STEAM TURBINE Project Training Report

BHARAT HEAVY ELECTRICALS LIMITED RANIPUR,HARIDWAR

I hereby certify that Mr. ABCD efg, a student of XYZ has undergone practical training from 02-06-2010 to 02-07-2010 in the organization. His field of training was General Awareness In Steam Turbine Manufacturing. His performance and condusct during the above training period was found Very Good.This training imparted is under the curriculum of the Institute of Study.

iaj Dated-02-07-2010 Training

Incharge/Vocational

ACKNOWLEDGEMENT I am highly grateful to Mr. ________________), Badarpur, for providing this opportunity to carry out 1 month industrial training at Bharat Heavy Electrical Limited(BHEL),Haridwar.

I would also like to express a deep sense of gratitude and thanks profusely to Mr. _______, Incharge of vocational training at BHEL, without the wise counsel and able guidance, it would have been impossible to complete the report in this manner.

Finally,I am indebted to all whosoever have contributed in this report and friendly stay at Bhart Heavy Electricals Limited(BHEL).

_______ _________ ______

STEAM TURBINE

A steam turbine works on the principle of conversion of High pressure & temperature steam into high Kinetic energy , thereby giving torque to a moving rotor.

For above energy conversion there is requirement of converging /ConvergingDiverging Sections

Such above requirement is built up in the space between two consecutive blades of fixed and moving blades rows.

Types Of Steam Turbine IMPULSE TURBINE = In a stage of Impulse turbine the

pressure/Enthalpy drop takes place only in Fixed blades and not in the moving blades REACTION TURBINE = In a stage of Reaction Turbine the Pressure/enthalpy drop takes place in both the fixed and moving blades.

DEGREE OF REACTION=( Heat drop in Moving stage) ( Heat drop in moving blade + Heat drop in fixed blade) In impulse stage ,degree of reaction is O Single stage impulse turbine is called as De-laval Turbine. Series of impulse stages is called as Rateau Turbine Double Stage Velocity Compounded impulse turbine is called as Curtis Stages 50% Reaction turbine is called as Parson Turbine Practically the degree of reaction of a stage can be 0 - 60% over the different stages of a turbine

Velocity Compounded Turbines -- Here the High temperature, Pressure Steam is expanded in a single row of fixed blades into very high velocity which is then fed to 2 or 3 rows of moving blades with one each guide/turning row placed in between the two moving stages. Pressure compounding Turbines-- Here the pressure is dropped in stages and employs low velocity of Steam in each stage. Each stage consists of Fixed blade( nozzles) and moving blades

.

Losses In Steam Turbine Friction losses Leakage losses Windage loss( More in Rotors having Discs) Exit Velocity loss Incidence and Exit loss Secondary loss Loss due to wetness Loss at theBearings(appx 0.3% of total output)

Main Losses In Steam Turbine FRICTION LOSS-- It is more in Impulse turbines than Reaction Turbines,because impulse turbines uses high velocity of steam and further the flow in the moving blades of the Reaction turbines is accelerating which leads to better and smooth flow(Turbulent flow gets converted to Laminar flow) LEAKAGE LOSS-- It is more in Reaction turbines than Impulse turbines because

there is Pressure difference across the moving stage of reaction turbines which leads to the Leakages. In Impulse turbine such condition is not there.

Leakage loss predominates over friction losses in the High Pressure end of the Turbine Friction Losses predominates over the Leakage's Loss in the Low Pressure end of the Turbine. It is observed that the Efficiency of The IP Turbine is the maximum followed by The HP and LP Turbine .

LMZ Turbines are more impulse in nature KWU Turbines are more reactive in nature Sparing Rateau and Curtis stages, all other stages of turbine is a mixture of Impulse and Reaction with varying degree of reaction. Pressure/Enthalpy drop is more in Impulse stage than in reaction. Comparatively Reaction Blade is more efficient than the Impulse blade. Impulse turbine requires fewer no. of stages than reaction turbine for same condition of steam and power requirement.

