TURBO-DRIVEN BOILER FEED PUMP
1. TURBINE INFORMATION Casing: The casing serves to contain and support the stationary and rotating parts of the turbine. The casing has been horizontally horizontally split in the plane of the shaft centerline. The vertical joint is made up permanently at the factory. The upper half of the casing contains the high pressure steam chest, the the steam steam admission valve seats and and the upper halves halves of the diaphragms. diaphragms. The casing supports have been designed to minimize effects of thermal thermal expansion and hold the turbine in axial alignment.
Shaft Packing: Shaft packings are provided at both ends of the turbine casing where the rotor passes through through it. These packings packings are of the metal metal labyrinth labyrinth type and they they are piped to and work in conjunction with the steam seal system to minimize leakage of steam from or air into the turbine turbine case along the shaft. Each labyrinth labyrinth ring is composed of four spring loaded, butt butt jointed segments which are recessed recessed into bores bores of the labyrinth housings or turbine turbine casing. casing.
Oil Guards: Shaft oil guards serve serve to prevent leakage of oil from the bearings along the shaft. shaft. The horizantally split oil guards are fitted into grooves in the lower bearing brackets and the bearing bracket caps.
Diaphragms: The diaphragms, mounted in grooves in the turbine casing act as partitions to divide the turbine into separate compartments compartments for each stage. They contain stationary nozzles which direct the steam into the following rotating stages. Each diaphragm is horizontal split through the plane of the shaft centerline. A drain hole is drilled through through the bottom of each diaphragm diaphragm to remove any condensate.
Stage Packing: To minimize steam leakage between turbine stages where the shaft passes passes through through each diaphragm, labyrinth type metal packing is used. These stage packings each consist of a number of segments. The segments are mounted in grooves in the inner periphery of the diaphragms.
Main Bearings: The main bearings supporting the rotor, are of the babbit-lined, babbit-lined, multiple tilting pad type. The bearings are similar in construction and are pressure lubricated.
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Thurst Bearing: The rotor is axially positioned by a double acting thurst bearing of the multipleshoe, self-aligning and equalizing type. This thrust bearing is mounted in the front bearing pedestal next to the radial bearing.
Rotor: The turbine rotor consists essentially of a shaft with wheels and blades, coupling hubs, a thurst collar and a spur gear used for the electronic governor and used for the tachometer. The spur gear has been mounted to the turbine rotor on high pressure end.
Turning Gear: An electric motor driven "B.H.S." turning gear type RDV-2 is furnished for turning the rotor at a speed of 100 rpm upon start up and after stopping the turbine, in order to maintain an equal heat distribution in the turbine rotor. For manual operation, the free end of the electric motor has been provided with a square. A ratchet wrench that fits on this square, can be used for manual turning. The turning gear can only be started when the turbine is at stand still. a) Automatic start - When the turbine is tripped, the turbine is at stand still and the disconnect coupling is at disengaged position, the release solenoid is shortly energised. This releases the swinging arm from the latch. The pinion will come down on the toothed wheel rim, which is mounted on the turbine shaft. When the pinion and toothed wheel rim engage, (detected by a limit switch) the gear motor will be started. When the pinion and the toothed wheel rim do not engage within a set time, operational mode will change from "automatic" to "off". One must then locally engage the mentioned gears by slight turning of the hand wheel of the electric motor. Now press push button "on" to start turning gear. b) Start by push button command - This start is similar to the automatic start except that the disconnect coupling is not necessarily disengaged position. c) Automatic stop at starting the turbine - When the turbine gear is driving the turbine rotor the forces on the teeth of the pinion and the toothed wheel rim are directed such that engagement is positively maintained. Now when turbine is started and speed increases, the turbine will have the tendency to drive the turning gear. Due to this the forces on the teeth of the pinion are in such direction as to disengage the turning gear. This causes an immediate and automatic release of the pinion from the toothed wheel rim through the lift of the swinging arm. This arm catches a latch and remains in disengaged position. Disengagement of the gear is detected by a limit switch which causes the E-motor to be switched off. The turning gear can also be stopped by: i) ii) iii)
Push button "off". This stops E-motor directly. By lowering the swing lever. The E-motor is stopped now via the limit switch. At lack of lube oil pressure the turning gear motor is automatically stopped.
