Source of the article:-Published by members of this site: February 2006-65438+June.
First, the system overview:
Characteristics of 1.DCS system
DCS system, also known as distributed control system, is a new control technology that computer technology monitors, operates, manages and controls the production process. Its functional characteristics are: strong universality, flexible system configuration, perfect control function, convenient data processing, centralized display operation, friendly man-machine interface, simple and standardized installation, convenient debugging, safe and reliable operation, etc.
2. Composition of decentralized control system
As a large-scale integrated control system with vertical stratification and horizontal dispersion, it relies on multi-layer computer network to connect the data processing equipment of various control equipment distributed in the whole plant, realize the coordination of all parts of information, and complete the functions of control, management and decision-making.
1) Its hardware equipment consists of a management and operation application workstation, a field control station and a communication network.
The management operation application workstation includes various functional service stations such as engineer station, operator station and historical data station.
The engineer station provides a man-machine interface for technicians to generate control systems, which is mainly used for system configuration and maintenance. Technicians can also monitor the application system through the engineer station.
B. The operator prime minister provides a man-machine interactive interface between technicians and the system database, which is used to monitor the status value display of data and the operator's operation on data points.
C. The historical station saves the historical data of the whole system for the configuration software, and realizes the functions of historical trend display, report printing and accident recall.
The field control station is used for the collection and processing of field signals and the realization of control strategies, and has reliable redundancy guarantee and network communication functions.
The communication network connects all the decentralized parts of the decentralized control system to complete the transmission of data, instructions and other information. In order to ensure the reliability of DCS, power supply, communication network and process control station all adopt redundant configuration.
2) The distributed control system software consists of real-time multi-task operating system, database management system, data communication software, configuration software and various application software.
3) The decentralized control system adopts modular design method in structure. Through flexible and reasonable configuration, the functions of analog control system (MCS), data acquisition system (DAS), boiler combustion control and furnace safety system (FSSS) and sequence control system (SCS) can be realized.
3. Explanation of terms
DCS decentralized control system refers to an intelligent network control system with decentralized control functions, decentralized risks, centralized operation display and decentralized structure.
DAS data acquisition system refers to a monitoring system which uses digital computer control system to detect the operation parameters and status of process systems and equipment, process, record, display and alarm the detection results, calculate and analyze the operation of the unit, and provide operation guidance.
MCS analog control system refers to the loop that automatically completes the adjustment of controlled variables through control variables.
CCS coordinated control system refers to the overall control of boiler-turbine generator set, which coordinates the operation of boiler and turbine in automatic state through a control loop, and sends instructions to the automatic control system of boiler and turbine to meet the needs of load change and give full play to the frequency modulation and peak shaving ability of the unit as much as possible. Its direct executive layer is the boiler fuel control system and the steam turbine control system.
SCS sequence control system refers to the automatic control system that starts or stops the auxiliary machines and auxiliary systems of thermal power units according to the sequence specified in the operation rules (input signal condition sequence, action sequence or time sequence).
FSSS furnace safety monitoring system refers to an automatic system that automatically controls boiler ignition and oil gun to prevent furnace explosion (implosion or explosion) caused by combustion flameout and overpressure. It includes burner control system BCS and furnace safety system FSS.
AGC automatic generation control is a system in which power grid dispatching automatically controls the generating power of units according to the load requirements of power grid for each power plant.
MFT full fuel trip refers to a measure to quickly cut off all fuel entering the furnace after the protection signal commands action or manual operation.
DEH steam turbine digital electro-hydraulic control system is a steam turbine control system composed of sensitive components, digital circuits designed according to electrical principle, amplification components designed according to hydraulic principle and hydraulic servo mechanism.
ATC or ATSC steam turbine starts automatically. According to the operation parameters and thermal stress calculation of the steam turbine, the steam turbine automatically starts from turning to initial load according to the program.
OPC overspeed protection control function is a control function for restraining overspeed, and there are two common types:
First, when the steam turbine speed reaches 103% of the rated speed, the medium and high pressure regulating valves automatically close; When the speed returns to normal, open these valves to maintain the rated speed.
Two. When the speed of the steam turbine accelerates, an override command is issued to close the high and medium pressure speed regulating valves; When the acceleration is 0, the normal speed is maintained by the normal speed control loop.
