VGB-R 105 e Content

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Thermal Behaviourof Steam TurbinesVGB R 105 M e

First edition 19 77Second , revised edition 1993

Published by:

Obtainable from:Verlag technisch wissenschaftlicher SchriftenP.O . Box 10 39 32, D-45039 EssenPhone 49 201 8128-200Fax +49 291 8128-329E-mail : mark@vgb .org

http ://www.vgb .orgur mit vorherigerGenehmigung de VGB gestattet


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Preface to the First EditionWhen starting and shutting down steam turbines or changing their poweroutputs, steam temperature variations are bound to occur that lead totemperature differences in and between the com ponents . These temperaturedifferences result in free expansions of the components relative to each other,deformations of the components themselves, and stresses in the o m p o n n t s. lf such expansions, deformations and stresses exceed certain limitsset by design features or the materials used, both immediate damage - axialor radial rubbing - and long-time damage - inadmissible permanentdeformation and crack formation - m ay occur.Finding solutions to this complex of problems is gaining importance in thefield of steam turbine construction and operation . While componentdimensions and thus the effects of major temperature differences inevitably be-come more pronounced as unit outputs increase, it is desirable to avoid avail-ability losses due to thermal overloads. in addition, more stringent systemrequirements are now placed on the roadability and Controllability of large tur-bo-generator sets . Last but not least, the expected increase in unit output andthe fact that conventional, medium-size and large power stations are beingpushed toward the peak and medium-load range by other, more economicstations - e .g . nuclear - providing the base load, lend greater importance tothe problems mentioned here.Being aware of the relevance of the problems, scientists and engineers havemade numerous theoretical studies, laboratory and field experiments in thepast years which led to a better understanding of the processes involved andthe possible damages that may occur. The results have revealed that majorparts of the brochure The Warm-Up Process in Steam Turbines , issued byVDEW in 1961, are now obsolete . Thus the VGB Working Group TurbineDevelopment has set itself the goal to describe the current state of the art . inorder to keep the work within reasonable limits, a restriction of the generallyapplicable information has proved to be necessary . However, the biblio-graphy enables the problems indicated to be dealt with in more detail.The Working Group for Turbine Development hopes that this updated pub-lication will be of interest not only to turbine manufacturers but also - andabove all - to power station design engineers and operators, and will servethe better understanding of the possibilities and limitations of the thermal be-haviour of turbines . lt should always be remembered that placing excessiverequirements on the start-up and loading behaviour of turbines will reduce


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the serve life of certain components . Mention is also made of the gentle modeof operation nowadays possible when suitable monitoring equipment orautomatic systems are used . The brochure is not meant to replace operatinginstructions or start-up curves supplied by the turbine manufacturers, althoughthe derivation of such curves is explained and typical start-up and loadtimes are specified.The brochure was drawn up in the VGB Working Group TurbineH a a sKatwerk UnonAG extensvecontributions being made by Dr. Busse and Mr. Kramer, Brown Boveri & Cie Mr . Andreae, Mr. Langbein, Dr. Loreck and Mr . Tmmers, Kraftwerk UnionAG, Mr. Cernoch, Dr. Martin, Mr. Mayer and Mr. Strtz, MaschinenfabrikAugsburg-Nrnberg AG.Members of the Working Group Turbine Development :Huppmann, Aldrian, Prof. Bammert, Buchwald, Dang , Prof . Dibelius, Haas,Haase, Dr. Hirschfelder, Hxtermann, Koch, Dr . Martin, Mitschel, Riedlinger,Schulte, Prof. Thomas n Wittich.