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Axial Position Device: At thurst bearing end the turbine is provided with two Bently Nevada probes to sense the axial position of the rotor. These probes, together with their connected instruments, will give electrical alarm and a trip signals, when the axial displacement becomes greater than a preset value. A dual voting system is used to reduce the possibility of a false alarm or shut down due to instrument failure. Simply stated a dual voting system consists of two transducers observing the same variable and their respective readouts. When a specific event occurs, both readouts must agree before an alarm or a trip is allowed.
Rotor Vibration Device: Two Bently Nevada probes are mounted at right angles in the bearing bracket cap over each end of the turbine shaft. These probes, together with their connected instrumentation, will measure the shaft vibration and total run out and will give an electrical alarm signal, when the vibration level rises above a preset value.
Differential Expansion Device: This device provides continuous monitoring of rotor growth relative to the turbine casing. On each side of the turning gear wheel a probe has been mounted which will give , together with the connected instruments, an alarm signal if the relative rotor displacement becomes greater than a preset value.
Case Expansion Device: A Bently Nevada probe has been mounted on the high pressure end of the turbine to indicate the thermal expansion during warming up.
Speed Indicator: The turbine is provided with an electric speed indicator consisting of a gear, a probe, a transmitter and an indicator. The probe is mounted on the front bearing housing and it senses the rotation of a gear with 60 teeth. The gear is mounted on the turbine shaft. The probe produces a pulse every time a tooth passes through its magnetic field. These pulses are converted into a "mA" signal that is fed into the indicator.
Breakable Diaphragm: A breakable diaphragm has been installed on the top of the exhaust casing. It consists of a rupture disk clamped between flangas. The disk will burst if the turbine exhaust gauge pressure will rise to 0.5 bar. Exhaust steam will pass then to atmosphere, reducing the excess exhaust pressure.
Seal Steam System: This system is designed to prevent leakage of steam from, or of air into the turbine. the system is used on the turbine when it is started up and while it is in operation. the pressure in the steam seal line is controlled by the seal steam control valve. During starting preparations the vacuum in the turbine would tend to suck air into the turbine. This is prevented however, by forming seals of steam in the sealing pockets of the shaft packing at the inlet and exhaust end of the turbine. During normal operation the first stage pressure causes steam to leak outward through the innermost gland packing at high pressure end of the turbine. Upon reaching the first
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steam seal pocket, most of this steam, together with leakage steam from the HP glands of the control valves, is piped through this steam seal line to maintain a positive pressure at the exhaust end sealing pocket. If the seal steam system pressure rises, steam is dumped, via the seal steam control valve, to a flash tank. Seal steam is prevented from escaping to atmosphere by maintaining a slight vacuum in the leak off pockets. This pockets are connected with the leak off system of the main turbine. Leakage steam from the glands of the trip throttle valves and the LP glands at the control valves, is also sucked off by this main turbine leak off system.
Steam Drain System: The steam drains supplement the previously described internal turbine drains and are used to drain water from the turbine, the seal steam line, the HP control valve casing and from the trip throttle valves before the turbine started and while it is running. Essentially this system consist of pipes and it is valved where required. These valves are opened during starting to remove any accumulation of condensate and they are closed when the equipment is in operation.
2. PUMP INFORMATION General: The pump is a multi-stage type having all impellers mounted in series and facing in the same direction. Liquid enters the suction nozzle, passes through the impellers and leaves through the discharge nozzle at opposite end of the casing. Each impeller operates within a diffuser which converts velocity to pressure. This process is repeated in the successive stages, each stage adding an increment of pressure. Discharge pressure is admitted to areas between inner and outer casing thus utilizing hydraulic forces to maintain sealing of individual stage joints and of the internal joints between the inner and outer casing.
Outer Casing: The outer casing is a forged cylindrical shell or barrel, which has nozzles to conduct the pumped fluid to and from the inner casing and rotor.
Inner Assembly: The inner assembly consists of diaphragms, diffusers and a rotor which are assembled together to form a single assembly. The inner assembly is positioned into the outer casing by a cylindrical fit and held in that position by bolts.
Inner Casing: The inner casing portion of the inner assembly consists of a combination of chrome steel diaphragms & diffusers. These form the hydraulic passages between successive stages.
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Rotating Element: The rotor basically consists of several impellers, a thrust collar, shaft sleeves and a balance drum mounted on the chrome steel shaft.
End Head: The end head closes the outer casing after insertion of the inner assembly. The end head supports the outboard seal housing and the outboard bearing housing.
