Topics of Presentation Overview of Turbine

Concept of Governing System

Functioning of EHC Circuits

Turbine Start Up Procedure

TSI & TSC System

Turbine Protection System

Turbine Block Diagram

Ext.No

Source Of Extraction Destination Equipments

1 13th stage of HPT HPH-8

2 CRH HPH-7

3 3rd stage of IPT HPH-6 *

3 3rd stage of IPT TDBFP

4 6th stage of IPT DEAERATOR

5 8th stage of IPT LPH-4

6 11th stage of IPT LPH-3

7 2nd stage of LPT LPH-2

8 4th stage of LPT LPH-1

Turbine Extractions

Turbine Components

Turbine: HPT, IPT, LPT1 and LPT2 Turbine Bearings: 08 Generator / Exciter Bearings: 04 Turbine Stop Valves: 04 (HPSV-1&2, IPSV-1&2) Turbine Control Valves: 08 (4 HPCV & 4 IPCV) CRH Check Valves: 02 ( With Bypass lines for warm up) Motor driven Shut Off valve in non-stabilized oil line to

Check Valve Motor driven warm up Shut Off valves for HPCV-3 & 4 Governing Box

Overview of Governing Box

Governing Box Components Motor operated Control Gear to generate resetting /

protection oil & control oil for S.V./ Summators

Two Manual trip devices

Two Over Speed Governor Slide valves (110 % & 111 %)

Two Remote Trip Solenoids

Slide Valve for ATT with two solenoids

Governing System Combination of throttle & nozzle governing IP Turbine has throttle governing – all four control

valves open simultaneously HP Turbine has nozzle governing – all four control

valves open in preset sequence Resetting of Turbine is done by Control Gear operation Operation of Stop & Control Valves and CRH Check

Valves are done by spring type hydraulic servomotors Servomotors are closed by spring action during loss of

oil pressure

Governing System HPT control valves open only after achieving preset load

(12% of 660 MW) Opening time of control valve is 1.5 sec Closing time of Stop valve in case of operation of

protection is 0.3 sec Turbine maximum speed is restricted to 108% in case of

generator disconnected from grid Over speed protection system stops steam supply in

HPC in < 0.5s Speed Controller Droop is adjustable from 2.5% to 8%

(with dead band of 0.04%)

Resetting of Turbine

Stabilized oil pressure of 50 Ksc is supplied to Control Gear

The control gear (AE001) is moved from closed position (0 degree) to open position (90 deg)

Oil is first supplied to reset the over speed governor slide valves

Subsequently Protection Oil is generated and supplied to protection devices

Finally, Control Oil for Stop Valves servomotors & Control Oil for EHC-summators are generated

Resetting of Turbine

Operation of Stop Valve

Control Oil pressure in S.V. servomotor moves up slide valve, providing Header Pressure Oil under the piston for S.V. opening

Header Pressure Oil is supplied to C.V. valve servomotors via locking pilot valve & traction/bush arrangements. Opening of C.V. is governed by Control Oil from EHC-Summator

During loss of Header Pressure Oil, the servomotors are closed by spring action

During loss of Control Oil pressure, Bush & Traction of Pilot valve travels up shutting off head pressure oil supply to C.V. servomotors, resulting control valve closing

During S.V. ATT, bush & Traction do not travel up due to slide valve downward movement by ATT motor

Operation of Stop & Control Valves

Components of EHC EHC comprises of following controllers:

1. Speed Controller

2. Pressure Controller

3. Load Controller

4. Position Controller

Selection of Controls EHC can be kept in Manual / Auto Mode as per

operator’s choice Manual mode can be selected only when Generator is

connected to grid

In Manual Mode, operator can directly open / close the control valves

Controllers can be selected in auto mode through P.B provided on operators console or through interlocks

Controller output in auto mode depends on set point and actual value

Speed Control Circuit

Logic-1

Speed Set Point

R

L

Speed Set Point = 0

Rate Logic

Logic - 2

Actual Speed (Mv3)

+

-Speed Controller O/P

Logic 1: Turbine protection operated / 2v4 stop valves closed / 2v3 speed measuring channels faulty / Deviation between actual speed and set point during run-up exceeded allowable value*

Logic 2: Speed gradient is controlled by minimum of TSE margin & gradient from selected Start up curve, given by the Turbine Manufacturer

Contd….

