Analysis of Electrical Fieldbus Control System

With the rapid development of China's power industry, the application of DCS is more and more extensive, but DCS mainly completes the automatic process control of steam turbines and boilers, and the automation of electrical parts is less. DCS generally does not fully consider the control of electrical equipment. Features, so whether it is functional or system structure, compared with network computer monitoring system, there is a big gap in terms of openness, advancement and economy.

1 Monitoring object of electrical fieldbus control system

The monitoring objects of the electric fieldbus control system mainly include: generator-transformer group, whose monitoring range mainly includes generator, generator excitation system, main transformer, 220kV circuit breaker; high-voltage factory working and standby power supply, and its monitoring scope mainly includes High-voltage factory working transformers, start-and-standby transformers, etc.; low-voltage factory power supply in the main plant, whose monitoring scope mainly includes low-voltage factory work and low-voltage factory transformers for main transformers such as utility transformers, lighting transformers, maintenance transformers and dust-removing transformers; Auxiliary workshop low-voltage factory power supply; power center to motor control center power feeder; unit unit generator and boiler DCS control motor; security power supply; DC system; AC uninterruptible power supply.

2 Characteristics of the electrical fieldbus control system

2.1 Electrical parameters change quickly

The electrical analog quantity is generally the current, voltage, power, frequency and other parameters. The digital quantity is mainly the signal of the switch state, protection action, etc. These parameters change rapidly, and the sampling speed of the computer monitoring system is high.

2.2 Electrical equipment is highly intelligent

Electrical system generator-transformer protection, start-standby transformer protection, automatic synchronizing device, factory power switching device, excitation regulator and other protection or automatic devices are microcomputer type, 6kV switch station protection for microcomputer comprehensive protection, 380V The switch station adopts intelligent switch and microcomputer type motor controller. All electrical equipments are intelligent, and can be easily communicated with various computer monitoring systems in two-way communication. In addition, the control of electrical equipment is generally the switching quantity control, the control logic is very simple, generally no adjustment or other control requirements, the control logic of the electrical equipment is simple.

2.3 Electrical equipment is less frequently controlled

Except during the starting and stopping process of the unit, some electrical equipments need to perform some switching or switching operations, and the electrical equipment generally does not need to be operated during normal operation of the unit. In the event of an accident, most of the relay protection or automatic device action removes the fault or performs power switching. And electrical equipment has good controllability, because electrical control objects are generally circuit breakers, air switches or contactors, which are flexible in operation and reliable in operation, and have good controllability compared with other controlled equipment in power plants. Sex.

2.4 The installation environment of electrical equipment is better and the arrangement is relatively concentrated.

Most of the electrical equipment is arranged in the electrical relay room and each electrical distribution equipment room. The equipment layout is relatively concentrated, and the installation environment has very little pollution of water vapor or dust, which provides favorable conditions for the local arrangement of the control equipment.

3 Electrical fieldbus control system configuration

Each unit is equipped with a fieldbus control system (fieldbusco nt sys sys-tem, FCS) to incorporate the generator-transformer unit, unit unit power system and utility power system of the unit electrical system into the FCS, and the FCS as the DCS. A subsystem that monitors the electrical system at the DCS operator station and connects to the DCS at the station control level via a redundantly configured communication server.

