Overview of Turbine Concept of Governing System Functioning of EHC Circuits Turbine Start Up Procedure TSI & TSC System Turbine Protection System
Tur urbine bine Extr traction actions Ext. Source Of Extraction Destination Equipments No 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: 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 has nozzle governing – all four control HP Turbine 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
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 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
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 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
+ R Speed Speed O/P Rate Logic - Set Point Controller L Logic - 2 Logic-1 Actual Speed Speed Set (Mv3) Point = 0 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 3 - 500 rpm 150 sec 300 sec Cold Startup 1200 rpm* 550 sec 300 sec ( > 72 H ) 3000 rpm 630 sec -------- 3 - 500 rpm 75 sec 120 sec Between 36H – 72H 3000 rpm 240 sec -------- 3 - 3000 rpm 360 sec -------- Between 8H – 36H 3 - 3000 rpm 300 sec -------- Between 2H – 8H
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
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
R STOP 3 L Correction Delay Element O/P + - Load Ref C.K.T Fast Tracking Freq. Corr Actual Load 2 5 Press. Corr 1 Max.Load Lim. Min.Load Lim. 6 Logic - 4 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 …
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
+ Actual Pr. Value PI MIN O/P Adder Block MAX Controller - M. S. Pr. Set Point Minimum Pr. Control Stage Max Controller Pr. Controller • 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
O/P- (0-150mA) + Control Signal From TC + MIN TO I/H + Posn. F/B - 1 PI CONVERTOR - MV2 Posn. F/B - 2 Biasing Current 0.8 to 1A Limiter • 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.
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
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