Gaskets: The joint between the end head and outer casing is the sole high pressure outside joint in the pump. This joint contains a confined flexitallic gasket which has been compressed by the heavy alloy steel bolting which secures the end head to the outer casing. This flexible gasket assures proper sealing even during transient temperature changes. There are no gaskets used at the internal high pressure joints nor at the inter stage joints.
Axial Balancing Device: The pressure difference acting on each impeller produces an axial force towards its inlet. The sum of the individual impeller thrust forces is counteracted by the axial balancing device. This device consists of a stationary balance sleeve and a rotating balance drum. The labyrinth teeth of the balance drum run in close clearance with the bore of the balance sleeve, acting as a pressure reducing bushing between the pump discharge and pump inlet pressures. The water, which leaks past the balance drum, is returned to the pump suction. The diameter of the balance drum and the pressures acting on it are such that an axial force is produced on the rotor, which counteracts the axial force caused by the impellers. For design reasons the axial force of the impellers is not fully counteracted by the down force for the whole of the working area of the pump. Therefore a double acting thrust bearing has been installed which takes up the resultant axial force. The stationary balance sleeve is bolted to the end head and sealed by a confined flexitallic gasket. The rotating balance drum is mounted with a shrink fit on a tapered portion of the shaft using a hydraulic tool. This type of mounting securely locks the balance drum against rotational and axial movement. In addition the drum is held in place by a retaining ring fitted in a groove in the shaft and shouldered against the drum. An "O" ring and a back-up ring are fitted in the balance drum bore to prevent leakage of hydraulic pressure oil when mounting or dismounting the balance drum.
Main Bearing: The rotor is supported by Glacier Babbitt lined, multiple tilting pad type bearings. The pads of each bearing are fitted into slots in a two-piece bearing housing and are located by screws. The horizontal split bearing housing is mounted in a bore in the bearing bracket. The bearing housing is prevented from rotation by a pin. Pressure lubrication is employed. Oil piped from the lubrication system flows to the bearings through passages in the bearing brackets. This oil passes out through the individual bearing drain.
Thrust Bearing: A thrust bearing, consisting of a rotating collar, which is mounted on the pump shaft and operating between two identical thrust elements, is provided to maintain
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the axial position of the rotor under all operating conditions. This bearing is located in a thrust bearing housing formed by the bearing bracket at non driver side. The bearing is lubricated by oil from the main oil system. The oil is led into the thrust bearing through holes in the bearing bracket and is sprayed between the shoes and the thrust collar at the leading edge of each pad. On reaching the collar, it turns outward between the shoes and escapes around the collar. The thrust bearing clearances are such that during normal operation there is an oil film on both sides of the collar, between the collar and the thrust faces. Thermocouples are installed in some of the thrust bearing shoes to measure the bearing temperatures.
Serrated Bushing Seal: The injection type serrated bushing seal consists of a seal housing containing a throttle bushing. Hardened, serrated type shaft sleeves are used to protect the shaft and serve as pressure breakdown devices. Cooled injection water is used to block the escape of high temperature water from the inside of the pump and also to form the seal. A temperature controlled injection type shaft seal system automatically controls the leakage of water along the shaft, and prevents the flashing of water in the shaft seal. The controlled variable for this system is the 0 temperature of the drain water leaving the shaft seal. The temperature (about 75 C.) of the drain water is controlled by regulating the flow of injection water to the seal. Strainers, in the supply line assure clean injection sealwater.
Warming-Up System: Warming-up system has been installed on the pump to keep the temperature 0 differance between the discharge end and the suction end below 25 C. Normally the pump is warmed up with the discharge line closed and the suction line open. Then the warm-up liquid is admitted to the pump through the warm-up connection and out through the suction nozzle. Thermocouples have been installed on the suction and discharge end which provides, together with a temperature switch, control signals for a motor operated valve in the warming-up supply line.
Axial Displacement Probes: The main pump has been provided with Bently Nevada probes by means of which the driver will be tripped if the axial displacement becomes greater than a preset value. A dual voting system is used to reduce the possibility of a false alarm or shutdown due to instrument failure.
3. OIL SYSTEMS The oil unit supplies lube oil to the turbine, main pump, coupling, Tacke gearbox, BHS turning gear and the booster pump. It also supplies oil to the governing oil system of the turbine. The oil reservoir supplies the oil required to operate the systems. Condition of the oil should be checked at least twice a year.
