Power Industry Standards of the People's Republic of China

Guide for 300MW Grade Steam Turbine Operation

DLT 6091996 Guide for 300MW grade steam turbine operation

Ministry of Power Industry of People's Republic of China Implemented on June 1, 1997 Approved on February 3, 1997

1 Scope 1.1 This guideline establishes the operation and technical management principle taking the safe and economic operation as basis and life management as the main line for the 300MW grade steam turbine. 1.2 The guide applies to domestic, imported-type and domestically made imported type sub-critical 300MW grade steam turbine, and the main principle applies also to the sub-critical 600MW steam turbine, and the imported units and other units can also refer to it for implementation. 1.3 The guide does not apply to supercritical steam turbines and nuclear power steam turbines. 2 Normative References The provisions contained in the following standards constitute the provisions of this standard through reference in this text. The editions indicated are valid at the time of publication of this guide. All standards are subject to revision, and parties using this standard should explore the possibility of using the latest version of the following standards. GB5578-85 Specification for Stationary Steam Turbines Driving Generator GB759687 Quality Criteria of Turbine Oilsin Service for Power Plants GBll34789 Mechanical Vibration of Large Rotating Machines with Speed Range from 10 to 200 r/s--Measurement and evaluation of vibration Severity in Situ GBl214589 Quality Criterion of Water and Steam for Generating Unit and Steam Power Equipment DL42891 Technical Rules for Power System Automatic Under-Frequency Load Shedding DLT56195 Guide for Chemical Supervision of Water and Steam in Thermal Power Plants

DLT57195 Guide for Acceptance, In-service Supervision and Maintenance of Fire-resistant Fluid Used in Power Plants DL501192 The Code of Erection and Acceptance of Electric Power Construction Section of Steam Turbine Set SD22387 Guide for Lay-up of Thermal Power Equipment in Fossil Fuel Power Plant (82) Hydropower Technology No. 63 Management Rules for Electric Power Industry Technology (Trial) (83) Hydropower Electro-production No. 47 Maintenance Instruction of Thermal Power Equipment in High-pressure Heater Electricity Safety Production [1994] No.227 Safety Code of Electric Power Industry (Thermal and Machine) 3 General Principles 3.1 The main tasks of steam turbine operation are to: distribute and use the service life of steam turbine reasonably, start and stop correctly, inspect and maintain better, adjust the control parameters strictly, adjust and test carefully and prevent and deal with accidents reliably so as to make the steam turbine in safe, economical, reliable and stable working condition. 3.2 The guide is formulated to guide the operation and maintenance correctly, strengthen the service life management of the steam turbine, further improve the operation of 300MW grade steam turbine and meet the needs of electricity production. 3.3 The guide is a commonly-used and principled technical regulation. It stipulates the general principles clearly that shall be complied with by the selection of start-stop mode for steam turbines, operation requirements, control scope of important operating parameters, normal and special operating mode, comes up with the main inspection, maintenance, testing, adjustment and others within the operation scope, and establishes the principles of prevention and treatment for common accidents. The manufacturers shall comply with the specific provisions (if any), and this guide shall be implemented if the manufactures do not have such provisions to comply with. 3.4 The operation code of on-site steam turbines is formulated based on this guide together with the technical documents issued by the manufacturers and the actual situations of equipment steam turbine. Main contents that shall be contained in the operation code are as shown in Appendix F (informative appendix). 4 Life Management for Steam Turbines In order to ensure the safe and economic operation of 300MW grade steam turbines, the on-site

operation and technical management shall be carried out taking the life management as the main line. 4.1 Distribute and Use the Service Life of Steam Turbine Reasonably 4.1.1 The service life distribution of heavy steam turbines generally depends on the turbine structure and characteristics of its application, the numbers of start-stop, change of operation conditions, the numbers of load rejection with auxiliary power, etc. The allocation shall be made according to different models and operation methods. 4.1.2 The creep life consumption accounts for 20 and 80% for the fatigue life expenditure according to the life management curve provided by the manufacture within the design service life of steam turbine. The unforeseen circumstances shall be allowed when distributing the service life of the steam turbines, and the generally, the life consumption only accounts for only about 80% and 20% for possible emergency accidents. The examples for life distribution of steam turbine are shown in Appendix E (informative appendix). 4.1.3 For the steam turbines with base load, the life consumption for each cold start can be larger, which shall be controlled in the range of 0.05%/times, the life consumption of peaking unit is mainly consumed in the hot start-stop, so the life consumption of each start-stop can be smaller, usually in 0.01%/time. 4.2 Supervision and Management over the Service Life of Steam Turbine Rotor 4.2.1 Each turbine should be drawn with starting curve for different operating modes based on the life management curve of steam turbines provided by manufacturers. And the examples of starting and stopping curves for steam turbine are shown in Appendix D (informative appendix). 4.2.2 The database of rotor life loss shall be established and improved gradually for each turbine, which is controlled by the service life management curve provided by the manufacturer so as to make the life loss of the steam turbine under control as well as guide the operators to start and stop, adjust the operation parameters and handle the abnormal operating conditions. 4.3 Principle for Reducing the Life Loss of Steam Turbine Rotor 4.3.1 Prevention of Brittle Damage to Steam Turbine Rotor in Startup a) Select the running steam parameters and shaft seal steam supply temperature reasonably according to the temperature of cylinder mental when start-up and control the rate of temperature rise of metal strictly. b) Take the metal temperature at the steam exhaust port of intermediate pressure cylinder or the turbine-exit temperature for reference, and determine if the metal temperature of rotor, especially the metal temperature of the central center of the intermediate pressure rotor, has exceeded the

FATT of the mental. c) Preheat the rotor under the state of turning machine for alignment if possible when starting up the steam turbine in cold state and turn the cold start into hot start. d) The intermediate pressure cylinder start-up mode in cold state can be used if the manufacturer permits to improve the start-up conditions of turbine. e) The over-speed tests of emergency governor cannot be conducted until the metal temperature of the last-stage central bore of the intermediate pressure rotor is above FATT, and generally it will take at least 4h to warm the steam turbine stably for the turbo-generator unit with 10%~25% rated load. 4.3.2 Reduce the life loss of turbine rotor in operation a) Avoid load changes substantially within a short time and control the change of the working medium temperature on the surface of the rotor within the maximum allowable range strictly. b) Control the idle running time after turbine load rejection strictly. c) Prevent the great mismatch of main and reheat steam temperature and shaft seal steam supply temperature as well as the metal temperature of the rotor surface. d) Prevent the wet steam, cold air and water from entering into the cylinder after the start-up, operation and shutdown of the steam turbine and before the turbine cools down completely. 4.4 Strengthen the reliability management and reduce the service life loss of steam turbine 4.4.1 The reliability index not only reflects the level and quality of design, manufacture and installation, but also is an important basis for technological transformation and technological progress, and it also directly reflects the operation and management of power plants and the equipment maintenance, which is an important part of operation and management for modern steam turbine. 4.4.2 Most equipment of the steam turbine is serviceable and its service life distribution has something in common. The service life loss resulting from the improper repair and maintenance can be found by reliability statistics analysis, thereby improving the operation method and repair and maintenance program and changing gradually from passive repair and maintenance to state monitoring and predictive maintenance so as to improve the equivalent available factor (EAF) of equipment, reduce the equivalent forced outage rate (EFOR), reduce the maintenance costs, extend the service life of the steam turbine and get more and safer economic benefits. 5 Startup of Steam Turbine

