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Abstract of Reserach Project

Wear investigation modell for primary and secondarycontrolled thermal power plants at the ENTSO-E-grid

Period:

01.08.2012 to 31.01.2015

Persons in charge:

University RostockDipl.-Phys. Maria RichterM.Sc. Andre BerndtM.Sc. Patrick MutschlerDipl.-Ing. Moritz HubelDr.-Ing. Jurgen NockeProf. Dr.-Ing. Harald WeberProf. Dr.-Ing. habil. Dr. h.c. Egon HasselProf. Dr.-Ing. habil. Manuela Sander

AlstomM.Sc. Sebastian BeckDr.-Ing. Klaus Helbig

Rostock, September 14, 2015

III

Contents

1 Introduction 1

2 Power plant models 1

2.1 Modelling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

2.2 Validation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

3 Inputs 3

3.1 Schedule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

3.2 Primary control demand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

3.3 Secondary control demand . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

4 Lifetime calculation 5

4.1 Damage mechanism and investigated components . . . . . . . . . . . . . . . 5

4.2 Fatigue of the components of the water-steam-cycle (except turbine) . . . . . 6

4.3 Lifetime calculation of Steam turbines . . . . . . . . . . . . . . . . . . . . . 6

5 Influence of primary control demand 8

5.1 Components of water-steam-cycle (except turbine) . . . . . . . . . . . . . . . 8

5.2 Steam Turbines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

5.3 Wear of turbine control valves . . . . . . . . . . . . . . . . . . . . . . . . . . 10

5.4 Comparison between different primary control principles . . . . . . . . . . . 10

6 Influence of secondary control 11

6.1 Components of water-steam-cycle (except turbine) . . . . . . . . . . . . . . . 11

6.2 Steam Turbines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

7 Summary 13

Institute of Electrical Power EngineeringChair of Technical Thermodynamics

Chair of Structural Mechanics

1

1 Introduction

In order to implement international climate

agreements, the expansion of renewable gen-

eration is regulated under the German Re-

newable Energy Sources Act (EEG). Thus,

the network operators are obliged to in-

tegrate the electricity of renewable energy

sources. Furthermore, fixed fees are estab-

lished by law. Because of the changing

weather conditions, the feed-in of electricity

generated by renewables sources lead to new

challenges for conventional thermal power

plants. To meet the current customer load

the difference between the load and inter-

mittent power supply must be provided by

conventional power plants. With the liberal-

ization of the electricity market the flexibil-

ity of a power plant is of an great economic

importance. When controlling the intermit-

tent power supply the participating power

plants perform dynamic processes which af-

fect all technical components. This leads to

fluctuations in temperature and pressure in

all steam carrying components and a life-

time reduction can occur. The aim of this

project is to determine the impact of these

services on the lifetime of the affected parts

of the power plants. The mode of opera-

tion of a power plant is determined by three

superposed input variables:

• power demand due to schedule

• primary control demand due to changes

in mains frequency

• secondary control demand demanded

by the transmission network operator.

These data will be analyzed to develop rep-

resentative scenarios which are the inputs

for the transient, physical power plant mod-

els. With these simulation models, it is pos-

sible to get pressure and temperature trends

for all modeled components. The simulation

is followed by an structural mechanics anal-

ysis.

2 Power plant models

The power plant models have been devel-

oped using the following reference power

plants for validation purposes: the coal-fired

power plant Rostock, a block of lignite-fired

power plant Janschwalde and the combined-

cycle plant Mainz-Wiesbaden. The software

Dymola is used as the development environ-

ment.

2.1 Modelling

In order to develop the simulation mod-

ells, the process is divided between the ther-

modynamic and the control engineering ap-

proach. The thermodynamic modeling of

the components of a power plant is based

on balance and transport equations as well

as equations of state. The component is

divided into small, interrelated control vol-

umes. For every volume the corresponding

balance equations for mass, momentum and

energy are solved.

The heat transfer is modeled according

to the physical transport equations for

heat conduction, radiation and convection.



2

The calculation of heat transfer coefficients,

emission and absorption coefficients is based

on [3]. The same applies to the description

of pressure losses.