Lubrication System:
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Lubrication oil is supplied from the main oil reservoir. This reservoir is a fabricated steel tank having a maximum operating capacity of about 4050 liters and a stand still capacity of 4500 liters, the tank scale is about 45 liters to a cm height. The tank is fitted with a deaeration tray to prevent foaming of oil entering the tank through the filler pipe or draining back to the tank from the oil system. A level glass is mounted on the side of the tank. The reservoir is equipped with a tank drain, an oil filter cap, two motor driven oil vapour extractors and low & high level alarm switches. The AC electric motor driven main oil pump is an 2 "Allweiler" pump designed to deliver 855 l/min. at a gauge pressure of 15kg/cm . The AC electric motor driven auxiliary oil pump is identical to the main oil pump. It will take over the oil supply if the main oil pump fails for any reason or 2 when the control oil gauge pressure drops to 7 kg/cm or when lube oil gauge 2 pressure drops to 1.6 kg/cm .The oil system is also provided with a DC electric motor driven emergency lube oil pump which will start if the lube oil gauge 2 pressure drops below 1.2 kg/cm for any reason. The main and auxiliary oil pump 2 discharge lines are fitted with relief valves, set at gauge pressure of 16 kg/cm to protect the pumps from damage due to excess pressure. Pressure indicators are installed on the discharge lines to determine the output pressure of the pumps and pressure switches are installed to start the standby pump if the discharge pressure of 2 the running pump drops to a gauge pressure of 7 kg/cm . The relief valve behind 2 the emergency oil pump is set at a gauge pressure of 5.2 kg/cm .After passing through check valves, the oil is directed to a three-way transfer valve. This valve permits passage of oil to either or both of the oil coolers, where the oil is cooled if 0 necessary to the proper operating temperature of 40 C. Thermometers are fitted at the inlet and discharge of the coolers, so that the operation of the coolers can be checked. A temperature switch has been installed on the cooler outlet line for giving an alarm when the oil temperature is too high. The switch has been set at 0 50 C. After passing from the discharge of the coolers, the oil is piped to a duplex oil filter. The filter is fitted with a pressure differential indicator and a pressure differential switch which will give an alarm signal at too high pressure 2 difference, setting 0.8 kg/cm . Before switching over a filter or cooler, make sure that the filter or cooler, that will be taken into service, is filled with oil and vented. 2 From the filter, the oil at a gauge pressure of 10 kg/cm , is piped to the turbine control oil system and, via orifice and check valve, to the bearings of the turbine and the pumps, to the turning gear, to the coupling between the turbine and the main pump and to the gear box. Several switches have been installed on the oil system. An oil separator has been installed on the oil unit. This separator should be in operation as long as the oil unit is in operation.
Control System:
Oil at a gauge pressure of 10 kg/cm 2 is delivered to the turbine control system. This system is described in the next section.
4. CONTROL SYSTEM (Please refer CONTROL OIL DIAGRAM –BFP TURBINE in schematic diary for the various valve numbers & solenoids mentioned in this chapter.)
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The turbine electronic controller provides electical outputs to position the steam admission valves. The electrical signals are converted to mechanical movements by a proportional electric/ hydraulic/mechanical actuator. The mechanical output of this actuator will position the control linkage of a hydraulic relay valve power servomotor. The servomotor positions the steam admission valves. The admission valves are designed so that the HP valve opens after fully opening of the LP valves. The turbine drives the booster pump and the main boiler feed pump. At normal operation the turbine speed will be controlled by signals from the boiler control system. The controller can be devided into three parts, namely: 1) 2) 3)
The speed controller The position controller The switchover from speed control to position control and reversed.
