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Steam turbine

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I try to explain about the steam turbine & components and how its work.

I try to explain about the steam turbine & components and how its work.

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  • A steam turbine can be considered as a rotary heat engine constructed of a number of cylinders (each cylinder comprises a cylinder casing that contains a rotor). Individual rotors are supported within their respective cylinder casing by journal bearings. The cylinder casing is the stationary component of the turbine while the rotating section of the turbine is referred to as therotor . The cylinder casing contains rows of stationary or fixed blades with rotating blades connected to the rotor. These rotating blades are installed between the fixed blades. The stationary blades are fitted into the cylinder casing in such a fashion as to direct or redirect the steam onto the next row of rotating blades. The cylinder rotors are coupled together and connected to the alternator rotor. Steam governor valves control the turbine output. A condenser installed at the exhaust or low pressure end of the turbine receives and condenses the steam prior to it being pumped back to the boiler.Principles of operation of a steam turbineWhen high temperature steam passes through a steam turbine; heat energy contained within the steam is converted into kinetic energy (energy due to motion). The steam flowing from the high pressure to a lower pressure is then converted in to rotating mechanical energy as the high velocity steam acts on a series of rows of blades mounted on the rotor. In a typical condensing turbine high pressure; high temperature steam is allowed to expand progressively in stages through the various rows of blades until it is exhausted to the condenser. As the steam progresses through the turbine the pressure reduces and the volume of the steam increases. To compensate for this volume increase the blade passages of the turbine take the shape of an expanding cone; with the largest diameter blades located at the low pressure end of the turbine. The amount of heat that is converted into kinetic energy by the fixed blades (or nozzles) is dependant on the design shape of these blades.
  • In a single stage impulse turbine the steam is expanded to the required pressure in fixed diaphragm nozzles thus producing high velocity steam. The expanded, accelerated steam is then directed onto the moving blades transferring its kinetic energy to the blades. The velocity of the steam (relative to the moving blades) as it leaves the blades should be zero; indicating that no further energy may be transferred to the moving blades. The characteristic features of an impulse turbine are :all the pressure drop of the steam occurs in the fixed nozzles no pressure drop occurs over the moving blades, ie. there is no pressure difference between the two sides of a row of moving blades (with this feature there is little tendency for steam to leak past the moving blades)
  • In practice it is impossible to achieve a pure reaction effect as the steam already has velocity when it reaches the moving blades. Therefore the steam on passing across the moving blades imparts some impulse to the blades due to its change in direction. The force developed by impulse compared with the force developed by reaction will depend on the blade speed/steam speed ratio. In a reaction turbine the steam expands when passing across the fixed blades and incurs a pressure drop and an increase in velocity. When passing across the moving blades the steam incurs both a pressure drop and a decrease in velocity.
  • Figure shows a two stage pressure compounded impulse turbine. The steam passes through the first set of nozzles where it looses pressure as it gains velocity. It then passes across the first row of moving blades where the steam velocity is reduced while imparting rotational force. The steam then enters the second row of fixed nozzles where it once again loses pressure as its velocity is increased. It then passes across the second row of moving blades where the steam velocity is reduced while imparting additional rotational force. The second row of nozzles (and any subsequent rows of nozzles) are installed on a diaphragm. This diaphragm minimises any steam leakage occurring around the nozzles due to the high pressure drop across the nozzles. When designing a steam turbine the actual number of stages installed will depend on the total energy available and desired blade speed.
  • Figure shows the arrangement of a velocity compounded impulse turbine giving a section of the blading corresponding to a graph of pressure and velocity as the steam flows through the turbine. As the steam flows through the fixed nozzles its pressure drops as its velocity is increased. It then enters the first row of moving blades where the kinetic energy of the steam is transferred to the moving blades forcing them to rotate. The steam pressure remains the same but the velocity decreases as it travels across the blades. The steam then enters the intermediate fixed blades which are installed in the cylinder between each row of moving blades. These fixed blades have no pressure or velocity drop across them as they only change the steam direction towards the next row of moving blades. The process continues through the remaining sets of moving and fixed blades until the steam exhausts the turbine.
  • You will notice that the turbine shown in Figure has what is referred to as a double flow LP cylinder. The steam enters the centre of the double flow cylinder and then divides and flows to opposite ends of the cylinder where it exhausts to the condenser. This type of arrangement provides sufficient cross sectional area for the large volume of low pressure steam. If a single flow design was employed an excessively large diameter cylinder would be required. With the double flow design the length of the blades are significantly reduced thus simplifying the construction while reducing the centrifugal force on the rotor. In addition the double flow arrangement balances out axial thrust on the rotor.
  • STRAIGHT CONDENSING TYPE In a Straight Condensing type steam turbine, the heat energy of steam is completely converted into mechanical energy (torque).The mechanical energy is utilized to generate power.The straight condensing type finds application in industries where power generation is prime objective e.g. captive power plant/ IPP.Straight condensing type is very common in places whereBleed is used for de-aeratorIncidental power generation
  • UNCONTROLLED EXTRACTION CONDENSING In an un-controlled extraction type, a tap is provided at a predetermined stage and a partial stream of steam is drawn out of the turbine.The un-controlled extraction of steam is deployed for process applications (with smaller quantity of steam flow and set temperature requirements) and Low Pressure heating application like de-aerator for heating solutions.This turbine setup is usually deployed in Independent Power Plants, Captive Power Plants and Co-generation plantsOne of the most versatile setup in terms of operation and intricate in terms of design. It provides a constant pressure steam through a controlled extraction at various loading conditions of the turbine based on seasonal variations.A control valve integrated with the steam path is provided at a predetermined stage. A partial steam flow is drawn out of the turbine at a constant pressure as per the process requirement. There are basically two types control valves a) Diaphragm, b) Passing/Throttle Valve, that controls the flow of steam at a preset pressure accommodating the seasonal variation of turbine load.The control system works on a closed loop feedback mechanism. The pressure at the user end is measured and a feed back is provided to the control system. Based on this error signal the feedback control system actuates a control valve designed to vary the area of the valve aperture and thereby regulate the pressure. This setup is applied for processes; where the steam pressure is a critical parameter.In some cases a nozzle/port is provided at a predetermined stage and an un-controlled high-pressure steam flow/bleed is drawn out of the turbine. This tap is provided before the controlled extraction in the steam path of turbine. Its utility is found mainly in LP heating requirements like de-aerator and processes.Controlled/ Un-controlled condensing type turbines are used in Co-generation application and offer maximum cycle efficiency to the user.
  • STRAIGHT BACK PRESSURE TYPE This is the most widely used back-pressure type turbine. Its aim is to expand the available steam through the turbine stages.The exhaust steam is connected to the process header.
  • As the name suggests the turbine rotor is the component of a turbine that rotates. Most modern turbines operate at either1800rpm when driving a 60Hz 4 pole generator, 3000rpmwhen driving a 50Hz 2 pole generator or 3600rpm when driving a 60Hz 2 pole generator. Special attention must be given to the construction of a turbine rotor due to the centrifugal force generated by the high speed operation. Turbine rotors are constructed by the following methods: Forged steel drum rotor Solid forged rotor Disc rotor Shrunk and/or keyed to the shaft Welded construction
  • The typical casing for an turbine consists of a cast high-pressure steam chest, an intermediate barrel section, and a separate exhaust casing. The barrel section is generally integral with the steam chest so that the vertical bolting joint is at one of the latter stages where internal pressures are very much reduced. The steam end, exhaust casing, nozzle ring, reversing blades and diaphragms are all split on the horizontal center line which allows for easy removal of the upper half of the turbine for internal inspection.
  • The diaphragms are machined on the outside diameter and assembled into grooves accurately machined in the casing. Cap screws, secured by locking, fasten the nozzle ring to the steam chest, while the diaphragm halves are locked in position by stops located at the horizontal split in the casing. Steam chest passages, nozzle block partitions and the valve opening sequence are all carefully designed to ensure even and rapid heating of the casing after steam is first admitted to the turbine.
  • The bolts or studs holding the flanges together must be tightened to precise values to effectively maintain their integrity once the cylinder is exposed to high temperatures. This is achieved by using a bolt or stud with a hole drilled through the centre. A carbon heating rod is inserted into these holes in the bolt or stud to heat the assembly during tensioning. This can be seen in Figure
  • With this method heating rods are insertion into the clamps during the tensioning process. The holes for these heating rods can also be seen in Figure.With casing flanges being much thicker than the casing itself they are slower to cool than the casing and are also slower to warm when the casing is heated. When rapid temperature changes occur the casing temperature changes much faster than the flange temperature thus subjecting the casing to abnormal and unwanted thermal stresses. These thermal stresses reduce the expected working life of the material.The most critical time when the greatest thermal stress occurs is when the turbine is being returned to service and the steam to metal temperature differences are at their greatest. To minimise the thermal stress occurring on the casings a system of flange warming is employed. The flange warming system supplies a regulated flow of steam through ducts or holes in the flanges and/or flange bolts/studs. Flange warming through flange ducts is shown in Figure 28. With this method warming steam passes through the flange and into the bolt/stud hole, it then passes along the bolt/stud outer shaft transferring heat to the casing and bolt/stud. It then passes through the flange to the next bolt/stud to continue the warming process.