For the calculation of state variables of wa-

ter respectively water vapor, the equations

of state are used in accordance with the

technical report IF97 [2]. The used media li-

braries include necessary material data and

material parameters for fresh air and flue gas

as well as widespread steel grades. For the

modeling of the control system a model of

the real control system is developed in close

cooperation with the power plant operators

and with the help of control plans.

This procedure is fundamental for the high

quality of the simulation models. Further-

more, by this approach it is possible to

perform a simulation-based optimization of

control parameters for optimized operation

of the real power plant.

2.2 Validation

The Validation is a process to ensure the

closeness to reality of the modells. There-

for measurement data of the power plant is

compared to the simulation data.

Chosen figures of the validation of the coal-

fired power plant are schown in the follow-

ing. As it can be seen, the simulated

trends (solid line) have a high similarity to

the meassured trends (dotted). A detailled

validation for all investigated power plants

can be found in the final report.

460

500

540

MW

Setpoint Generator Output

0 0.5 1 1.5 2 2.5 3 3.5 4

450

500

550

t / h

MW

Generator Output

Figure 1: Validation of the generator output for asecondary control demand of the power plant Ros-tock

460

500

540

MW

Setpoint Gnerator Output

0 0.5 1 1.5 2 2.5 3 3.5 4

500

550

600

t / h

◦ C

Tlifesteam

T after RH

Figure 2: Validation of temperatures of the boilerfor a secondary control demand of the power plantRostock



3

460

500

540MW

Setpoint Gnerator Output

0 0.5 1 1.5 2 2.5 3 3.5 4

40

45

50

t / h

kg/

s

Coal mass flow

Figure 3: Validation of the coal consumption for asecondary control demand of the power plant Ros-tock

3 Inputs

3.1 Schedule

The resulting schedules for the reference

power plants Rostock, Jaenschwalde and

Mainz-Wiesbaden were grouped into classes

based on their size. It has been determined

how often a load change (positive and nega-

tive) of a particular class occurs per year.

These frequencies are summarized for the

year 2011 in table 1.

load changePower plant 15 % 25 %

Janschwalde 229 6

15 % 30 % 40 %Rostock 267 75 75

Mainz-Wiesbaden 515 465 130

Table 1: Annual frequencies of load change scenariosof the investigated power plants in % of the nominalpower

3.2 Primary control demand

An extensive frequency analysis was pre-

pared to investigate the influence of the pri-

mary control on the components of a power

plant. The histogram in figure 4 shows

the deviations of the frequency setpoint of

50 Hz. By averaging the measured frequency

−0,2 −0,1 0 0,1 0,20

20

40

60

Deviation of the frequency setpoint in Hz

Durationin

day

s

Figure 4: Histogram of frequency deviations in year2011 with a sample time of 1 s

the load noise is reduced. The relation be-

twen the deviation of the mains frequency

and full-time hours is evident (figure 5).

0 2 4 6 8 10 12 14 16 18 20 22 24

49,95

50,00

50,05

time

frequency

inHz

Figure 5: Averaged mains frequency of the year 2011

By the measured mains frequency around

the full-time hours eight characteristic fre-

quency curves were determined (see fig-



4

ure 6). To represent the full year these

curves were superimposed with load changes

and extrapolated.

50 60 70

49,90

50,00

50,10

t / min

f/Hz

class 1class 2class 3class 4class 5class 6class 7class 8

Figure 6: Characteristic frequency scenarios

Figure 7 shows the occurrence of load

changes of full time hours for different times

of a day. Between 20 o’clock and 4 o’clock

negative load changes are more frequent.

This correlates very well with the drop of

frequency in the averyged mains frequency

signal of the year 2011 (Figure 5) as well

as with the determined network frequency

curves of the amplitude classes 1 (drop of

the mains frequency) to 8 (overshoot of

the mains frequency (see Figure 8)). The

same applies to the early hours of 4 o’clock

to 12 o’clock, with predominantly positive

load changes and therfore a overshoot of the

mains frequency occurs.