Speed Control / Position Control: Three speed sensors each receive signals from one of the three magnetic speed pickups. The pick ups are installed on the turbine and they face a 60 teeth gear wheel, which is mounted on the turbine rotor. Each pick up generates an output voltage pulse every time a gear tooth goes through the pick up magnetic field. Because the gear has 60 teeth the frequency equals the number of revolutions of the turbine shaft. The AC pick up signal is converted in the speed sensor to a DC voltage, which is proportional to the speed of the turbine. This DC voltage speed signal is sent through a high signal selection circuit to the speed control in such a way, that when one speed sensor fails the speed control continuous operation. If all three speed sensors fail, the system will automatic transfer from speed control" to "position control". In this control mode the speed governor no longer sets the turbine control valves but this is done then by the position control. The steam admission valves will lock in the position they had just before the failure occurs. In this situation the position of the valves can be changed manually by push button commands raise/lower to the "digital ramp position control" in order to maintain the required feed water needs. A bumpless automatic transfer is provided to return from "position control" to "speed control". This basically operates as follows: After a "request mode transfer" is given by push button command, the speed set point will automatically be set such that the output of the speed governor equals the output of the position control. This is done by a window comparator that compares the output of the speed governor with the output of the position control and gives raise lower signals to the "digital speed reference". When the output of the speed governor equals the output of the position control the transfer from "position control" to "speed control" takes automatically place, the automatic tracking of the "digital speed reference" stops and the automatic tracking of the "digital ramp position control" for normal operation starts again. Thus the position control follows the speed governor output again. At frequencies below 350 Hz (equals to 350 rpm) the signal from the speed pickup is insufficient to drive the speed sensor. This means that below this speed the control system is in "position control" mode. Consequently the turbine is started up using the position control and when the turbine speed is above 500 rpm the system is transferred to the "speed control" mode.
Speed Reference: 8
The speed set point is provided by a "digital speed reference". The "digital speed reference" can be operated manually by push button raise/lower or by the analog 4-20 mA feed water control signal (or automatically, when changing from "position control" to "speed control" mode, as described above). When the feed water control signal sets the speed set point, raise/lower signals are given to the "digital speed reference" by a window comparator that compares the output of the "digital speed reference" with the feed water control signal. The speed range that can be set manually by push buttons is 500 rpm to trip speed. The speed range that can be set by the feed water control signal is 2000 rpm to max. continuous speed. Upon loss of the feed water control signal (signal being far below 4mA) the speed setting automatically switches to manual.
Power Supplies: The speed governor is powered by power supply 1 or 2. At failure of one power supply the speed governor remains in operation. The position control is powered by power supply 3. Consequently the powers for the speed governor can be switched off for repairs of the speed governor while the turbine remains in operation by means of the position control during operation. The three independent overspeed switches receive power from all 3 power supplies. This means that these overspeed switches are always powered when the turbine is in operation. The switches have been set at 5925 Hz(rpm).
Servomotor: The function of the servomotor is to open or close the turbine steam admission valves in response to governing demands. It consists of a pilot valve and a power piston (the power piston's stem is connected to the valve lifting lever) a hydraulic amplifier which also consists of a pilot valve (which is connected to the output shaft of the Woodward actuator) and a power piston. The power piston of the hydraulic amplifier acts to position the servomotor pilot valve. The operation of the servomotor is as follows: Assume that the pilot valve of the hydraulic amplifier is moved downward by the Woodward actuator. Oil will be admitted at the bottom side of the amplifier's power piston causing the piston to move upward. The pilot valve of the servomotor will also be moved upward and oil will be admitted to the top side of the main power piston and oil from the bottom side is ported to drain. This strokes the main power piston downward, thereby opening the steam admission valves. When the power piston move, the pilot valves will be returned to their central position by the action of the respective external feedback linkages. Limit switches have been installed for valve position indication and they will give a reset condition signal to the reset system when the valves are closed.
Steam Admission Valves: These valves control the flow of steam through the turbine by means of the nozzle valves and operating gear. The assembly includes the high pressure control valve and the low pressure nozzle valves. All the valves are operated by the servomotor through a common linkage. The valve gear is adjusted so that all the low pressure nozzle valves open in sequence before the high pressure control valve starts to open. When the high pressure control valve is wide open, so are all the low pressure nozzle valves. The high pressure control valve is mounted in a lifting block and is aligned with its valve seat. The lifting block is carried by a lifting rod, which is connected to the valve lever by the lifting link. The servomotor power 9
piston actuates the valve lever to position the high pressure control valve through a connecting linkage. When the lifting block is raised, the high pressure control valve is opened. The admission valves closing spring on the HP control valve will close the steam admission valves in the event of a governor oil pressure or linkage failure.
Tripping System: Automatic tripping is accomplished by turbine overspeed, too high bearing metal temperature, too high axial displacement and too low lube oil and/or trip oil pressure. Under all these actions the turbine trip solenoids will be activated and trip oil pressure is released to drain, allowing the steam trip valves to close, thus shutting off the steam flow to the turbine and causing the turbine to shut down. At a trip of the turbine, also the turbine control valves will be closed through a contact that causes the Woodward actuator to run to the closed position.
