THERMAL STRESS
THERMAL STRESS
HOW IT IS GENERATED IN TURBINE?HOW IT IS GENERATED IN TURBINE?During operational changes of the Turbine say Start-up, Loading &
During operational changes of the Turbine say Start-up, Loading &
unloading the surface of the Turbine components gets heated or
unloading the surface of the Turbine components gets heated or
cooled immediately as it comes in contact with the steam.
cooled immediately as it comes in contact with the steam.
Whereas internals of the turbine components are not able to
Whereas internals of the turbine components are not able to
response that fast.
response that fast.
The result is a differential temperature between Surface (T
The result is a differential temperature between Surface (Tss) ) & & MidMid
metal (T
metal (Tmm)which generates Thermal stress.)which generates Thermal stress.
Because
Because Thermal StressThermal Stress
Ts – Tm (
Ts – Tm (
T)
T)
The more the value of
The more the value of
T the more will be the
T the more will be the
thermal stress
TSE
TSE
WHAT IS THE NEED ?WHAT IS THE NEED ?•
• The The Turbine Turbine is is equipped equipped with with TSE TSE to to assist assist in in optimized optimized Start-
Start-up,operation & Shutdown without impairing the expected
up,operation & Shutdown without impairing the expected
operating life.
operating life.
•
• Time is a prime importance while start-up,loading operation of Time is a prime importance while start-up,loading operation of
Turbine.
Turbine.
•
• At t At the he samsame tie time me it ait also lso very very necnecessessary ary to kto keeeep thp the te thermhermalal
stress
stress in in turbine turbine components components under under control.control.
TSE
TSE
is specifically designed for achieving both
is specifically designed for achieving both
the above mentioned objectives at the same
the above mentioned objectives at the same
time.
The components of TSE
The components of TSE
TSE
TSE
basically consists of three sections.
basically consists of three sections.
1. INPUT SECTION
1. INPUT SECTION
2. COMPUTING DEVICES
2. COMPUTING DEVICES
3.
INPUT SECTION
INPUT SECTION
Input section needs
Input section needs
•
•
Temperature inputs from Turbine components.
Temperature inputs from Turbine components.
•
•
ACTUAL LOAD
ACTUAL LOAD
•
Temperature Inputs
Temperature Inputs
•• TSE takes temperature inputs from five Turbine
TSE takes temperature inputs from five Turbine
components.
components.
They are
They are
1. Emergency Stop Valve.
1. Emergency Stop Valve.
2. HP Control Valve.
2. HP Control Valve.
3. HP Turbine casing.
3. HP Turbine casing.
4. HP Turbine Shaft.
4. HP Turbine Shaft.
5.
WALL TEMPERATURE SENSORS
WALL TEMPERATURE SENSORS
•• The The Temperature Temperature inputs are inputs are supplied supplied by by Ni Ni Cr-Ni Cr-Ni thermocouples thermocouples known asknown as WT SENSORS
WT SENSORS •
• Temperature inputs for stationery parts are obtained from WT Temperature inputs for stationery parts are obtained from WT SensorsSensors having Two legs.
having Two legs. •
• One leg is inserted at 95% One leg is inserted at 95% of the metal depth nearing surface measureof the metal depth nearing surface measure
surface temperature (T
surface temperature (TSS) & another leg is i) & another leg is inserted at 55% of materialnserted at 55% of material
thickness (T
thickness (Tmm).).
•
• For TFor TS &S & TTmm for rotating parts Tfor rotating parts TSS is taken from a plis taken from a place where the Radialace where the Radial
clearance between Casing & Rotor is minimum.
clearance between Casing & Rotor is minimum.