  • Sometimes screw threads exist on the outer and inner portion. These interlock, to produce the long characteristic path which slows leakage. For labyrinth seals on a rotating shaft, a very small clearance must exist between the tips of the labyrinth threads and the running surface. Labyrinth seals on rotating shafts provide non-contact sealing action by controlling the passage of fluid through a variety of chambers by centrifugal motion, as well as by the formation of controlled fluid vortices. At higher speeds, centrifugal motion forces the liquid towards the outside and therefore away from any passages. Similarly, if the labyrinth chambers are correctly designed, any liquid that has escaped the main chamber becomes entrapped in a labyrinth chamber, where it is forced into a vortex-like motion. This acts to prevent its escape, and also acts to repel any other fluid. Because these labyrinth seals are non-contact, they do not wear out.
  • Consider a Turbine-Generator operating with the most basic form of manual throttle control. As Load is increased the turbine speed will drop due to the increased electrical output demanded for the same steam input. On sensing the decrease in speed the operator will manually increase the throttle valve opening to increase steam flow and restore the turbine to the correct speed shows a hypothetical Speed-Load Characteristic for such a Turbine-Generator. Each time the throttle valve is adjusted the turbine settles at a new speed-load characteristic, if left on a single setting the turbine speed would fall as load was increased in line with that shown on the graph. For every new setting of the manual throttle valve there would be a new speed load characteristic each approximately parallel to each other. While manual operation may be suitable for a turbine operating under steady load condition the response of an operator controlling the turbine manually is not sensitive enough to cater for a constantly varying load. An automatic control system is required that can both sense changes in turbine speed and make appropriate adjustments to the steam flow to the turbine in order to return the turbine speed to the required set point.
  • A simple fly ball governor is connected to the turbine through a secondary drive. As the turbine speed increases the speed of the governor also increases proportionately. The increased speed causes the fly balls to swing out further with increased centrifugal force and in so doing operate a mechanism to close in on the throttle valve setting, reducing steam flow to the turbine and reducing speed. As speed decreases the opposite effect is achieved. In a simple fly ball governor has replaced the operator manually controlling the turbine speed. The fly ball governor will be more responsive to speed variation and adjustments will be made far more frequently than in the case of the operator. Speed is regulated within a narrow band with A and B being the bounds of the upper and lower speed limit (The speed band between A and B is shown magnified in the figure for emphasis, however in practice the bandwidth is so small that it is usual to consider the two lines A and B as coincidental forming one line C as shown) The smaller the speed dead band (between A and B) and the smaller the slope of the governor speed-load characteristic, the more sensitive the governor. The drop in speed from no load to full load expressed as a percentage of the desired or no load speed is referred to as the governor “droop characteristic”. All governors of machines, which are to operate in parallel, should have some droop for reasons of stability and the droop should be identical if they are to share load in direct proportion to their capacity. This ensures stability and is desirable when two or more turbines are operating in parallel.
  • Figure 58shows a turbine fly ball governor fitted with speeder gear. The fly balls move out under centrifugal force as the speed increases against the restraining action of Spring A located between the fly balls. An addition adjustable Spring B connects the speeder gear to the governor linkage. It is not possible to make adjustments to the fly ball spring while the device is rotating, however, the adjustable spring B attached to the speeder gear tends to govern the movement of the sleeve X in conjunction with spring B. With the operation of the linkage to the governor valve the effects of spring B and spring A are additive. The overall effect of altering the tension in spring B is the same as altering the tension in spring A of a governor which had no speeder gear, that is, to shift the speed load characteristic to anew position approximately parallel to the original position.
  • TDP-1conceptsTDP-1 offers guidance on how to identify systems that have the potential to allow water to enter the turbine and to design, control, maintain, test and operate these systems in a manner that prevents any significant accumulation of water. This is the first line of defense in preventing turbine water damage.Preventing turbine water damage - ASME Standard TDP-1TDP-1 was initially developed in response to a rash of water induction incidents in the 1960s as power plants scaled up above 150 MW. TDP-1 now includes conventional steam (Rankine) cycle and Combined-Cycle power plants. Nuclear power plants are covered under TDP-2.In Figure shows a typical drain pot with redundant level elements. This configuration is typically used in "high risk" areas. One change in this standard that is shown is the level sensing device, which is labeled as a level element (LE). Drains should be installed at each low point in the motive steam piping. Drain Pots are recommended at the following locations to enhance condensate collection:Cold reheat line at first low point downstream of the steam turbine exhaust. (This application requires redundant level elements.)Motive steam lines that operate (admit steam to the steam turbine continuously) with less than 100°F (56°C) superheat unless a continuous drain has been provided. (This application requires redundant level elements.)Motive steam lines with attemperators - e.g. attemperator in HP steam line. The drain pot should be between the attemperator and the steam turbine. (This application requires redundant level elements.)
  • Motive steam lines that are prone to water accumulation during operation, for which large drain collection areas and/or water detection devices are desired. Motive steam lines that will be under vacuum during steam turbine start-up and shutdown. Branches and legs that will be stagnant during various operating modes, unless a continuous drain has been provided. At the steam turbine end of long horizontal runs (more than 75´).Automatic drain control systemsAs plant structures become more complex and a larger number of drains are involved, plants are adding automatic controls to simplify operation. Any automatic control system used to control steam line drain valves identified in this Standard should be designed so that the system has a means of initiating automatic valve actuation and a separate means of verifying the appropriateness of the automatic action. If an inappropriate action is taken, an alarm should be provided. For example, if a drain valve is closed automatically based on a timer, something other than the timer - such as a level element that would alarm if water were still present in the steam line - should be used to verify that the timer initiation was appropriate. 
  • TDP-1conceptsTDP-1 offers guidance on how to identify systems that have the potential to allow water to enter the turbine and to design, control, maintain, test and operate these systems in a manner that prevents any significant accumulation of water. This is the first line of defense in preventing turbine water damage.Preventing turbine water damage - ASME Standard TDP-1TDP-1 was initially developed in response to a rash of water induction incidents in the 1960s as power plants scaled up above 150 MW. TDP-1 now includes conventional steam (Rankine) cycle and Combined-Cycle power plants. Nuclear power plants are covered under TDP-2.
  • n of Heat from BearingsFriction is the primary cause of heat generated in a bearing. The oil is continuously undergoing shearing action which results in the dissipation of heat within the oil. In addition to friction, heat is also delivered to the bearing by conduction along the shaft on steam turbines, ID Fans and any auxiliary operating at elevated temperatures. In these cases oil not only acts as a lubricant but also as a coolant to extract the heat and maintain bearing temperatures below trip or damage values. On steam turbine for instance the oil flow is ten times greater than necessary for normal lubrication. In order to remove this heat oil coolers are usually provided to maintain the oil at safe working levels ( approx 40 Deg C ). Several combination of water cooled oil coolers can be used for this purpose, with either two by 100 % duty coolers or three by 50 % coolers for redundancy. Oil temperature exiting bearings is usually in the range of 60 – 70 Deg C and oil temperatures exit coolers in the range of 38 –  45 Deg C. The oil temperature can be controlled by either automatically regulating the flow of Cooling Water supplied to the in service coolers or by a thermostatically controlled oil regulating valve which by-passes hot oil around the coolers.OperationWhether the turbine is in service or on turning gear, extreme care must be taken when placing coolers in-service to ensure the supply of lubricating oil is NOT interrupted. Out of service coolers must be fully primed and vented on the oil side to remove any entrapped air in the cooler ( particularly after maintenance ) and pressurised to full working pressure before the cooler outlet valve is opened. This is to not only prevent a interruption to flow but also avoid pressure disturbances which can equally cause a turbine trip or bearing damage. Similarly, the Cooling Water side of the heat exchanger must also be primed to prevent air locking when placing in-service. Out of service coolers, when not isolated for maintenance, are kept in stand-by mode in preparation for a quick return to service if needed. In this mode both Oil and CW inlet valves remain open with outlet valves closed. The coolers are fully primed and at working pressure.Oil Purification Units Once oil is allowed to settle over a period of time water and solid contaminants will eventually settle at the bottom of the oil tank. This forms a layer of sludge and water below the oil, which can be manually drained off once detected. Main Oil Tank sight glasses with manual drain cocks or valves are usually provided for manual level monitoring and detection of water. A separate sludge compartment or settling section is sometimes provided to separate the contaminated oil from healthy working oil. Gravity separation alone is not an effective means of oil purification as it cannot remove all impurities. For this reason additional oil purification systems are usually employed to clean on line the main turbine lubricating oil.Oil Centrifuge : An oil centrifuge operates on the principle of centrifugal forces acting on the different densities of oil and water / impurities. In much the same way as impurities separate out naturally by the force of gravity. A centrifuge imparts rotating centrifugal forces to speed up the separation process. Water and impurities, because of their higher densities compared to oil will separate or be thrown out from the oil in the centrifuge.