Modifiations In The Blades In Terms Of Efficiency T2

It is comparatively flat blade with thinner inlet

T4

It is More Curved and thicker inlet

Tx

More Curved, thicker inlet but thinner outlet

3DS

Three Dimensional with reduction in secondary losses

Steam Turbine Types In general, there are three types of steam turbines Straight condensing turbines Back-pressure and topping turbines Extraction turbines

Steam Turbine Pressure Classifications Turbines are also classified by the pressure of the steam, which is supplied to the casings. •

A high pressure (HP) turbine

•

An intermediate pressure (IP) turbine A low pressure (LP) turbine

STEAM TURBINE(ST) The steam turbine (ST) type ALSTOM DKYZ2-1N41 is a two-casing, triple pressure reheat, condensing steam turbine. The first casing consists of the HP turbine and the second casing of the IP and LP turbine. The two turbine shafts are coupled rigidly together. HP live steam enters the HP turbine through one stop and one control valve and is expanded to reheat pressure. The cold reheat steam is mixed with the IP steam generated in the HRSG and reheated in the reheater section. The hot reheat steam is admitted to the IP turbine section via two IP turbine admissions, both equipped with one stop and one control valve. At the IP turbine exhaust the steam is led back on the outside of the IP turbine inner casing towards the LP turbine inlet. Between the IP turbine exhaust and the LP turbine inlet, the additional LP steam is admitted through one stop valve and one control valve. In the LP turbine, the steam expands to exhaust pressure and then finally enters the water cooled condenser.

Major Components Of Steam Turbine

The main components of ALSTOM steam turbines are: Casings Blading Blade carriers with stationary blades Welded disc rotor with rotating blades Dummy piston Rotor coupling Gland seals Bearings Stop and control valves Drain lines Rupture diaphragm (for condensing turbines only)

CASINGS Turbine casings are pressure vessels which contain the steam so that it can perform work by causing rotation of the turbine shaft. The type and size of casing materials are determined primarily by the steam pressure and temperature conditions . Components mounted in the casing are the blade carriers, turbine shaft and shaft seals. Blade carriers hold and maintain the stationary blades in place. The turbine shaft and rotating blades provide the torque to rotate the generator shaft. The mechanical energy conversion takes place across the stationary and rotating blades.

Shaft seals provide sealing between the casing and shaft. They prevent HP steam from leaking out and air from entering into the LP turbine, which is under vacuum.

HP Casing HP turbine casings are of double design type, based on the steam pressure and temperature at which the turbine will operate and the application for which the turbine was designed. In the steam inlet plane the inner casing is axially fixed to the outer casing at the level of the flange. The inner casing is also supported laterally by sliding keys at the flange level. At the steam inlet end, centering is achieved by keys located in the upper and lower parts. At the exhaust end, centering is accomplished by a centering bolt. The outer and inner casing is made of cast steel. Pre-stressed bolts hold the upper and lower casings together at the center line. The flange design is such that it ensures complete tightness of the joint without the need for sealing materials.

Exhaust Casing The LP exhaust casing can be of cast or welded fabrication. Depending on the design and application it may be bolted to the HP casing at the vertical flange or it may be totally separate.

BLADING

Turbine blades convert the thermal energy of heat, pressure and velocity into mechanical energy, which is then supplied to the generator via the rotor. Each stage consists of stationary and rotating blades. There are basically two types of blade designs in use today, impulse and reaction. Figure 2 shows the differences between them.

Reaction Blading In the impulse design, theoretically all the pressure drop is across the stationary blading and essentially none across the rotating blades. This design is characterized by a long, slender rotor with diaphragms, which are used for sealing. In the reaction design, there is an equal pressure drop across both the stationary and rotating blades, which leads to very similar blade profiles. As shown in Figure 5, the reaction design is characterized by a drum type rotor. Since there is a pressure drop across the rotating blades, a thrust is developed which must be compensated either by a dummy or balance piston (Paragraph 2.5) or a modified steam path layout. Generally, the same blade profile is used for the entire turbine with the exception of the control stage and the last stages of the LP turbine. Blade heights vary to match steam conditions throughout the turbine. Both stationary and rotating blades are made from pieces of solid material. The rotating blade is an integral unit consisting of the root, blade profile and shroud. Ridges are machined into the outside diameter of the shroud, which is used to increase efficiency. Together with sharp-tipped, caulked-in sealing strips on the casing, the ridges form a stepped labyrinth. Thus, small blade clearances are achieved without affecting reliable operation. Axial spaces between the strips and casing take into account relative expansion between the two components. All HP and IP rotating blades have rhombic roots which fit into circumferential grooves in the rotor. A complete blade row with no opening gates or special blades is obtained by inserting spacers between the blade roots and using a 3-piece locking spacer to complete the row. A closed shroud ring is achieved by introducing a slight torsional pre-tensioning of the blades during assembly. Depending on the degree of stress, rotating blades have either 2 or 4 root serrations to transmit the centrifugal forces to

the rotor. The stationary blades of the HP turbine also have rhombic roots, held in circumferential grooves by means of a shoulder on the inlet side.