Rolling Speed Gradient CurveSpeed gradients as per Manufacturer’s start up curve are as follows:Rolling Condition

Target Speed Preset Time Min. Halt Time

Cold Startup ( > 72 H )

3 - 500 rpm 150 sec 300 sec

1200 rpm* 550 sec 300 sec

3000 rpm 630 sec --------

Between 36H – 72H3 - 500 rpm 75 sec 120 sec

3000 rpm 240 sec --------

Between 8H – 36H 3 - 3000 rpm 360 sec --------

Between 2H – 8H3 - 3000 rpm 300 sec --------

Speed Control Circuit Speed Controller will be switched on automatically in

case generator breaker opens (with Turbine controller on auto) or Turbine trips

Turbine speed measurement is be done by using 3 sensors (eddy current type)

The mean* of the three sensors is taken as actual speed

Incase of one sensor fault, maximum of rest two sensors will come in service

Incase of two sensor fault, Turbine trip signal is generated to trip the turbine

Speed Ref Tracking: After Synchronization, with other controller in service, the speed controller tracks the actual speed between 49HZ to 51HZ (adjustable)

Islanding Mode: If actual speed exceeds speed reference by a preset limit under Generator Breaker in closed condition, Islanding mode occurs – Transferring Turbine to Speed Control mode

Speed Control Circuit

Load Control Circuit Load Control On: Load Controller will be switched on

automatically if Turbine controller is kept on auto and connected to the grid under “Turbine Latched” condition.

Load Control Off: Load controller will be switched off under following conditions:1. Manual control mode is switched on

2. The Generator has disconnected from the grid3. The grid frequency has gone beyond allowable limits4. Load Measurement faulty (2/3 sensors faulty)5. M.S. Pres. measurement faulty (2V3 sensors faulty)

6. Unit is in Pressure Control mode

Load Control Circuit

Load Ref

R

L Delay Element

Max.Load Lim. Min.Load Lim.

Correction C.K.T

Freq. Corr

Press. Corr

Fast Tracking

Actual Load

+-

O/P

Logic - 4

5

6

STOP3

21

Logic-1: CMC ON, when load ref. will come from CMC circuit, where TSC

Margin calculation controls the gradient

Logic-2: The Load reference tracks actual load for bump less transfer

once it is connected to the grid.

Contd…

Logic-3: Load Reference will be stopped under the following Conditions:

1. TSC Margin is less than permissible value*

2. The difference between the actual and reference value is not in allowable range

Logic-4: Maximum and minimum load set points, set by the Operator

Logic-5: External Frequency Influence ON - actual frequency will be tracked at a predefined delayed rate, with an adjustable droop to help in loading and unloading of the machine within a band of frequency

Contd…

Load Control Circuit

Load Control Circuit

Logic – 6: The Pressure correction is divided into two Parts:

1. Before the “HPC On” is generated, the pressure correction will be calculated with R.H. pressure

2.After “HPC On” is generated, the pressure correction will be calculated with M.S pressure

HPC On: The point at which the HP Control Valves starts Opening (12% of full load)

Load Measurement: Three Transducers with mean* value selection

Incase of one of the transducer failed, maximum of rest two.will be selected

Pressure Control Circuit

Pressure Control is switched ON by the operator or automatically through Turbine Control on auto when HPC is in operation

Pressure Controller is automatically deactivated under the following conditions:

1. GCB Open2. The frequency is more than allowable value*3. M.S. pressure transducers failed (2V3)4. Manual Control switched on5. Load control is On6. HPC is out of operation

Pressure Control

• M.S. pressure set point is dictated by Boiler Master

• Limitation of pressure drop to impermissible value is ensured by minimum pressure controller

• Limitation of pressure rise to impermissible value is ensured by a protective control stage maximum steam pressure controller, which comes into operation through maximum value selector

Adder Block

M. S. Pr. Set Point

Actual Pr. Value +

-PI

ControllerMIN

Minimum Pr.Controller

MAX

Control Stage Max Pr. Controller

O/P

Position Control Circuit

• A PI controller is used to generate the signal to the current amplifiers through Limiter• Command to HP control valves extends under “HPC ON” condition• Loss of current signal to I/H Converter results in closing of the C.V.

MV2

Posn. F/B - 1

Posn. F/B - 2

Control Signal From TC+

- PI

+

+MIN

Limiter

O/P- (0-150mA)

Biasing Current 0.8 to 1A

TO I/HCONVERTOR

Operation of I/H Converter

I/H Converters control the opening and closing of the corresponding control valves

Individual I/H converters get command from Turbine controller

50 Ksc Header Pressure Oil holds the piston (2) up against spring action

As the slide valve (1) moves as per I/H converter, 35 Ksc control oil output is regulated for C.V. servomotor operation

When 50 KSC Governing oil pressure collapses, piston (2) travels down due to spring action – thus draining the oil line of C.V. servomotor

Operation of I/H Converter

Control Valve Opening Curve

Turbine Start Up Sequence Start Turbine rolling with Speed Control on from barring

speed to 500 rpm After achieving desired criteria, raise speed set point to 1200

rpm* and subsequently to 3000 rpm After synchronization Load Controller gets switched On –

raise load > 80MW when “HPC ON” signal is generated Turbine Pressure Control will be automatically switched On After HPCV demand crosses 80%, switch ON Position

controller to hold 80% as the o/p to control valves for raising pressure to rated value

Switch ON Pres. Controller to raise load to rated value Switch ON Load Control after load reaches the rated value