3.3 Secondary control demand

For the secondary control, current measure-

ment series were evaluated for each power

plant. The secondary control scenarios de-

pend on the maximum offered secondary

control output. These are

20-4 o’clock 4-12 o’clock 12-4 o’clock0

50

100

150 pos./neg. LC 0-15 % PN——–

pos./neg. LC 0-15 % PN——–

pos./neg. LC 0-15 % PN——–

pos./neg. LC 0-15 % PN



time

Quan

tity

per

year

Figure 7: Time of scheduled changes of the powerplant Rostock

1 2 3 4 5 6 7 80

500

1000

1500

Class of amplitude

frequency

2011

20-4 o’clock

4-12 o’clock

12-20 o’clock

Figure 8: Frequency of changes in mains frequencyof the year 2011

• ±5 %PN for the lignite-coal fired power

plant,

• ±10 %PN for the coal-fired power plant

and

• ±23 %PN for the combined cycle power

plant.



5

4 Lifetime calculation

4.1 Damage mechanism and

investigated components

A reduction in the service of application or

the failure of the components is caused by

different effects:

• mechanical load

– fatigue

– crack growth

• thermal load

– scaling

• tribological stress

– abrasion / erosion

– adhesion

– tribochemical reaktions

• corrosion

– intercrystalline corrosion

– stress crack corrosion

– vibration crack corrosion

In cooperation with the steering commitee

the investigation was focused on

1. fatigue: lifetime reduction of compo-

nents

2. wear: valuation of the stress of turbine

control valves due to adjustment travel

The essence of this research project is the

investigation of the cyclic mechanical stress

due to pressure and temperature fluctua-

tions in the individual components of the

power plant. These are caused by primary

and secondary control demands. Therefore

the life consumption is evaluated on a me-

chanical basis.

In order to evaluate the influence of the pri-

mary and secondary control, a full model

of the water-steam cycle for each power

plant is needed. In advance the level

of detail was set. The following compo-

nents were investigated: high pressure pre-

heaters, collectors and distributors (of econ-

omizer, evaporator, superheater stages, re-

heater stages), spray atemperators, compo-

nents of the steam pipe, turbine control

valves, turbine, condenser, low pressure pre-

heater and feedwater tank.

In consultation with manufacturers the gen-

erator has not been investigated since it is

not critical for the investigated strain.

During the project, the turbine manufac-

turer Alstom has been involved, which in-

vestigated the complex turbine. Thus, the

structural mechanics approach differs from

the approach of the other components.

For the analysis of the components of

the water-steam cycle (except turbine) the

nominal stress approach after the current

DIN EN 12952 is applied. The turbo kit

is investigated using the local concept with

FEM calculations.



6

4.2 Fatigue of the components of

the water-steam-cycle

(except turbine)

For the components of the water-steam cy-

cle, the cyclic load of components due to

pressure and temperature fluctuations are

investigated using the operating strength

analysis according to DIN EN 12952 [1]

(nominal stress approach). It considers the

tensions on the inner surface of the transi-

tion between two cylinders or between cylin-

ders and spheres at the hole edge. In par-

ticular thick-walled components suffer under

high thermally induced stress, which are en-

hanced by the notch effect of the nozzle ge-

ometries.

The thermally induced stress are calculated

conservatively as thermal shock stress. This

stress is a result of the temperature differ-

ence between two consecutive extreme val-

ues of the temperature-time function, mate-

rials and notch factors.

Finally, the load-time function is calculated

by superposition of the mechanical and ther-

mally induced stress. The result is classi-

fied in terms of load cycles with the rain-

flow counting method [4]. The influence of

surface roughness and welds is taken into ac-

count by multiplying with correction coeffi-

cients. To determine the resulting partial

damage of the determined cycles, the cor-

responding stress amplitudes are compared

with the tolerable amplitudes of the Woh-

ler curve. The addition of all partial damage

leads to the total damage of the component.

Figure 9: Considered socket geometry ofDIN EN 12952 (nominal stress approach [1])

4.3 Lifetime calculation of Steam

turbines

The lifetime calculation of the steam tur-

bine rotors for the power plants Rostock and

Jaenschwalde were performed by ALSTOM.

The comprehensive supervision of all com-

ponents of a steam turbine is serving to tar-

get and ensure long term reliability, flexi-

bility and high availability of the machine.

Lifetime supervision is based on theoretical

calculations and non-destructive testing of

highly stressed components.

