With the rapid development of China’s electric power industry, the application of DCS is more and more extensive. However, DCS mainly completes the automatic process control of steam turbine and boiler, and the automation of electrical part is less combined. DCS generally does not fully consider the control characteristics of electrical equipment, so whether it is functional or not, DCS mainly completes the automatic process control of steam turbine and boiler Compared with the network monitor system, the system has a large gap in openness, advanced nature and economy.
1 monitoring object of electric fieldbus control system
The monitoring objects of electric fieldbus control system mainly include: generator transformer group, whose monitoring scope mainly includes generator, generator excitation system, main transformer, 220kV circuit breaker; high voltage auxiliary working and standby power supply, and its monitoring scope mainly includes high-voltage plant working transformer, main transformer and 220kV circuit breaker Starting standby transformer, etc.; low voltage auxiliary power supply in the main power house, whose monitoring scope mainly includes low-voltage auxiliary work, public transformer and lighting transformer Low voltage auxiliary transformer of main plant such as transformer, maintenance transformer and dust removal transformer; auxiliary workshop low-voltage auxiliary power supply; power feeder from power center to motor control center; unit generator and boiler DCS control motor; security power supply; DC system; AC non-stop power supply.
Characteristics of electric fieldbus control system
2.1 fast change of electrical parameters
The electrical analog quantity is generally the current, voltage, power, frequency and other parameters, while the digital quantity is mainly the switch state, protection action and other signals. These parameters change rapidly, which requires high sampling speed of computer monitoring system.
2.2 the intelligent degree of electrical equipment is high
The generator transformer unit protection, start-up standby transformer protection, automatic synchronization device, auxiliary power switching device, excitation regulator and other protection or automatic devices of the electrical system are all microprocessor-based, and the 6kV switching station protection is microcomputer integrated protection with 380V on Intelligent switch and microcomputer type motor controller are adopted in the station closing. All electrical equipment has realized intelligence, which can conveniently communicate with various computer monitoring systems in two-way. In addition, the control of electrical equipment is generally switch control, the control logic is very simple, generally no regulation or other control requirements, the control logic of electrical equipment is simple.
2.3 the control frequency of electrical equipment is low
In addition to some switching or switching operations for some electrical equipment during the start-up and shutdown of the unit, the electrical equipment generally does not need to be operated during the normal operation of the unit. In the case of accidents, relay protection or automatic device action to remove the fault or switch power supply. And the electrical equipment has good controllability, because the electrical control objects are generally circuit breakers, air switches or contactors. Their operation is flexible and reliable, and compared with other controlled equipment in power plant, it has good controllability.
2.4 the installation environment of electrical equipment is good and the layout is relatively centralized
Most of the electrical equipment is concentrated in the electrical relay room and the electrical distribution equipment room. The equipment layout is relatively centralized, and the installation environment is rarely polluted by water vapor or dust, which provides favorable conditions for the local layout of control equipment.
Configuration of electric fieldbus control system
Each unit is equipped with fieldbus control system (FCS), which includes generator transformer unit, auxiliary power system and public auxiliary power system of unit electrical system into FCS. As a subsystem of DCS, FCS is realized in DCS operator station The electrical system is monitored and connected with DCS at the station control level through redundant communication server.
3.1 network structure
Electrical FCS adopts hierarchical and distributed computer control system, which is hierarchical in system function and decentralized in equipment layout. The network structure is 3-layer equipment and 2-layer network mode. The 3-layer equipment refers to the monitoring master station layer, communication sub station layer and bay layer, and the layer 2 network refers to the Ethernet connecting the monitoring master station layer and the communication sub station layer and the field bus network connecting the communication sub station layer and the Bay layer. The monitoring master station layer is composed of dual redundant system host, engineer station, network switch and dual redundant communication server responsible for communicating with DCS and sis The multi serial communication server installed in the electrical relay room and the communication management machine installed in each distribution room are composed. The bay level equipment mainly includes the intelligent measurement and control device installed in the electrical relay room, 6kV switch cabinet and 380V switch cabinet, integrated protection measurement and control device, motor controller and intelligent instrument, etc. The communication manager and the monitoring master station are connected by dual redundant optical fiber Ethernet, and can be connected with bay level equipment by PROFIBUS, lon, can, industrial Ethernet or other field buses according to the equipment conditions. Its main function is not only to manage the data of each integrated intelligent measurement and control unit, but also to complete the processing of real-time data and the management of distributed database. The station control layer Ethernet of the public auxiliary power system is independently networked, and is connected with the unit automation system Ethernet through the communication gateway. The engineer station of the unit unit is shared, and only the operation instructions of one unit control system can be accepted by means of software and hardware locking.
