start-stop control system, the above work can be done manually by the CRT. When the machine stops, the generator and the power grid are disconnected. The electrical power system and the system of the same period of time are used to switch the power supply of the plant. The switching is completed and the electrical system is locked.

1.2.4 Generator Excitation System The system is equipped with two sets of redundant microcomputer automatic voltage regulators (AVRs), which can complete debugging, setting, retreat, switching, and operation of the device through the operation keypad installed on the local control cabinet panel. The device communicates with the DCS via the communication interface in two-way communication with nearly 60 signals. It sends all the information to the DCS for display, recording, alarming and other comprehensive uses. Through the CRT, the AVR performs various functions such as remote setting, returning, switching, and operation for manual control of various functions. AVR accepts other relevant status information of the unit in the DCS and executes the command from the start-stop system to complete 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, AVR is an independent working system in the excitation function, and it is also a functional control station for the entire control system of the unit.

1.2.5 Auxiliary Electrical System The display, recording and alarming of the operation, control, and status parameters of the security power supply, diesel generator, DC power supply system, and all power equipment are entered into the DCS. At the same time, each power plant still serves as the execution terminal of the thermal control sequence control system.

Twenty-four auxiliary transformers such as coal transportation, ash removal, and chemical water production only maintain the operating status and parameter monitoring in the DCS. Each independent protection device and the investment and return control are located in the local control cabinet, which saves the number of processing. Block switch control board and some cables. In fact, for this kind of system, two redundant PLCs can be set up between power distributions, and the operation control logic and status signals are set therein. Two-way communication is established with the DCS through the twisted pair lines, and the line selection operation blocks are configured in the DCS. Status display point window), issuing commands and receiving status information to achieve the purpose of CRT monitoring, so that it is more economical and reasonable.

1.2.6 Control of the boosting station The monitoring of the 220 kV substation and 500 kV boosting station of Yangcheng Power Plant did not enter the DCS. In order to let the value of the network control understand each unit's operating conditions, the DCS of each unit was originally designed to set up a CRT terminal at the network control through the remote bus, and the entire information of each unit can be adjusted. However, from the use of Units 1 and 2, this preparation method is neither economical nor convenient. In this regard, after all units are put into production, it is planned to communicate the main information of each of the six units to a server first through communication, and then connect a CRT through it to complete the information display of the six units in the network control. In the future, this information can also be connected to plant-level MIS.

2 Commissioning and commissioning As the electrical control system enters the DCS, commissioning of the DCS of the unit unit DCS, Issue 12, 2001, No. 12 of China Power Co., Ltd. brings new problems to the commissioning of the T-discussion and recommendation I, especially the power-supply and DCS of the unit plant. The contradiction of electrification is most prominent in Unit 1. Yangcheng Power Plant Unit 1 has been preparing all aspects of DCS charging for 2 months prior to receiving power from the plant. Firstly, the electronic room between the DCS control cabinets is cleaned and the DCS energized environment is relatively guaranteed. The engineer station and the CRT are temporarily placed in the electronic room; the UPS system is powered by the construction power supply and is qualified for debugging and can supply DCS power normally. After these conditions are basically met, start the engineering station and three DCS control cabinets related to the plant power system, perform system restoration and commissioning and make some temporary settings to ensure the operation of the plant power system. At the same time, debugging of other thermal control system functions in these three cabinets is completed. After the plant is powered by electricity, the other cabinets are gradually started with the completion of the installation work. The DCS is commissioned in accordance with the traditional method and is coordinated with the trial operation of the unit. The trial run and the installation of the DCS were all completed. The power plant was used for power cuts for 3 to 5 days. Each part of the DCS was designed in place, and the wiring of the thermal control system in the three cabinets was improved. Restart DCS to debug the system. Unit 1 has improved and perfected the electrical control system in the DCS for four times, so that the control system of the entire DCS and the unit has reached a good state and realized all the functions of the original design.

After the electrical control system enters the DCS, there are also new problems in the division of labor and coordination of the electrical and thermal control 2 professional commissioning work. In principle, the thermal control personnel shall be responsible for the debugging of the DCS device and all electrical information processing functions. The electrical control, interlocking and protection logic function debugging shall be completed by the electrical personnel. All electrical control functions shall be conducted by the electrical personnel responsible for the test.

Some of the information in the electrical system enters the DCS through communication. This is a technical difficulty in system debugging. Must be debugged bidirectional configuration optimization, from the perspective of the overall system to allocate the communication period, cycle, rate, each cycle of the amount of transmission and interrupt mode and information priority level of each subsystem; otherwise it will cause information loss, blocking, crashed Adverse consequences.

3 Discussion of several issues 3.1 Advantages of electrical control in entering DCS Through the practice and adjustment of Yangcheng Power Plant No. 1 unit, it can be seen that the control of large-scale thermal power unit units has all systems including the electrical system covered by DCS. Advantages: Make the entire generator set adopt modern tools and means to achieve high-level and perfect monitoring; Improve the reliability of electrical control; Unit control information to achieve the maximum degree of sharing, is 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 achieved full centralized control operation.

3.2 About Coverage and Configuration Modes From the perspective of the usage of Units 1 and 2, the electrical control system can fully enter the DCS, but the entry will inevitably increase the I/O points and internal configuration capacity and expand the scale of the DCS. DCS prices are usually based on I/O points, which obviously increases DCS investment. And because DCS can not directly accept PT, CT and other signals, the current and voltage will increase the conversion cost. Therefore, economic considerations should be included when deciding on the coverage of DCS for electrical control. Depending on the specific conditions of the DCS, electrical control devices, power plant characteristics, etc., the overall system can be pursued to be feasible, reliable, and reasonable, and there is no need to force everything to be implemented by the DCS.

3.3 Design cooperation and function allocation Traditional DCS application design is completed by the thermal control professional, and after the electrical control enters the DCS, which functions, what form to enter, enter the logical function design and access to information processing and division of work with electrical special devices, The establishment of data communication protocols such as contact, DCS, and independent electrical control devices must be planned by the electrical professional and coordinated with thermal control professionals. This 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 debugging is appropriate. And after a system runs live, it may not be allowed to exit for a long time or for many years. However, thermal control logic and design parameters are usually determined through trial and error, changes are numerous, any one function or any one of the setting parameters must be modified, the engineer station must carry out code transmission to the process control station. Most of the DCS do not have online transmission functions. Part of the output status of the station may be in an arbitrary state during the off-line process 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 function or parameters may cause the electrical system to malfunction. Therefore, attention must be paid to this issue when assigning process stations for electrical control functions in the DCS. On the other hand, the power generation for the new unit is often earlier than the normal restoration and charging of the DCS. Therefore, when assigning the process station to the electrical control function, it is also convenient to locally charge in advance to meet the power consumption of the plant.

3.4 Device clock coordination problems The control unit of the entire unit is composed of a combination of DCS and several independent microprocessors and digital devices, each with its own clock. In the engineering design, it is necessary to consider the establishment of the synchronous clock protocol of the system. Otherwise, the information in the system will be disordered.

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