The calculations comprise components are

exposed to operate temperatures beyond

400◦C. Typically, those components are the

HP and IP turbine rotors, the inner casing

and the inflow pipe. During a lifetime cal-

culation, general creep and low cycle fatique

of highly loaded components is determined.

Damages due to erosion, corrosion and at-

trition will not be examinated during the

investigations.

For transient operations of a steam turbine,

the highly stressed area (usually the first

rotor groove) is controlled by the start-up

probe Turbomax with respect to excessive

lifetime consumption. By the experience of



7

many investigations it is known that the ro-

tor is the leading component for cyclic fa-

tigue. The procedure for the calculation of

lifetime consumption is organized as shown

below. Turbine blades are not considered as

fatigue critical.

Regarding the operation the turbine steam

conditions may differ from design param-

eters. This causes deviation in the pre-

designed trend of fatigue due to operational

requirements. Depending on supervision,

type and frequency of starts and changes in

loading, the fatigue process of components

is affected additionally. Due to the increas-

ingly volatile power generation, the loading

properties on the steam turbine are highly

variable. The calculations are therefore no

longer performed on representative events.

Modern FEM calculations considering holis-

tic operational data from the power plant

data servers.

The determination of total fatique E from

creep and low cycle fatigue is carried out

according to the rules of Robinson and

Palmgren-Miner. Experiments have shown

that turbine components can achieve their

failure limit even for values of S<1 if the

proportion of creep and low cycle fatique is

variable. Therefore, the calculated end of

life is determined on an exhaustion of S =

0.75, considering the standard range of vari-

ation of stress for steam turbines.

To obtain a highly qualitative statement of

controlling influences on the fatigue of the

turbine components, the cyclic strain fatigue

was calculated for different load control sce-

narios.

Figure 10: Three-dimensional representation of thestress distribution within a IP rotor (plant Ros-tock). Calculation using transient finite elementmethod.

Due to the high complexity of the com-

ponents the use of a local approach with

2D/ 3D finite element (FE) models are re-

quired.

The focus of the investigation was on the

HP and IP turbine rotors. The exact ge-

ometry and thermodynamic boundary con-

ditions were modeled by an in-house tool.

All calculation results are therefore based

on the respective load case. A generic so-

lution is not recommended due to numerous

model variables and boundary parameters.

The influence of different groove geometries

and groove depths in the turbine rotor, loca-

tion of the cavity, company-specific material

parameters and different types of transient

control strategies (e.g. start-up, shutdown

primary loadcontrol, low load, ...) is too

large to provide general statements.

The required process data for the analy-

sis of the load control processes, such as

steam pressure and temperature, were ex-

tracted from the dynamic cycle simulations

and transferred to the thermodynamic cal-

culations of the heat transfer coefficient in

order to subsequently carry out FEM cal-

culations. As a result, the time profiles of

stress, strain and temperature within the



8

turbine rotors could be determined, which

then served as input parameters for the de-

termination of cycle numbers. This was

done based on Wohler diagrams taken

from a Alstom-internal database, describ-

ing the material properties of steam tur-

bines in particular. For the evaluation of the

influence of the delivery of system services

on the lifetime of the steam turbines,cycle

numbers of reference cycles were calculated.

They considered different start-up and shut-

down processes. They were put in relation

to the results for operating cycles with pri-

mary and secondary control.

5 Influence of primary

control demand on the

lifetime of components

5.1 Components of

water-steam-cycle (except

turbine)

The usually simultaneously occurence of a

load change with a primary control power

demand can lead to damage. This has

been verified for some components of the

combined cycle power plant and the coal

power plant. Because of the relative small

load changes of the investigated lignite-fired

power plant no damage was determined.

The following figures (figure 11 and 12) show

the annual damage sums for load changes

superposed with primary control demand in

relation to pure load changes .