The steam turbine shall speed up with load stably within reasonable life loss, prevent the differential expansion exceeding limits, the temperature difference of cylinder exceeding limits, static and dynamic friction, abnormal vibration of shafting and other unusual circumstances, avoid the abnormal operation of auxiliary equipment and thermal control device that may endanger the safety of the host and minimize startup time and reduce the startup overhead so as to obtain the best safety economic benefits. 5.1 Classification of Startup Mode 5.1.1 Classify according to the admission mode of cylinder at startup a) High-pressure cylinder starting-up (or high-pressure and intermediate-pressure unite starting-up ) b) Intermediate-pressure cylinder starting-up 5.1.2 Classify according to the metal temperature at governing stage for high pressure cylinder starting-up; classify according to the metal temperature at first pressure stage of intermediate pressure for intermediate pressure cylinder starting-up. The specific division temperature should be prescribed by the manufacturer and classified as follows: a) Cold start b) Warm start c) Hot start d) Extreme hot start. 5.1.3 Classify according to downtime a) Cold start: The metal temperature drops below 40% of is rated load after the turbine shuts down for more than 72h. b) Warm start: The metal temperature drops down at 40%~80% of is rated load after the turbine shuts down for 10h~72h. c) Extreme hot start: The metal temperature remains or is close to its rated load when the turbine shuts down within 1h. 5.1.4 Classify according to valve control mode

a) Main stop valve start-up; b) Control valve start-up. 5.2 Required conditions before startup 5.2.1 System Requirements: a) All systems and equipment of steam turbine functions properly and the valve positions are correct. b) The steam, water, oil system and equipment flushing are qualified. c) The instrument, sound-light alarm, equipment status and parameters display normally. d) The control system of the computer operates continuously for more than 2 hours. 5.2.2 Tests are proven qualified totally before startup 5.2.3 Jigger: The steam turbine shall be turned for alignment before running, mainly to reduce running inertia and eliminate thermal bending. So, turning gear should be run continuously for 4h, and not less than 2h for special circumstances. 5.2.4 Steam Supply for Shaft Sealing and Vacuuming of Condenser a) Steam Supply for Shaft Sealing 1) The stationary rotor is not allowed to supply steam for shaft seal steam to avoid the rotor form thermal bending. 2) HP, IP and LP steam supply for shaft sealing shall match with the metal surface temperature of rotor shaft seal, which shall not exceed the allowable deviation specified by manufacture. Superheat degree should not be below 14 C in order to prevent condensation heat transfer that may make the rotor surface generate excessive thermal stress, which may result in metal fatigue so as to increase the life loss. b) Vacuuming of Condenser 1) The steam turbine shall not be vacuumed when the shaft seal doesnt supply steam to condenser. It has been stipulated that the domestic units in China are required to vacuum first and then supply the shaft seal steam at cold start in early stage; otherwise stipulated by manufacturer, the original provisions can be executed. 2) Establish and maintain appropriate condenser vacuum before running to facilitate heating of

steam turbine, and ensure the temperature of exhaust steam does not exceed limits and the bypass system can be put into use in a timely manner. 5.2.5 By-pass System: a) The configuration, type, capacity and control level of the bypass system shall be in accordance with the characteristics of the units or relevant design codes. b) The startup method with bypass system should be proposed by the manufacturer, such as IP cylinder startup or HP and IP control valve and bypass coordinated starts, etc. c) The automatic, interlocking and protection shall function properly and is put into use before the bypass system is put into use. d) The HP and IP cylinder steam flow shall match with each other when using the bypass system, which shall meet the minimum cooling flow of HP and IP and LP cylinder at different working conditions. e) If the bypass system shall exit automatically if it cannot be set under hot standby state when the steam turbine operates so that the water hammers can be avoided in steam pipelines when putting in use. 5.2.6 The steam turbine is not allowed to run or connected into grid in case one of the following occurs: a) All tachometers are out of order. b) The speed governing system fails to maintain idling or the dynamic overspeed exceeds the operating value of the overspeed governor after load rejection. c) The HP and IP main throttle valve, governing valve, HP cylinder exhaust check valve and any extraction check valve in reheating system cannot be closed tightly, or jammed or malfunctions d) The overspeed governor fails in the overspeed tests. e) Any tripping protection of the steam turbine fails. The trip protection required by the steam turbine is shown in Appendix A1 (standard appendix). f) Any main control parameters of steam turbine are out of surveillance or any main control device malfunctions. The main monitoring parameters of steam turbines are as shown in Appendix A2 (standard appendix), and the main control devices required by the steam turbine are as shown in Appendix A3 (standard appendix). g) Any one of the startup oil pumps, fire resistance oil pumps, lubrication pumps, emergency oil

pumps, jacking oil pumps fails or one of its automatic starting devices is out of order. h) The temperature differences of the inner walls of the HP and IP outer cylinders is greater than or equal to 56. i) The deviation value of the rotor eccentricity at the original peak phase is greater than 0.02mm. j) The turning gear fails; the jigger remains still or the jigger current exceeds limits. k) There is clear metallic sound between the static and rotating parts or other abnormal sound. l) The quality of the steam, water and oil is below standard. 5.3 Cold Starts 5.3.1 Running Parameter Selection: The main and reheat steam pressure in front of the main throttle valve and temperature hall meet the requirements of starting curve provided by the manufacturer when the steam turbine starts up in cold state. The overheat degree of the main steam entering into the steam turbine shall be at least 50, but not greater than 426. The temperature differences between two pipelines shall not be more than 17. The temperature differences between the main and reheat steam of the HP and IP combined cylinder turbine are generally 28, may be up to 28 42 in a short time but not greater than 80. 5.3.2 Check the main and auxiliary equipment as well as the relevant system thoroughly, which shall have the condition for startup before the steam turbine runs. 5.3.3 Running of Steam Turbine: a) Cut off the steam admission quickly when the turbine runs to 600r/min, and the friction check should be carried out in the 5min; listen carefully to the sound within the turbine and speed up after confirming there is no friction in flow path, the bearing oil return works properly. The rising rate is 100r/min. b) The warm-up time and the rolling speed shall be carried out in accordance with the startup curve provided by the manufacturer. c) Check or medium-speed warmup shall be carried out when the speed is up to the first-order critical speeds of HP and IP rotors. d) The warm-up time and temperature shall meet the requirements prescribed by the manufacturer. 5.3.4 Measure and record all relevant data after the steam turbine runs at constant speed and

relevant tests can be carried out after being checked thoroughly and found to work properly, and the reset can be raised to constant speed at the rising rate of 200r/rain per minute. 5.3.5 Grid-connection and on Load: a) Warm up with 5% rated load after the grid-connection, and run stably for at least 30min under such load. For every 2 variation in main steam temperature, the stable warming up time shall be increased for 1min. b) Control the load acceleration and the changing rate of the main and reheat steam parameters in line with the requirements of the startup curve. c) Load up to the predetermined load and ensure that the corresponding drain valve is closed. d) Check and confirm that the vibration of the turbine, cylinder expansion, differential expansion, axial displacement, temperature of bearing metal, temperature of return oil, fuel system pressure, temperature and other primary monitored parameters are within normal range. e) HP and LP heaters shall be started randomly, and when the extraction pressure of the deaerator is higher than the internal pressure of the deaerator, and can overcome the static pressure caused by height differences, it shall be switched to extract the steam for this section and the deaerator shall be under sliding-pressure operation. f) Adjust the condenser vacuum according to the load increases, switch or put the pumps, circulating pumps, drain pumps and other auxiliary equipment into use. 5.4 Hot Start 5.4.2 Running Parameter Selection Determine the parameters of running according to the starting curve provided by the manufacturer based on the cylinder temperature when the steam turbine starts up in hot state. 5.4.2 Running a) Drain the main and reheat steam pipelines completely, and the drainage for the cylinder block is opened for 5min and then turned off before the turbine is started and run at extreme hot state. b) Speed up when the turbine is found to work properly after rub checks after running, but the rising rate shall not be less than 200r/min per minute. c) Connect to grid as soon as possible through necessary checks and found normal after constant speed.

