WELCOMEWELCOME TO TO

ALL ALL

STEAM TURBINE GOVERNING SYSTEM

By Mr. V.MANI. ACM/Turbine Efficiency

GOVERNING SYSTEMGOVERNING SYSTEM

Digital Electro-Hydraulic Governing system.

No mechanical Governing back up.

Automatic Startup, Synchronization and Loading of

Turbine.

Automatic Unloading.

Operator actions reduced to the minimum during

normal operation.

DEHC CONTROLSDEHC CONTROLS

Consists of two portions

Digital Electronic controller

Electro-Hydraulic convertor.

Speed control - Speed loop

Unit loading (Manual control)-Manual loop

MW Controller (with Coordinated mode)-Load loop

Main steam pressure controller-Pressure loop

Limiters &Trimming device

Automatic turbine tests.

Rotor Stress Evaluator

EHC CONTROLLER FUNCTIONSEHC CONTROLLER FUNCTIONS

EHC CONTROLLER FUNCTIONSEHC CONTROLLER FUNCTIONS

Speed loop

Manual loop

Load loop

Pressure loop

Selection circuit

Admission controller

Control valve

Used during start up only Speed measurement Speed set. Speed control Critical speed range logic (800-1300&2300-2750rpm) Acceleration limiter action. Synchronization

SPEED CONTROL SPEED CONTROL

SPEED CONTROL SPEED CONTROL

Speed Controller

Speed Target

Speed reference

limiter

From RSE

Speed reference

+

Actual SpeedSet from

DCS

Acceleration protection.-Generator Breaker Open.• Speed > 75%(2250rpm)• Acceleration >25% of rated speed(750 rpm/min)-Generator breaker closed.• Speed > 101%(3030rpm)• Acceleration >20% of rated speed (600rpm/min)

SPEED CONTROL SPEED CONTROL

Initial load pick-up

Manual control

UNIT LOADING (MANUAL MODE)UNIT LOADING (MANUAL MODE)

MS pressure measurement MS pressure set MS pressure controller

MAIN STEAM PRESSURE CONTROLLER MAIN STEAM PRESSURE CONTROLLER

( (TURBINE FOLLOW MODETURBINE FOLLOW MODE))

MAIN STEAM PRESSURE CONTROLLER MAIN STEAM PRESSURE CONTROLLER

( (TURBINE FOLLOW MODETURBINE FOLLOW MODE))

+

Pressure controller

MS Pressure

set

Actual MS

Pressure

MW measurement MW set MW controller MS pressure correction

MW CONTROLLER MW CONTROLLER

(ALONG WITH COORDINATED MODE)(ALONG WITH COORDINATED MODE)

MW CONTROLLER MW CONTROLLER

(ALONG WITH COORDINATED MODE)(ALONG WITH COORDINATED MODE)

Actual MW

+MW Reference

MW controller

HP exhaust temp limiter.

Reheat pressure limiter.

Condenser pressure limiter.

Main steam pressure limiter.

Run-back limiter.

LIMITERSLIMITERS

Adjusts steam flow to HP/IP Turbine during

speed run up and unit loading to avoid churning

of the rotor.

TRIMMING DEVICETRIMMING DEVICE

Coordinate Boiler & Turbine operation.

Run back system operation.

Permissive load >10%.

CO-ORDINATED MODE (CMC MODE)CO-ORDINATED MODE (CMC MODE)

Load setter – Load set By board Engineer.

- Load limiter- Limit the set to Max level & Min level.

- Load rate control- Set By board Engineer or From RSE.

-Load capability limiter- Limit the set by mills capability.

-Load set correction by frequency influence - if enabled.

-Load demand signal to Boiler Master&Turbine MW control

CO-ORDINATED MODE OPERATIONCO-ORDINATED MODE OPERATION

- Load demand signal to Turbine MW control set

point. (corrected by MS pressure controller)

&

- MS pressure controller signal corrected by Load

demand signal to Boiler Master control.

CO-ORDINATED MODE-OPERATIONCO-ORDINATED MODE-OPERATION

Turbine operation.

-Turbine MW control.

-Turbine control valve operation.

CO-ORDINATED MODE (CMC MODE)CO-ORDINATED MODE (CMC MODE)

Boiler operation.