•
• The TThe Tmm is calculated with fair degree of accuracy by means of followingis calculated with fair degree of accuracy by means of following
equation. equation. • • Tm Tm = Ts = Ts [ 1- [ 1- (0.6(0.692 e 92 e -t/T1 -t/T1 + 0.+ 0.131 131 e -t/e -t/T2 T2 + 0.+ 0.177 177 ee -t/Tk ) ] -t/Tk ) ] Where,
Where, Ts Ts : : Surface Surface Temperature Temperature T1 T1 : : 2408.312408.31 Tm
•
• The millivolt (D.C.) output from thermocouple is fed to AnalogThe millivolt (D.C.) output from thermocouple is fed to Analog
Signal Conditioning Cabinet (CJJ05) where it is converted into
Signal Conditioning Cabinet (CJJ05) where it is converted into
4-20
4-20 mA mA signals signals are are fed fed into into TSE TSE CABINET CABINET (CJJ01).(CJJ01).
•
• Act Actual sual speepeed md measeasured ured from from Halls Halls ProbProbe pe providrovided ed in tin turbinurbinee
front pedestal as 4-20 mA signal fed into TSE CABINET.
front pedestal as 4-20 mA signal fed into TSE CABINET.
•
• Act Actual Lual Load oad of Tof Turbourbo-Ge-Generanerator itor is ms measeasured ured & a & a currecurrentnt
signal of 4-20 mA signal fed into TSE CABINET for actual
signal of 4-20 mA signal fed into TSE CABINET for actual
Load indication & computation of Load Margins.
Computation
Computation
•
• The five turbine components has got five computing channels inThe five turbine components has got five computing channels in
computing devices.
computing devices.
•
• Each Computing channel calculates the differenceEach Computing channel calculates the difference TaTa from Tsfrom Ts
& Tm.
& Tm.
Ta = Ts-Tm
Ta = Ts-Tm
•
• The calculated temperature differenceThe calculated temperature difference TaTa is compared with theis compared with the
permissible temperature difference
permissible temperature difference Tp.Tp.
∀
∀ TpTp is derived from limit curve of that particular componentis derived from limit curve of that particular component
already fed into TSE hardware.
already fed into TSE hardware.
•
• These Limit Curves are nothing but maximum permissibleThese Limit Curves are nothing but maximum permissible
temperature difference allowed w.r.t. Tm while heating & cooling.
•
•
The difference between
The difference between
Tp &
Tp &
Ta is
Ta is
called margin.
called margin.
•
•
Comparing
Comparing
Ta
Ta
against
against
Tp
Tp
on the +ve side,
on the +ve side,
we get UPPER
we get UPPER
MARGIN & the same on the
MARGIN & the same on the
–ve side we get LOWER M
Suppose at any particular condition
Suppose at any particular condition
Ts of
Ts of HP Casing HP Casing = = 300 300 deg cdeg c
Tm of HP Casing = 240 deg c
Tm of HP Casing = 240 deg c
∆ Ta= Ts-Tm= 300-240=60 deg c
∆ Ta= Ts-Tm= 300-240=60 deg c
From upper limit curve when Tm = 240 deg c
From upper limit curve when Tm = 240 deg c
Then Max upper permissible temp diff (∆ Tpu) = 100 deg
Then Max upper permissible temp diff (∆ Tpu) = 100 deg
c
c
Max lower permissible temp diff (∆ Tpl) = -60 deg c
Max lower permissible temp diff (∆ Tpl) = -60 deg c
So the Upper margin =
•• The inference of the above computation of upper &
The inference of the above computation of upper &
lower temperature is that Surface temp
lower temperature is that Surface temp T
T
sscan
can be
be
increased by 40 deg c (to the level of 340 deg c) is
increased by 40 deg c (to the level of 340 deg c) is
known as
known as
Upper margin
Upper margin
.
.
•• Similarly
Similarly T
T
sscan be decreased by 120 deg c is known
can be decreased by 120 deg c is known
as
as
Lower margin.
Lower margin.
•
•
Thus the upper & lower margin for all the five turbine
Thus the upper & lower margin for all the five turbine
components calculated in similar fashion.
components calculated in similar fashion.