5.4.3 Grid-connection and on Load a) Load up to the load point corresponding to the startup curve after grid-connection, and confirm that the temperature of lower cylinder of the steam turbine wont drop down anymore so as to reduce the cooling of the cylinder and the rotor. b) Manage the main and reheat steam parameters to be stable and the temperature differences do not exceed the limit 5.5 Provisions for Steam Turbine under Operation 5.5.1 If the turning gear cannot be disengaged in a timely manner after the steam turbine runs, switch off and stop the turbine. 5.5.2 Stop the jacking oil pump when the speed is raised up to 1200rmin. 5.5.3 If the turbine vibrates abnormally when it runs at 80%~85% first-order critical speed of shaft, dont speed up forcibly but identify the causes and eliminate the troubles and then pass through the critical speed after the vibration is normal. 5.5.4 Pass through the critical speed quickly and smoothly and the speed should not stay in that range. 5.5.5 Manage the temperature rise rate of the cylinder metal to be 2~2.5 /min, and the temperature dropping rate to be 1~1.5 /min; stabilize the speed or load and extend the warming-up time. 5.5.6 Pay attention to the coordination of adjacent professional to prevent the substantial fluctuations in steam parameters and load when startup. 5.5.7 Monitor and record the changes in cylinder expansion values, which shall be even and uniform, if the sliding key system is found to be jammed or stuck, prolong the warm-up time or discuss the solutions to prevent cylinder vibration caused by uneven expansion. 5.5.8 The oil temperature of the oil cooler outlet shall be adjusted and controlled at 3845 after running and during running, and that of the fire-resistant oil cooler outlet shall be controlled at 40~ 5 degrees centigrade. 5.5.9 The exhaust cylinder water-spray shall be put into operation when the steam turbine runs to 600r/min and stop the operation at 15% of rated load. The turbine can operate for a long term when the temperature of the exhaust hood does not exceed 65 C under normal conditions, and the load shall be limited to no more than 80~C. If the measures taken dont work before grid connection, and when the temperature of low-pressure cylinder exhaust steam reaches 120~C, the steam turbine should be shut down.

5.5. 10 The steam turbines that carry out peak-load-dispatching operation in two shifts shall select the running parameters and temperature rising rate properly according to the metal temperature of the cylinder when startup, and accelerate the on-load speed and reduce the cooling time of the turbine rotor. 6 Operation of Steam Turbine 6.1 Give consideration to the safety and economy when operating the steam turbine, and adhere to the principle of safety first. 6.2 Normal Operation of Steam Turbine 6.2.1 Monitor the main parameters of the steam turbine and its changes shall comply with the provisions according to the provisions on normal operation and control parameter limits. 6.2.2 Make routine inspection and maintenance periodically according to prescribed content. 6.2.3 Analyze the parameters printed out or copied regularly each hour so as to make the unit operate under economic state. 6.2.4 Switch and test the relevant equipment regularly. 6.2.5 Load Adjustment: a) Adopt variable pressure or constant pressure--sliding pressure--constant pressure mode. b) The load changing rate shall subject to the adaptability to variable working conditions at governing stage when operating under constant pressure, which shall meet the requirements of life management curve, generally at l2 of rated load per minute. c) The load changing rate shall be determined by the adaptability of the boiler when operating under constant pressure, generally at 2%-3% of rated load per minute. d) The steam turbine with cut-out governing shall avoid operating at the load transitional point for a long term so as to reduce the throttle loss of the governing valve. e) The operation mode of auxiliary equipment shall meet the corresponding requirements of load adjustment. 6.2.6 The Control Range and Allowable Deviation of Steam Parameters a) The steam parameters shall be managed within the allowable range during the operation, when

exceeding the limits or having such tendency, make adjustment and record the limits of exceeding, overtime and accumulative time, and make corresponding process. b) The allowable deviation of steam parameters is as shown in Table 1. Table 1 The Allowable Deviation of Steam Parameters (In terms of Rated Value)

Parameter Name Limits The average pressure within any 12-month period 1OOp

Maintain the allowable pressure of continuous operation under such average pressure

105p Main steam pressure

The allowable deviation under exceptional circumstances, but the accumulative time of the 12-month period shall be

l 20p

Cold-reheat steam pressure 125p The average temperature within any 12-month period 1OOt

Maintain the allowable temperature of continuous operation under such average temperature

t+8

The allowable deviation under exceptional circumstances, but the accumulative time of the 12-month period shall be 400h t+(814)

The allowable deviation under exceptional circumstances is 15min per hour, but the accumulative time of the 12-month

period shall be 80h

t+(1428)

Main steam temperature

Non-permitted value >t+28 Note: 1. p. refers to the rated main steam value (MPa);p1 refers to the rated cold reheat steam pressure (MPa); t refers to the rated temperature of main steam or reheat steam. 2. The temperature limits only apply to the situation oft566. 6.2.7 The quality of the steam, water and oil shall meet the standards. The process for the deterioration of the water vapor quality is shown in Appendix B (Standard Appendix). The commonly-used standard for the cleanliness of the fuel system is shown in Appendix C (Standard Appendix) 6.3 Special Operation of Steam Turbine 6.3.1 The provisions for load limits prescribed by the manufacturer shall be implemented strictly when part or the whole of the HP heater stops; in particular, manage the main steam flow and monitored section pressure as well as the extraction pressure of each section not to exceed the maximum allowable design value, and pay attention to the influence on the steam temperature of the boiler. 6.3.2 Manage the vacuum under allowable range when half side of the condenser stops, otherwise run with reduced load. Attention shall be paid to monitor the expansion of the steam turbine, axial thrust and the differential expansion of LP cylinder shall not exceed the limits.

7. Shutdown of Steam Turbine 7.1 Normal Shutdown of Steam Turbine 7.1.1 Shutdown Mode: a) Shutdown at compound variable pressure b) Shutdown at sliding parameters. 7.1.2 Complete the testing of the lubrication oil pump, jacking oil pump and turning gear before shutdown in order to shut down the steam turbine safely. If the tests fail, the shutdown can be postponed for non-critical failure condition so as to eliminate the faults. 7.1.3 Shutdown of Steam Turbine: The shutdown of the steam turbine is the inverse process of the startup, so the basic requirement of startup can also apply to startup in principle, but the temperature dropping rate is less than the temperature rising rate, generally controlled at 115min. a) Select the shutdown mode and temperature drop object of cylinder according to the shutdown object and characteristics of the equipment. b) The load, steam parameters and the temperature changing rate of the HP and IP cylinder metal shall be always under control and comply with the shutdown curve. The superheat of the main and reheat steam shall be less than 50 at all time when shutting down at sliding parameters. c) With the decrease in load and main steam parameters, special attention shall be given to the differential expansion, absolute expansion and changes in temperature of the each bearing, axial displacement and so on, and steam supply for shaft seal, vacuum and each system of auxiliary equipment shall be adjusted and switched in a timely manner. The stable operation of deaerator shall be ensured so as to prevent the vaporization caused by mismatch of the pressure and temperature. d) Ensure the trap of each part of the unit can be turned on at different working conditions. e) Special attention shall be paid to the speed change of the steam turbine after the step-out of the generator, and switch off and stop the generator when speed increases abnormally. f) Record the idling time of the turbine rotor accurately after the shutdown, which is an important basis to determine whether the static and rotating parts of the steam turbine function properly. The jacking oil pump shall be opened when the speed drops down to 1200rmin as stipulated. g) Maintain the vacuum at normal shutdown till the coast-down of the turbine reaches 400rmin, which can damage the vacuum.

7.1.4 Jigger: a) The turning gear shall be put into use immediately after the rotro is at a standstill. b) The eccentricity of the rotor is found to exceed the maximum allowable value or a clear metallic sound is heard during the turning is running, the continuous turning shall be stopped, but changed to intermittent turning for 180. The causes shall be identified and eliminated, and the turning cannot be put into continuous operation until the eccentricity is restored to normal. The causes shall be identified and eliminated as soon as possible when the electric barring device cannot work properly as the result of the turning motor failure, and it shall be made manually for intermittent turning for 180, and the turning shall be put into continuous operation when the eccentricity is restored to normal and the rotor can rotate freely. It is forbidden to turn or run forcibly by mechanical methods. c) The metal temperature of the steam turbine at the governing stage or IP first pressure stage is more than 150, and it is required to stop the continuous turning for a short time, so normal oil supply for bearing must be guaranteed so as to prevent the damage to the Babbitt of the bearing caused by overheat and perform intermittent turning manually during this period of time. d) Record the stop time of the turning as well as the eccentricity of the rotor and the phase at that time accurately when the turning is stopped for a short period of time, and determine to perform intermittent turning manually for 180~ straight shaft or put the turning into continuous operation according to the changes of the eccentricity. d) When the metal temperature of the HP cylinder metal is less than 150, stop the turning, but pay attention to the eccentricity of the rotor; if there are significant changes, identify the causes and perform intermittent turning. 7.2 Process for Exceptional Cases during the Shutdown of the Steam Turbine The effective technical and safety measures shall be development if the shutdown cannot be performed properly due to the defects of the equipment during the shutdown so that the steam turbine can be shut down safely. 7.2.1 If the regulating system assembly is found to be jammed during the load shedding. It is not proper to disconnect the generator, and if necessary, shut down the steam turbine or close the stop valve of the main steam and then disconnect the generator after confirming the load at "0MW". 7.2.2 If the extraction check valve is struck or cannot be closed tightly, turn off the stop valve to prevent the overspeed caused by backflow of the steam into the steam turbine. 7.2.3 Adjust manually timely if the automatic control system fails to prevent the steam turbine out