  • SystemThe system consists of a set of glands fitted to the turbine, and a steam supply and exhaust system to service them.The system above shows the two means of controlling the gland receiver pressure; the first is by having a dump in split range with the make-up valve, the second is the use of a pressure regulating valve which dumps excess pressure to the exhaust line. The normal operating pressure is around 0.1 to 0.2 bar.
  •  The gland sealing section of the system is constructed of an inlet pressure regulating valve and a dump valve. Under low load conditions gland sealing steam is supplied via the inlet regulating valve from the auxiliary header to seal the turbine HP, IP and LP glands which are all operating under different pressures. As the load increases the leakage back through the glands of the higher pressure areas of the turbine is adequate to seal the lower pressure glands and the inlet regulating valve closes. With a further increase in load the leakage from the HP glands continues to increase and pressure increases within the gland sealing system. This pressure needs to be dissipated or it will over pressurize the gland sealing system. To alleviate this pressure the dump valve begins to open and regulates the gland sealing steam system by dumping this excess pressure.This dumped gland sealing steam and any leak off steam from the lower pressure glands is not wasted but piped under a slight negative pressure back to the gland steam condenser. Condensate flowing through the gland steam condenser is heated by the condensing steam which is drained back to condenser via the condenser flash box to join the condensate. As the extraction system is operating under a slight negative pressure air can be drawn across the outer section of the glands and into the system. This air becomes entrained with the extraction steam and travels to the gland steam condenser where it is removed by the gland steam condense extraction fan.
  • The gland steam condenser is utilised as a low pressure noncontact feed water heater with the discharge drainate flowing to the condenser via the condenser flash box. The gland condenser is fitted with a gland condenser extraction fan to remove any air that accumulates in the top of the gland stream condenser after the steam air mixture is separated.
  • PurposeIn thermal power plants, the primary purpose of a surface condenser is to condense the exhaust steam from a steam turbine to obtain maximum efficiency and also to convert the turbine exhaust steam into pure water (referred to as steam condensate) so that it may be reused in the steam generator or boiler as boiler feed water.
  • Steam ejectors have been employed for removing air from steam surface condensers since the beginning of the Industrial Revolution and the advent of steam power. They are the simplest, most reliable method known of pumping gases. In the air removal application for the power industry, ejectors and condensers are employed to evacuate air and any other non-condensable gases from the steam spaces of the condenser that services a steam turbine. Gas removal is done for the purpose of eliminating the “insulating” effect that non-condensable gases have on the transfer of heat through the tubes to the cooling medium. Without a vacuum system, air leakage would severely reduce the efficiency of the heat transfer process resulting in the condenser surface area increasing many times for a given steam load.
  • Reasons: Potential benefits for the use of a vacuum breaker valve are: Reduce the vacuum Reduce turbine speed as quickly as possible. Reduce the possibility of turbine rotor vibration in over-speed condition.Reduce the loss of turbine lubricating oil pressure.Reduce the loss of turbine hydrogen seal oil pressure.

Transcript

  • 1. Prepared by: Mohammad Shoeb Siddiqui Senior Shift Supervisor Saba Power Company Cell # +92 321 4598293
  • 2. What is Steam Turbine?  A Steam Turbine is a device that extracts Thermal Energy from pressurized Steam and uses it to do Mechanical Energy on a rotating output shaft.  Steam Turbine is device where Kinetic Energy (Heat) converted into Mechanical Energy (in shape of rotation).  Turbine is an Engine that converts Energy of Fluid into Mechanical energy & The steam turbine is steam driven rotary engine. This Presentation is base on basic of Steam Turbine & 134 MW Toshiba Steam Turbine. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 3. Rating & Design Data  Turbine Type: SCSF-36, single cylinder, single flow Reheat condensing turbine.  Rated output: 134 MW  Speed: 3000 RPM  Direction of Revolution: Counter-clock-wise (seeing from turbine front End)  Steam Condition:  Main Steam Press. (before MSV): 16548 kpa (g)  Main Steam Temp. (before MSV): 538oC  Reheat steam Temp. (before CRV): 538oC  Exhaust pressure: 6.77 kpa (g) Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 4. Rating & Design Data  Number of Extraction: 6  Number of Stage: 21 HP Turbine: 9 stages IP Turbine: 7 stages LP Turbine: 5 stages  Number of Wheel: 21 Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 5. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 6. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 7. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 8. In order to better understand turbine operation, Four Basic Classifications are discussed. Type of Steam Flow & Division of Steam Flow, describes the flow of steam in relation to the axis of the rotor. indicates whether the steam flows in just one direction or if it flows in more than one direction. Way of Energy Conversion & Type of Blading, Reaction, Impulse and Impulse & Reaction Combine. identifies the blading as either impulse blading or reaction blading. Type of Compounding & Cylinder arrangement refers to the use of blading which causes a series of pressure drops, a series of velocity drops, or a combination of the two. (number of cylinders; whether single, tandem or cross-compound in design) Exhausting Condition & Number of Stages is determined by whether the turbine exhausts into its own condenser or whether it exhausts into another piping system. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 9. 1. Type of Steam Flow Turbines may be classified according to the direction of steam flow in relation to the turbine wheel or drum - Axial. - Radial. - Mixed - Tangential Or Helical. - Reentry Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 10. Radial Flow: A turbine may also be constructed so that the steam flow is in a radial direction, either toward or away from the axis. In figure illustrates an impulse, radial flow, auxiliary turbine such as may be used as a pump drive. The radial turbine is not nor mally the preferred choice for electricity generation and is usually only employed for small output applications Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 11. Axial Flow: The great majority of turbines, especially those of high power, are axial flow. In such turbines the steam flows in a direction or directions parallel to the axis of the wheel or rotor. The axial flow type of turbi ne is the most preferred for electricity generation as several cylinders can be easily coupled together to achieve a turbine with a greater output. . Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 12. Reverse Flow In some modern turbine designs the steam flows through part of the high pressure (HP) cylinder and then is reversed to flow in the opposite direction through the remainder of the HP cylinder. The benefits of this arrangement are:  outer casing joint flanges and bolts experience much lower steam conditions than with the one direction design  reduction or elimination of axial (parallel to shaft) thrust created within the cylinder  lower steam pressure that the outer casing shaft glands have to accommodate A simplified diagram of a reverse flow high pressure cylinder is shown in Figure Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 13. 2. Way of Energy Conversion & Types of Blading - Impulse turbines - Reaction turbines - Impulse & Reaction Combine Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 14. By Types of Blading: The heat energy contained within the steam that passes through a turbine must be converted into mechanical energy. How this is achieved depends on the shape of the turbine blades. The two basic blade designs are: 1. Impulse 2. Reaction Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 15. Impulse: Impulse blades work on the principle of high pressure steam striking or hitting against the moving blades. The principle of a simple impulse turbine is shown in Figure. Impulse blades are usually symmetrical and have an entrance and exit angle of approximately 200. They are generally installed in the higher pressure sections of the turbine where the specific volume of steam is low and requires much smaller flow areas than that at lower pressures. The impulse blades are short and have a constant cross section. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 16. Reaction: The principle of a pure reaction turbine is that all the energy contained within the steam is converted to mechanical energy by reaction of the jet of steam as it expands through the blades of the rotor. A simple reaction turbine is shown in Figure. The rotor is forced to rotate as the expanding steam exhausts the rotor arm nozzles. In a reaction turbine the steam expands when passing across the fixed blades and incurs a pressure drop and an increase in velocity. When passing across the moving blades the steam incurs both a pressure drop and a decrease in velocity A section of reaction type blading is shown in Figure Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 17. Impulse stage Whole pressure drop in nozzle (whole enthalpy drop is changed into kinetic energy in the nozzle) Reaction stage Pressure drop both in stationary blades and in rotary blades (enthalpy drop changed into kinetic energy both in stationary blades and in the moving blades in rotor) Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 18. An impulse stage consists of stationary blades forming nozzles through which the steam expands, increasing velocity as a result of decreasing pressure. The steam then strikes the rotating blades and performs work on them, which in turn decreases the velocity (kinetic energy) of the steam. The stream then passes through another set of stationary blades which turn it back to the original direction and increases the velocity again though nozzle action. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 19. In Reaction Turbine both the moving blades and the non- moving blades designed to act like nozzles. As steam passes through the non-moving blades, no work is extracted. Pressure will decrease and velocity will increase as steam passes through these non- moving blades. In the moving blades work is extracted. Even though the moving blades are designed to act like nozzles, velocity and pressure will decrease due to work being extracted from the steam. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 20. This utilizes the principle of impulse and reaction. It is shown diagrammatically : There are a number of rows of moving blades attached to the rotor and an equal number of fixed blades attached to the casing. The fixed blades are set in a reversed manner compared to the moving blades, and act as nozzles. Due to the row of fixed blades at the entrance, instead of nozzles, steam is admitted for the whole circumference and hence there is an all-round or complete admission. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 21. Compounding of Impulse Turbine  This is done to reduce the rotational speed of the impulse turbine to practical limits. (A rotor speed of 30,000 rpm is possible, which is pretty high for practical uses.)  Compounding is achieved by using more than one set of nozzles, blades, rotors, in a series, keyed to a common shaft; so that either the steam pressure or the jet velocity is absorbed by the turbine in stages.  Three main types of compounded impulse turbines are:  a) Pressure compounded,  b) velocity compounded and  c) pressure and velocity compounded impulse turbines. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 22. With pressure compounding the total steam pressure to exhaust pressure is broken into several pressure drops through a series of sets of nozzles and blades. Each set of one row of nozzles and one row of moving blades is referred to as a stage This involves splitting up of the whole pressure drop from the steam chest pressure to the condenser pressure into a series of smaller pressure drops across several stages of impulse turbine. The nozzles are fitted into a diaphragm locked in the casing. This diaphragm separates one wheel chamber from another. All rotors are mounted on the same shaft and the blades are attached on the rotor. Pressure staging is also known as RATEAU staging. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 23. When the velocity energy produced by one set of fixed nozzles is unable to be efficiently converted into rotational motion by one set of moving blades then it is common to install a series of blades as shown in Figure. This arrangement is known as velocity compounding. Velocity drop is arranged in many small drops through many moving rows of blades instead of a single row of moving blades. It consists of a nozzle or a set of nozzles and rows of moving blades attached to the rotor or the wheel and rows of fixed blades attached to the casing. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 24. This is a combination of pressure-velocity compounding. Most modern turbines have a combination of pressure and velocity compounding. This type of arrangement provides a smaller, shorter and cheaper turbine; but has a slight efficiency trade off. Turbines using this arrangement are often referred to as CURTIS turbines after the inventor. Individual pressure stages (each with two or more velocity stages) are sometimes called CURTIS stages. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 25. This setup of a nozzle followed by a set of moving blades, non-moving blades, and moving blades makes up a single Curtis stage. After steam exits the nozzle there are no further pressure drops. However, across both sets of moving blades there is a velocity drop. This causes the Curtis stage to be classified as velocity compounded blading. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 26. Turbines can be arranged either single cylinder or multi-stage in design. The multi-stage can be either velocity, pressure or velocity-pressure compounded (discussed as earlier. Single cylinder construction or Single Flow Turbine Single cylinder turbines have only one cylinder casing(although may be is multiple sections). Steam enters at the high pressure section of the turbine and passes through the turbine to the low pressure end of the turbine then exhausts to the condenser. Figure shows a single cylinder turbine with a high, intermediate and low pressure section contained within the one cylinder casing. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 27. Tandem construction or Compound Flow Turbine Dictated by practical design and manufacturers considerations modern turbines are manufactured in multiple sections also called cylinders. Greater output and efficiency can be achieved by coupling a number of individual cylinders together in what is referred to as tandem (on one axis). Tandem compound Large electric power generating turbines commonly have a high pressure casing, which receives superheated steam directly from the boiler or steam generator. The high pressure turbine may then exhaust to an intermediate pressure turbine, or may pass back to a reheat section in the boiler before passing to a reheat intermediate pressure turbine. The reheat turbine may then exhaust to one or more low pressure casings, which are usually two exhaust flow turbines, with the low pressure steam entering the middle of the turbine and flowing in opposite directions toward two exhaust end before passing into the condenser. When the turbine casings are arranged on a single shaft, the turbine is said to be tandem compounded. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 28. Tandem construction or Compound Flow Turbine A tandem two cylinder turbine with a single flow high pressure (HP) cylinder and a double flow low pressure (LP)cylinder is shown in Figure. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 29. Tandem Three Cylinder Turbine It has a double flow LP cylinder with an IP cylinder arranged so that the steam flow through it is in the opposite direction to the HP cylinder. This design also greatly reduces the axial thrust on the rotor. Tandem three cylinder turbine is shown in Figure as under: Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 30. Tandem Four Cylinder Turbine Large modern turbines are required to deliver high output and are generally constructed of four cylinders with the exhaust steam from the HP cylinder passing through are heater before entering the IP cylinder. Tandem Four cylinder turbine is shown in Figure as under: Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 31. Tandem Cross-Compounding Turbine In cross compound turbines, the high- pressure, exhaust passes over to intermediate or low pressure casings which are mounted on separate shafts. The two shafts may drive separate loads, or may be geared together to a single load. In some larger overseas installations that operate at 60 hertz (frequency) the use of cross-compounding is some times employed. Cross-compounding is where the HP and IP cylinders are mounted on one shaft driving one alternator while the LP cylinders are mounted on a separate shaft driving another alternator. This is done so as the LP cylinder with its large diameter blading can be operated at a greatly reduced speed thus reducing the centrifugal force. Tandem cross-compounding turbine is shown in Figure: Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 32. Tandem four cylinder turbine with reverse flow The final turbine arrangement that is becoming increasingly popular is the “Tandem four cylinder turbine with reverse flow HP cylinder, double flow IP and twin double flow LP cylinders”. This arrangement is shown in Figure: Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 33. 04. Number of Stages - Single stage - Multi-stage Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 34. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor In an impulse turbine, the stage is a set of moving blades behind the nozzle. In a reaction turbine, each row of blades is called a "stage." A single Curtis stage may consist of two or more rows of moving blades.
  • 35. 5. Exhaust Conditions - Condensing - Extraction - Back-pressure Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 36. By steam supply and exhaust conditions:  Condensing  Extraction, (Automatic or controlled )  Non-condensing (back pressure),  Mixed pressure (where there are two or more steam sources at different pressures),  Reheat (where steam is extracted at an intermediate stage, reheated in the boiler, and re- admitted at a lower turbine stage). Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 37. Condensing Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor The condensing turbine processes result in maximum power and electrical generation efficiency from the steam supply and boiler fuel. The power output of condensing turbines is sensitive to ambient conditions. The cooling water condenses the steam turbine exhaust steam in the condenser creating the condenser vacuum. As a small amount of air leaks into the system when it is below atmospheric pressure, a relatively small compressor (Vacuum pump) or Air Ejector System removes non-condensable gases from the condenser.
  • 38. Extraction Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor In an extraction turbine, steam is withdrawn from one or more stages, at one or more pressures, for heating, plant process, or feed water heater needs. They are often called "bleeder turbines.“ The steam extraction pressure may or may not be automatically regulated. Regulated extraction permits more steam to flow through the turbine to generate additional electricity during periods of low thermal demand by the CHP system. In utility type steam turbines, there may be several extraction points, each at a different pressure corresponding to a different temperature. The facility’s specific needs for steam and power over time determine the extent to which steam in an extraction turbine is extracted for use in the process.
  • 39. Back-pressure Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor Figure shows the non- condensing turbine (also referred to as a back- pressure turbine) exhausts its entire flow of steam to the industrial process or facility steam mains at conditions close to the process heat requirements.