•
•
The minimum upper margin & minimum lower margin
The minimum upper margin & minimum lower margin
among them is selected separately for display purpose
among them is selected separately for display purpose
& as well fed to EHC for controlling speed rate & load
& as well fed to EHC for controlling speed rate & load
rate.
•• TSE OUTPUT SIGNAL GOES TO
TSE OUTPUT SIGNAL GOES TO
•
•
TSE DISPLAY
TSE DISPLAY
•
•
TSE MARGIN RECORDER
TSE MARGIN RECORDER
•
•
ATRS
ATRS
•
•
CMC
CMC
•• EHC
EHC
SPEED CONTROLLER
SPEED CONTROLLER
LOAD CONTROLLER
LOAD CONTROLLER
TSE DISPLAY
TSE DISPLAY
•
•
TSE DISPLY
TSE DISPLY
TSE DISPLAY has two
TSE DISPLAY has two separate sections
separate sections
1. One is up
1. One is up
to synchronisation stage.
to synchronisation stage.
2. Another for
2. Another for
Load condition.
Load condition.
The sections are illuminated according to
The sections are illuminated according to
operating mode
operating mode
•
•
ADMISSION OR TURBINE MODE HAS THE
ADMISSION OR TURBINE MODE HAS THE
MARKING ON WHITE SCALE INDICATES
MARKING ON WHITE SCALE INDICATES
THE ACTUAL SPPED OF THE TG
THE ACTUAL SPPED OF THE TG
SET.
SET.
•
•
THE UPPER BOUNDARY OF
THE UPPER BOUNDARY OF
TRANSPARENT SECTOR INDICATES THE
TRANSPARENT SECTOR INDICATES THE
UPPER MARGIN FOR SPEEDING UP.
UPPER MARGIN FOR SPEEDING UP.
•• THE TOP RECTANGLE(ADM. MODE) & LED
THE TOP RECTANGLE(ADM. MODE) & LED
(TURBINE MODE) GETS ILLUMINATED AND
(TURBINE MODE) GETS ILLUMINATED AND
INDICATES THE COMPONENT WHICH IS
INDICATES THE COMPONENT WHICH IS
CAUSE FOR IMPOSING MARGIN.
ADMISSION MODE
ADMISSION MODE
•
•
ADMISSION MODE IS
ADMISSION MODE IS
SELECTED BEFORE OPENING
SELECTED BEFORE OPENING
STOP VALVES.
TURBINE MODE
TURBINE MODE
•
•
THIS MODE IS SELECTED BEFORE
THIS MODE IS SELECTED BEFORE
OPENING THE CONTROL VALVES FOR
OPENING THE CONTROL VALVES FOR
SOAKING OR SPEEDING UP.
SOAKING OR SPEEDING UP.
•
•
PRE-SELECTION SWITCH FOR SELECTION
PRE-SELECTION SWITCH FOR SELECTION
OF ADMISSION OR TURBINE MODE ARE
OF ADMISSION OR TURBINE MODE ARE
PROVIDED ON THE CONSOLE.
PROVIDED ON THE CONSOLE.
•• THE ABOVE TWO MODES ARE DISPLAYED
THE ABOVE TWO MODES ARE DISPLAYED
ON THE L.H.S. OF TSE DISPLAY.
LOAD MODE
LOAD MODE
•
• THE TSE INDICATOR SWITCHES OVER TO RIGHT HANDTHE TSE INDICATOR SWITCHES OVER TO RIGHT HAND
SECTION ONCE THE LOAD >2% MCR.
SECTION ONCE THE LOAD >2% MCR.
•
• DURINNG LOAD OPERATION THE DISPLAY INDICATESDURINNG LOAD OPERATION THE DISPLAY INDICATES
•
• ACTUAL LOAD ( ACTUAL LOAD ( MARKING)MARKING)
•• UPPER & LOWER LOAD MARGINS WHICH SIGNIFIESUPPER & LOWER LOAD MARGINS WHICH SIGNIFIES MAXIMUM LOADING & UNLOADING LIMIT AT
MAXIMUM LOADING & UNLOADING LIMIT AT THATTHAT MOMENT.
