Main components of steam turbine: Stationary components: Almost all stationary parts are two halves. Diaphragm: Partitions between pressure stages in a turbine casing are called diaphragms. They hold the vaneshaped nozzles and seals between the stages. Usually labyrinth-type seals are used. One-half of a diaphragm is fitted into the top of the casing, the other half into the bottom as in Fig. and Fig. . The interstage diaphragms are located in grooves in the casing accurately Fig. Top Diaphragm and bottom diaphragm from Michigan State University power plant [9] Fig. Two Diaphragm halves Steam nozzles: Steam nozzles are installed on the peripheral of the diaphragms. There are admission Nozzles and interstage Nozzles their function is to accelerate the steam flow to high velocity by expanding it to low pressure. Located in the casing are the steam-admission nozzles which are cut into a solid block of bronze or alloy steel, depending on steam conditions. Nozzles are so proportioned as to be contributory to efficient operation and are made of corrosion- and erosion-resistant materials. This nozzle block is bolted to the steam chest, which in turn is bolted to the base of the turbine casing. The entire assembly of nozzles for one stage is called a diaphragm. The casing ) Fig. The cylinder of an impulse turbine is frequently referred to as the wheel casing.assembly with the stationary blading or nozzles is referred to as the turbine cylinder. . The rotor is statically and dynamically balanced to ensure smooth operation throughout its operating range. The shaft is rust protected at the gland zones by a sprayed coating of stainless steel. wheel and Shrouds [ ] Rotating parts: Rotors for small turbines consist of a machined-steel disk shrunk and keyed onto a heavy steel shaft. buckets. (See Fig. Nozzles. diaphragm. Thrust-bearing collar and oil impeller may be carried on a stub shaft bolted to the end of the rotor. Rotors for large turbines are formed from a single piece forging. (Fig. Rotors are machined. they are dynamically balanced and tested. Forgings of this type are carefully heat treated and must conform to specifications. including both the journals and the coupling flange. and after the blades are in place. ) . . The ends of the blades are made to fit these dovetail channels.) 1. (Siemens Westinghouse Power Corp. On the circumference of the wheels are located blades or buckets to receive the steam and convert it into useful work.Fig. (See Fig. ) Fig.4. Rotor of a turbine in Michigan State University power plant ] . (c) rotor for noncondensing single-extraction turbine. The rims of the wheels have dovetail channels for receiving the blades. (d) rotor for condensing doubleextraction turbine. (b) rotor for non-condensing turbine. Rotors for various types of turbines (a) rotor for condensing turbine.2.1 Wheel: A simple turbine consists of a shaft on which is mounted one or more wheels (discs). There are many blades in each turbine stage. or circumference. Figure 1. as well as its reliable performance. are a schematic showing how the blade size varies as the steam flows through the turbine. it expands and its volume increases. of each wheel located on the shaft are blades where steam is directed and converted into work by rotation of the shaft (Fig.29). ). Blades not only must handle the steam velocity and temperature but also must be able to handle the centrifugal force caused by the high speed of the turbine. (Fig. A vibration of the moving blades could cause contact with the stationary components.Turbine blades: On the outer portion.1. as the steam flows through the turbine.31 and Figure 1. and larger turbines have more stages. depends on the design and construction of the blades. Vibration has to be monitored continuously and corrected immediately when required. Any vibration in a turbine is significant because there is little clearance between the moving blades and the stationary portions on the casing. This increased volume is handled by having longer blades and thus a larger casing for each stage of the turbine. The turbine efficiency. .1. which would result in severe damage to the turbine. Fig. Turbine blades of a turbine in Michigan State University power plant ] . 1. The tips of the blades pass through holes in the shroud ring.Fig A Turbine blade Shroud ring: It is placed around the blades outer ends (Fig.26). The . The function of shrouds: a. Confine the steam to the blade path and prevent steam axial flow. extra lacing is sometimes used.ends are then welded so that they are held securely by the ring. a McGraw-Hill publication. When the blades are very long.) . Double-flow low-pressure turbine showing variation in blade size. Stiffen the blades against vibration b. Fig. (Power Magazine. 1. The one at the lowpressure end of a condensing turbine must be packed to prevent the leakage of air into the condenser.1: Shrouds 2: Diaphragm 3: Nozzles 4: wheel 5: Blades 6: Shaft Fig.3 . Turbine components Packing: (steam Sealing) The shaft at the high-pressure end of the turbine must be packed to prevent leakage of steam from the turbine. Types of packing: .3 ) and Interstage steam sealing Fig. There are external steam sealing (high pressure sealing at the boiler side and low pressure sealing at the condenser side Fig.1. Carbon packing.Labyrinth packing. Water seals. Fig. Flexible metallic packing. external steam sealing [9] . It gets its name from the fact that it is so constructed that steam in leaking must follow a winding path and change its direction many times. This device consists of a drum that turns with the shaft and is grooved on the outside. The drum turns inside a stationary cylinder . Interstage steam sealing Labyrinth packing Labyrinth packing is used widely in steam turbine practice.Fig. 3 ). Steam in leaking past the packing is subjected to a throttling action. This action produces a reduction in pressure with each groove that the steam passes.) . (a) Water-sealed glands and labyrinth seals as used on the high-pressure end of condensing turbines. There are many different types of labyrinth packing. (Siemens Westinghouse Power Corp. The amount of leakage past the packing depends on the clearance between the stationary and the rotating elements.that is grooved on the inside (Fig. Fig1. The steam that leaks past the labyrinth packing is piped to some low-pressure system or to a low stage on the turbine. Fig. (b) Labyrinth-type gland as used on no condensing turbines. The amount of clearance necessary depends on the type of equipment. steam temperatures. and general service conditions. but the general principle involved is the same for all. Water seals are used in connection with labyrinth packing to prevent the steam that passes the packing from leaking into the turbine room. The illustrated designs are typical of those found on operating turbines. Seal designs are continuously being improved to minimize steam leakage and thus improve turbine performance. Each labyrinth consists of a multiplicity of seals to minimize steam leakage. Figure1. They are used singly or in combination. In this case the leakage to the condenser is water instead of air. Such a seal is also used on the low-pressure end of condensing turbines. forming a seal.3 shows water-sealed glands and labyrinth seals as used on the high-pressure end of condensing turbines. The runner rotates in a chamber in the gland casing. In some designs. The glands are usually supplied with condensate water for sealing to prevent contamination of the condensate water. . water is supplied to the chamber at a pressure of 3 to 8 psi and is thrown out against the sides by the runner.Water seals: A water-packed gland consists of a centrifugalpump runner attached to the turbine shaft. depending on the service required. The seal rings are spring backed and made of material that permits close running clearances with safety. Carbon packing: Carbon packing is composed of rings of carbon held against the shaft by means of springs. Steam seals are used in connection with carbon packing. a slight leak is desirable because a small amount of steam keeps the packing lubricated. except that care must be exercised in adjusting.002 in of clearance per inch of shaft diameter. Due to the high speed at . because if there is a slight packing leak. In operating a turbine equipped with carbon packing. When adjustments are made while the turbine is cold. The width of the groove in the packing casing should exceed the axial thickness of the packing ring by about 0. The application is the same as when this packing is used for other purposes. Flexible metallic packing: It is used to pack small singlestage turbines operating at low backpressure.001 to 0. carbon packing should have from 0. In most cases the pressure in the casing of these turbines is only slightly above atmospheric pressure. This is essential when carbon packing is used on the low-pressure end of condensing turbines. Each ring fits into a separate groove in the gland casing.005 in. steam instead of air will leak into the condenser. Carbon packing is sometimes used to pack the diaphragms of impulse turbines. even a small amount of friction will cause overheating. Utility turbines use journal bearing instead of ball or roller bearings. . Bearings: Bearings support and/or properly position the turbine rotor with respect to the stationary turbine parts. Journal bearings have a smooth surface of a soft material called Babbitt. The bearings are fed with oil as the rotor turns. Types of bearings: Journal Bearings.1 Journal Bearing: Their main function is to the journal or radial bearings support the weight of the rotor and position it radially. Figure 1. Thrust Bearings. it produces a pumping action that builds up pressure and a film of oil between the journal surface and the Babbitt so that in normal operation the surfaces never touch.which the shaft operates. .36 shows the pressure distribution of the oil in the bearing. The clearance between the collar and the shoes is small. and steam pressure is .Fig. and ) consists of a collar rigidly attached to the turbine shaft rotating between two Babbittlined shoes. Formation of Oil Film in Journal Bearing Thrust Bearing: The thrust bearing absorbs axial forces on the rotor and positions it axially with respect to the stationary turbine parts. The thrust bearing (see Figs. The piston is attached to the spindle. The bearing is lubricated by circulating oil to all its moving parts. the collar comes into contact with the shoes. Axial position of the bearing and turbine rotor may be adjusted by liners. (The one shown in Fig. ) is used when a large thrust load must be carried to maintain the proper axial position in the turbine cylinder. The Kingsbury thrust bearing (Fig. The impulse turbine does not require as large a thrust bearing as the reaction turbine because there is little or no . The difference in pressure produces a force that balances the thrust exerted on the rotating blades. With this arrangement. If the shaft starts to move in either direction. Almost 10 times as much pressure per square inch can be carried on the Kingsbury-type bearing as on the ordinary thrust bearing. on each end of the bearing. the pressure is distributed equally not only between the different segments but also on the individual segments. 