HDV1Vert

HDV1Samm

HDV2Vert

HDV2Samm

UEH1Vert

UEH4Vert

0.2

0.4

0.6

0.8

1

1.2

1.4

SP

R/S

ref

Figure 11: Annual relative damage due to primarycontrol SPR in a coal-fired power plant

HD-TromSteigrohre2

HD-TromSpWStutz

0.2

0.4

0.6

0.8

1

1.2

1.4

SP

R/S

ref

Figure 12: Annual relative damage due to primarycontrol SPR in a combined cycle plant

As it can bee seen, the components of the

coal-fired power plant which are exposed to

high temperature like superheater stage 4

suffer from an increased damage of 20 %.

The high pressure drum of the combined cy-

cle plant suffers from an increased damage

of 30 %. The absolute values of the annual

damage sum have an order of 10−4. There-

fore the influence of the primary control de-

mand on the lifetime of the components in-

vestigated with DIN EN 12952 are negligi-

ble.



9

5.2 Steam Turbines

Power plant Rostock Due to the quality

of the control of the hard coal-fired power

plant, the investigations of control processes

do not lead to significant changes in the

steam temperatures in the HP and IP tur-

bines and thus caused a negligible lifetime

consumption compared to the observed ref-

erence cycles. (figure 13).

100 200 300 400 500 600 700 8000

0.2

0.4

0.6

0.8

1

Zeit [min]

NormierteVergleichsspan

nung

ReferenzzyklusLW30 + PR8PR8

Figure 13: Exemplary v.Mises comparison stresstrend in the first rotor groove of the IP turbine Ro-stock

In addition, separate lifetime calculations of

the control scenarios were performed. All

results were within the fatigue limit range.

As an example, table 2 is presented. The

start-up and shut-down process of the HP

turbine have an huge impact on the life-

time. Depending on the event combination

the number of cycles varies up to a factor of

three.

However the calculation of additional life-

time consumption the control events load

change (LC), primary control (PC) (table

3) show a negligible influence on the consid-

Cyclenumber Shut-down 1 Shut-down 2Hot start 4287 2598

warm start 7440 2394

Table 2: Number of cycles of a hot start (HS) andwarm start (WS) with different shutdown events.First HP turbine rotor groove Rostock.

ered reference cycles. The number of cycles

differs insignificant and can be neglected.

Cyclenumber LC30 LC30 + PCHS+SD01 4287 4227HS+SD02 2598 2598WS+SD01 7440 7120WS+SD02 2394 2386

Table 3: Number of cycles of the reference scenarios(HS / WS + SD) with a 30 % load change (LC30)and a selected control scenario (PC). First rotorgroove of the HP turbine.

Cyclenumber Shut down 1 Shut down 2Warm start 8463 5366Hot start 8752 2511

Table 4: Number of cycles of a hot and warm startwith different shut down events. First rotor grooveof the IP turbine Rostock.

The calculations of the IP turbine indicates

a similar behavior. Furthermore the influ-

ence of load control interventions is rated as

negligible (table 4 and 5).

Power plant Janschwalde

For the lifetime calculations of the two

steam turbines of the lignite power plant op-

erating data were analyzed by two and a half

years in order to select the necessary refer-

ence cycles. The start up and shut down

processes caused higher temperature gradi-

ents in the lifesteam, as in the previously

considered power plant. This led to higher

strain amplitudes within the material and



10

Cyclenumber LC30 LC30 + PCWS+SD01 8463 8463WS+SD02 5366 5366HS+SD01 8752 8752HS+SD02 2511 2511

Table 5: Number of cycles of the reference scenarios(HS / WS + SD)) with a 30 % load change and aselected control scenario. First grove IP rotor Ros-tock.

thus to an decrease of numbers of cycles of

the reference cycles.

Cyclenumber Shut down 1 Shut down 2Hot start 1503 3259

Table 6: Number of cycles of a hot start and differ-ent shut down events (SD). First groove IP turbineJanschwalde.

In the result no impact on the cyclic strain

fatigue and the lifetime consumption can be

verfied. Table 6 and 7 confirm that the

stress and strain amplitudes of the reference

cycles were not exceeded.

Cyclenumber LC25 LC25 + PCHS+SD01 1503 1503HS+SD02 3259 3259

Table 7: Number of cycles of the reference scenar-ios with a 25% load change and a selected controlscenario. First groove IP rotor.

All control scenarios were analyzed and eval-

uated separately. The results were within

the fatigue limit.