•• TSE OUTPUT SIGNAL GOES TO
TSE OUTPUT SIGNAL GOES TO
•
•
TSE DISPLAY
TSE DISPLAY
•
•
TSE MARGIN RECORDER
TSE MARGIN RECORDER
•
•
ATRS
ATRS
•
•
CMC
CMC
•• EHC
EHC
SPEED CONTROLLER
SPEED CONTROLLER
LOAD CONTROLLER
LOAD CONTROLLER
•
•
Speed controller output (
Speed controller output (
EHC OUTPUT)
EHC OUTPUT)
gets blocked if
gets blocked if
Turbine speed >2850 r.p.m.
Turbine speed >2850 r.p.m.
and
and
TSE
TSE
GETS
GETS
FAULTED
FAULTED
•
•
LOWER MARGIN IS NOT USED IN SPEED
LOWER MARGIN IS NOT USED IN SPEED
CONTROLLER AS TURBINE COASTING
CONTROLLER AS TURBINE COASTING
DOWN IS NATURAL.
•
•
NEGATIVE LOAD MARGIN CAN
NEGATIVE LOAD MARGIN CAN
UNLOAD THE MACHINE WHEREAS
UNLOAD THE MACHINE WHEREAS
REDUCRD LOWER MARGIN CAN
REDUCRD LOWER MARGIN CAN
PREVENT TURBINE FROM
PREVENT TURBINE FROM
UNLOADING.
TSE
TSE
INFLUENCE
INFLUENCE
TO
TO
ATRS
ATRS
•
• SGC Turbine can not be made ON if TSE is N/A.SGC Turbine can not be made ON if TSE is N/A.
•
• TSE upTSE upper mper margin is argin is one oone of criteria f criteria needed needed for thefor the
next step (No. 15) and subsequently speed raise
next step (No. 15) and subsequently speed raise
to 3000 r.p.m.
to 3000 r.p.m.
•
•
Speed raise is held up till upper margin is not
Speed raise is held up till upper margin is not
more than 30 deg c.
more than 30 deg c.
•
• SGC Turbine start up programme gets switched off SGC Turbine start up programme gets switched off
while Rolling (600-2850 r.p.m.)if TSE
while Rolling (600-2850 r.p.m.)if TSE Upper MarginUpper Margin
<0 deg c.
<0 deg c.
•
USE OF MARGIN IN CMC
USE OF MARGIN IN CMC
•• Minimum of
Minimum of TSE lower margin
TSE lower margin
&
& Unit Load Rate
Unit Load Rate
(in CMC Console) is
(in CMC Console) is considered as allowable load
considered as allowable load
rate
rate at
at which
which the
the unit
unit would
would be
be unloaded.
unloaded.
•• Minimum of
Minimum of TSE upper margin
TSE upper margin
&
& Unit Load Rate
Unit Load Rate
is considered as allowable load rate at which
is considered as allowable load rate at which the
the
unit would be loaded.
TSE TEST
TSE TEST
•• For checking the proper functioning of the five computingFor checking the proper functioning of the five computing
channels from INPUT SECTION up to DISPLAY, known INPUT
channels from INPUT SECTION up to DISPLAY, known INPUT
signals can be applied (by pressing test buttons) to get a
signals can be applied (by pressing test buttons) to get a
predetermined results.
predetermined results.
•• Testing of five computing channels are possible only if Testing of five computing channels are possible only if
1. NO EHC FAULT
1. NO EHC FAULT
2. NO TEST PROGRAMMING BLOCK FROM ATRS
2. NO TEST PROGRAMMING BLOCK FROM ATRS
If there is any deviation TSE should not be used till fault is cleared