Overview of Turbine Concept of Governing System Functioning of EHC - - PowerPoint PPT Presentation

 Overview of Turbine  Concept of Governing System  Functioning of EHC Circuits  Turbine Start Up Procedure  TSI & TSC System  Turbine Protection System

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

Tur urbine bine Extr traction actions

 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

 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

 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

• il pressure

 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%)

 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

 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

• ff

head pressure

• il

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

EHC comprises of following controllers:

• 1. Speed Controller
• 2. Pressure Controller
• 3. Load Controller
• 4. Position Controller

 EHC can be kept in Manual / Auto Mode as per

• perator’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

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 Curve

Speed gradients as per Manufacturer’s start up curve are as follows:

Rolling ng Conditio ion n 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 – 72H

3 - 500 rpm 75 sec 120 sec 3000 rpm 240 sec

• Between 8H – 36H

3 - 3000 rpm 360 sec

• Between 2H – 8H

3 - 3000 rpm 300 sec

 Speed Controller will be switched on automatically in

case generator breaker opens (with Turbine controller

• n 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

 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 grid
• 3. The grid frequency has gone beyond allowable limits
• 4. Load Measurement faulty (2/3 sensors faulty)
• 5. M.S. Pres. measurement faulty (2V3 sensors faulty)
• 6. Unit is in Pressure Control mode

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

STOP

3 2 1

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

• nce 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…

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 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 Open
• 2. The frequency is more than allowable value*
• 3. M.S. pressure transducers failed (2V3)
• 4. Manual Control switched on
• 5. Load control is On
• 6. HPC is out of operation

• 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

Controller MIN

Minimum Pr. Controller

MAX

Control Stage Max

• Pr. Controller

O/P

• 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/H CONVERTOR

 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

• peration

 When 50 KSC Governing oil pressure collapses, piston

(2) travels down due to spring action – thus draining the

• il line of C.V. servomotor

 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

 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

 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.Shel Vib. (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

• f

the Turbine is calculated by measuring the temperatures of following components:

• 1. HPC Rotor and Outer Casing
• 2. IPC Rotor and Outer Casing
• 3. 2 HP Stop Valves
• 4. 2 IP Stop Valves
• 5. 4 HP Control Valves
• 6. 4 IP Control Valves

Turbine protection system consists

• f

Two Independent channels, each

• perating

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 speed
• 3. Over speed Trip #2 at 111% of rated speed
• 4. Governing oil pressure < 20 Ksc

Contd..

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…

 Gen seal oil level of any seal oil tank Very Low (2V3)* <

0 mm;Td=15 sec (Arming with any two stop valves

• pen)

 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

• pen)

 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…

 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…