  • 40. 4. Rotational Speed - Regular - Low-speed - High-speed 5. Inlet steam pressure - High pressure (p>6,5MPa) - Intermediate pressure(2,5MP a <p<6,5MPa) - Low-pressure (p<2,5MPa) Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 41. 8. Application - Power station - Industrial - Transport Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 42. In actual practice, not all of the energy in the steam is converted to useful work. Losses common to all turbines are described below: Loss of working substance. Loss of steam along the shaft through the shaft glands where the shaft penetrates the casing. Work loss. Loss due to mechanical friction between moving parts. Throttling loss. Wherever there is a reduction in steam pressure without a corresponding production of work, such as in a throttle valve. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 43. Leaving loss. The kinetic energy of the steam leaving the last stage blading. This leaving loss can be minimized by lightly loading the last stage blading by increasing the annular exhaust area of the turbine. This is often optimized through economic studies. Windage loss. This is caused by fluid friction as the turbine wheel and blades rotate through the surrounding steam. Friction loss as the steam passes through nozzles and blading. Diaphragm packing loss as the steam passes from one stage to another through the diaphragm packing. Tip leakage loss in reaction turbines as steam passes over the tips of the blades without doing any useful work. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 44. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 45. Rankine cycle with superheat Process 1-2: The working fluid is pumped from low to high pressure. Process 2-3: The high pressure liquid enters a boiler where it is heated at constant pressure by an external heat source to become a dry saturated vapor. Process 3-3': The vapour is superheated. Process 3-4 and 3'-4': The dry saturated vapor expands through a turbine, generating power. This decreases the temperature and pressure of the vapor, and some condensation may occur. Process 4-1: The wet vapor then enters a condenser where it is condensed at a constant pressure to become a saturated liquid. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 46. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 47.  Foundation  Rotor or Shaft  Cylinder or Casing  Blades  Diaphragm  Steam Chest  Coupling  Bearings  Labyrinth Seal  Front Pedestal  TSI  D-EHC (Governor)  MSV (Main Steam Stop Valve)  CV(Control Valve)  IV (Intercept Valve)  CRV (Combined Reheat Valve)  Turbine Turning Gear  Turbine Bypass & Drains  Atmospheric Relief Diaphragm (Rupture Disk)  Lube Oil System  EHC Oil System  Gland Steam System  Condenser  Steam Jet Ejector  Vacuum Breaker Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 48. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 49.  Frame (Base): Supports the stator, rotor and governor pedestal.  Shell: Consists cylinder, casing, nozzles, steam chest & bearing.  Rotor: Consists of low, intermediate, and high pressure stage blades, and possible stub shaft (s) for governor pedestal components, thrust bearing, journal bearings, turning gear & main lube oil system.  Governor Pedestal: Consists of the EHC oil system, turbine speed governor, and protective devices Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 50. An multistage steam turbines are manufactured with solid forged rotor construction. Rotors are precisely machined from solid alloy steel forgings. An integrally forged rotor provides increased reliability particularly for high speed applications. The complete rotor assembly is dynamically balanced at operating speed and over speed tested in a vacuum bunker to ensure safety in operation. High speed balancing can also reduce residual stresses and the effects of blade seating. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 51. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 52. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor The casings of turbine cylinders are of simple construction to minimize any distortion due to temperature changes. They are constructed in two halves (top and bottom) along a horizontal joint so that the cylinder is easily opened for inspection and maintenance. With the top cylinder casing removed the rotor can also be easily withdrawn with out interfering with the alignment of the bearings.
  • 53. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor Most turbines constructed today either have a double or partial double casing on the high pressure (HP) and intermediate pressure (IP) cylinders. This arrangement subjects the outer casing joint flanges, bolts and outer casing glands to lower steam condition. This also makes it possible for reverse flow within the cylinder and greatly reduces fabrication thickness as pressure within the cylinder is distributed across two casings instead of one. This reduced wall thickness also enables the cylinder to respond more rapidly to changes in steam temperature due to the reduced thermal mass.
  • 54. The high-pressure end of the turbine is supported by the steam end bearing housing which is flexibly mounted to allow for axial expansion caused by temperature changes. The exhaust casing is centerline supported on pedestals that maintain perfect unit alignment while permitting lateral expansion. Covers on both the steam end and exhaust end bearing housings and seal housings may be lifted independently of the main casing to provide ready access to such items as the bearings, control components and seals. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 55. HP Turbine Casing IP Turbine Casing LP Turbine Casing Atmosphere Relief Diaphragm HP Turbine Casing CV CV Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 56. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 57. One method of joining the top and bottom halves of the cylinder casing is by using flanges with machined holes. Bolts or studs are insertion into these machined holes to hold the top and bottom halves together. To prevent leakage from the joint between the top flange and the bottom flange the joint faces are accurately machined. A typical bolted flange joint is shown in Figure. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 58. Another method of joining the top and bottom cylinder flanges is by clamps bolted radially around the outer of the cylinder. The outer faces of the flanges are made wedge-shaped so that the tighter the clamps are pulled the greater the pressure on the joint faces. This method of joining top and bottom casings is shown in Figure. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 59. Blade design is extremely important in attaining high turbine reliability and efficiency. A large selection of efficient blade profiles have been developed and proven by extensive field service allowing for optimal blade selection for all conditions of service. Blades are milled from stainless steel within strict specifications for proper strength, damping and corrosion resistant properties. Disk profiles are designed to minimize centrifugal stresses, thermal gradient and blade loading at the disk rims. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 60. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor 09HP Turbine Blades 07 IP Turbine Blades 05 LP Turbine Blades Rotary Blades
  • 61. Partitions between pressure stages in a turbine's casing are called diaphragms. They hold the vane-shaped nozzles and seals between the stages. Usually labyrinth-type seals are used. One-half of the diaphragm is fitted into the top of the casing, the other half into the bottom. Nozzle rings and diaphragms are specifically designed and fabricated to handle the pressure, temperature and volume of the steam, the size of the turbine and the required pressure drop across the stage. The nozzles used in the first stage nozzle ring are cut from stainless steel. Steam passages are then precision milled into these nozzle blocks before they are welded together to form the nozzle ring. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 62. The nozzles in the intermediate pressure stages are formed from profiled stainless steel nozzle sections and inner and outer bands. These are then welded to a circular center section and to an outer ring then precision machined. The low-pressure diaphragms in condensing turbines are made by casting the stainless nozzle sections directly into high-strength cast iron. This design includes a moisture catching provision around the circumference which collects released moisture and removes it from the steam passage. Additional features such as windage shields and inter-stage drains are used as required by stage conditions to minimize erosion. All diaphragms are horizontally split for easy removal and alignment adjustment. Mohammad Shoeb Siddiqui Senior Shift Supervisor Steam Turbine Components And Relative Equipments
  • 63. Mohammad Shoeb Siddiqui Senior Shift Supervisor Steam Turbine Components And Relative Equipments Various root fixing shapes have been developed for turbine blading to suit both construction requirements and conditions under which turbines operate. The most popular types of blade root fixing available are:  Grooves  Straddle  Rivet
  • 64. Mohammad Shoeb Siddiqui Senior Shift Supervisor Steam Turbine Components And Relative Equipments Groove construction The groove type of root fixing fits into a machined grove around the circumference of the rotor wheel or disc. Some examples of typical groove type blade root designs are shown in Figure A while a rotor disc with a machined groove arrangement is shown in Figure B. Blade roots are installed through the closing blade window and then slid around the circumference of the disc into their desired position. The last blade root is installed in the closing blade opening and secured in position by dowel(s).
  • 65. Mohammad Shoeb Siddiqui Senior Shift Supervisor Steam Turbine Components And Relative Equipments Straddle construction Straddle construction is where the blade root fits over the machining on the outer periphery of the rotor wheel or disc. An example of straddle fir-tree blade root construction is shown in Figure A. while the disc peripheral machining is shown in Figure B. Once again with this type of construction the blade roots are installed through the closing blade window slid around the circumference of the disc into position, then the last blade inserted is doweled in the closing blade window location.
  • 66. Mohammad Shoeb Siddiqui Senior Shift Supervisor Steam Turbine Components And Relative Equipments Rivet construction Rivet construction is where the blade root either inserts into a groove or straddles the disc and all blades are doweled into position. Peripheral blade fixing On larger blading where the blade length is relatively long a system of lacing wire or shroud rings are installed to give the blading additional support and reduce vibration. The lacing wire is installed a small distance from the outer ends of the blades while the shoud rings are fitted to tangs on the outer edges of the blades and secured by peening the tangs. A section of blading showing the installation of the lacing wire is shown in Figure A while a section of blading showing shroud ring installation is shown in Figure B.