BPC bypass control system is the general name of automatic input of turbine bypass system and automatic control system of steam pressure and temperature in bypass system.
ETS steam turbine emergency trip system is a control system to realize the emergency stop of steam turbine operation when the important parameters of the unit cross the line and other abnormal working conditions.
The electro-hydraulic regulating system of MEH feed water pump is a control system which uses microcomputer control and hydraulic actuator to realize control logic and drive the steam turbine of feed water pump.
UPS uninterrupted power supply
RB auxiliary machine fault load reduction is a control measure for the main and auxiliary machine faults of the unit, that is, when the main and auxiliary machines (such as feed water pump, blower, induced draft fan, etc.) fail, the load of the unit can be quickly reduced.
4. Main contents of operation and maintenance of decentralized control system
Including the inspection of necessary items before the system is put into operation. After the inspection is qualified and everything is ready, the system is powered on, and the system is started according to the relevant steps, and all parts of the system are checked to be normal, and then put into online operation. After the normal operation of the system, do a good job of daily maintenance, find out the reasons in time when problems are found, and decide the input and exit of thermal control equipment according to the operation of the thermal control system.
5. Common faults of decentralized control system
1) Communication network faults mainly include node bus fault, local bus fault and address recognition error.
2) Hardware failures, mainly man-machine interface failures and process channel failures.
3) Human failure, misoperation in system maintenance or fault handling.
4) Power failure
5) SOE does not work properly
6) Failure caused by interference. It mainly includes the grounding situation of the system, power supply quality, switching between active and standby processors of the process control processor, high-power wireless communication equipment, etc.
6. Testing of decentralized control system
1) disturbance test of analog control system
The analog control system put into operation should be regularly tested for disturbance, which is divided into internal disturbance test and external disturbance test.
A. Internal disturbance test (including fixed value disturbance): it is required to be carried out under 70% load, and the disturbance amount is 10% of the full range of the tuning medium.
B. External disturbance test (load disturbance): The load disturbance test can be carried out when the load of the unit is above 70%, and the load changes according to fast, medium and slow three working conditions.
The main tests include:
Disturbance test of BCS of unit
Condition: The water level of drum A is adjusted to a proper position, and the load remains unchanged.
B furnace negative pressure regulating system and air supply regulating system are in automatic state.
C. Under stable working conditions, the main steam pressure should be kept within the range of 0.2MPa of the given value.
The powder feeder is running normally. Put the intermediate powder feeder into automatic adjustment, and the speed of manual powder feeder is about 450~500 rpm.
E during the test, there should be a fireman and a work manager.
F. Conduct on-site supervision and guidance to the technicians in the master control class, professional workers in the production department, professional workers in thermal engineering and professional workers in furnace transportation.
Disturbance test of changing the fixed value of main steam pressure
The conditions are the same as above
AFSC disturbance test of unit air supply regulation system
Condition: The water level of drum A is adjusted to a proper position, and the load remains unchanged.
The oxygen and air volume transmitters indicate accurately.
C furnace negative pressure regulating system is in an automatic state.
Blower baffle has a certain adjustment margin.
E. under stable working conditions, the main steam pressure should be kept within the range of 0.2MPa of the given value.
F during the test, there should be a fireman and a supervisor or above.
G master class technicians, production department experts, thermal experts, furnace transport experts on-site supervision and guidance.
CCS disturbance test of coordinated control system of unit unit
Condition: The water level of drum A is adjusted to a proper position, and the load remains unchanged.
B furnace negative pressure regulating system, fuel regulating system and air supply regulating system are in automatic state.
C. Under stable working conditions, the main steam pressure should be kept within the range of 0.2MPa of the given value.
D during the test, there should be a fireman and a working director or above to operate.
E. Conduct on-site supervision and guidance to the technicians in the master control class, professional workers in the production department, professional workers in thermal engineering and professional workers in furnace transportation.
2) Control other function tests
RB test of unit
Test conditions:
A. The cold RB test of A.CCS and FSSS and the cold RB test when the two systems are jointly adjusted have been completed and succeeded; The hot and cold tests of other thermal systems and related majors such as machinery, furnace and electricity have been completed.