Impulse Blading Impulse type moving blades (for H.P Turbine) are machined from solid bar and the roots and spacers formed with the blade . Tangs are left at the tips of the blades so that when fitted imposition in the wheel shrouding an be attached. Impulse Type Fixed Blading , The fixed blading in an impulse turbine takes the form of nozzles mounted in diaphragms. The diaphragms is made in two halves, one half being fixed to the upper half of the cylinder and the other half diaphragm to the lower half on the cylinder.

LP Blading LP blading, which is a mixture of impulse and reaction blading, operates in a slightly different environment. Steam passing through this section on its way to the condenser, expands from superheated steam to the point of saturation. Wet steam or droplets of water form, which can affect the blading. To prevent blading erosion, the leading edges of the blades are induction hardened. The long, last-stage blades of condensing turbines are drop-forged. Due to the length of this blading, additional stresses caused by centrifugal forces can occur. Therefore, the attachment of the blade to the rotor may be of rhombic or fir-tree design.

Dummy(Balance) Piston The design of reaction blading results in a pressure drop across both stationary and rotating blades. This means that a thrust force is applied to the rotor in the direction of steam flow. The most common method to reduce this force is to alternate the flow direction in the different stages (HP, IP, LP) and to use a dummy or balance piston. The diameter of this piston is calculated as to minimize the force. This force varies with the different operation data (MW output). It is transmitted via the axial bearing to the casing, and from there to the foundation.

Rotor flange coupling To be able to separate the turbines into smaller units (i.e. gas turbine, steam turbine and generator) each rotor is equipped with a coupling. Couplings are introduced to increase the ability for individual overhaul and transport. Coupling flanges have honed bores into which coupling bolts with expansion sleeves are screwed. During operation, torque is transmitted by the shearing force of the bolts and sleeves. At the same time, the radially pretensioned sleeves center the coupling halves so they do not slip, even in cases of electrical disturbances with high transient loads. We differentiate between rigid and flexible couplings. In the case of single shaft combined cycle power plants both designs are integrated to adapt to the special need. The generator is located in between the steam and the gas turbine.

Clutch coupling The gas turbine and the generator are one unit and are coupled rigidly with an expansion sleeve coupling. The steam turbine is used only in

combination with combined cycle and therefore the coupling is flexible. The design is made in such a way that the steam turbine can be started individually and will be coupled to the generator at nominal speed.

Gland Seals Stationary and rotating turbine components must be sealed to prevent steam leakages into the atmosphere, air leakages into the LP turbine, maintain the correct and efficient steam flow within the turbine. Since contact-type shaft sealing can cause distortion and deformation of the rotor, sealing segments are designed to be non-contacting during operation thus limiting friction effects. The seal is built as a labyrinth for the steam which, passing the labyrinth, continuously loses pressure.

Gland Seal System A proper function is guaranteed by two subsystems, the suction steam system with a pressure slightly below the atmospheric pressure, the sealing steam system with a pressure slightly above the atmospheric pressure. The pressure side as well as the suction side of the gland steam system is connected to all turbine sections. The supply steam is taken from the cold reheat steam line on low load operation. At normal operation, sealing is done by leaking steam from the HP & IP ST glands & no cold reheat steam is required. The 2 x 100 % fans downstream of the gland steam condenser creates a slight vacuum on the suction side of all glands and the sucked off gland steam is condensed in the 1 x 100 % condenser, which is cooled by main condensate. The condensed steam is returned to the flash box.

LUBRICATION Turbine bearings are hydro dynamically Lubricated. For this to happen following things are important 1. Viscosity of oil which is directly related to the oil Temperature. 2. Rotation/speed of the Rotor. 3. Desired Clearances/Converging Wedge in the Bearings. (convergence should be in the direction of rotation) In fact the Pressure of the Lube oil is mainly just to ensure that oil reaches the Bearing. However it is also very important and requires to be maintained as per design.

