Mukharji TSE

7/31/2019 Mukharji TSE

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THERMAL STRESS HOW IT IS GENERATED IN TURBINE?

During operational changes of the Turbine say Start-up, Loading &

unloading the surface of the Turbine components gets heated or

cooled immediately as it comes in contact with the steam.

Whereas internals of the turbine components are not able to

response that fast.

The result is a differential temperature between Surface (Ts) & Mid

metal (Tm)which generates Thermal stress.

Because Thermal Stress Ts Tm ( T)

The more the value of T the more will be the

thermal stress.


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TSE WHAT IS THE NEED ?

The Turbine is equipped with TSE to assist in optimized Start-

up,operation & Shutdown without impairing the expected

operating life.

Time is a prime importance while start-up,loading operation of

Turbine.

At the same time it also very necessary to keep the thermal

stress in turbine components under control.

TSE is specifically designed for achieving both

the above mentioned objectives at the same

time.


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The components of TSE

TSE basically consists of three sections.

1. INPUT SECTION

2. COMPUTING DEVICES

3. OUTOUT DEVICES


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INPUT SECTION

Input section needs

Temperature inputs from Turbine components.

ACTUAL LOAD

ACTUAL SPEED


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Temperature Inputs

TSE takes temperature inputs from five Turbinecomponents.

They are

1. Emergency Stop Valve. 2. HP Control Valve.

3. HP Turbine casing.

4. HP Turbine Shaft.

5. IP Turbine Shaft.


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WALL TEMPERATURE SENSORS

The Temperature inputs are supplied by Ni Cr-Ni thermocouples known as

WT SENSORS

Temperature inputs for stationery parts are obtained from WT Sensorshaving Two legs.

One leg is inserted at 95% of the metal depth nearing surface measure

surface temperature (TS) & another leg is inserted at 55% of materialthickness (Tm).

For TS & Tmfor rotating parts TS is taken from a place where the Radialclearance between Casing & Rotor is minimum.

The Tmis calculated with fair degree of accuracy by means of followingequation.

Tm = Ts [ 1- (0.692 e -t/T1 + 0.131 e -t/T2 + 0.177 e-t/Tk ) ]Where, Ts : Surface Temperature T1 : 2408.31

Tm : Mid metal Temperature T2 : 457.08t : Time in minutes Tk : 56.62


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The millivolt (D.C.) output from thermocouple is fed to Analog

Signal Conditioning Cabinet (CJJ05) where it is converted into

4-20 mA signals are fed into TSE CABINET (CJJ01).

Actual speed measured from Halls Probe provided in turbine

front pedestal as 4-20 mA signal fed into TSE CABINET.

Actual Load of Turbo-Generator is measured & a currentsignal of 4-20 mA signal fed into TSE CABINET for actual

Load indication & computation of Load Margins.


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Computation

The five turbine components has got five computing channels in

computing devices. Each Computing channel calculates the difference Ta from Ts

& Tm.

Ta = Ts-Tm The calculated temperature difference Ta is compared with the

permissible temperature difference Tp.

Tp is derived from limit curve of that particular componentalready fed into TSE hardware.

These Limit Curves are nothing but maximum permissible

temperature difference allowed w.r.t. Tm while heating & cooling.


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The difference between Tp & Ta iscalled margin.

Comparing Ta against Tp on the +ve side,

we get UPPER MARGIN & the same on the

ve side we get LOWER MARGIN.


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Suppose at any particular condition

Ts of HP Casing = 300 deg c

Tm of HP Casing = 240 deg c

Ta= Ts-Tm= 300-240=60 deg c

From upper limit curve when Tm = 240 deg c

Then Max upper permissible temp diff ( Tpu) = 100 deg

c

Max lower permissible temp diff ( Tpl) = -60 deg c

So the Upper margin = ( Tpu- Ta) =100-60=+40 deg c& the Lower margin = ( Tpl- Ta) =-60-60 =-120 deg c

Th i f f h b i f &


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The inference of the above computation of upper &

lower temperature is that Surface temp Tscanbe

increased by 40 deg c (to the level of 340 deg c) is

known as Upper margin. Similarly Ts can be decreased by 120 deg c is known

as Lower margin.

Thus the upper & lower margin for all the five turbine

components calculated in similar fashion.

