In this paper, Hebei Guohua Dingzhou Power Plant analyzed the characteristics of electrical system control, combined with the actual application of the actual situation of the introduction of the electrical system into the scope of DCS monitoring and control requirements, and on the DCS hardware configuration, software functions, public system control and other issues Explore and provide reference for similar projects in the future.
Keywords electrical system DCS
INTRODUCTION Guohua Dingzhou Power Plant has adopted DCS control system for its thermal control and formed four systems: DAS, MCS, SCS, and BMS. From the actual operating conditions, DCS achieves its control function better, and it has played a safe, economical, reliable advantage, and achieved good results, and the electrical control broke the conventional control method - using a disk drive For a hard-handed operation, the electrics are included in the DCS control. This not only makes use of the DCS mature decentralized control technology, but also improves the electric control level. After the electrical control is incorporated into the DCS, the DCS can be fully utilized to make the electrical anti-misoperation and other functions more convenient and complete, and the related amount of display, alarm and the control and regulation of the electrical equipment are organically combined to effectively improve the entire electrical system. Control security and reliability.
1. Characteristics of electrical system control Compared with thermal engineering automation, electrical systems have many different points in the control requirements and operation process. The main features of electrical performance are:
(1) The electrical equipment is less controlled than the thermal equipment, and the operating frequency is low. When some systems or equipment are operating normally, they are operated only for several months or longer.
(2) Automatic protection of electrical equipment requires high reliability and fast operation. Transmission and transformation group protection movement speed requirements within 40ms; automatic quasi-synchronous time using synchronous voltage mode, speed, voltage adjustment and sliding pressure control requirements within 5ms; voltage automatic adjustment device fast excitation requires a very short time; plant fast-cutting device fast The switching time is generally less than 60 to 80 ms, and the phase difference of synchronization authentication is 5° to 20°.
(3) Guohua Dingzhou Power Plant adopts two units sharing one unit/standby, and the maintenance of any unit cannot affect the normal operation of another unit. The DCS control method is that the DCS of each unit can achieve the control of the common part, and the two operating rights are completely equal.
(4) The interlocking logic of the electrical system of the electrical equipment is relatively simple, but the operating mechanism of the electrical equipment itself is complicated.
Therefore, the electrical system of the unit is integrated into the DCS control, requiring high reliability of the control system. In addition to the normal start and stop and operation, it is required to realize real-time display of various data and status under abnormal operation and accident conditions, and provide corresponding operation guidance and emergency handling measures to ensure that the automatic control of the electrical system is in the safest and most reasonable. Working conditions.
2. The scope of integration of the gas system into DCS monitoring According to the characteristics of operation and electrical control of the unit unit of Guohua Dingzhou Power Plant, the application of the electrical system of the generator-transformer unit and the plant power supply is included in the DCS monitoring in the application of the project. .
The electrical systems within the main building from the booster station (excluding the booster station) to the power plant side are all included in the DCS monitoring. The main systems are summarized as follows:
The monitoring range of the unit's electrical control system includes:
1. Generator-transformer group (including circuit breakers, knife switches);
2. Generator excitation system;
3. High-voltage plant power supply;
4. Unit low voltage transformer, PC incoming line and segment;
5. Security power supply and diesel generator sets;
6. Unit unit DC system (monitoring only);
7. UPS system (monitoring only).
The public electric control system monitoring range includes:
1. High-pressure start/back-up (including circuit breakers and switch brakes);
2. Utility low voltage transformer, PC incoming line and segmentation.
Electrical main protection safety automatic devices are still difficult due to the requirement of DCS to achieve its function, and it is necessary to increase the considerable cost. In principle, it is not required to achieve its function through DCS, but still retain its device, but they use RS485 interface to communicate with DCS. The reserved automatic protection devices are as follows:
Transmission and transformation group protection device; automatic synchronization device (ASS); automatic voltage adjustment device (AVR); factory power fast cutting device; fault recording device.
3. The control level and technical level reached by the DCS when the electrical system is integrated into the unit The whole process of automatic program control from the boiler ignition to the generator and the net load with the initial load is sufficient when the unit is fully started, or the DCS can be safely stopped when the unit is stopped.
The control level of the start-stop control of the unit is:
When the unit is normally started, the DCS will be put into AVR when the generator reaches rated speed. When the generator voltage reaches the rated value, the DCS will be put into the synchronization device. The synchronous period of the generator and the power grid is automatically realized by the device during the same period. During the same period, the AVR and the DEH are controlled by the DCS. When the conditions of the same period are met, the generator circuit breaker is commanded to close.
When the unit is shut down normally, the main switch is tripped and the steam turbine is jumped (the main valve is closed), and the generator is de-energized.