  • 67. Steam chest: The steam chest, located on the forward, upper half of the HP turbine casing, houses the throttle valve assembly. This is the area of the turbine where main steam first enters the main engine. The throttle valve assembly regulates the amount of steam entering the turbine. After passing through the throttle valve, steam enters the nozzle block. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor Steam Turbine Components And Relative Equipments
  • 68. With multi-cylinder turbines it is necessary to have some method of connecting individual cylinder rotors. It is also a requirement to connect the turbine to the alternator rotor. To achieve these connections we use a device known as a coupling. These couplings must be capable of transmitting heavy loads and in some turbines are required to accommodate for axial expansion and contraction. The types of couplings generally employed in power plants are:  Flexible coupling  Solid shaft coupling Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor Steam Turbine Components And Relative Equipments
  • 69. Flexible couplings Where axial shaft movement is required a flexible coupling is employed and these are either: 1. Sliding claw (or tooth) 2. Flexible connection (between the two flanges) With both of the above flexible couplings it is necessary to have a separate thrust bearing for each shaft to maintain the same relative position between rotor and cylinder casing. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor Steam Turbine Components And Relative Equipments
  • 70. Sliding claw (or tooth) Sliding claw couplings consists of an inner gears or tooth coupling half. The inner half is shrunk onto its respective shaft and secured by keys or driven pins. The outer coupling half; machined in the reverse shape is installed onto the other shaft. The gear or teeth coupling is positioned inside the outer coupling half where it is able to slide back and forth to allow for expansion or contraction. A diagram of a sliding claw coupling prior to the inner claw section being inserted into the outer half is shown in Figure A, while a gear tooth coupling is shown in Figure B. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor Steam Turbine Components And Relative Equipments
  • 71. Flexible connection coupling Flexible connections such as the bibby coupling are constructed in two halves. Each half is shrunk onto their respective shaft and secured with keys or driven pins. The halves are machined with groves parallel or nearly parallel to that of the alignment of the shaft. Flexible spring steel grids are inserted into these machined groves and held in place with an outer cover. This type of coupling is effective in allowing axial expansion and contraction along with the ability to tolerate minor misalignment. A bibby coupling is shown in Figure. The flexible couplings just mentioned are by no means the only flexible couplings available but they are the preferred choice for high load applications. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor Steam Turbine Components And Relative Equipments
  • 72. Solid shaft coupling When shaft movement is not required it is usual to install a solid type coupling. Two flanges are installed onto their respective shafts and then the two flanges are bolted together to form a solid joint as shown in Figure A. Often teeth are machined on the outer rim of these couplings and used as a point for barring the turbine shaft. (more about barring the turbine later). Figure B shows a solid shaft coupling with a barring gear fitted Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor Steam Turbine Components And Relative Equipments
  • 73. Turbine Bearings  Journal Bearing: The turbine rotors are supported by two journal bearings. Both the No.1 and No.2 bearings are of a double-tilting pad type. The bearing metal is divided into six pads which are self-aligned. A center adjustment of these bearings can easily be made with shimmed pads. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 74. Turbine Bearings Journal Bearing Design Data: Bearing # Location Type Nominal dia in inches Nominal effective width in inches 1 HP DTP 15” 8” 2 LP DTP 18” 12” Note; D.T.P stands for Double Tilting Pad Steam Turbine Components And Relative Equipments Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 75. Turbine Bearings DOUBLE TILTING PAD TYPE JOURNAL BEARING Double tilting pad bearing provides maximum stability and freedom from shaft vibration. The tilting-pad design consists generally of six steel pads (shoes) with Babbitt linings on the bearing surface. The pads are installed on the inner of bearing ring, and can move radial and axial direction. Therefore, the pads Move smoothly, and maintain the correct alignment at all conditions. Hook fits in the inner of bearing ring retain the pads, and the pads are prevented from rotating by means of loose-fitting lock pins. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 76. Turbine Bearings TAPERED-LAND THRUST BEARING The thrust bearing is located on the main shaft of the turbine. Independently mounted inside the standard, the thrust bearing absorbs the axial thrust of the turbine and generator rotors, which are connected by a solid coupling. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 77. Turbine Bearings TAPERED-LAND THRUST BEARING This tapered-land thrust bearing consists of two stationary thrust plates and two rotating Thrust collars on the turbine shaft which will provide the front and back faces to the bearing. These plates are supported in a casing so that they may be positioned against the rotating faces of the collars. The thrust collar faces are machined and lapped, producing smooth, parallel surfaces. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 78. Thrust Bearing Thrust Bearing # 1 General Bearing General Bearing Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor Steam Turbine Components And Relative Equipments
  • 79. A labyrinth seal is a type of mechanical seal that provides a tortuous path to help prevent leakage. An example of such a seal is sometimes found within an axle's bearing to help prevent the leakage of the oil lubricating the bearing. A labyrinth seal may be composed of many grooves that press tightly inside another axle, or inside a hole, so that the fluid has to pass through a long and difficult path to escape. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor Steam Turbine Components And Relative Equipments
  • 80. Labyrinth seals are utilized as end gland seals and also inter- stage seals. Stationary labyrinth seals are standard for all multistage turbines and grooves are machined on the rotating part to improve the sealing effect. The leakage steam from the outer glands is generally condensed by the gland condenser. Some leakage steam from the intermediate section of the steam end gland seals can be withdrawn and utilized by re- injecting it into the low-pressure stage or low- pressure steam line. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor Steam Turbine Components And Relative Equipments
  • 81. Turbine front standard supports the No.1 bearing, thrust bearing and the front end of the turbine casing. Front standard is shaped like a box. Upper half of the standard can be disassembled at horizontal flange. A manhole located front of upper half is used oil strainer maintenance. This box is not only the bearing standard but control box which contains some important equipment. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor FRONT STANDARD & TSI Steam Turbine Components And Relative Equipments
  • 82. There are some instruments and button on the outside of the front pedestal cover. These are used for turbine operation and supervision. Some protective devices and speed detectors are installed inside the standard. Inside space of the standard is connected to oil tank and is kept slightly vacuum so that the oil drain or mist inside can not leak out. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor FRONT STANDARD & TSI Steam Turbine Components And Relative Equipments
  • 83. Lubricating oil is supplied from oil pipe which is located left side of front standard and flow out to oil tank through 1ST journal and thrust bearings. Oil strainer is located up stream of bearing. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor FRONT STANDARD & TSI Steam Turbine Components And Relative Equipments
  • 84. Toothed-wheel for speed sensors The turbine rotating speed is sensed by the magnetic pickups faced to the toothed-wheel (96 teeth) installed on the control rotor. The pulse signal is produced when each tooth passes the pickups. The frequency signals from two (2) pickups are converted into digital value proportional to the turbine speed through F/D (Frequency to Digital) converters. Other three (3) sensors are located around toothed-wheel. These sensors are used for trip detector. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor FRONT STANDARD & TSI Steam Turbine Components And Relative Equipments
  • 85. The electromagnetic pickup use for speed detector is fixed facing the tooth face of the speed detecting gear connected directly to the rotor end of the turbine. (Inside of front standard) The turbine speed can be detected as the sine wave frequency signal in proportion to the turbine speed. This frequency signal is converted to an digital signal by means of the F/D converter to become a feedback signal to the speed control circuit. Over speed detector also make frequency signal in proportion to the turbine speed. They face to tooth- wheel on control rotor. Pickup is used eddy current type. Clearance between sensor face and tooth face is different from electromagnetic pickup type. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor FRONT STANDARD & TSI Steam Turbine Components And Relative Equipments
  • 86. Turbine Supervisory Instrumentation (TSI) or Turbine Supervision Equipment (TSE) is a generic term used in the power generation industry. TSI refers to instrumentation systems that specifically perform measurements of critical control parameters on large steam turbine generator trains. The size of the machines can range between 50–1200 MW and their age can often be in excess of 30 years. TSI systems are normally a mandatory requirement. The same technology is employed on other turbine types and in other industries, such as the hydrocarbon- processing sector. Steam Turbine Components And Relative Equipments Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 87. Although the turbine is not readily accessible during operation, the turbine supervisory instrumentation is sufficient to detect any potential malfunction. The turbine supervisory instrumentation includes monitoring of the following: (1) Vibration and eccentricity (2) Thrust bearing wear (3) Exhaust hood temperature and spray pressure (4) Oil system pressures, levels, and temperatures (5) Bearing metal and oil drain temperatures (6) Shell temperature (7) Valve positions (8) Shell and rotor differential expansion (9) Shaft speed, electrical load, and control valve inlet pressure indication (10) Hydrogen temperature, pressure, and purity (11) Stator coolant temperature and conductivity (12) Stator-winding temperature (13) Collector air temperatures (14) Turbine gland sealing pressure (15) Gland steam condenser vacuum (16) Steam chest pressure (17) Seal oil pressure Steam Turbine Components And Relative Equipments Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 88. The use of, and experience with, TSI assists in reducing operating costs of the generation units by: • Reducing Turbine Roll Time: During the run-up and coast-down of large turbines, there are extensive soak periods to ensure stationary and rotating parts thermally expand equally. These periods are usually of a conservative length, but times can be further reduced with continuous and accurate measurement of key expansion clearances (and related parameters) available with TSI systems. • Time Between Overhauls: By using precise TSI measurement information, in an outage, the exact amount of work can be scheduled with reduced risk of unknown problems occurring after the overhaul is completed. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor Steam Turbine Components And Relative Equipments
  • 89. Diagnostic and Troubleshooting The trending of TSI data provides the user with the machine’s basic operating characteristics. Early detection of changes in trended data and comparison to normal conditions allows decisions to be made more quickly and inexpensively. More advanced analysis methods of this same raw data can diagnose problems like mass unbalance, misalignment, loose or broken parts, shaft cracks, seal rubs, and bearing instabilities caused by improper lubrication or bearing design. Early identification of these problems allows for corrections to be made at a time that is convenient to both the work force and system load. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor Steam Turbine Components And Relative Equipments
  • 90. Automatic Shutdown Sometimes unanticipated problems arise quickly, however, TSI has the capability to limit damage to the machine and protect against total destruction or catastrophic failure. Confining damage flagged by vibration can make the difference between a two week outage and three to six months of down time. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor Steam Turbine Components And Relative Equipments TSI system measurements can be broken down into four major categories: Motion Measurements Eddy current (proximity) probes, case mounted velocity (seismic) transducers, shaft riders, and/or accelerometers can be used to monitor vibrations. Monitoring points may include vibration on main turbine generator and exciter, may also be used to measure rotor eccentricity.