3.2 data acquisition
For generator transformer unit, high-voltage auxiliary transformer and start-up standby transformer, except for a small amount of analog signal, high-voltage side circuit breaker, disconnector, grounding switch position signal, control circuit disconnection and allowing remote operation signal, generator transformer unit and start-up standby transformer All control signals of transformer are directly connected with DCs by hard wiring, other monitoring signals are connected to FCS through special measurement and control device, and then sent to DCs by communication mode. Special electrical devices such as generator transformer unit and start-up standby transformer protection, automatic voltage regulation device (AVR), synchronization device, fault recorder, fast switching of auxiliary power, diesel engine, DC system and AC (direct) current uninterrupted power supply (UPS) system are equipped with communication interfaces, which are connected to FCS through multi serial communication server.
The auxiliary power supply of the power plant is divided into high-voltage auxiliary working and standby power supply, low-voltage auxiliary power supply system of the main power house and low-voltage auxiliary power supply system of the auxiliary workshop. The low-voltage auxiliary power supply of the main power house includes low-voltage auxiliary service and public transformer, lighting transformer, maintenance transformer, dust removal transformer and its 380V distribution Low voltage auxiliary power supply for auxiliary workshop includes coal handling system, industrial wastewater treatment station, dumper, circulating water system, make-up water system transformer and its 380V power distribution device. In order to adapt to the idea of centralized control of water, coal and ash auxiliary system of the project, auxiliary workshop auxiliary power supply system is included in unit DCS monitoring. According to the scheme of setting control points for thermal control water, coal and ash separately, 380V power supply system of auxiliary workshop can also be controlled by corresponding PLC.
In order to make the connection of control system more simple, the acquisition mode of combining hard wiring and field bus is adopted for the important auxiliary power supply of the main power house, such as 6kV auxiliary power system, boiler, steam turbine and main power house public system, i.e. important Di signals (such as closing position of circuit breaker, tripping position of circuit breaker, allowable position of circuit breaker, etc Hard wiring is reserved for allowable operation and fault) and do signals (such as circuit breaker closing instruction, circuit breaker tripping instruction, etc.), and all other information of the circuit is sent to FCS and DCS through Fieldbus in communication mode, while the non important auxiliary power supply for the unit, such as maintenance, lighting, electric dust removal and auxiliary workshop auxiliary power system, is provided All hard wiring of auxiliary power supply system is cancelled, and communication mode is used for monitoring and control.
For the unit unit motor, because it is closely connected with the thermal system of the unit, the acquisition mode of combining hard wiring and field bus is adopted. At the same time, the important information related to the monitoring logic should be retained, and the hard wiring method should be used to access to DCS for monitoring. The information collected by FCS for electrical system analysis and management, such as protection setting value, fault current and voltage waveform, is sent to the engineer station of FCS for analysis and processing, not to DCS, but can be sent to sis and management information system (MIS) through independent communication interface.
With the continuous improvement of power plant automation level, computer control of electrical system has become the mainstream of current design, and the control mode has gradually changed from simple DCS monitoring to high-level operation management functions such as fault analysis, information management, equipment management, automatic meter reading and simulation training Therefore, the application of Fieldbus Technology in electric control system of power plant is promoted. The application of FCS in the control process of thermal power plant is beneficial to improve the automation level of electrical system in thermal power plant, save engineering investment, and is worthy of popularization and application.