B under the condition of full load of the unit, the following automatic systems have been running:
Coordinated control system. Can run normally, TF mode works normally.
Deaerator water level control system
Furnace negative pressure control system
Gas supply control system
Main fuel control system
Three-impulse control system of steam pump in water supply control system
Inlet steam temperature control system
Reheat steam temperature control system
DEH runs normally in coordinated mode.
The FSSS interlock test was successful, and the RB action logic was normal.
TF mode adjustment meets the requirements.
"Unit Load Swing Test" has been completed, and the control performance meets the unit operation requirements.
There are no major defects in the main and auxiliary equipment.
The TPC function test of DEH system is successful, and the load reduction rate meets the requirements.
Test Introduction: (Blower RB)
When the unit load is above 180MW. Action process: When the load is greater than 180MW, after a blower trips, CCS will automatically switch the control mode from coordination to TF, stop ADS (remote automatic dispatching mode), lock the set point of main steam pressure in a proper position, and the steam turbine control at CCS side will automatically switch to TF to prevent the pressure from dropping too much. At the same time, the furnace side FSSS cuts two layers and manually gives the remaining two layers to the coal mill, and LDC (Load Command Computer) outputs to reduce the load.
AGC test. Check the ability of the unit to adapt to the change of load command requirements, so that the unit can track the output of load command required for intermediate adjustment at a certain rate within a certain range.
Load rejection test of unit. Quality of turbine governing system.
3) Protection interlock test
Boiler protection interlock test
Fan interlock test
Interlocking test of grinding group
Debugging of all valves of boiler
Machine-boiler electric interlocking
Protection interlock test of overhaul change
Protection interlock test in case of abnormal operation
7. Basic principles of emergency treatment measures for 7.DCS system faults
1) Emergency treatment measures of DCS system
When all the operator stations fail (all the upper computers are blank or crashed), if the main and standby hard manual operation and monitoring instruments are available, and the normal operation of the unit can be temporarily maintained, it will be switched to the standby operation mode, and the fault will be eliminated at the same time, and it will be switched to the operator station operation mode, otherwise it should be stopped immediately.
When all operator stations fail (all upper computers are blank or crashed), the units without reliable backup hard manual operation and monitoring instruments should stop immediately.
When the communication network of the distributed control system fails, all data cannot be refreshed (crashed), and the above measures should be taken.
When the communication network of the main analog control MCS system fails or both the main and auxiliary control units DPU fail (crash or power failure), the unit without reliable backup hard manual operation and monitoring instruments should be stopped, and when the safe and reliable operation of the unit cannot be maintained, it should be stopped immediately.
When the communication network of FSSS system fails or both the main and auxiliary control units DPU fail (crash or power failure), the unit without reliable backup hard manual operation and monitoring instruments should be stopped, and the unit should be stopped immediately if it cannot maintain safe and reliable operation.
Emergency treatment measures for functional failure of DCS system
When some operator stations fail and only a few operator stations can monitor and operate, the available operator stations should continue to maintain the stable operation of the unit, but at this time, major operations should be stopped, accident prediction should be made, and maintenance personnel should be contacted for handling.
When DEH loses power and causes the turbine to trip, it should be regarded as turbine trip. If it does not cause the turbine to trip, switch DEH to hard manual operation and continue to maintain the stable operation of the unit. But at this time, if there are no special circumstances, stop running, predict the accident and contact the maintenance personnel immediately.
MFT protection should act in time after FSSS (or CCS) loses power, otherwise it should be stopped manually. If the manual MFT button is invalid, the measures of "stopping the power supply of the powder exhausters A and B, the coal pulverizer and the coal feeder, stopping the work of the powder feeder and stopping the standby power supply" should be taken immediately, and the oil inlet quick-break valve and the oil return recirculation valve should be closed at the same time.
After the auxiliary machine loses power by program control, the operators should try their best to stabilize the operation of the unit, strengthen monitoring, and immediately contact the maintenance. If the operation cannot be maintained (the operating equipment trips and the standby equipment cannot be started), emergency measures shall be taken to stop the unit operation.