Power plant Mainz-Wiesbaden The

power plant Mainz-Wiesbaden operates

a Siemens steam turbine. At that, no

investigations have taken place.

5.3 Wear of turbine control

valves

The primary control demand has a great

influence on the activity of turbine control

valves and turbine extraction valves. As an

example, the high-pressure valves of a lignite

power plant were investigated using mea-

sured data. The primary control demand

increases the annual valve path by 1,35 and

the number of reversal points by 1,15. This

reduces the period of application by 20 %.

Because of the use of measured data and

the relative high time difference between

two measurments these factors are under-

estimated.

5.4 Comparison between

different primary control

principles

With the help of the simulation models, it

is possible to study different primary con-

trol principles. The following three princi-

ples were investigated: the life steam throt-

tling due to the HD-valves, the condensate

holdup by reducing the turbine tap mass

flow to the low pressure preheaters and the

throttling of the turbine tap mass flow to the

high pressure preheaters. These three prin-

ciples have a different impact on the compo-

nents. This can be seen in figure 14.

The figure shows the maximal stress am-

plitude in relation to the fatigue strength.

Values above 100 % lead to damage in the

component. Due to condensate hold up and



11

throttling the turbine tap mass flow to the

high pressure preheaters, components of the

boiler like the superheater stages 3 and 4

and the reheater stage 1 and 2 have their

maximal stress amplitudes reduced. but the

stress amplitudes in the corresponding pre-

heaters are increased. However, the fatigue

strength is never exceeded.

6 Influence of secondary

control demand on the

lifetime of components

6.1 Components of

water-steam-cycle (except

turbine)

For a hard coal-fired and combined cy-

cle power plant the simultaneous occurence

of load changes and secondary control de-

mand increases the loss of life span in re-

lation to a pure load change operation.

The following components of a hard coal

fired power plant suffer of an increaed wear:

high pressure preheaters (+30 %) and super-

heater 1 (+20 %) and 4 (+15 %) (see fig-

ure 15). In addition 9 other components (see

figure 16) have their lifespan decreased.

HDV1Vert

HDV1Samm

HDV2Vert

HDV2Samm

UEH1Vert

UEH4Vert

0

0,2

0,4

0,6

0,8

1

1,2

1,4

SS

R/S

ref

Figure 15: Relative increase of the damage for oneyear of continious secondary control demand in acoal-fired power plant

In a combined cycle power plant the

secondary control demand leads to an

increase of wear in the following compo-

nents: riser pipe (+400 %) and feedwater

socket (+300 %) of the high pressure

NDV1

NDV2

NDV3

NDV4

HDV1S

HDV2S

HDV3S

Eco

V

Eco

S

VerdpfS

UH2S

UH3S

UH4S

ZUH1S

ZUH2S

0

20

40

60

σm

ax/σ

din

%

Frischdampf-Androsselung

Kondensatstau

HD-Vorwarmer-Androsselung

Figure 14: Maximal stress amplitudes of selected components for different primary control principles (valuesrelated to fatigue strength)



12

HDV1V

HDV1S

HDV2V

HDV2S

HDV3S

VerdpfV

VerdpfS

”UH1V

”UH1S

EK1

”UH2V

”UH3V

”UH3S

EK2

”UH4V

0

0,5

1,0

·10−4Spro

Jah

r

ohne Sekundarregelungmit Sekundarregelung

Figure 16: Absolute values of damage for one yearcontinuous secondary control demand in a coal-firedpower plant

drum (see figure 17).

HD-TromSteigrohre2

HD-TromSpWStutz

1

2

3

4

SS

R/S

ref

Figure 17: Relative increase of damage for one yearof continious secondary control demand in a com-bined cycle plant

However, the respective damage sums have

an order of 10−4. So they are negligible. In

a lignite-fired power plant the amplitudes of

the load changes with the secondary control

demand are relative small and don’t lead to

any wear.