  • 91. Position Measurements Eddy current probes, LVDTs and linear/rotary potentiometers can be used to monitor thrust bearing wear, rotor position, casing (shell) expansion, differential expansion and control valve position. Speed Measurements Active or passive electromagnetic or eddy current probes can be used to monitor main turbine speed and acceleration, over-speed detection, zero speed detection. Process Measurements Thermocouples or RTDs can be used to monitor bearing white metal temperature, shell differential temperature, and lube oil temperature. Piezoelectric or strain gauge pressure transducers can be used to measure oil and hydraulic pressures. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor Steam Turbine Components And Relative Equipments
  • 92. Thermocouples for water Induction When water flows into the turbine due to an unexpected accident, there occurs a difference in temperature between the upper half and the lower half of the casing. As a result, (humped effect) phenomenon is generated on the casing, giving great damages to HP and IP casings, rotor blade, and thrust bearing. To detect any flow of water, therefore, thermocouples are provided at several positions of the upper and lower parts of the casing respectively to watch the difference in temperature between the upper and lower parts of the casing. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor Steam Turbine Components And Relative Equipments
  • 93. At the time of cold starting of the turbine, there occurs a difference in temperature between the internal and external surfaces of casing with subsequent generation of thermal stress, which shortens the lives of turbine parts, To control the lives of turbine parts, a thermocouple is provided at each part of the casing for the purpose of carrying out life control for the parts. For the information on the fitting positions, see the thermocouples mounting drawings. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor Steam Turbine Components And Relative Equipments
  • 94. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor Principles Of Governing During operation of a Turbine-Generator Unit the Load carried by the Generator may vary over time. In order to respond to changing System Load demands the amount of steam directed to the Turbine must be varied in proportion to each demand. The function of a governor is to provide rapid automatic response to load variations. STEAM TURBINE SPEED CONTROL
  • 95. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor STEAM TURBINE SPEED CONTROL
  • 96. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor STEAM TURBINE SPEED CONTROL The Speeder Gear of a Turbine Governor In order to maintain the system frequency constant and at the same time allow load variation to occur, it is necessary to be able to compensate for the loss of speed experienced with increasing load and the speed increase which accompanies load rejection. To achieve this a device is fitted in conjunction with the governor which effectively changes the speed-load characteristic of the turbine in such a way that speed effectively becomes independent of load. The device is known as the speeder gear.
  • 97. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor STEAM TURBINE SPEED CONTROL Relays In all but the smallest turbine, it is necessary to use some means of amplifying the power of the governor in order to maintain a small sensing and control device and yet still have the motive force to position large sized throttle valves. The devices used as amplifiers are known as relays. The most common type of relay uses an oil system employing valve and a power piston. There are two types of these relays in use: • Double acting • Single acting
  • 98. System Features Application: D-EHC system can be applied to control, protection and monitoring of steam turbines for various type of power plants including conventional fossil-fired power plants, combined cycle plants, co-generation plants, and atomic power plants. Powerful and reliable controllers: High-speed control with state-of-the-art microprocessor based control system Distributed and hierarchical architecture consists of; System controller, Master controller, Programmable logic device, Valve interface Normal Operation: During Normal Operation, the main stop valves, intermediate stop valves and intercept valves are wide open. Operation of the T-G is under the control of the Electro-Hydraulic Control (EHC) System. The EHC System is comprised of three basic subsystems: the speed control unit, the load control unit, and the flow control unit. The normal function of the EHC System is to generate the position signals for the four main stop valves, four main control valves, and intermediate stop valves and intercept valves. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor Steam Turbine Components And Relative Equipments
  • 99. Improved monitoring and operation ability: Windows-2000¨ based HMI (Human Machine Interface) and IES (Integrated Engineering System) Standard interface (RS232C Modbus, TCP/IP Ethernet, opc, etc.) with external systems Fully automatic turbine startup sequences turbine is automatically started based on start up sequence determined by inlet steam/turbine metal temperature miss-match, which enables optimum operation and longer equipment life. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor Steam Turbine Components And Relative Equipments
  • 100. D-EHC System (Steam Turbine Startup) Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor Auto Start Sequence Manual Start Steam Turbine Components And Relative Equipments
  • 101.  Turbine speed and Load Control  Automatic Turbine Start-up control  Line Speed Matching Control  Full Arc admission (FA)/Partial Arc admission (PA) Transfer, if applicable  Initial Pressure Regulator (IPR)  Power Load Unbalance (PLU)  Turbine Trip Function  Turbine Trip Initiation (Primary overspeed, backup overspeed, EHC failure)  Test Function (Valve Test, Overspeed Trip Test, Back up Overspeed Trip Test)  Control and monitoring function of turbine generator auxiliaries  Extraction Steam Pressure Regulation (if applicable)  Thermal Stress Calculation  TSI (Turbine Supervisory Instruments) monitoring  Back up operation and monitoring at monitor panel of EHC cabinet  Interface with Distributed Control System (DCS) Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor Steam Turbine Components And Relative Equipments
  • 102. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 103. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 104. The main stop valve is located in the main steam piping between the boiler and the outlet piping to turbine control valve chest in turbine casing. The main stop valve has one inlet and two identical outlet pipe connections. Outlet pipes are welded directory. The primary function of the main stop valves is to quickly shut off the steam flow to the turbine under emergency conditions such as failure of the control valves to close on loss of load. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 105. The control valves are arranged into an upper and lower valve group with each group mounted on common chest which is an integral part of the upper and lower turbine outer shells. Each control valve admits steam from the valve chest of its group to an individual nozzle box, after that controlled steam flow into a particular section of the turbine first stage nozzles. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 106. During starting and loading operation without turbine bypass system the intercept valves are operated fully opened for full arc admission starting. They remain fully open during transfer of steam flow control to the control valves, as well as all other periods of normal operation. The other side, when turbine bypass system is available for the starting up and loading. The intercept valves are used to control the steam flow to the intermediate turbine in conjunction with the control valves. After the turbine bypass operation is finished the intercept valves will be fully opened by EHC control system. The primary function of the intercept valve is pre-emergency protection: however, they also trip closed upon actuation of the emergency trip system. The secondary one is to control the steam flow during the starting and loading with turbine bypass system. The reheat stop valve is provided to quickly shut off the steam flow storage in the reheater line to the turbine under emergency condition. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 107. Two combined reheat valves are provided, one in each hot reheat line. Supplying reheat steam to the turbine. As the name implies. The combined valve is actually two valve. The intercept valve and the reheat stop valve, incorporated in one valve casing. Although they utilize a common valve casing, these valves provide entirely different functions. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 108. The motor driven turning gear is mounted on the turbine bearing cap, adjacent to the turbine-generator coupling so as to mesh with a bull gear (spacer disk gear type). Which is bolted between the turbine- generator coupling faces. The primary function of the turning gear is to rotate the turbine-generator shaft slowly and continuously during shutdown periods when rotor temperature changes occur. Turning Gear Driven Motor Turning Gear Driven Chain Turning Gear Turning Gear Oil Supply Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 109. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor When the turbine is shutdown, cooling of its inner elements is continues for many hours. If the rotor is allowed to remain stationary during this cooling period, distortion begins almost immediately. This distortion is caused by the flow of hot vapors to the upper part of the turbine casing, resulting in the upper half of the turbine being at a higher temperature than the lower half. The parts do not return to their normal position until the turbine has cooled to the point where both the upper and lower halves are at approximately the same temperature.
  • 110. Water induction can happen at any time; however the most common situations are during transients such as start up, shut down and load changes. In figure illustrates the percentage of times various events contribute to water induction for a conventional steam cycle. It is interesting that only 18 percent of water induction incidents occur when the unit is at load. Turbine drains are necessary to avoid slugging nozzles and blades inside the turbine with condensate on start-up; this can break these components from impact. The blades were designed to handle steam, not water. Turbine casing drains remove the condensate from the turbine casing during warm-up, securing, maneuvering and other low flow conditions. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 111. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor Steam Turbine Components And Relative Equipments Turbine Water Induction Protection (TWIP) Turbine Water Induction Protection, often abbreviated as TWIP, is the broad category of equipment that is installed to prevent water damage to steam turbines. Any connection to the turbine is a potential source of water either by induction from external equipment or by accumulation of condensed steam. Steam turbine damage by water induction is a costly economic, safety and reliability concern. The American Society of Mechanical Engineers (ASME) formed a committee to address this issue, and the first standard was issued in 1972. ASME publication ASME TDP-1-1998 is titled “Recommended Practices for the prevention of Water Damage to Steam Turbines used for Electric Power Generation”. This practice covers the design, operation, inspection, testing, and maintenance of these systems. TWIP equipment is installed in the following power
  • 112. In Figure shows a typical drain pot with redundant level elements. This configuration is typically used in "high risk" areas. One change in this standard that is shown is the level sensing device, which is labeled as a level element (LE). Drains should be installed at each low point in the motive steam piping. Drain Pots are recommended at the following locations to enhance condensate collection: Cold reheat line at first low point downstream of the steam turbine exhaust. (This application requires redundant level elements.) Motive steam lines that operate (admit steam to the steam turbine continuously) with less than 100 F (56 C) superheat unless a continuous drain has been provided. (This application requires redundant level elements.) Motive steam lines with attemperators - e.g. attemperator in HP steam line. The drain pot should be between the attemperator and the steam turbine. (This application requires redundant level Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 113. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor Steam Turbine Components And Relative Equipments Turbine Water Induction Protection (TWIP) 1. Main steam system, piping and drains 6. Turbine drain systems 2. Reheat steam systems, piping and drains 7. Turbine steam seal system, piping and drains 3. Reheat attemperating system 8. Main steam attemperator sprays 4. Turbine extraction systems, piping and drains 9. Start-up systems 5. Feedwater heaters, piping and drains 10. Condenser steam and water dumps. TWIP equipment is installed in the following power plant systems: Avoid discharging high-energy bypass steam into the area between the condenser hotwell and the tube bundle Locate the curtain spray and bypass sprayer a safe distance from the condenser tube bundles to allow a sufficient reduction in kinetic energy, so that high-energy steam does not reach areas above and below the tube bundles and cause a recirculation backflow with entrained water toward the turbine. Determine an incidence angle of high-energy steam jets that will avoid reflected velocity vectors toward the turbine exhaust.