Trip Valves: The high pressure, and low pressure steam inlet lines are provided with a trip valve. These valves will immediately shut off the steam supply to the turbine when a turbine trip occurs. These valves are opened by the trip oil pressure and will be closed by spring force if the trip oil pressure drops below a certain value. The valves are provided with an electronic exercise system for checking the functioning of the electronic overspeed trip system and the freedom of the trip valve moving parts during operation. This system consists of a signal generator, several relays and switches and solenoid valves. The system functions as follows: By pushing the "TEST" knob circuit 1,2 or 3 the output of the signal generator is supplied to the speed switch 1,2 or 3 of the Woodward. At the same time, solenoid 307 will be switched into the test position and will prevent the turbine from tripping when solenoid valve 308 is energized (opened). Increase the output of the signal generator, upon reaching the trip frequency, solenoid valve 308 will be energized and oil is drained from the trip valve cylinder causing the piston to move in the valve closing direction by spring force. The piston stops automatically as soon as the piston closes drain hole. This position will be indicated by the lamp "Trip valve test position". Decrease the output of the signal generator and release the "Test" knob. Check to see that the trip valve' s piston returns to its normal position. Repeat this procedure for the second trip valve. The above described test should be done once a week. The oil cylinder of each trip valve is equipped with a relay valve which opens a large flow area around it for fast tripping upon loss of trip oil pressure, without using large oil lines. When the emergency system is reset, the relay valve closes under influence of the trip oil pressure. On steam side the valves are fitted with an integral steam strainer.
Overspeed Trip: Besides the three electronic speed switches as described above, the unit is also provided with a mechanical overspeed trip. This device is a spring loaded plunger set radially in the overspeed trip body. This body is mounted to the pinion of the gearbox. At the designed tripping speed(5900 rpm) the centrifugal force of the plunger overcomes the counteracting force of thr plunger spring, the plunger moves outward and strikes the nut of the handtrip device causing trip oil pressure to drain, which results in closing of the trip valves. For test purposes the overspeed trip 10
can be made to act at operating speed (without tripping the unit) by filling the plunger with oil. To test the mechanical overspeed trip during operation handle as follows: 1) 2) 3) 4)
5)
6)
While running the unit at 4700 ±50 rpm. push the test valve 310 into test position. This will prevent the turbine from tripping. Open valve 301, Thus admitting oil into the overspeed plunger causing the plunger to move outward. Make sure that the plunger has struck the hand trip device nut. If necessary readjust the overspeed trip device. Close valve 301, wait a few minutes so that oil can leave the plunger causing the plunger to retract.( TO AVOID DAMAGE TO THE HAND TRIP DEVICE, DO NOT ATTEMPT TO RESET IT BEFORE THE PLUNGER OF THE OVERSPEED HAS RETRACTED.) Reset the hand trip device.(TO PREVENT THE TURBINE FROM TRIPPING, THE HAND TRIP DEVICE MUST BE RESET. BEFORE RETURNING TEST VALVE 310 TO THE NORMAL POSITION.) Release test valve 310 so that it returns to the normal position.
The above described test should be done at least every two months. During this test the mechanical overspeed trip can not shutdown the turbine. The unit however is still protected against overspeed by the overspeed switches which are part of the woodward governor.
Handtrip Device: This device is mounted on the gearbox at free pinion end. When the stem of this device is moved by the overspeed trip plunger, it will be moved into the valve body. This opens the valve and releases the pressure in the trip oil line, causing the trip valves to close. The hand trip device can be manually reset, but normally this will be done by the action of its solenoid 311. The solenoid is energised then for some time to close the valve against spring force until it is held closed by trip oil pressure. BEFORE RESETTING THE HAND TRIP DEVICE, MAKE SURE THAT THE OVERSPEED PLUNGER HAS RETRACTED. IF NOT, RESETTING WILL CAUSE DAMAGE TO THE TRIPPING MECHANISM.
Testing Tripping Mechanisms: The operation of all tripping mechanisms should be checked on initial starting and each time the unit is started after a prolonged shut down or overhaul. The functioning of the trip system should be tested at stand still and in the following manner: 1) 2) 3) 4)
Make sure that the main steam block valves are closed. Start the main or auxiliary lube oil pump and check the oil pressures. Reset the trip oil system. Trip the unit by releasing lube oil pressure.