Essen, November 1977

Preface to the Second EditionThe second revision of this guideline was made by a team including Andreae,Dr . Busse, Hxtermann, Dr. Peter, Strtz and Wolf.Members of the Working Group for Turbine Development : r. Linnemann, Aldrian, Dr. Bohnstedt, Prof. Dibelius, Prof. Haas, Hebel,Hedstrm, Hxtermann, Huppmann, Jensen, Keysselitz, Neft, Riedlinger,Schulte, Prof. Stetter, Trinkle n WolfEssen May 1990

VGB TECHNlSCHE VEREINlGUNGDER GROSSKRAFTWERKSBETREIBER E .V


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Contents

Page lntroduction2 Temperature Differences ln components2 Factors influencing the determination

of temperature zones2 Heat transfer22 .2 lnfluence of materials32 .2 Temperature distribution in components82 .2 .1 Simplified solution of the differential equation92 .2 .1 Stationary temperature distribution32 .2 .2 Quasi-stationary temperature distribution42 .2 .3 Nonstationary temperature distribution72 .2 .2 Multidimensional heat flow83 Expansion and Deformation of componentso3 Determination of absolute and relative thermal expansion13 .2 influence of centrifugal force and internal pressure33 .3 Effects of relative expansion on components design43 .4 Bending of rotors53 .5 Hogging of casings64 component Loading74 Component load types74 Unidimensional thermal stressesand restrained thermal expansion74 Stationary thermal stresseso4 .2 Quasi-stationary thermal stresses14 .1 .3 Nonstationary thermal stresses24 .2 Multidimensional stress distribution54 .2 Notching effects6

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5 Assessment of Loads95 Creep strength of materials15 Constant creep load25 .2 Variable creep load25 .3 Relaxation45 .2 Fatigue behaviour of materials55 .3 Assessment of material fatigue86 Recommendations for steam Turbine operation36 Definition of terms36 lnitial state46 .2 Start-up46 .2 .1 Acceleration to nominal speed46 .2 .2 Load application46 .3 Load and temperature changes56 .2 influence of the mode of operation on the start-up processand on load changes56 .2 Modes of operation56 .2 .2 lnfluence of the steam temperature and heat transfer

on component temperature changes66 .2 .3 lnfluence on the start-up process and on load changesfor superheated steam turbines86 .2 .3 .1 Start-up process86 .2 .3 .2 Load changes at constant live steam temperatureunder load96 .2 .4 Influence on the start-up process and on load changesof saturated steam turbines36 .3 Standard data for turbine start-up and load changes56 .3 Cooling process66 .3 .2 ldealized start-up diagrams86 .3 .3 Standard start-up times96 .3 .4 Standard temperature steps and transientsin components16 .3 .5 Standard load steps and transients3

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6 .4 General rules for superheated and satured steam turbinestart-up and load change86 .4 Start-up and shutdown8

6 .4 .1 Starting the gland steam system86 .4 .2 Warming up the piping and valve bodies06 .4 .3 Preheating and pressure build-up 92n the high-pressure turbine.4 .4 Start-up, acceleration to nominal speed, no-load operation, 93oad application.4 .5 Load changes and shutdown processes86 .4 .2 Function of warm-up pipes and drains86 .4 .3 Saturated steam turbines97 Supervision of the Therma l Behaviour of Turbines

in operation97 .1 Monitoring temperatures007 Steam temperatures007 Live and reheat steam temperatures007 .2 Exhaust steam temperature017 .3 Gland steam temperature027 .2 Component temperature027 .2 Valve body temperatures037 .2 .2 Turbine casing temperatures037 .2 .3 Rotor temperature047 .2 Monitoring of free expansiono47 .2 Monitoring of stationary components047 .2 .2 Monitoring of rotating components057 .2 .3 Monitoring devices and where to locate them057 .3 Monitoring deformation067 .3 Monitoring of stationary componentso67 .3 .2 Monitoring of rotating components077 .3 .3 Monitoring equipmento87 .3 .4 Monitoring of the foundationo87 .4 Monitoring of loads097 .4 Monitoring of stationary components107 .4 .2 Monitoring of rotating components107 .4 .3 Monitoring equipment117 .4 .4 Service life monitoring11

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8 Automatic Start Up118 Purpose118 .2 Technological structure of the automatic system128 .3 Operating principle138 .4 Automatic processing of thermal criteria169 Turbine Protection system81 Symbols and Indices1910 Symbols1910 .2 Indices21 References228

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VGB-R 105 e Content