The minimum upper margin & minimum lower marginamong them is selected separately for display purpose

& as well fed to EHC for controlling speed rate & load

rate.


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TSE OUTPUT SIGNAL GOES TO

TSE DISPLAY

TSE MARGIN RECORDER

ATRS

CMC

EHC

SPEED CONTROLLER

LOAD CONTROLLER

TSE DISPLAY


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TSE DISPLAY

TSE DISPLY

TSE DISPLAY has two separate sections

1. One is up to synchronisation stage.

2. Another for Load condition.

The sections are illuminated according to

operating mode


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ADMISSION OR TURBINE MODE HAS THEMARKING ON WHITE SCALE INDICATES

THE ACTUAL SPPED OF THE TG SET.

THE UPPER BOUNDARY OF

TRANSPARENT SECTOR INDICATES THEUPPER MARGIN FOR SPEEDING UP.

THE TOP RECTANGLE(ADM. MODE) & LED(TURBINE MODE) GETS ILLUMINATED ANDINDICATES THE COMPONENT WHICH ISCAUSE FOR IMPOSING MARGIN.


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ADMISSION MODE

ADMISSION MODE IS

SELECTED BEFORE OPENING

STOP VALVES.


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TURBINE MODE

THIS MODE IS SELECTED BEFOREOPENING THE CONTROL VALVES FOR

SOAKING OR SPEEDING UP.

PRE-SELECTION SWITCH FOR SELECTION

OF ADMISSION OR TURBINE MODE ARE

PROVIDED ON THE CONSOLE.

THE ABOVE TWO MODES ARE DISPLAYED

ON THE L.H.S. OF TSE DISPLAY.


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LOAD MODE

THE TSE INDICATOR SWITCHES OVER TO RIGHT HANDSECTION ONCE THE LOAD >2% MCR.

DURINNG LOAD OPERATION THE DISPLAY INDICATES

ACTUAL LOAD ( MARKING)

UPPER & LOWER LOAD MARGINS WHICH SIGNIFIES

MAXIMUM LOADING & UNLOADING LIMIT AT THATMOMENT.


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TSE OUTPUT SIGNAL GOES TO

TSE DISPLAY

TSE MARGIN RECORDER

ATRS

CMC

EHC

SPEED CONTROLLER

LOAD CONTROLLER


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Speed controller output ( EHC OUTPUT)gets blocked if

Turbine speed >2850 r.p.m.

and

TSE GETS FAULTED

LOWER MARGIN IS NOT USED IN SPEED

CONTROLLER AS TURBINE COASTINGDOWN IS NATURAL.


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NEGATIVE LOAD MARGIN CANUNLOAD THE MACHINE WHEREASREDUCRD LOWER MARGIN CAN

PREVENT TURBINE FROMUNLOADING.

TSE INFLUENCE TO ATRS


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TSE INFLUENCE TO ATRS

SGC Turbine can not be made ON if TSE is N/A.

TSE upper margin is one of criteria needed for thenext step (No. 15) and subsequently speed raiseto 3000 r.p.m.

Speed raise is held up till upper margin is notmore than 30 deg c.

SGC Turbine start up programme gets switched offwhile Rolling (600-2850 r.p.m.)if TSE Upper Margin


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USE OF MARGIN IN CMC


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USE OF MARGIN IN CMC

Minimum ofTSE lower margin & Unit Load Rate(in CMC Console) is considered as allowable load

rate at which the unit would be unloaded.

Minimum ofTSE upper margin & Unit Load Rate

is considered as allowable load rate at which the

unit would be loaded.


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TSE TEST For checking the proper functioning of the five computing

channels from INPUT SECTION up to DISPLAY, known INPUTsignals can be applied (by pressing test buttons) to get apredetermined results.

Testing of five computing channels are possible only if1. NO EHC FAULT

2. NO TEST PROGRAMMING BLOCK FROM ATRS

If there is any deviation TSE should not be used till fault is cleared


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Procedure adopted in case of lost upper Margin

The turbine should not be loaded further.

Reduction of steam temperature by cuttingdown firing.

Soaking the turbine for sufficient time period.


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Procedure adopted in case of lost lower Margin

Avoidance of further unloading.

Increase firing to increase steam temperature.

Soaking the machine.


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Mukharji TSE

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