Important points As rotor rotates at low speed ,initially there is no film lubrication but as its speed increases there is conversion of boundary layer lubrication into Film lubrication. From zero speed to appx. 540 RPM there is no continuos film between rotor and bearings and there is chance of rubbing between rotor and Bearing. Therefore JOP is used to prevent the contact between rotor and bearings. At Above 540 RPM the JOP can be Switched off, as film lubrication comes into picture. It is to be noted that when the surfaces are parallel the volume flow rate at inlet is less than the outlet flow rate and film can,t sustain. Therefore for a stable film, area needs to be convergent to ensure equal volume flow throughout the length. The minimum clearance depends upon following - Viscosity of oil

- Speed of Rotor - Load on the rotor

Types of Bearing Cylindrical Bearing( Single wedge ring) This has single oil inlet Elliptical Bearing( Double wedge bearing) This has double oil inlet Segment Bearing( Multi wedge Bearing)

Bearings Cylindrical bearings are normally used for system where no transients are envisaged particularly in turbines without controlling stage, whereby one side radial impulse due to steam forces is not there. Multi wedge bearings are used by installing bearings in segments . Each Segment will have its own wedge. Multi wedge bearings can take more load ,can dampen the sudden disturbance on shaft and there is no formation of Oil Whirl and low frequency vibration components.

FUNCTION OF BEARINGS support the rotating shaft and maintain its correct position in the radial and axial direction between the stationary and rotating components. To minimize friction and dissipate the heat generated by shaft rotation, bearings are lubricated and cooled by the lube oil system. ALSTOM turbine rotors are supported by a single bearing between the individual turbine sections. This single bearing concept establishes welldefined bearing loads. Basically two types of bearings are used:

Journal (radial) bearings support the weight of the turbine rotor and, during operation, define the shaft's radial position. Thrust (axial) bearings establish the shaft's axial position between the rotating and stationary components. Both types operate on the hydrodynamic principle, that is, the metallic running surfaces are separated by a small oil film during operation. The bearings are also known as sliding contact bearings since the shaft slides on the film of oil introduced between the shaft and the housing. Since metal-to-metal contact will immediately lead to pitting and destruction of the bearing, the lubricating oil film must be present whenever the shaft is rotating. Because the lubricating oil is incompressible, it creates a pressure between the bearing and shaft. The pressure increases until an equilibrium point (which depends on the shaft's circumferential velocity, the viscosity of the oil, and the load on the bearing) is reached. This pressure build-up between the shaft and bearing also produces internal friction heat, which is removed through the oil supplied to the bearing

Operational Aspects The journal bearing around which the shaft rotates consists of a casing, a shell and a thin metal coating, called the bearing babbitt. The babbitt, normally made of a soft material called white metal, supports the shaft and absorbs foreign particles. Particles larger than the narrowest part of the lubrication film between the shaft and the bearing babbitt can damage both the shaft and the bearing. However, since soft white metal is used, the particles become imbedded in it, thus minimizing the risk of damage to the shaft. If the lubricating medium fails, the shaft will make contact with the soft white metal. The soft babbitt will melt from the resulting friction, thus forming a kind of lubricating film. Damage is thus confined to the bearing, whereas if the hard shaft were to come into contact with a hard bearing metal, both the shaft and the bearing would experience heating and more damage would occur. The maximum acceptable metal temperature of a radial bearing is determined by the temperature at which the bearing babbitt material becomes soft. With white metal, this limit is approx. 150 °C. Temperature

sensors are mounted in the bearings to monitor this condition. The turbine operation system dispatches an alarm if the temperature exceeds the normal operation temperature by more than 10 °C (factory set value) and trip the unit at temperatures >120 °C.

Journal Bearing Journal bearings support the shaft in the radial direction and maintain its position to prevent contact between stationary and rotating parts during operation. Each bearing consists of horizontally split shell halves. Radial movement of the bearing within its housing is prevented by doweling the upper shell. The shell halves, held in a horizontally split spacer ring, can be readily adjusted relative to the housing by means of shims and guide plates. The lubrication oil enters from both sides through slots at the horizontal split and performs the following functions: Cooling of the bearing Supply the oil for the oil film (hydrodynamic principle) The jacking oil enters in its pockets to lift the shaft (hydrostatic priciple) Establishes an oil film (hydrodynamic principle) Reduces the break-away torque required for turning gear operation when the unit is started To ensure long term operating integrity the bearing is supplied with a thermocouple, placed as close as possible to the bearing babbitt metal, at a point where the highest temperature is expected during normal operation. With allowances for a certain safety margin, this temperature is generally limited to 120°C (trip value). Actual alarm values are set during commissioning of the unit.