-Boiler Master auto.

-Coal Master auto- controls fuel rate.

-Air Master auto- controls air rate.

CO-ORDINATED MODE (CMC MODE)CO-ORDINATED MODE (CMC MODE)

ROTOR STRESS EVALUATOR(RSE)ROTOR STRESS EVALUATOR(RSE)

Protects the rotor against inadmissible thermal stress.

Calculates the Thermal Stress of HP & IP rotor Indicates Loading &unloading margin The stress capability of Turbine is fully utilised all

the time. Alarm the Board Engineer Trips the Turbine while exceeding the limit. Saves time when running-up the steam turbine. Relieves the Board Engineer from supervisory

functions.  RSE can be enabled & disenabled any time in DCS  

ROTOR STRESS EVALUATOR(RSE)ROTOR STRESS EVALUATOR(RSE)

• HP& IP starting probe temp is used for calculating HP & IP Loading margin and HP unloading margin.

• Lowest value between the loading margin of HP & IP rotor and unloading margin of HP rotor is normally selected for controlling purpose.

UPPER & LOWER MARGINS OF RSEUPPER & LOWER MARGINS OF RSE

Permissible thermal stress for unloading

Permissible thermal stress for loading

Mean Integral Wall Temp

The

rmal

Str

ess

DT

= T

i - T

m

B

A

C

D

G

E

F

H

Tm

LEGEND

Ti- Inner surface metal temp

Tm- Mean integral wall temp

AC- Current thermal stress while loading the turbine

AB- Upper margin

AD- Lower margin

EG- Current thermal stress while loading the turbine

EH- Upper margin

EF- Lower margin

ROTOR STRESS EVALUATOR(RSE)......ROTOR STRESS EVALUATOR(RSE)......

Rotor Stress EvaluatorRotor Stress Evaluator Calculates:Calculates:• The Accelebration level during start up• The Stop accelebration level(in case of low margin)• The run back level(decrease speed in case of negative

margin.)• The Loading gradient of the Turbine• The very high stress limit when Turbine is loaded.

(Unload the turbine)• The trip levels for extremely high stress.

STEAM TURBINE SUPERVISORY SYSTEMSTEAM TURBINE SUPERVISORY SYSTEM

The turbine must be supervised for safe running conditions.

The turbine supervision system is an inductive / electronic type system.

Parameters measured are used for indication, annunciation and for trip purpose.

STEAM TURBINE SUPERVISORY SYSTEMSTEAM TURBINE SUPERVISORY SYSTEM

Includes measurement of: Absolute Expansion. Differential Expansion. Axial position.(Thrust bearing wear) Relative shaft vibration

Absolute Thermal Expansion of Turbine cylinder with respect to fixed point .

Measured at HPT front pedestal. Measured on LVDT principle. Indicates complete expansion of casing with out

any constraint. Indication purpose only. No protection.

ABSOLUTE CASING EXPANSIONABSOLUTE CASING EXPANSION

Differential Expansion is the difference in the thermal expansion of rotor and casing.

HP differential expansion measured at HPT front pedestal.

LP differential expansion measured at LPT rear pedestal.

Measured by proximity sensors. DE tends to increase during start up, loading and

unloading and shut down. Uncontrolled DE is unsafe for operation. Indication purpose only. No protection.

DIFFERENTIAL EXPANSIONDIFFERENTIAL EXPANSION

Axial shift is the physical shift of rotor due to the action thrust on it.

Turbine rotors are perfectly balanced using balancing pistons.

The shift of rotor happens in case of unbalanced condition.

To maintain proper axial position and take care of any unbalanced axial thrust TG rotor is positioned and supported by collar thrust bearing.

Thrust bearing located between HPT& IPT. Measured on non-contact inductive principle. Trips the Turbine if value exceeds +0.8mm.

AXIAL POSITION (THRUST BEARING WEAR)AXIAL POSITION (THRUST BEARING WEAR)

Indicates the safe running of equipment. Relative shaft vibration is measured in all the 5

bearings at 450 angle &3150 angle Non contact type transducers used. Alarm level 170µ Trip level 260µ

ROTOR VIBRATIONSROTOR VIBRATIONS