of control. 7.2.4 If the main and reheat steam parameters are out of control or water entrained by steam occurs during the shutdown at sliding parameter, stop the turbine immediately. 7.3 Forced Cooling after Shutdown of Steam Turbine 7.3.1 Special attention shall be given to the prevention of the bending of main shaft as well as not to increase the life loss for the forced cooling after shutdown of steam turbine. 7.3.2 Select cooling mode and methods after careful tests and calculation, which shall be reviewed and approved by competent authorities of technology. 7.3.3 The introduction and extraction of the cooling medium shall be designed reasonably to prevent the local thermal stress and stress concentration as well as prevent the ponding during the operation or parts falling down to the pipeline equipment. 7.3.4 It shall be guaranteed that the turning can function properly during the whole process of cooling, and it is prohibited to introduce the cooling medium when the rotor is under static status. 7.3.5 Strengthen the control over the current of the turning, the eccentricity of the rotor, axial displacement, expansion of the steam turbine, differential expansion, metal temperature and other important parameters, and stop cooling if any abnormal situation or limits exceeding is found. 7.3.6 The forced cooling system and its operation shall be as simple as possible, and the monitoring instrument of the sensitive position for the cylinder thermal stress shall be calibrated correctly and its control index shall also be determined. 7.3.7 Control the cooling rate strictly and the temperature dropping rate for the cylinder shall not exceed 812. 7.3.8 At least turning continuously for 8h in order to guarantee even cooling of rotor and cylinder after the completion of the forced cooling. 7.4 Maintenance after Shutdown of Steam Turbine 7.4.1 Effective rust and erosion prevention measures shall be taken to avoid damages to the themal dynamic equipment during the shutdown (standby) period in order to ensure the safe and economic operation of the turbine equipment. 7.4.2 The selection of the rust and erosion prevention against the shutdown (standby) equipment shall be determined by the status of the shutdown equipment, the length of the outage period, the supply of the rust and erosion resistance materials and medicament and its quality, rigor of the equipment system, ambient temperature, process requirements of the rust and erosion method and

other comprehensive factors. 7.4.3 The rust and erosion prevention is a thorough and careful technical job covering a wide range, and the uniform cooperation of each profession shall be strengthened and prepared in advance. The required time shall also be included into the maintenance plan, and the medicament shall also be tested and qualified. The effect of the rust and erosion prevention shall be checked and recorded when removing the rust and erosion prevention maintenance and the technical file of rust and erosion prevention shall be established. 7.4.4 The rust and erosion prevention measures for shutdown (standby) steam turbine usually include: a) Hot Air Drying Methods: Isolate the steam-water system that may enter into the steam side of the cylinder and condenser and drain all water in the cylinder and steam extraction pipe, and when the temperature of the cylinder metal drops to 80 , blow hot air at 5080 into the cylinder; the air pressure within the cylinder shall be less than 0.04MPa, and the measure the humidity of the air discharged from the cylinder regularly, whish shall be less than 70% (at room temperature value) or equal to ambient relative humidity. b) Desiccant Dehumidification Methods: This method is applicable to safekeeping and maintenance of steam turbine with ambient humidity/s (the atmospheric humidity is not higher than 70%) and cylinder of water-free. After the turbine is tested qualified by hot air drying methods after shutdown, put the desiccant into the cylinder. Check the moisture absorption of the desiccant often during the maintenance period and replace immediately if the desiccant fails. Record the quantity of the desiccant that is placed into the cylinder and take them out when the maintenance ends. 7.4.5 The rust and erosion prevention methods for shutdown (standby)HP heater generally include: a) Nitrogen Charging Method: Fill in with nitrogen while relieve the pressure and drain off the water at waterside, and stop filling in with nitrogen after the water is drained out completely and the nitrogen pressure is stable at 0.5MPa; fill in with nitrogen when the pressure at steam side drops to 0.5MPa and stop filling in with nitrogen after the drainage is completed and the nitrogen pressure is stable at 0.5MPa (if the pressure drops during the maintenance, identify the causes and make supplement in a timely manner). The purity of nitrogen used shall be greater than 99.5%, but not less than 98%. Ammonia Hydrazine Method: Drain off the water completely when the pressure at steam side drops to zero after outages, and the fill in with solutions with hydrazine of of 200mg/L (the pH value of added ammonia is adjusted to 10~10.5) and seal up the heater. 7.4.6 The rust and erosion prevention methods for other shutdown (standby) equipment: a) Drain off the water from the deaerator, LP heaters, condensers and water side of the oil cooler

when they are out of service for a long time, and blow dry with compressed air after cleaning. b) Rotate the auxiliary equipment to get ready for the long-term outage maintenance, inspect the equipment under disassembled condition and refit in accordance with the relevant provisions after rust-proof treatment. c)Perform oil circulation periodically to regulate the oil system that may shut down for a long time. 7.4.7 Take special measures to prevent the corrosion of equipment that is placed in coastal area with heavy salt fog and under corrosive atmosphere. 7.4.8 The effective anti-freezing measures shall be taken in cold seasons. 8 The Thermal Control and Test of Steam Turbine 8.1 Thermal Equipment of Steam Turbine 8.1.1 The automation level of 300MW grade steam turbine in China has been significantly improved due to the wide use of computer. The computer has become the main thermal control equipment after the conventional analog instrument and manual manipulator have been reduced, and the repair and maintenance should be strengthened to reduce and prevent misadjusting, protection mal-operation and strive to improve the quality; meanwhile, the personnel training shall be strengthened so as to improve the technical proficiency of the equipment maintenance and operating personnel. At present, the distributed control system (DCS) used by 300MW grade steam turbine generally consists of the following subsystems: Data acquisition system(DAS) Sequence control system (SCS) Steam Turbine: Digital electro-hydraulic (DEH) Boiler feed pump turbine electro-hydraulic of water-feeding pump(MEH) Modulating control system (MCS) Among them, DEH and MEH may not adopt DCS to achieve. In addition to the above system and equipment, there shall also be systems and equipment with security monitoring and protection function, such as ETS and TSI. 8.1.2 The control system of computer shall cover the following functions: a) Speed control b) Load control and limitation; c) Unit coordination and control;

d)Auxiliary equipment interlocking protection; e) Stress monitoring and control; f) Valve management and testing; g)Protection and on-line test; h) Safety monitor and protection; i) Data acquisition as well as daily report, hourly report, instant printing, over-limit alarm and accident recollect printing. 8.1.3 Main instrument, automatic regulating system, thermal control and protection equipment shall be put into operation together with the main equipment, and shall not be shut down without approval of relevant competent authorities of technology. The computer system shall be tested on relevant functions before the startup of the unit, and operators shall take part in and make confirmation when testing. 8.2 Testing of Steam Turbine 8.2.1 Tests before the startup of the steam turbine: a) Static characteristic test of speed governing system of the steam turbine b) Shutdown protection test of all steam turbines and turbine-boiler-generator interlock tests c) Non-return valve on HP exhaust line, extraction check valve, control valve, switch of governing valve and protection interlocking tests. d) The protection tests of deaerator, heater and other main auxiliary equipment. e) Start-stop and protection interlocking tests of various oil pumps, water pumps and fans. f) The rotating equipment is proven reliably after operating continuously for a period of time. 8.2.2 Tests during the startup of the steam turbine: a)Local and remote shutdown tests of overspeed governor. b) Leak tests of main throttle valve and governing valve. 1) Perform the tests when the steam turbine operates at rated steam pressure, under normal

vacuum and with dead load. 2) When the main throttle valve or the governing valve is turned on completely while the other is off completely respectively, it shall be ensured that speed of the steam turbine drops below 1000rmin. 3) When the main steam pressure is relatively low but not lower than 50% of the rated pressure, the drop-out value of turbine speed can be corrected in accordance with the following equation: n(ppo)X1000 rmin Whereas: P --- Main steam pressure at the test; p--- Rated main steam pressure. c) Oil charging tests of emergency governor: 1) Conduct at constant speed or during normal operation. 2)The two emergency governors shall be tested respectively. 3) The operation, audible and visual indication of the emergency governor shall be correctl d) Overspeed test: 1) The tests must be performed if any of the following occurs: Newly installed steam turbine or after overhaul; Re-start the turbine one month after the shutdown; Before the load shedding; After the emergency governor is disassembled or adjusted. 2) The overspeed tests shall not be performed if any of the following occurs: The local or remote shutdown is not normal; The HP and IP main throttle valve and the governing valve cannot be turned off tightly; Any of the bearings vibrates abnormally at rated speed; The temperature of any bearing is higher than the limit value. 3) Key points: The steam turbine operates for more than 4h with 1025 of rated load before tests and maintain the steam parameters stable during the period; Mechanical overspeed as well as 103% and 110 of electric overspeed protection control tests shall be performed respectively;