Combined Thrust And Journal Bearing The thrust bearing maintains the rotating shaft in a defined axial position within certain limits with respect to the turbine’s stationary components. It also withstands the axial thrust caused by blading reaction

and steam pressure on unbalanced areas. In contrast to journal bearings whose babbitt surface is white metal, thrust bearing surfaces are bronze. Thrust bearings operate on the hydrodynamic principle described above. The axial bearing allows the shaft to move within certain limits (shaft position alarm value: ±0.4 mm, shaft position trip value: ±0.8 mm). This movement is monitored and is an indication for axial forces. Depending on the application. ALSTOM provides either a single-disc thrust bearing or a combined double-disc thrust and journal bearing. Each thrust bearing contains the following components: Bearing body Spring rings Thrust bearing pads Floating rings We will describe a combined double-disc thrust and journal bearing. The combined thrust and journal bearing contains both a journal bearing and a self-aligning thrust bearing. It transmits thrust forces from the rotor to the bearing casing. Spacer rings are used to adjust the axial clearance of the thrust bearing. Shims between the bearing shell and adjusting plate allow radial and axial adjustment of the bearing. Pressurized Lube oil is fed through slots to the journal bearing. After the oil leaves the journal bearing in an axial direction, it flows past the thrust bearing pads and drains into the bearing casing. Jacking oil is fed from the bottom of the radial bearing. The temperature of the bearing pads is monitored and provides an indication of the health of the bearing and the unit. The normal rule for maximum thrust bearing temperature is that it should not exceed 100 °C. During commissioning the temperature rise across the thrust bearing is normally set not to exceed

Turbine Steam Valves Steam inlet valves perform one of two functions, protection or control. Steam inlet stop valves perform the protective function of stopping steam flow through the turbine unit. These valves are in either the open or closed position.

Steam inlet control valves regulate the flow and/or the pressure of steam through the turbine. Their position, from closed to fully open, is determined by the turbine electronic controller Stop Valves Stop valves are safety devices, which block the flow of steam to the turbine during shutdown and abnormal operating conditions. The valves have only two states, fully open for start-up and normal operation, and fully closed for shutdown. They are placed in their fully open position by hydraulic servomotors. To ensure their proper operation, the valves must be tested at the intervals recommended in the Operation Manuals. This test can be performed during operation.

Main Inlet Stop valves Valve Construction The balance, single-seat valve is equipped with a steam strainer, which serves as a flow stabilizer. The strainer also protects the valve's internals and the turbine from damage caused by solid particles. The diffuser is fitted into the valve housing block with a press fit and is secured by a cylindrical pin. The valve body is provided with an exhaust connection. With a balanced type valve design, the pressure across the valve disc must be reduced to a certain minimum value before the valve can be opened, that is, pressure must be equalized. For example, when the stop valve is in its closed position, full steam pressure may exist on one side of the valve while vacuum or some slightly positive pressure may exist on the other side. To open the valve, pressure across the valve must be reduced. This is accomplished with a pilot valve. When the pilot valve is opened, the pressure on both sides of the valve essentially equalizes, and the main valve disc will open. The valve is positioned by a valve actuator, supplied with high pressure hydraulic fluid. If the valve must close because of a disturbance, the spring,

steam, and hydraulics all help to minimize the closing time. The valve head is forced against the lock, which prevents vibrations caused by steam flow. To prevent spindle leakage into the atmosphere, the valve is connected to the gland steam system. The closing movement is also initiated by the pilot stroke. Pressure between the valve head and lock builds up, helping the stop valve actuator to lift the valve head from the lock and carry out the full closing stroke. If the control valve is not yet closed, the valve head is pulled onto the seat of the diffuser by suction caused by the steam flow. Steam flow is blocked. A sealing element minimizes steam leakage.

Control Valves Control valves regulate steam flow to the turbine during start-up and normal operation. During low load operation they also control steam pressure. If there is a disturbance, both the control valves and the stop valves close to block the flow of steam to the turbine. The opening sequence of the control valves is determined by application and design. For example, all valves may open in parallel or they may open sequentially; they may open individually or they may open in a group. They control the speed of the unit from startup to synchronous speed. When the unit is synchronized to the system, the control valves regulate admission steam pressure and load. Valve Construction (Main Control Valves) Each valve is an angle type, single-seat valve, integrated into a valve housing block. A flow equalizer distributes the flow of steam to the throttling point. The bell-type valve body and spindle are firmly connected. Sealing points and guide sections are specially hardened. Piston rings seal the valve body from the steam chamber. A sealing element provides sealing against atmosphere. A connection to the seal steam exhaust system is also provided. Control valves can assume any position between fully open and fully closed, temporarily or on a continuous basis. Each control valve is operated via a

directly coupled hydraulic control valve actuator and is designed so that little power is required to position the valve. In the fully open position the valve spindle is locked steam-tight against the valve body and is insensitive to vibration excitation. During flow control operation, the closing movement is effected by steam flow and the stop valve being in the open position. The closing force of the control valve actuator is aided by suction, caused by the flow of steam. Flow through the valve depends on admission steam pressure and valve stroke as established by the turbine electronic controller.