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5)
Observe the action of the trip valves to see that they trip instantly with no evidence of sticking or binding.
5. OPERATION Normal Starting Preparations: 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.
11. 12. 13. 14. 15. 16.
Energize all control and alarm circuits and verify their action. Make sure that the HP trip valve is closed. Make sure that the LP trip valve is closed. Place the turbine controller in the position control mode. Make sure that the output of the position controller is 0%. Make sure that the gland steam condensor is ready for operation. Drain condensate from the steam lines, turbine case and trip throttle valves by opening their respective drain valves. Check the oil level and the condition of the oil. Be sure, the oil is in good condition, uncontaminated by water sludge or other foreign matter. Start the main oil pump and vent the oil system thoroughly. Fill the stand by oil cooler and filter. Start the oil vapour extractor of the oil reservoir. 2 Check the oil pressures. Lube oil gauge pressure should be 2 kg/cm at the turbine. If necessary adjust relief valve 109. Control oil gauge pressure should 2 be 10 kg/cm at the turbine. If necessary adjust relief valve 108. Make sure that the auxiliary oil pump and the emergency oil pump start at the correct oil pressures. Engage the coupling between the turbine and the main boiler feed pump. Start the turning gear. Open the turbine drains. Start the steam supply to the turbine gland seal system. Gland seal steam gauge pressure should be 0.1 kg/cm 2. Put the condensing system into operation. Warm the boiler feed pump thoroughly by putting the warming up system in the automatic mode, check to see that: A) B) C)
Temperature differential between suction and discharge ends 0 of pump case is 25 C or less. 0 Higher pump case temperature is within 30 C of operating temperature. In emergencies it is allowed to start a pump without warming
up. 17. 18. 19.
20.
After warming up the pump, close the valve in the warming up supply line. .Make sure that the drains of the pump case are closed and that the pump the discharge valve is closed Make sure that the valves in the gland seal water lines to the opened. main pump and in the seal water lines to the booster pump are Vent the seal water system and coolers thoroughly. Make sure that the drain lines from the seal housings are open.
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21. 22.
Open the valves in the recirculation line. Fill the pump with boiler feed water, being sure pump is fully vented. Pump may be filled from seal injection system, or through warm up connection. 0 23. Set control valves for the seal injection system (approximately 75 C.). 24. When the water pressure in the pump approximates the suction pressure, open the valve in the suction line. 25. Make sure that the booster pump is ready to operate. 26. Thoroughly drain and preheat the steam supply lines. 2 27. Make sure that the turbine vacuum is below 0.3 kg/cm absolute. 28. Reset the turbine trip system and test the tripping mechanisms as described in control section. 29. After testing the trip mechanisms, reset the trip system again.Make sure that the trip valves open. 0 30) When the lube oil temperature has reached at least 35 C., and the steam just 0 before the LP trip valve is at least 40 C. superheated, open the steam admission valves (by raising the output of the position control) to bring the turbine up to speed of about 1000 rpm so that the turbine may be heated evenly. NOTE: After a black out the turbine can be started with auxiliary steam of 16 0 bar and 210 C. It must be ensured that no water, from the inlet piping, can enter the turbine. 31) Operate at 1000 rpm for not less than a quarter of an hour. During the warming up period listen carefully for any rubbing, unusual noise or vibration. Also during the warming up period check oil pressures, oil temperatures, oil flow to bearings and general mechanical performance of the unit. NOTE: If abnormal vibration, noise or any other erratic condition should develop, shut the unit down immediately and investigate the cause. 32) Throttle all steam drain valves to a quarter turn open. 33) After the turbine has been thoroughly warmed (that means casing 0 temperature is within 50 C. from the steam temperature) and the vibrations 2 are normal, and vacuum is below 0.3 kg/cm absolute, increase the speed by raising the output of the position control. Increase the speed in steps of 20 rpm/sec. The control system will automatically change over from position control to speed control when the turbine speed reaches the minimum speed setting of the digital speed reference. CAUTION: Care should be exercised when the unit is accelerating or decelerating through the critical speeds. Prolonged operation is limited to speeds at least 10% removed from critical. 34) Increase the speed by means of raising the digital speed reference. 35) The boiler feed pump is discharging through the recirculation line. The unit can be operated satisfactory under these conditions until the pump is ready to be put on the line. 36) Check the operation of the oil system. The cooling water flow through the oil cooler should be adjusted so that the temperature of the oil leaving the cooler is 0 50 C. 2 37) Check that the seal steam gauge pressure is 0.1 kg/cm . Make required correction. 38) Close the turbine drains except the drain behind the HP trip valve. This drain must always be open.