Perform the tests twice at 110 111 of rated speed for the mechanical overspeed operation, but the differences between the speed of such two operations shall not be greater than 06 if the speed reaches 3330rmin, but the emergency governor still does not operate, stop the turbine immediately; The test duration shall be kept within 15min. e)Load Shedding Tests: The unit and power grid shall have required conditions before tests, and perfect measures shall be developed. The tests shall be performed with the approval of the relevant superior competent authorities of technology. 8.2.3 Please see Table 2 for tests and switch of steam turbine under operation. Table 2 Tests and Switch under Operation Item Name Standard and Methods Frequency Movement of HP,IP main throttle valve and governing valve

Once every day

Movement of extraction check valve

Without jam Whole stroke or part of stroke

Once every week

Fire-resistance oil pump, AC oil pump and emergency oil pump

Start and stop normally for 35min

Once every week

Low vacuum, low lubricant oil pressure and low fire resistance oil pressure

Perform on-line and operate normally

Once every month

Oil charging tests of emergency governor

Operate properly Run for 2000h

Vacuum leakage test Turn off the air valve at 80of the rated load and start recording 30s later, and it can be considered as qualified when the average dropping rate of vacuum is not greater than 040kPamin within 5min, with total dropping of not greater than 2kPa

Once every month

Standby water feed pump Start and stop properly and operate for 35min

Standby for over one month

Switching of rotating auxiliary equipment

Switching operation Once every month

Regular thermal tests Test the thermal efficiency of the steam turbine

Before and after overhaul

Assessment thermal tests Assess the efficiency of the steam turbine

Put into operation newly or after reconstruction

9 Main auxiliary equipment 9.1 Feed Pump 9.1.1 Identify the causes if the turning gear of the steam feed pump does not operate, and it is prohibited to turn the gear and run forcibly without identifying the causes. 9.1.2 The standby feed pump can warm up the pump properly, and when the temperature differences between the highest temperature and lowest temperature of the pump casing exceed the limits, it shall exit from linkage for standby. 9.1.3 The recirculating stop valve of the feed pump under operation and standby status shall not be turned off. 9.1.4 It is forbidden to turn on the feed pump if the check valve cannot be closed tightly; close the outlet valve immediately if the check valve is found to be badly sealed, but the oil pump shall operate continuously, and take other effective measures to control the inversion of the feed pump; if the check valve of the standby feed pump is found to be sealed badly, exit from the standby status immediately. 9.2 Circulating Pump 9.2.1 Prevent the circulating pump under operation from water loss and air containing. 9.2.2 The circulating pump laid underground shall be equipped with reliable anti-flooding measures. 9.2.3 The outlet butterfly valve shall be closed while the circulating pump stops to prevent the inversion. 9.3 Condenser 9.3.1 The trap introducing the condenser shall be closed tightly during the operation to avoid local runoff and cracks. 9.3.2 Check if the LP stream extraction pipeline originated from the steam side of the condenser leaks during the maintenance. 9.3.3 Test the water quality of the condensation water and the circulating water periodically in order to prevent leaks and scaling.

9.3.4 The circulating water shall be clean, and the water temperature and volume shall be adjusted according to the changes in seasons and load to meet the requirements of the circulating rate, terminal temperature difference and temperature rising. The concentration ratio of the circulating water shall be controlled strictly by blowdown and chemical feeding and other ways. The microbial attachment and blockage shall be prevented for open circulating water system. 9.3.5 Flush the condenser with rubber ball periodically, handle the defects of the equipment and calculate the rate of ball recovery for each flush and record the changes of the terminal temperature difference and vacuum. 9.4 HP Heater 94.1 It is not allowed to put into operation if the protective operation of the HP heater is abnormal. 9.4.2 The causes shall be identified to prevent the steam turbine from water when the HP heater operates and ensure continuous water supply to boiler. 9.4.3 Avoid HP heater to operate at low water level. 9.4.4 Handle the abnormality when the HP heater in operation adjusts the abnormality automatically, and stop the HP heater when the water level is out of control. 9.4.5 Make analysis on the changes in terminal temperature differences of HP heater and the opening of the regulated drain valve periodically. 9.4.6 The newly installed or overhauled safety valve of HP heater can be put into operation after being proven qualified by calibration. 9.4.7 The HP heater shall be started randomly under normal conditions. Generally, water can be supplied first into the HP heater when the unit is under operation, but steam can be supplied first, but special attention shall be given to reduce the thermal impact on the tube sheet, pipe orifice and barrel and other parts and the steam shall be supplied from low pressure to high pressure just like that of the extraction pressure. 9.5 Deaerator 9.5.1 The safety valve operation test shall be performed after the deaerator is overhauled or the safety valve is overhauled, and it cannot be put into operation if the test fails. 9.5.2 Control the water level strictly to operate in normal range. 9.5.3 Prevent the deaerator from overheat and over-pressure when the load increases abruptly or the HP heater trips.

9.5.4 Prevent the vaporization of deaerator caused by decompression if the load decreases abruptly or the steam extraction stops suddenly. 10 Accident Prevention and Handling for Steam Turbine 10.1 Basic Principle for Accident Prevention 10.1.1 The accident shall be handled based on the principle of "Protecting personal safety, Protecting power grid and Protecting equipment" when the accident occurs. 10.1.2 Key points for Handling when the Accident Occurs: a) Determine whether the accident has happened according to the instrument display and equipment abnormality. b) Handle the accident quickly, and remove the threat to human safety, power grid and equipment to prevent the failure propagation. c) Disconnect or stop the faulty equipment immediately if necessary, and ensure the equipment without defects can operate normally. d) Identify the causes quickly and eliminate the accidents. 10.1.3 Record the observed phenomenon, the process of the accident development and time as well as the eliminating measures that are taken in details. 10.1.4 Keep the relevant date related to accident occurrence and handling process. 10.2 Accidental Shutdown of Steam Turbine Break vacuum for shutdown if any of the following occurs: 10.2.1 The speed of the steam turbine rises to 3330rmin, while the overspeed protection does not operate. 10.2.2 The steam turbine vibrates strongly in a sudden or exceeds the trip value. 10.2.3 There are obvious metallic sounds or noise within the steam turbine. 10.2.4 The axial displacement reaches the limit value or the metal temperature of thrust bearing pad exceeds the limit. 10.2.5 The lubricant oil supply interrupts or the oil pressure drops to the limit value, but the

standby pump fails to start up. 10.2.6 The oil level in the lubricating oil tank drops to the limit value, but oil make-up fails. 10.2.7 The temperature for any one of the bearing pad increases suddenly, and exceeds the prescribed limit value. 10.2.8 Water hammer occurs in the steam turbine, and the temperature differences between the upper and lower cylinder exceed the limit, and the temperature of the main and reheat steam drops down for 50 suddenly within 10min and waters enters into the steam extraction pipeline and exceeds the trip value. 10.2.9 The shaft seal of the steam turbine rubs and sparks. 10.2.10 The generator and the exciter smoke and are on fire or the hydrogen system explodes. 10.2.11 The oil system of the steam turbine is on fire and is hard to be extinguished, which threads the safety of the unit. 10.3 Prevention and Handling of Typical Accidents 10.3.1 Overspeed of Steam Turbine a) Main Hazards: It will lead to loosening and deformation of the impeller, falling-off of the blade and shroud, bearing damage, rotating and static friction and even broken shaft. b) Main Features: The speed rises up and exceeds the operation value of overspeed governor. c) Main Causes: 1)The generator sheds the load to zero and the speed governing system of the steam turbine cannot work properly. 2)The speed is out of control when the overspeed governor is having overspeed test. 3)The inlet valve of the main and reheat steam, non-return valve of regenerative extraction steam and others jam or cannot be closed tightly after disconnecting the engine. d) Kep Points for Handling