START UP CURVES OF TURBINE AFTER SHUTDOWN OF THE UNIT

Start Up Curves Nomenclature To – S.H Live steam temperature. Trh – R.H steam temperature Po – S.H outlet steam pressure Prh – R.H. steam pressure Go – Electrical Load of TG Ne – Live steam flow from boiler N – Turbine rotor speed A – Steam Admission B – Synchronization C – HPC switch on D – HPCV open with 20% Throttle reserve & Loading with

constant HPCV position & HP heaters charged E – HPCV no-3 opening. Throttle pressure reduced F – Full Load

START UP CURVES OF TURBINE AFTER SHUTDOWN OF THE UNIT

START UP CURVES OF TURBINE AFTER SHUTDOWN OF THE UNIT

Turbovisory Instruments Turbo Generator consists of 12 bearings – 8 for Turbine

& 2 for Generator & 2 for Exciter

For Bearing no. 1-10, abs. brg. vibration is measured in 3 components (Horizontal, Vertical & Horizontal axial)

For Bearing no. 11 & 12, abs. brg. vibration is measured in 2 components (Horizontal & Vertical)

Absolute shell vibration is measured for all the bearings in 2 components (Horizontal & Vertical)

Rotor Relative Vibration is measured in all the bearings in 2 components

Absolute Rotor Vibration is derived from Absolute Bearing Shell Vibration and Rotor Relative Vibration for all the bearings

Axial Shift measurement is done in Bearing no. 3

Eccentricity measurement is done in Bearing no. 1

Turbine Speed sensors and Key phasor are Installed in Bearing no. 1

Turbovisory Instruments

Brg. No. Abs. Brg. Vib. Abs.ShelVib.

(2Comp)

Rel.Rotor Vib.

(2 Comp)

Ang. Dis. Brg. Shell

(2 Comp)

Casing Exp.

Rotor Exp.3 Comp 2 cmp

1 Y N Y Y N Y (HPC) Y

2 Y N Y Y N

3 Y N Y Y N

4 Y N Y Y Y Y (IPC) Y

5 Y N Y Y Y

6 Y N Y Y Y Y (LPC-1) Y

7 Y N Y Y Y

8 Y N Y Y Y Y (LPC-2) Y

9 Y N Y Y Y

10 Y N Y Y N

11 N Y Y Y N

12 N Y Y Y N

Turbovisory Instruments

The Stress Margin of the Turbine is calculated by measuring the temperatures of following components:

1. HPC Rotor and Outer Casing2. IPC Rotor and Outer Casing3. 2 HP Stop Valves4. 2 IP Stop Valves5. 4 HP Control Valves6. 4 IP Control Valves

TSC System

Turbine Protection System Turbine protection system consists of Two

Independent channels, each operating the corresponding solenoid (220V DC) to trip the Turbine in case of actuation of remote protection

Hydraulic Protection: Apart from the Electrical Trip, Turbine is equipped with the following Hydraulic Protections:

1. Local Manual Trip (1V2)2. Over speed Trip #1 at 110% of rated speed3. Over speed Trip #2 at 111% of rated speed4. Governing oil pressure < 20 Ksc

Contd..

Turbine Protection System

Contd…

Axial shift Very High (2V3) [-1.7mm, +1.2mm]

Turbine bearing vibration : Very High (2V10 including X & Y directions)* >11.2mm/sec (Td=2 sec)

Lube oil tank level very Low (2V3)* Td=3sec (Arming with two stop valves open)

Lub oil pressure Very Low (2V3) < 0.3 Ksc; Td =3 sec (Arming with two stop valves open)

Condenser pressure Very High (2V3) > - 0.7ksc (Arming with condenser press < 0.15 ksc Abs)

Contd..

Turbine Protection System

M.S. temp Very Low (2V3) < 470 deg C (arming > 512 deg C)*

M.S. temp Very High (2V3) > 565 deg C*

HRH temp Very Low (2V3) < 500deg C (arming > 535 deg C)*

HRH temp Very High (2V3) > 593deg C*

HPT outlet temperature Very High (2V4) > 420 deg C

Contd…

Turbine Protection System

Gen seal oil level of any seal oil tank Very Low (2V3)* < 0 mm;Td=15 sec (Arming with any two stop valves open)

All Generator seal oil pumps OFF (3V3)* Td: 9 sec (Arming with any two stop valves open)

Generator Stator winding flow Very Low (2v3) < 17.3 m3/hr; Td =120 sec (Arming with any two stop valves open)

Generator hot gas coolers flow Very LOW (2V3)* : <180m3/hr; Td=300sec(Arming with any two stop valves open)

Generator cooler hot gas temp. Very High(2V4) > 85 deg (Td = 300sec

Contd…

Turbine Protection System

MFT operated: (2V3)

Deareator level Very High (2V3) > 3400 mm*

HP heater level protection operated (2V3)*

Generator Electrical protection operated (2V3)

Turbine over speed protection operated (114%)

Turbine Controller failure protection operated (2V3)

Contd…

Turbine Protection System