3) Emergency measures for simultaneous offline of a pair of DPUs
When a pair of main and auxiliary DPUs of DCS system control unit DPU are offline, it is not necessary to stop the machine, and maintenance personnel should be contacted immediately for handling. Maintenance personnel should check which points are called by other systems and participate in protection or interlocking. Before (DPU) is promoted to master control, the protection or interlock shall be temporarily released.
When a pair of main and auxiliary DPUs of ECS system control unit (DPU) go offline, it is not necessary to stop the machine, and contact the maintenance personnel immediately. The electrical specialty will replace the DPU online after taking corresponding safety measures according to the actual operation of the unit.
When a pair of main and auxiliary DPUs of general MCS system control unit (DPU) go offline, emergency measures should be taken to stop the operation of the unit according to the operation conditions of the unit, if the operation parameters reach shutdown.
When a pair of main and auxiliary DPUs of SCS system control unit (DPU) go offline, we should try to stabilize the unit operation, and the operators should strengthen monitoring and immediately contact the maintenance personnel for handling. When the operation of the equipment cannot be maintained (the operating equipment trips and the standby equipment cannot be started), emergency measures shall be taken to stop the operation of the unit.
When a pair of main and auxiliary DPUs of the FSSS system control unit (DPU) are offline, emergency measures should be taken to stop the operation of the unit. If the manual MFT button is invalid, measures should be taken to stop the power supply of the powder exhauster A and B, the coal pulverizer A and B, the coal feeder A, the powder feeder and the standby power supply at the same time, and close the oil inlet quick-break valve and the oil return recirculation valve.
When the control unit (DPU) of IDAS system (small data acquisition system) goes offline, it is not necessary to stop the machine, and the maintenance personnel should be contacted immediately to replace the DPU online.
When a pair of main and auxiliary DPUs of DEH system control unit (DPU) fail offline, DEH will be switched to hard operation and DEH will be switched to hard operation, so as to continue to maintain the stable operation of the unit. But at this time, if there are no special circumstances, the operation should be stopped and the accident of the unit should be predicted. At the same time, maintenance personnel should be contacted immediately to replace DPU online.
4) Emergency treatment measures for single DPU offline
No matter which system control unit (DPU) has a single DPU offline fault, the operation should contact the maintenance personnel in time for online replacement.
If a single DPU of the system control unit (DPU) runs and goes offline, it shall be handled according to the safety measures when both DPUs are offline.
5) Emergency treatment measures for lost configuration files
When it is found that the configuration files of a pair of main and auxiliary DPUs of DAS system, ECS system and DEH system control unit (DPU) are lost, the operator should contact the maintenance personnel in time for handling. Maintenance personnel should do the following: download the DPU with the configuration file in the auxiliary control state, confirm which points need to be forced according to the call of measuring points, and promote the DPU with the auxiliary control to the main control after the force is completed.
When it is found that the configuration files of a pair of main and auxiliary DPUs of MCS system control unit (DPU) are lost, the operator should contact the maintenance personnel in time for handling. According to the actual situation of configuration file loss or backup hard manual operation and monitoring instrument settings, decide whether to shut down. Maintenance personnel should follow the following processing steps: download the complete configuration of the auxiliary control DPU, and check the configuration file before upgrading to the main control to confirm that the configuration file is correct. For the equipment that may cause disturbance, the AO output should be set according to the actual feedback value of the field equipment, and then the auxiliary control DPU should be upgraded to the main control.
When a pair of main and auxiliary DPUs of SCS system control unit (DPU) is found missing, the operation will notify the maintenance in time. According to the actual situation of configuration file loss, the shutdown or shutdown or emergency rescue is decided according to the following steps: download the complete configuration of the auxiliary control DPU, and check the configuration before upgrading to the main control to confirm that the configuration is correct. For the equipment that will cause disturbance, the DO output should be set according to the feedback of the actual equipment on site, and the auxiliary control DPU should be upgraded to the main control after all the errors are confirmed.
When it is found that the configuration file of the control unit DPU of the FSSS system is lost, the unit operation should be stopped urgently according to the unit operation. If the manual MFT button is invalid, measures should be taken to stop the power supply of powder exhauster A and B, coal pulverizer and coal feeder at the same time, and turn off the powder feeder and standby power supply at the same time.