Topics of PresentationOverview of Turbine

Concept of Governing System

Functioning of EHC Circuits

Turbine Start Up Procedure

TSI & TSC System

Turbine Protection System

Turbine Block Diagram

Turbine Extractions

Turbine Components

Turbine: HPT, IPT, LPT1 and LPT2Turbine Bearings: 08Generator / Exciter Bearings: 04Turbine 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 ValveMotor driven warm up Shut Off valves for HPCV-3 & 4Governing Box

Overview of Governing Box

Governing Box ComponentsMotor 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 SystemCombination 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 SystemHPT control valves open only after achieving preset load (12% of 660 MW)Opening time of control valve is 1.5 secClosing time of Stop valve in case of operation of protection is 0.3 secTurbine maximum speed is restricted to 108% in case of generator disconnected from gridOver 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

Resetting of TurbineStabilized 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

Operation of Stop Valve

Operation of Stop & Control ValvesControl 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

Components of EHC EHC comprises of following controllers:

1. Speed Controller

2. Pressure Controller

3. Load Controller

4. Position Controller

Selection of ControlsEHC can be kept in Manual / Auto Mode as per operators choiceManual 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-1Logic 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 Manufacturers start up curve are as follows:

Speed Control CircuitSpeed 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 Control CircuitSpeed 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 CircuitLoad 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 CircuitLogic-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

Load Control CircuitLogic-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 frequencyContd

Load Control CircuitLogic 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 selectionIncase of one of the transducer failed, maximum of rest two.will be selected

Pressure Control CircuitPressure 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 BlockM. S. Pr. Set Point Actual Pr. Value +-PI ControllerMINMinimum Pr.ControllerMAXControl Stage Max Pr. ControllerO/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.

Operation of I/H Converter

Operation of I/H ConverterI/H Converters control the opening and closing of the corresponding control valvesIndividual I/H converters get command from Turbine controller 50 Ksc Header Pressure Oil holds the piston (2) up against spring actionAs the slide valve (1) moves as per I/H converter, 35 Ksc control oil output is regulated for C.V. servomotor operationWhen 50 KSC Governing oil pressure collapses, piston (2) travels down due to spring action thus draining the oil line of C.V. servomotor

Control Valve Opening Curve

Turbine Start Up SequenceStart Turbine rolling with Speed Control on from barring speed to 500 rpmAfter achieving desired criteria, raise speed set point to 1200 rpm* and subsequently to 3000 rpmAfter synchronization Load Controller gets switched On raise load > 80MW when HPC ON signal is generatedTurbine Pressure Control will be automatically switched OnAfter HPCV demand crosses 80%, switch ON Position controller to hold 80% as the o/p to control valves for raising pressure to rated valueSwitch ON Pres. Controller to raise load to rated valueSwitch ON Load Control after load reaches the rated value

START UP CURVES OF TURBINE AFTER SHUTDOWN OF THE UNIT

Start Up Curves NomenclatureTo S.H Live steam temperature.Trh R.H steam temperaturePo S.H outlet steam pressurePrh R.H. steam pressureGo Electrical Load of TGNe Live steam flow from boilerN Turbine rotor speedA Steam AdmissionB SynchronizationC HPC switch onD HPCV open with 20% Throttle reserve & Loading with constant HPCV position & HP heaters chargedE HPCV no-3 opening. Throttle pressure reducedF Full Load

START UP CURVES OF TURBINE AFTER SHUTDOWN OF THE UNIT

START UP CURVES OF TURBINE AFTER SHUTDOWN OF THE UNIT

Turbovisory InstrumentsTurbo 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

Turbovisory Instruments

TSC SystemThe 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

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 SystemContd

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

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)* : 85 deg (Td = 300sec

Contd

Turbine Protection SystemMFT 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