HD

-Tro

mD

am

pfs

tutz

HD

-Tro

mS

teig

roh

re1

HD

-Tro

mS

teig

roh

re2

HD

-Tro

mF

allro

hre

HD

-Tro

mS

pW

Stu

tz

MD

-Tro

mS

teig

roh

re1

0

2

4

6·10−4

Spro

Jahr

ohne Sekundarregelungmit Sekundarregelung

Figure 18: Absolute values of damage for one yearcontinuous secondary control demand in a combinedcycle plant

6.2 Steam Turbines

The superposition of the load changes by a

negative secondary load control signal leads

to an increase of power adjustment and thus

to the transient processes that are resulting

in larger temperature gradients. This leads

to increased lifetime consumption, which is

caused by scheduled load changes.

The impact on the lifetime consumption due

to significant load changes or low load oper-

ation is significant higher compared to any

control operation. This could have an ad-

ditional impact on the cyclic lifetime con-

sumption (table 8).

Cyclenumber LC25 LC + SCHS+SD01 1503 1503HS+SD02 3259 3259

Table 8: Number of cycles of the reference scenarioswith a 25% load change (LC25) and a simultaneous5% secondary load control scenario (SC). IP turbineJaenschwalde.

It has been noted that the influence of par-



Bibliography 13

tialload or lowload is considered as domi-

nant in the investigations and amplified by

possible load control actions.

7 Summary

By liberalization and energy transition ther-

mal power plants in the overall electrical

power supply system are facing increased

requirements and an increased wear. This

can be seen in increased startups and shut-

downs, increasing load gradients and an in-

creased operation modes in low load. This

leads to an operation beyond their primary

dimensioning. Lifetime reduction respec-

tively failure of components are induced by

diverse wear mechanisms

• mechanical wear

• thermal wear

• tribological wear

• corrosion

The influence of primary and secondary con-

trol on fatigue strength corresponding to

DIN EN12952 on selected thick-walled com-

ponents of the water-steam-cycle (except

turbine) were investigated. As a result no

critical influence on the lifetime was deter-

mined. The influence of primary control

on control valves of turbines by tribologi-

cal wear was investigated with the help of

turning points and the overall valve path.

It could be shown that this system service

lead to an at least 20% reduced period of ap-

plication. The overall investigation assumed

integer components without any flaw. Nev-

ertheless the primary and secondary control

and the corresponding frequent small load

changes lead to an increased crack growth

and as a consequence to failure of the com-

ponent. To make a statement about the

overall influence of the liberalisation and en-

ergy turnaround on thermal power plants

the following aspects have to be investigated

in addition

• future scenarios, e.g. load change gra-

dients

• extended tribological investigations,

e.g. friction

• investigation of additional components,

e.g. flue gas system

• inclusion of low load operation

• inclusion of startups and shutdowns

• stress due to decreasing inertia in the

transmission network, e.g. ROCOF

The shown detailed, dynamic power plant

models are suitable for this continuative in-

vestigations.

Bibliography

[1] DIN EN 12952-3 Wasserrohrkessel und

Anlagenkomponenten - Teil 3: Kon-

struktion und Berechnung fur drucktra-

gende Kesselteile. Deutsche Fassung EN

12952-3, 2011.

[2] Dooley, R.B.: Revised Release on the

IAPWS Industrial Formulation 1997 for



Bibliography 14

the Thermodynamic Properties of Water

and Steam. Technical Report, The Inter-

national Association for the Properties

of Water and Steam, 2007.

[3] Gnielinski, V: VDI-Warmeatlas.

Verein Deutscher Ingenieure, 10. Au-

flage edition, 2006.

[4] Internetseite von MATLAB Cen-

tral: Rainflow Counting Algorithm by

Adam Nieslony. www.mathworks.com,

2003.

Index Of Abbreviations

Abbreviation Meaning

2D/ 3D two-/ threedimensional

fig. figure

DT STeam Turbine

E fatigue

ECO Economizer

FEM Finite-Elemente-Method

GuD Combined-Cycle

HD, HP high pressure

HDV high pressure preheater

HS hot start

KW power plant

LW load change

MD, IP intermediate pressure

ND, LP low pressure

NDV low pressure preheater

PR, PC primary control

Sref reference damage sum

Samm, S collector

SD shut down

SpWStutz feedwater nozzle

SR secondary control

Abbreviation Meaning

Trom drum

UH, UEH superheater

Vert, V distributor

vgl. compare

WS war start

ZUH, ZUEH reheater



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