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.
Institute of Electrical Power EngineeringChair of Technical Thermodynamics
Chair of Structural Mechanics
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
Institute of Electrical Power EngineeringChair of Technical Thermodynamics
Chair of Structural Mechanics
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-
Institute of Electrical Power EngineeringChair of Technical Thermodynamics
Chair of Structural Mechanics
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
pos./neg. LC 15-30 % PN
pos./neg. LC 30-40 % 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.
Institute of Electrical Power EngineeringChair of Technical Thermodynamics
Chair of Structural Mechanics
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.
Institute of Electrical Power EngineeringChair of Technical Thermodynamics
Chair of Structural Mechanics
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
Institute of Electrical Power EngineeringChair of Technical Thermodynamics
Chair of Structural Mechanics
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
Institute of Electrical Power EngineeringChair of Technical Thermodynamics
Chair of Structural Mechanics
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.
Institute of Electrical Power EngineeringChair of Technical Thermodynamics
Chair of Structural Mechanics
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
Institute of Electrical Power EngineeringChair of Technical Thermodynamics
Chair of Structural Mechanics
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
Institute of Electrical Power EngineeringChair of Technical Thermodynamics
Chair of Structural Mechanics
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)
Institute of Electrical Power EngineeringChair of Technical Thermodynamics
Chair of Structural Mechanics
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-
Institute of Electrical Power EngineeringChair of Technical Thermodynamics
Chair of Structural Mechanics
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
Institute of Electrical Power EngineeringChair of Technical Thermodynamics
Chair of Structural Mechanics
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
Institute of Electrical Power EngineeringChair of Technical Thermodynamics
Chair of Structural Mechanics