3.1 Network structure

The electrical FCS adopts a layered and distributed computer control system, which is layered in system functions and distributed in equipment layout. The network structure is a Layer 3 device Layer 2 network, the Layer 3 device refers to the monitoring master station layer, the communication substation layer and the bay layer, and the Layer 2 network refers to the Ethernet that connects the monitoring master station layer and the communication substation layer and the connected communication substation. Fieldbus network of layers and bays. The monitoring main station layer is composed of dual redundant system hosts, engineering stations, network switches and dual redundant communication servers responsible for communication with DCS and plant level monitoring system (SIS). The communication substation layer is mainly installed in the electrical relay room. The multi-serial communication server is composed of a communication management machine installed in each power distribution room. The interval layer equipment mainly includes an intelligent measuring and controlling device installed in an electrical relay room, a 6kV switch cabinet and a 380V switch cabinet, a comprehensive protection and monitoring device, a motor controller and Smart meters, etc. The communication management machine and the monitoring main station adopt dual redundant fiber-optic Ethernet connection, and the interval layer device can be connected by Profibus, LON, CAN, industrial Ethernet or other field bus according to the equipment condition, and its main functions are completed. In addition to the data management of the intelligent measurement and control unit, it also completes the processing of real-time data and the management of distributed databases. The station control layer Ethernet of the utility power system is independently connected to the Ethernet of the unit automation system through the communication gateway, and the engineering station of the unit unit is shared, and only one unit control system can be accepted by means of software and hardware blocking. Operation instructions.

3.2 Data collection

For generator-transformer group, high-voltage factory transformer and start-and-standby transformer, except for a small amount of analog signal, high-voltage side circuit breaker, isolating switch, grounding switch position signal, control circuit disconnection and allowing remote operation signal, generator-transformer All control signals of the group and start-standby transformers are directly connected to the DCS by hard wiring. Other monitoring signals are connected to the FCS through a dedicated measurement and control device, and then sent to the DCS by communication. Electrical special equipment such as generator-transformer group and start-and-standby transformer protection, voltage automatic adjustment device (AVR), synchronizing device, fault recording, fast switching of plant power, diesel engine, DC system and AC power supply The (UPS) system has a communication interface, and accesses the FCS through a multi-serial communication server.

The power plant power supply is divided into high-voltage factory working and standby power supply, main plant low-voltage factory power supply system and auxiliary workshop low-voltage factory power supply system. The main plant low-voltage factory power supply includes low-voltage factory work and utility transformers, lighting transformers, overhaul transformers and The dust removal transformer and its 380V power distribution device, etc., auxiliary power plant low-voltage factory power supply includes coal handling system, industrial wastewater treatment station, dumper, circulating water system, water supply system transformer and its 380V power distribution device. In order to adapt to the centralized control of the water, coal and ash auxiliary systems of the project, the power supply system of the auxiliary workshop is included in the unit DCS monitoring. For the scheme of separately setting control points for heat control water, coal and ash, the auxiliary workshop 380V power supply system can also be incorporated into the corresponding programmable logic controller (PLC) control.

In order to make the control system wiring more simple, the important plant power supply for the main plant, such as 6kV plant power system and boiler, steam turbine, main plant public system, etc., use the combination of hard wiring and field bus, that is, important DI signals (such as The circuit breaker closing position, circuit breaker trip position, allowable operation, fault) and DO signal (such as circuit breaker closing command, circuit breaker trip command, etc.) retain hard wiring, and all other information of the circuit is sent through communication through the field bus. FCS and DCS; and the power supply of the unit is not important, such as maintenance, lighting, electric dust removal and auxiliary workshop power system, etc., all the hard wiring of the power supply system of the plant is cancelled, and the communication mode is used for monitoring and control.

For the unit unit motor, due to the close connection with the unit thermal system, the combination of hard wiring and field bus is adopted. At the same time, important information related to the monitoring logic should be retained, and the hard wiring method is adopted to access the DCS for monitoring. . The information of the analysis and management of the power supply system collected by the FCS, such as the protection setting value, the current and voltage waveforms at the time of failure, is sent to the FCS engineering station for analysis and processing, and is not sent to the DCS, but can be sent to the SIS through an independent communication interface. And Management Information System (MIS).

4 Conclusion

With the continuous improvement of the automation level of power plants, the use of computer control in electrical systems has become the mainstream of current design. The control method has gradually evolved from simple DCS monitoring to high-level with fault analysis, information management, equipment management, automatic meter reading and simulation training. The development of the operation management function has promoted the application of fieldbus technology in the electrical control system of the power plant. Applying FCS to the thermal power plant control process is conducive to improving the automation level of the thermal power plant electrical system and saving engineering investment, which is worthy of promotion and application.

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