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39) 40)
41)
Open the pump discharge valve to put the pump on the line. Increase the speed up to the minimum feed water control speed. At reaching this speed, the feed water control signal will be balanced with the actual speed setting. This balancing is completed when the feed water controller has no intention to provide a raise or lower command to the digital speed reference. The contact for remote speed setting can now be closed and the feed water signal will provide raise and lower commands to the digital speed reference. Check to see that the proper vacuum is being maintained on the turbine exhaust.
NOTE: - In Unit # 4,5 & 6 TDBFP ‘B,’ a new controller has been installed & commissioned under R & M. The operating procedure for this controller is as follows: 1. After ensuring all permissive, give RESET command. 2. After turbine RESET, for rolling the turbine give GOVERNOR START command. 3. After giving GOVERNOR START command give RAISE command for control valve opening. 4. After attaining the turbine speed 1000 rpm SPEED CONTROL will be automatically active (no need of REQUEST CHANGE). 5. After attaining the speed 1000 rpm, further give RAISE command till saturation (until RAISE push button lamp glows). This will not affect control valve opening or turbine speed. 6. After 1000 rpm turbine speed, control valve opening will be controlled by SPEED SET POINT. 7. After 1000 rpm, by raising the SPEED SET POINT turbine speed can be increased for required loading. RUNNING - A least once every shift, the following log checks should be made: 1) 2) 3)
4) 5) 6) 7)
8)
Unit speed Oil temperature and pressure. The condition of the oil should be checked at least every six months. Bearing temperatures. The unit must be tripped when the bearing metal 0 0 temperature increases to 120 C. The alarm setting should be adjusted at 5 C. above the initial stabilised operating temperature. Unit vibrations. Any sudden increase in vibration level must be investigated and the cause corrected before operation is continued. Seal steam pressure. Check to see that the gland steam system operates properly. Exhaust vacuum. Sealing water temperature. Make sure that the control valves of the seal water system are set properly(approx. 75 0C.).If the temperature of the 0 booster pump sealing water outlet, exceeds the normal value of 65 C., check the sealing chamber and the cooling water supply to the sealing water cooler. If every thing is found o.k., inspect the filters and coolers in the sealing water system. If the temperature of the main pump seal water outlet, 0 exceeds 80 C, check the sealing chamber, the water supply to the seals and the seal water filters. Pump inlet and outlet pressures and temperatures. Make sure that there is always a sufficient normal suction head is available, the pump may get
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09) 10) 11)
12) 13)
damaged if the normal suction head is too low. Therefore, pay special attention to the filters in the suction piping. Also a pressure drop in the deaerator may lead to a loss of normal suction head. For this reason the pressure drop must be restricted. Pump flow. Flow through the balance piping, kicker stage and bleed off line. Under certain conditions, the temperature differentials of a running pump may be higher than the differentials given for putting a cold or standby pump on the line. This is permissible, only if the flow through the pump exceeds the recirculation flow of the pump. Test the electronic exercise system off the turbine trip valves once a week as described in the control section. Test the mechanical overspeed trip device every two months as described in the control section.
STOPPING
1) 2) 3) 4) 5) 6) 7) 8)
Decrease the speed until the minimum flow valve opens and the pump does not supply feed water to the boiler any longer. Trip the turbine with help of the hand trip device or with one of the other trip devices. Make sure that the trip valves close instantly. After turbine rotor comes to the rest, disengage the coupling between the main pump and the turbine, and start the turning gear. Open the turbine drains. Break the turbine vacuum. Stop the steam supply to the gland steam system. The turning gear can be stopped when the turbine casing 0 temperature is below 70 C. The oil supply can be stopped when the turbine rotor is at stand still.
NOTE - If it should be necessary to restart the unit before it has cooled down, it should be done in accordance with the start up curve. Prepared by: Shri R Subhedar, SS (O)
(The above write-up was lost when opr/kstps4 was accidentally deleted. Shri ANS Suryanarayan, Engr (O) has made a concerted effort to retrieve all the valuable data. This write-up also has been possible due to his diligence. TDBFP ‘B’ controller operation information is supplied by Shri R B Dwivedi – C&I )
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