  • 114. Water induction damage Water induction can damage steam turbines in several ways. The damage can be caused by the impact of large slugs of water or by the quenching effect of cold water on hot metal. The severity of water damage can vary from minor seal rubs all the way to catastrophic damage to the turbine. Generally, water damage falls into the following categories: Thrust bearing failure Damaged blades Thermal cracking Rub damage Permanent warping distortion Secondary effects Secondary effects include items such as seal packing ring damage, pipe hangar and support damage, damage to instrumentation and controls, etc. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 115. Sources of water induction Water can be inducted into a steam turbine from several sources. The following are some of the most common sources of water: Motive steam systems Steam attemperation systems Turbine extraction/admission systems Feedwater heaters Turbine drain system Turbine steam seal system Start-up systems Condenser steam and water dumps (steam bypass) Steam generator sources Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 116. Turbine bypass systems should be provided with the same level of protection as motive steam piping. These should include drains and drain pots (if applicable) with power-operated drain valves. Attemperators in bypass systems that discharge to the cold reheat system (or any other line connected back to the steam turbine) should be designed to the same requirements on motive steam system attemperators. Non-return valves should be provided in the cold reheat system to prevent the reverse flow of bypass steam into the steam turbine. Designers should carefully consider the location, design and orientation of large steam dumps (such as turbine bypasses) into the condenser. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor Turbine Bypass system
  • 117. The atmospheric relief diaphragm is a safety feature which protects the exhaust hood and condenser against excessive steam pressure in case the condenser water for any reason is lost. The device consists of hard rolled silver bearing copper sheet of sufficient area to pass full throttle steam flow at a safe protective pressure. In normal operation of the turbine with proper vacuum conditions, the diaphragm is dished inward against the supporting grid by atmospheric pressure should the vacuum conditions fail for any reason and the internal exhaust hood pressure raise to approximately 5 psig, it would force the diaphragm outward against the cutting knife. The diaphragm would be cut free as a disk relieving the exhaust pressure to atmosphere. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor Steam Turbine Components And Relative Equipments
  • 118. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor Steam Turbine Components And Relative Equipments
  • 119. Steam Turbine Components And Relative Equipments Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 120. Function The function of lubrication is to interpose a film of lubricant such as grease or oil between the moving surfaces in a bearing. Lubrication reduces friction, minimizes wear, provides cooling and excludes water and contaminants from bearing components. The protection of rotating heavy machinery depends greatly on the effective operation and supervision of lubricating oil systems and bearings. Steam Turbine Components And Relative Equipments Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 121. Steam Turbine Components And Relative Equipments Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor Establishment of Oil Film Oil lubricated bearings rely on the physical separation of the two bearing surfaces by a thin film or wedge of oil. In order to establish and maintain this oil film the following conditions must be established. 1) There must be relative motion between the two beari ng surfaces to build up sufficient pressure within the oil to prevent the film breaking down. 2) There must be an uninterrupted supply of oil available to the bearing. 3) The bearing surfaces must not be parallel and need a narrow angle between them. This is to enable the oil to be shaped into a thin wedge tapering off in the direction of the motion
  • 122. Steam Turbine Components And Relative Equipments Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor Oil Film Dynamics 1). With the shaft at rest the journal lies in the bottom of the bearing. The weight of the shaft tends to squeeze the oil out of the bearing so that metal to metal contact occurs. 2). As the shaft commences to rotate the first action of the journal is to climb up the bearing wall until it begins to slip and some metal to metal contact occurs. 3) As the shaft continues to increase in speed the oil is dragged around by virtue of viscosity until it forms a thin oil wedge. it's
  • 123. Steam Turbine Components And Relative Equipments Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor Oil Film Dynamics 4) With the shaft now at final or rated speed the increased pumping action on the oil increases the journal internal oil pressure. This displaces the journal from the central position in the bearing enabling an ideal oil wedge to be created.
  • 124. Steam Turbine Components And Relative Equipments Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor Components of a Turbine Lubricating Oil System • Main Oil Tank • Oil Purification Systems • Oil Pumps • Oil Coolers • Strainers / Filters • Instrumentation • Jacking Oil Pumps • Hydraulic Accumulator
  • 125. Steam Turbine Components And Relative Equipments Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 126. Prepared by Mohammad Shoeb Siddiqui Steam Turbine Components And Relative Equipments The purpose of the gland steam system is to reduce steam leakage to a minimum and to prevent air ingress. Or Function of the gland sealing system falls into two categories: • Seal the turbine glands under all operating conditions • Extract leak-off steam from the turbine glands.
  • 127. Prepared by Mohammad Shoeb Siddiqui Steam Turbine Components And Relative Equipments Steam leakage leads to the requirement for increased make up; this increases the load on the feed and boiler water treatment chemicals and to a deterioration of the working environment surrounding the power plant. Air ingress leads to a loss of vacuum and hence reduction in plant efficiency, and causes problems of thermal stressing around the gland as well as increases oxygen content of the exhaust steam.
  • 128. Prepared by Mohammad Shoeb Siddiqui Steam Turbine Components And Relative Equipments Gland Steam Condenser The gland steam condenser is cooled by the condensate extracted from the main condenser and so acting as a feed heater. The gland steam often shares its condenser with the air ejector reducing the cost of having two units. A fan is fitted to induce a flow through the system without incurring a negative pressure in the final pocket as this would allow the ingress of air. This is ensured by the fitting on valves to the exhaust line from the glands so enabling the back pressure to be set.
  • 129. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor A surface condenser is a commonly used term for a water- cooled shell and tube heat exchanger installed on the exhaust steam from a steam turbine in thermal power stations. These condensers are heat exchangers which convert steam from its gaseous to its liquid state at a pressure below atmospheric pressure. Where cooling water is in short supply, an air-cooled condenser is often used. An air- cooled condenser is however significantly more expensive and cannot achieve as low a steam turbine exhaust pressure as a water- cooled surface condenser.
  • 130. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor For water-cooled surface condensers, the shell's internal vacuum is most commonly supplied by and maintained by an external steam jet ejector system. Such an ejector system uses steam as the motive fluid to remove any non-condensable gases that may be present in the surface condenser. The Venturi effect, which is a particular case of Bernoulli's principle, applies to the operation of steam jet ejectors. Motor driven mechanical vacuum pumps, such as the liquid ring type, are also popular for this service.
  • 131. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 132. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor The purpose of a Vacuum Breaker Valve is to quickly allow air into the vacuum space of the condenser and low pressure turbine exhaust hood. The vacuum breaker valve is usually located on the steam turbine or the condenser shell/transition. A vacuum breaker valve is typically operable by a controller responsive to losses of load on the steam turbine. Once opened, the vacuum breaker valve will allow air into the steam space to quickly reduce the existing vacuum and hence reduce the acceleration of the steam turbine upon loss of load by the generator.
  • 133. (1) Emergency trip pushbutton in control room (2) Boiler Trip, Turbine trip (3) Low condenser vacuum (4) Low lube oil pressure (5) LP turbine exhaust hood high temperature (6) Thrust bearing wear (7) Emergency trip at front standard (8) Low hydraulic fluid pressure (9) Loss of EHC (10) Excessive turbine shaft vibration (11) Loss of two speed signals - either Normal Speed Control or Emergency Over speed Trip (12) Over Speed Trip 1 (13) Over Speed Trip 2 Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 134. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor
  • 135. Prepared by Mohammad Shoeb Siddiqui Senior Shift Supervisor Saba Power Plant Pakistan shoeb.siddiqui@sabapower.com shoeb_siddiqui@hotmail.com shoeb_siddiquipk@yahoo.com