Rupture Diagram/Blow-off Valve The rupture diaphragm is normally placed on top of the LP casing. It is used on condensing type turbines to protect the exhaust casing and condenser against internal over-pressure if the primary safety devices fail. It is a planned weak point and breaks as soon as the diaphragm's design pressure is reached. The cross-section or opening is cleared to allow steam from the LP housing to escape into the surrounding area via a guide tube. During normal operation the rupture diaphragm rests against the support because of the negative pressure in the LP casing. Instead of having a rupture diaphragm installed a safety blow-off valve can be provided. This device has the same task as the diaphragm but has one major advantage that it doesn’t need to be replaced after operation. The safety blow-off valve is normally placed at the condenser neck.

Thermal Stress,Turbine Expansion And Fixation The process of bringing the turbine from room temperature to its operational state results in major changes in the temperature of the turbine rotor and casings. The rate at which these changes occur effect the life of the turbine's components.

Thermal Stress The materials of which turbine components are made have been studied, and conservative guidelines have been established for allowable rates of temperature change during start-up, normal operation and shutdown. Observing these values will ensure long-term availability of the unit. Failure to observe them can result in additional thermal stress and a consequent reduction in component life. ALSTOM turbine controllers are provided with a program to calculate and reduce thermal stress (TURBOMAX). It is essential that the rate of temperature change be kept within the limits established by ALSTOM. As long as the rates of temperature change remain within the established guidelines, no adverse effects will result. The turbine's rotating and stationary components operate at temperatures and pressures well above ambient conditions; typical values are pressures in the range of 100-245 bar (~1400-3550 psi) and temperatures up to 570 °C (1058 Fahrenheit). The axial and radial distances between these components must be kept at a minimum if the unit is to operate at maximum efficiency. At the same time, reductions in the distance between them cause severe damage if the components actually rub against one another.

Absolute Expansion Clearances between the components are established by the fixed points of the rotor and casing. The fixed point of the casing with respect to the foundation is shown on Figure 15. As the temperature increases to its operating value, the casing freely expands in the direction of the thrust bearing. The distance the casing expands from its cold condition (room temperature) to any other state is known as absolute expansion.

Differential Expansion

The relative distance between the rotor and casing during both steady-state and transient operation (start-up, changes in load and shutdown) is defined as differential expansion. If differential expansion is maintained within the design limits established by ALSTOM, there is no possibility of rubbing between the stationary and rotating components and hence no damage will occur. The casings’ radial fixations are designed so that free radial expansion is ensured, thus maintaining the concentricity of the rotors and casings. The arrangement of axial fixed points and fixations is such that axial differential expansions caused by thermal expansion of the rotors and casings are minimized. This permits reduced axial blade and gland seal clearances. As shown, the rotor's fixed point with respect to the casing is determined by the thrust bearing. When the unit is heated from a cold state, the rotor expands at a much faster rate than the massive casing does. This expansion is known as positive expansion and is indicated by a “rotor long condition”. When the unit reaches its normal operating state and temperature and pressure stabilize, the casing will also reach its steadystate expansion value. A reduction in load or temperature will have the opposite effect, that is, the rotor will being to shrink sooner than the casing does. This contraction is known as negative expansion or a rotor short condition.

Turbine Auxiliary System Certain auxiliary systems such as the lubrication, jacking oil, turning gear, control fluid, gland steam, LP hood spray, and vacuum breaking systems are required if the turbine components described above are to operate properly. These systems are described in subsequent sections of this course.

Drain Lines The turbine and the steam lines are equipped with drain lines, which allow

condensate, formed in the turbine/steam lines during start-up, to escape. This ensures that no water remains in the turbine steam lines, casings or valves, which could otherwise cause extensive damage to the unit. The proper function of the drain system is very important (see separate section on drain system).

Atmospheric Drain Vessel The atmospheric drain vessel (ADV) collects steam turbine external drains from the steam system. After separation in the ADV steam is discharged to atmosphere and condensate is discharged to the cooling tower basin by means of 1 x 100 % ADV pump. An ADV overflow line is also provided to drain the accumulated condensate in case of pump failure.