The requirements for plant power system control are:
When the unit starts, it supplies power to the factory load through the start/standby transformer; when the unit is used normally, it is supplied by the plant and is supplied to the 400VMCC low-voltage load to start the necessary auxiliary equipment; In order to protect the safety of the equipment and systems, the plant-use fast-cutting device should quickly switch the factory-use working load to the start-up/stand-by; when confirming the loss of the voltage in the security-defining section, the emergency backup diesel power supply should be started to ensure the safety of the equipment. .
According to the requirements of the above control level, the requirements for incorporating DCS into electrical monitoring are:
(1) The generator system can achieve program control and soft hand control so that the generator can raise the speed from zero and increase the pressure until the grid and the initial load.
(2) The plant power system can be implemented according to the requirements of program control and soft hand operation in the start/stop phase and normal operation phase.
(3) It can display and record in real time the various data and status of the normal operation, abnormal operation and accident state of the above-mentioned transformer-generation system and plant power supply system, and provide operation guidance and emergency treatment measures.
(4) The unit unit (furnace electromechanical) realizes full CRT monitoring.
4 For DCS software and hardware requirements Guohua CLP 2 unit units, electrical main wiring using generator - transformer unit unit wiring, connected to 220kV/500kV power distribution system, the main plant 6kV high voltage factory bus with two working sections and Dedicated public section wiring.
4.1 Hardware Configuration Description After the electrical system control is included in the DCS monitoring, its functions can be divided into two parts: data acquisition (DAS) and sequential control (SCS). Since the electrical quantity has no special requirements compared to the thermal quantity, the relative movement speed Fast, highly reliable control functions are achieved by means of reserved electrical special devices, so in principle no special requirements are imposed on the hardware of the DCS. The configuration requirements for hardware are the same as those for the thermal industry, and their functions are integrated into the functions of the DCS. However, due to historical reasons, DCS is in charge of thermal workers. However, thermal workers do not know much about the principle of electrical control. In the aspects of design, debugging, production and maintenance, the electrical system still needs electrical personnel to complete this part of the work. In addition, during the construction of the project, the power-receiving part of the electrical related plant needs to be debugged and put into operation beforehand. In the electric control function part, the DCS sequential control (SCS) and the electric on-site separate controller facilitate the smooth implementation of the actual work. Its data collection part is integrated with thermal engineering.
4.2 Software Function Description
4.2.1 DAS function of data acquisition system The data acquisition system (DAS) can continuously collect and process all important measuring point signals and equipment status signals related to the electrical system, so as to provide operators with relevant operating information in time and realize the safe operation of the unit. In case of any abnormal working condition of the unit, it will promptly report an alarm to improve the availability of the unit. Generally has the following functions:
(1) Display: Including operation display, bar graph display, trend display, alarm display, etc.
(2) tabulation records: accident recall records, event sequence (SOE) records, etc.
(3) Historical data storage and retrieval.
4.2.2 Sequential Control System SCS (G/A) Function The logic design of Guohua CED's electrical system control part is relatively simple, and it can only achieve single operation, 1-way, 2-way and bus-coupled locking. This design method makes DCS lose the significance of automation and does not fundamentally improve the automation level of electrical system control. This is also a project to be improved by Guohua Electric Power.
5. Configuration of standby monitoring equipment Based on the operating experience of the completed 300 MW generating units, the DCS used in the control of boilers and stoves in Jiujiang, Xinyang and Yiyang Power Plants was centered on the CRT and keyboard monitoring, and the display instruments and operations on the control panel were reduced as much as possible. , switch, alarm window, etc., only reserved backup monitoring equipment:
(1) All analog signals enter the DCS display without a separate control panel.
(2) Keep only a small number of important electrical switches and cancel the electrical control screen/disk. The control function is implemented in the DCS. The manual synchronization switch is also reserved as an automatic synchronizing device backup operation. The reserved hands-on switch is: generator trip switch trip button; diesel generator emergency button.
(3) The number of soft light words displayed on the CRT should be kept around 30 in the alarm light plate, which should be placed separately from the thermal alarm. This is not conducive to monitoring. It is recommended that the thermal warning be uniformly arranged.
6 Common system control methods For the common systems of the two units, such as the factory, utility, and backup power systems, as in the thermal control system, the configuration of the DCS enables one unit to stop running, and the other unit can operate. The public system is monitored and reliable measures are required to ensure the uniqueness of its control commands, ie only one DCS system command is allowed to control the public equipment at the same time. The DCS of the two units cannot be coupled together because of the existence of a common system.
The DCS system of Guohua Dingzhou Power Plant adopts Siemens TXP7.4. The public system control uses the public system terminal bus to interconnect with the total bus of Unit 1 and Unit 2. This saves hardware configuration and saves engineering costs. However, the disadvantage of this configuration is that when the DCS of the utility system fails, both units must be stopped, causing great inconvenience to the maintenance of the utility system DCS.
7 Concluding remarks The above talks about Guohuading's monitoring of electrical systems into DCS applications and hopes to provide a reference for future infrastructure projects.
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