1) Shut down the unit immediately and confirm that the speed shall drop down. 2) Check and open the vent valve of HP steam lead pipe. 3) If the speed keeps on rising, take measures to isolate and release the pressure decisively. 4)Identify the causes of overspeed and eliminate the fault, and the steam turbine can be restarted only after it has been confirmed by thorough checks that steam turbine functions properly. And it can be connected to grid with load after the overspeed governor and the overspeed protection device are calibrated and can operate normally. 5) Focus on inspection and monitoring of the vibration, internal sounds, bearing temperature, axial displacement, thrust pad temperature and others when restarting turbine, and stop startup if any abnormality is found. e) Preventive Measures 1) Check the installation quality of the HP and IP main throttle valve and governing valve carefully before startup and check if the open-close movement of each valve is flexibly. 2)Any of the overspeed protections fails, which cannot be eliminated during the operation, shut down and eliminate. 3) Perform the oil charging tests for overspeed governor, online tests for the shutdown protection and the movement tests for the main throttle valve and governing valve and the extraction check valve of each section regularly. 4) If the main throttle valve or governing valve jams during the shutdown, try to reduce the load to "0"MW, shut down the steam turbine and then disconnect the engine. 5) Strengthen the supervision on the quality of the steam, water and oil, which shall meet the standards. 6) The speed monitoring and control system shall work properly. 10.3.2 Strong Vibration of Steam Turbine a) Main Hazards: It will lead to bearing damage, rotating and static friction and even break the unit down. b)Main Causes: )The rotating and static friction or main shaft bending.

2)The quality of the rotor is uneven or the blade falls off. 3)The bearing cannot work properly or the bearing block is loosened. 4) Water enters into the cylinder or the cylinder is deformed due to cold steam. 5)Off center or the coupling is loosened. 6)Sliding key system jams resulting in uneven expansion. c) Key Points for Handling 1)After the turning of the steam turbine and before the first-order critical speed of shafting, shut down and identify the causes rather than reduce the speed and warm up when any bearing shows 0.04mm vibration or shaft vibration of any bears exceeds 0.12mm. 2) The vibration amplitude of the rotating shaft of the steam turbine generator unit changes abruptly and exceeds 25% of the upper limits as stipulated in Area B in Table 3 under stable conditions, which generally indicates damages to the unit or signs of malfunction or warning for some irregular changes, and the measures shall be taken immediately to control the vibration within the allowable vibration limits, otherwise the unit should be shut down decisively. 3) The vibration displacement limits for the rotating shaft of the steam turbine generator unit are as shown in Table 3 at rated speed of 3000r/min or stable operating conditions with load, and the minimum value for the vibration limits stated in the table shall be adopts for the 300MW and above turbines that are manufactured using introduced technology at present. The supporting bearing vibration displacement limit is generally 0.03mm, when the unit is equipped with the device to measure the shaft vibration, the shaft vibration monitoring shall prevail. Table 3 The Vibration Displacement Limits for Rotating Shaft of Large-scale Steam Turbine Generator Unit

Rated Speed 3000rrain( Peak-to-Peak Value) Area Upper Limit

Relative Displacement

Absolute Displacement

Evaluation

A 80 100 The unit that is put into operation newly fall within this area in general.

B 120165 150200 It can be considered as qualified basically and can operate for long term.

C 180260 250320 In general, it is considered as disqualified, but it can operate for a limited period of time before remedial measures are taken.

D Above the upper limits stipulated in Area C

It is considered as dangerous because its severity can damage the unit.

10.3.3 Bearing Damages a) Main Hazards: It can damage the shaft neck, the rotating and static friction can damage the steam turbine when it gets severe. b) Main Signs: 1) The temperature of the bearing Babbitt rises up significantly or the bearing smokes. 2) The metal temperature of thrust bearing pad rises up when the thrust bearing is damaged. 3) Babbitt shred residue is found in returned oil. 4) The vibration of the steam turbine increases; c) Main causes: 1)Oil supply to bearing is interrupted or the amount of the lubricant oil is smaller. 2) The oil pressure is low, but the oil temperature is high or the oil quality is below standard. 3)The bearing is overloaded or the thrust bearing is overloaded, and the jacking oil pressure is low or it does not jack up when turning. 4) The bearing clearance and the tightening force is much too big or too small. 5) Water enters into the steam turbine or water hammer occurs. 6) The bearing liner is damaged due to the long-term large vibration. 7) The automatic interlock of AC and BC oil pump does not work properly, and the relevant interlock and the protective settings are incorrect, which will lead to abnormal oil supply at accidents. d) Key Points for Handling 1) Shut down emergently when the bearing is found faulty during the operation. 2) The turning shall not be made forcibly when it cannot be put into operation after the shutdown resulting from the bearing damage, but the reliable isolation measures shall be taken to prevent water or cold steam from entering into the cylinder.

3) Clean the oil systems thoroughly after the bearing is damaged and ensure to start up again after the oil quality is satisfactory. e) Key Points for Prevention: 1) Strengthen the supervision and adjustment of the oil temperature and the oil pressure, and keep close watch over the temperature of the bearing Babbitt and returned oil and identify the causes and eliminate them if any abnormality is found. 2) The automatic and standby equipment of oil system is reliable, and shall be tested periodically and strictly. The shutdown and switch of the oil pump or the oil cooler shall be smooth and careful to prevent bearing burnout due to oil breakoff. 3) The oil cleaning device shall operate properly and the oil quality meets the standards. 4) Prevent the water from entering into the steam turbine and partial circulation from damage and avoid main shaft bending and bearing vibration 5)The rotor of the turbine generator must be grounded firmly. 6) Adjust the interlocking setting for AC and DC oil pumps carefully before startup and check if the wiring is correct. 10.3.4 Blade Damage a) Main Hazards: It will lead to the rotating and static friction of the steam turbine, deterioration of operating conditions and vibration caused by uneven quality of the rotor. b) Main Signs: )The vibration increases. 2) The vibration of critical speed increases abnormally. 3)Metallic sounds or noise can be heard during turning. 4) The hardness of condensation water increases. 5)The pressure of monitored section rises up. c) Causes:

1) The blade frequency is below standards or its manufacturing quality is poor. 2) The overspeed of the steam turbine or the operating frequency deviates from the normal value for a long time may lead to the fatigue of blade. d) Key Points for Handling: 1) Shut down emergently after confirming that there are obvious metallic sounds within the steam turbine or the steam turbine vibrates strongly. 2) If the pressure at governing stage or the extraction pressure is found abnormal during the operation with reference to the vibration, axial displacement and changes in metal temperature of the thrust bearing, confirm that the blade falls off and to shut down. e) Key Points for Prevention: 1) Take strict precautions against overspeed of the steam turbine and water hammer. 2) Control the steam turbine to operate under specified parameters and load and avoid operating at low steam temperature, low vacuum, low frequency and with overload. 3) Strengthen the supervision on the quality of steam and water. 4) Pay attention to the maintenance after the shutdown of the steam turbine. 5) Perform frequency measurements and crack detection for the blade periodically. 10.3.5 Main Shaft Bending a) Main Hazards: It will lead to strong vibration of steam turbine or rotating and static friction, and even damages to the steam turbine when it gets worse. b) Main Signs: 1) If the eccentricity of the turbine rotor exceeds the limits, which cannot be restored to normal value by continuous turning for 4h. 2) The vibration at critical speed increases significantly. c) Main Causes:

1) The steam turbine vibrates or the rotating and static parts rub. 2) Water enters during the operation; especially the water or cold steam enters into the cylinder resulting from improper maintenance after shutdown at startup or shutdown 3) Thermal bending resulting from large temperature differences between upper and lower cylinder. d) Key Point for Handling: Shut down immediately after confirming that the main shaft bends and the turbine shall not be restarted until the causes are found and eliminated. e) Key Points for Prevention: )Measure the eccentricity of the rotor and the turning current shall be normal before the steam turbine runs each time and after the shutdown. If the thermal bending of the rotor occurs before running, the turning time shall be prolonged appropriately, and if the thermal bending occurs during the speed-up, the warming-up time shall be extended, but the turbine shall be shut down if the thermal bending gets worse or warming-up is invalid. 2) The effective isolation measures shall be taken to prevent water and cold steam from entering into cylinder when the steam turbine is under turning state. 3) It is forbidden to run the steam turbine when the temperature differences between the upper and lower cylinders of the steam turbine or the eccentricity of the rotor exceeds the limits. 4) Drain completely and monitor the vibration, differential expansion, expansion, axial displacement, sliding key system of the cylinder and so on during the startup of the steam turbine, and avoid main shaft bending caused by rotating and static friction. 5)Check and confirm that the vibration of bearings are normal when the speedup of the steam turbine is at 8085 of first-order critical speed for HP and IP rotor; if the abnormal vibration is found, switch off and shut down till under turning state. 10.3.6 Water Intrusion into Turbine a) Main Hazards: It will lead to deformation of cylinder, collision and main shaft bending, etc. resulting from the disappearing of the rotating and static clearance b) Main Signs:

) The temperature differences between the upper and lower cylinders increase obviously. 2) The temperature of the main and reheat steam drops suddenly and the superheat decreases. 3) The vibration of the steam turbine increases. 4) The steam extraction lines vibrate. 5)The turning current increases under turning state. c) Main Causes: 1)The main and reheat steam temperature of boiler is out of control or the water is entrained by steam caused by instantaneous increase in main steam flow. 2)The reheater is full of water and flows backward to steam turbine. 3)The drainage for steam supply for shaft seal or the regenerative extraction steam pipeline is blocked, and the waterlogging or drainage flows into cylinder. 4) DEH or primary temperature components fails d) Key Points for Handling: 1) Shut down the turbine emergently when the main and reheat steam temperature drops suddenly, which exceeds the prescribed value or drops to the limit value during the operation. 2) If the water is found to enter into the steam turbine during the turning, keep turning till the temperature differences between upper and lower cylinder of steam turbine is restored to normal. And strengthen the supervision of the internal sounds, eccentricity of rotor, turning current and so on. 3) If the water enters into the steam turbine during the speeding up, shut down the turbine for turning. 4) Identify the causes and eliminate them when the steam turbine gives out alarms for water intrusion into steam turbine. Shut down the turbine if the vibration, differential expansion and changes in temperature differences between upper and lower cylinder reach the outage value. e) Key Points for Prevention: 1) The steam turbine shall be equipped with water-induction prevention and monitoring device, which can be put into operation reliably.

2) The cylinder cannot be opened for drainage if the temperature differences between the upper and the lower cylinder is not big during the shutdown to prevent the water and cold steam of the anti-drainage system from entering into the cylinder, and start up the turbine at extreme hot state before running and then shut off 5min later. 3)The valve of the drainage piping shall be cleaned and checked to ensure the smooth operation. 4)The adjustment of the water level of the heater and deaerator shall be stable and the water level alarm and protection shall be reliable. 5)There should be sufficient quantity and reliable temperature measurement elements for cylinder mental and parameter display, and conduct calibration periodically. 10.3.7 Abnormal Adjustment and Control System a) Main Hazards: It will result in the malfunction of partial or whole regulation and control function, and it is unable to maintain the operation of the unit when it gets worse, and even cause the operation parameters to exceed the limits and the protection operates and trips. b) Main Causes: 1) The regulation and control device is abnormal or the controlled device works improperly. 2) The regulation and control power blacks out or the power quality is abnormal. 3)The regulation and control air pressure is low or air loses c) Key Points for Handling: 1) When two sets of the computer system runs, one of which is switched on for operation while the other one fails and then the faulty computer will exit from operation. When the computer fails and is unable to regulate or control automatically, it can be adjusted and maintained for operation manually. When both computers fail, the steam turbine intertrips; otherwise, the turbine can be switched off and shut down. 2)Try to make the unit operate stably at original state due to blackout of the control power and pay attention to supervise the main parameters; the equipment that must be operated can be operated locally, and apply for shutdown if it cannot be restored within a short period of time to ensure the safety of the unit. 3) When the compressed air for control loses air locally, try to change over to adjust or control manually as much as possible according to the impact on the overal operation of the unit, and if it

is impossible to maintain operation, it may lose air source or completely; reduce the load and shut down immediately when the unit safety is affected. d) Prevention Measures: 1)The computer for regulation and control shall be equipped with reliable power supply, which usually is powered by UPS; however, it shall be ensured that power voltage, frequency and harmonic quality and others are qualified because there are too many types of control power; it shall have the capacity of anti-interference from inside and outside to prevent voltage fluctuation or dead halt or mal-operation caused by poor cabinet grounding. 2) Strengthen the management and maintenance of the main host room and cabinet and make moisture-proof, anti-dust, anti-static, protection against electromagnetic interference and aeration-cooling treatment according to provisions to prevent damages to computer module caused by improper maintenance. 3) In addition to strengthen the normal maintenance of the air compressor for control, the supplied air shall be dewatered and drained for drying to prevent the operation failure caused by corrosion to air conduit and pneumatic control elements as well as avoid waterlogging and freezing within the pipelines in cold seasons. 4)The operator on duty shall be familiar with the operation characteristics (air-to-open, air-to-close and air-to-maintain) of the pneumatic control equipment after losing air so as to process respectively. 10.4 Analysis and Handling for Common Accidents 10.4.1 Dropping of Turbine Vacuum a) Main Hazards: The dropping down of turbine vacuum not only decreases the economical efficiency of the units, but also leads to surge of last stage blade of HP cylinder, abnormal rotor vibration and others, and even accidents to steam turbine. b) Main Causes: 1)The cooling water is insufficient or interrupted. 2)The heat exchange efficiency of the condenser decreases. 3) The vacuum system leaks or the equipment functions improperly. 4) The shaft seal system is out of order.

5) The water level of the condenser is out of control. c) Key Points for Handling: 1)If the vacuum drops, compare with the turbine-exit temperature sheet of HP cylinder and make confirmation as well as identify the causes, and process correspondingly. 2) Control the load as prescribed when the vacuum drops, and the low automatic load shedding and protection device of vacuum shall not be removed. If the load drops down to 30% of the rated load and the vacuum still cannot be restored, the load can be reduced to "0" MW and then shut down the turbine. 10.4.2 Abnormal Main and Reheat Steam Parameters a) Main Hazards: Over-temperature and over-pressure or low temperature not only affects the economic operation of the steam turbine, but also plays an important role in affecting the service life of the steam turbine. The high-temperature creep life consumption of rotor increases in proportion to the over-temperature time, while the low temperature will lead to water erosion of last stage blade. b) Main Causes: 1) The boiler is out of control or the desuperheating water is abnormal. 2) HP bapass valve is opened by mistakes or leaks. 3) The exhaust steam pressure of and temperature of HP cylinder is relatively high. 3) Sudden Outage of HP Cylinder Extraction c) Key Points for Handling: 1) Contact the person in charge for restoration immediately if the parameters exceed the limit while focus on the supervision of the vibration, differential expansion and changes in axial displacement and make thorough inspection on the steam turbine. 2)Record the off-limits and time of off-limits. 3) Shut down if the parameter exceeds the prescribed time or reaches the limit value. 10.4.3 Sudden Change of Load

a) Main Hazards: The axial thrust of the steam turbine changes abruptly which is caused by great fluctuation of load, and it may lead to the melting of the thrust pad or the wear of the steam path. b) Main Causes: 1)The control system of the steam turbine is out of order or the governing valve operates improperly. 2) HP and LP bypass mis-operates or the regenerative extraction steam stops suddenly. 3)The abnormal changes of grid frequency or the boiler operates abnormally. c) Key Points for Handling: 1)Analyze the causes for the sudden rise of the load or sudden drop in line with relevant gauge, drop the load to the rated value when exceeding the limits and analyze and confirm that the internal of the steam turbine is normal. 2) The load changes suddenly, which is caused by abnormal changes of the boiler, the throttle flow of the steam turbine shall be adjusted correspondingly to stabilize the steam parameters; if the load changes are caused by abnormal grid frequency, try to meet the load requirements as much as possible and also prevent the steam turbine from operating with overload. 3) Switch to the manual-operated mode immediately if the control system is out of order. 4)The governing valve falls off with load according to the allowable flow, and it is not allowed to increase or decrease the load when the governing valve jams. 10.4.4 Load Shedding of Generator a) Main Hazards: 1) It may lead to the sudden changes of the axial thrust for the steam turbine, and will result in wear of the steam path. 2) Lead to the overspeed of the steam turbine. b) Main Causes: The power grid or generator, the main transformer fails, and the main oil switch of the generator trips.