1. and the shaft is held in proper position. The openings between the segments permit the oil to enter the bearing surfaces.) The thrust collar is the same as that used in the common type of thrust bearing.37 is a combination of the Kingsbury and collar types. Larger thrust bearings have several collars on the shaft and a corresponding number of stationary shoes. The thrust shoes are made up of segments that are individually pivoted. located at the retainer rings.exerted on one side and atmospheric pressure is exerted on the other side. These conditions make necessary some method of cooling. Reaction turbines that do not have some method of balancing the force caused by the drop in pressure in the rotating blades must be equipped with large thrust bearings.pressure drop through the rotating blades. In some cases the bearings are cooled by water jacketing. the thrust bearing must be used to ensure proper clearance between the stationary and rotating elements. Turbine bearings are subjected to very severe service and require careful attention on the part of the operator. . in others the oil is circulated through a cooler. Most turbines operate at high speed (3600 rpm) and are subjected to the heat generated in the bearing itself as well as that received from the hightemperature steam. However. Fig. Main and thrust bearings: (a) main bearing. (b) section of thrust bearing and housing.) . (c) thrust bearing cage in place. (Siemens Westinghouse Power Corp. support the rotor bearings and to have internal surfaces that will efficiently assist in the flow of steam through the turbine.1. . Turbine thrust end showing balance piston and thrust bearing. The inner shells in turn support and position the other internals. The casing is divided into two halves upper casing and lower casing Fig. The HP/IP turbine always has shells or castings. The inner shells are supported and positioned within the outer shell.Casing: Casings are steel castings whose purpose is to Fig. there are two shells used to split up the pressure and temperature change. The casing also supports the stationary blades and nozzles for all stages and also it keeps the steam in the turbine and the air out. When steam pressures and temperatures are high enough.39. The shells have bolted joints at the horizontal centerline to permit assembly of the internals. In operation.diaphragms and labyrinth seals. and so is under a partial vacuum in operation. The low pressure turbine always has inner and outer shells or casings. usually at the end of turbine. . Shells are most common in smaller and older units and casings on larger newer units. The exhaust hood is connected directly to the condenser. the shells are covered with insulation to prevent heat loss. The outer shell or casing prevents air from entering the turbine exhaust and condenser and directs the steam from the turbine exhaust to the condenser. There is a safety device (rapture disc) in the exhaust hood to prevent excessive pressure buildup if the condenser loses its vacuum. DC auxiliary pump. 1. Main oil pump. . Hydraulically driven pump. AC auxiliary pump.Fig.8 Oil pumps: To pump the lubricating oil to the bearings. Steam driven pump.).39 Single-casing condensing turbine for approximately35-MW output. (Siemens Westinghouse Power Corp.1. . Temperature indicators. Support all measuring equipments (Pressure indicators. It contains the inlet control valves and the admission nozzles Fig. Also it is not insulated. Speed indicators. Steam chest (Nozzle box): In high-temperature turbines these components are separate from the main turbine structure.Front standard: It is an extension to the turbine connected to it through a key.1.. the steam chest is usually mounted directly on the casing. speed governor. . . over speed trip and thrust wear detector). In smaller units.). The function of the front standard : Support all control systems (Main oil pump. 4 shows another design. (Siemens Westinghouse Power Corp. .1 Turbine steam admission section.) . and the illustration identifies the major components. governor valve. including the steam inlet.1. ] The steam chest and valve assembly shown in Fig. and valve actuators. the throttle valve.Fig. 1. Regardless of whether or not a hand valve is provided. the steam is made to pass through the governor-controlled admission valve contained in the steam chest.Fig. Single-seated valves are used.4 ) is cast integrally with the cylinder cover with a cored passage from each valve to a nozzle group. and an operating hand valve that is used for manual adjustment to obtain maximum efficiency. (Siemens Westinghouse Power Corp. arranged in parallel within the steam chest and surrounded by steam at throttle pressure. The . a strainer. It contains a governor valve. The multi valve steam chest (Fig.).1. [1] The steam chest is bolted to the base and is made of iron or steel. since there are numerous designs with different features that vary between manufacturers. Turbine steam chest and valve assembly. These are only typical illustrations of a small turbine design. ) Turning gear: If a turbine is shut down and the rotor was allowed to rest in one position then due to unequal heating the spindle bends. Simplified steam chest with multiple valves. with an unbalanced force tending to close the valves. Fig. For these reasons most large steam turbines are provided with motor driven gear to turn the rotor slowly while the unit is out of service Fig.1.44 . 1. (Siemens Westinghouse Power Corp.1. and Fig.4 . opening the valves in sequence. vibration may occur when the turbine is started again. If the turbine is a large one.governor mechanism raises and lowers the valve-lift bar in a horizontal plane. Rotates the turbine rotor at low speed (20-30 rpm) before starting up. Decreases the starting torque. Turning gear of a steam turbine at Michigan State University power plant ] .The function of turning gear: Rotates the turbine rotor after shutdown at low speed. Fig.1. Simplified Turning Gear .1.Fig.
Report "56018305 Main Components of Steam Turbine"