c) Key Points for Handling: 1) First, confirm if the steam turbine intertrips, and check the speed upswing at the same time. 2) If overspeed, take decisive measures immediately and make the speed down. It is not allowed to restart until the causes are identified and eliminated. 3) Check and confirm that the oil supply of the lubricant oil system is normal. 4) If the manufacturer permits the use of the station service power or allows the turbine to idle, switch off and shut down the turbine within 3min. The reverse power protection shall function when the power transformation motor of the generator operates, or switch off and shut down. 10.4.5 Malfunction of Oil System a) Main Hazards: 1) The control system is out of order, which is caused by the abnormal control oil system. 2) The bearing is damaged resulting from the abnormal lubricant system. 3) The leakage of the oil system is easy to lead to fire. b) Main Causes: 1) The oil quality is below standard. 2)The equipment of the oil system is abnormal. 3) Oil pipeline leaks. c) Key Points for Handling: 1) Shut down decisively if any one of the oil pressure and oil level drops to limit value. Identify and process the causes if the oil system is found abnormal. 2) Pay attention to fire protection when processing the leaks of oil system. Try to find the causes when the oil pressure drops but the oil level of oil tank remains unchanged; shut down the turbine emergently for process when the oil pressure endangers the safety operation of the unit. 3) The appropriate measures shall be taken when the oil quality is below standard, and if the oil quality still cannot meet the standard, shut down the turbine for oil replacement. 4) The standby oil pump or the DC emergency oil pump shall be started to guarantee the oil for

lubricating when the oil pump under operation fails, but the turbine shall be shut down immediately. 10.4.6 Failure of Main Steam and Water Pipeline a) Main Causes: 1) Become thin due to flush, fatigue and damage, poor welding and vibration. 2) Poor material selection and improper supports and hanger 3) Over-temperature, over-pressure and water hammers, etc caused by improper operation. b) Key Point for Handling: 1) Isolate the faulty location quickly within the minimum range. 2) When the main and reheat steam and main feedwater pipeline breaks, shut down the turbine emergently and prevent burns and take fire prevention measures when the high temperature steam leaks. 3) Try to isolate and eliminate the problem when the LP steam and water pipeline break, if necessary, shut down for process and pay attention to prevent the equipment from being inundated by water. 4) Strengthen the supervision on the metal of the pressure-containing member, in particular, pay attention to measure the wall thickness of the drain pipe socket, elbow and welded junction, etc. and flaw detection. 10.4.7 Axial Displacement Increases a) Main Hazards: The thrust bearing is damaged, which may lead to the wear of the rotating and static parts of steam turbine when it gets worse. b) Main Causes: 1) Main steam parameters, vacuum and load fluctuate greatly, which leads to the increase in axial thrust. 2) The increase in scale of the steam path, broken blade or steam leakage may lead to the increase in axial thrust.

3) Fuel cut or wear of the thrust bearing. c) Key Points for Handling: 1)First, check the changes in the temperature of the thrust bearing pad and related parameters when the axial thrust displacement increase. 2) If it is still unable to restore after measures are taken, reduce the load decisively. 3) Shut down for process when exceeding the limits. 10.4.8 Outage of Station Service Power Key Points for Handling: a) Shut down immediately if the station service power blacks out completely. Start the DC emergency oil pump to ensure the oil supply of the bearing when the emergency power supply works improperly. If the turning motor is out of power, try manual turning after the rotor remains standstill. Start up the unit after confirming the startup requirements have been met through thorough inspection and after the station service power is restored. b) The standby auxiliary equipment shall be put into operation when the station service power blacks out; strengthen the checks and adjustment to the steam turbine; if the operation cannot be maintained, shut down the turbine. c) Try to maintain the original operation state if the power for thermal control blacks out, if necessary, make adjustment and monitor the meters locally. Shut down if the steam turbine operates abnormally led by the outage of the power supply or the power cannot be restored within 30min. Special measures shall be taken to shut down the steam turbine safely and reliably when shutting down the turbine. 10.4.9 The steam turbine deviates from normal frequency a) Main Hazards: It may damage the blade due to near the resonant frequency. b) Key Points for Handling: When the turbine operates but deviates from normal frequency, pay attention to check the vibration of the steam turbine and the rotatory equipment and prevent the steam turbine and rotatory auxiliary equipment from operating with overload. It is required to meet the requirements of the power grid under the premise of ensuring the safety operation of the steam turbine. The steam turbine is allowed to operate continuously at the power frequency of 485505Hz, and

the power frequency shall be limited if it deviates from the allowable range prescribed by the manufacturer, and when it reaches the limit value, the generator shall be disconnected. 10.4.10 Fire Extinguishing for Boiler Key Points for Handling: a) Shut down the steam turbine immediately if the boiler is on fire. b)Dewater completely when restoring the steam turbine. c) Determine the proper HP and LP bypass opening before adopting HP cylinder to start the running, so as to ensure the non-return valve on HP exhaust line can open automatically and the HP and IP cylinder steam flow match with each after the steam turbine runs. d)The load shall be increased quickly and smoothly to prevent the water entrained with steam caused by great fluctuation of main steam pressure. Adjust and put the auxiliary equipment into operation in a timely manner. 10.4.11 Oil System Firing a) Main Hazards: It may lead to the shutdown of the steam turbine or damages to equipment, even threat the personal safety. b) Main Causes: 1) Oil system leaks to high temperature parts 2) The cable is on fire or caused by other fire. c) Key Points for Handling: 1) Put the fire out and report to the leader and contact the fire department. 2)Use the fire-fighting equipment correctly to put the fire out and prevent burns or suffocating. 3) Take isolation measures quickly and immediately to prevent fire spread. 4) Shut down the turbine emergently and immediately if the fire cannot be put out quickly and it threats the safety of the steam turbine seriously. 5) Control the oil drainage speed appropriately when it is required to open the emergency oil

drainage valve so as to ensure the non-interruption of lubricant before the rotor is at static. 6) It is prohibited to start the HP oil pump when the oil system is on fire, and the lubricant oil can be reduces so as to reduce the oil leaks, if necessary; the oil system shall be shut down if it is forced to do so. d) Key Points for Prevention 1)The oil system shall adopt flange connection as less as possible in design and installation, and the oil pipeline shall be reliable and stable to prevent vibration, wear and leaks. The heat preservation shall remain intact for the high temperature pipeline equipment near the oil pipeline, and the surface temperature shall not be greater than 50 with metal shielding. 2)Strengthen the routine inspection, eliminate and take measures if minor leaks are found to avoid oil leaking to the high temperature pipeline equipment and causing fire. 3) The emergency oil drainage valve of the oil system shall be equipped with eye-catching signs, and it shall be placed in a place that can facilitate the operation and that is not easy to be surrounded by fire, and shall be treated with lead seal to avoid mis-operation. 4)It is not allowed to use open fire on the oil system that has not been cleaned completely. 5) It is not allowed to extinguish the fire of oil system with water. The on-site fire-fighting equipment shall be complete and sufficient, and the operator shall be familiar with the methods for using the fire-fighting equipment and extinguishing methods, and perform anti-accident exercise for fire prevention and fire extinguishing periodically.