A short insight to governing of steam turbines.This will be more useful and mean more to Power Plant professionals and for those who are beginners or trainees in the Thermal Power Plants.Descrição completa
Steam Turbine Valves Information
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Thermodynamics - Steam Turbine
Steam Turbine Control System
Basic of Steam Turbine
Turbine • The turbine converts the high-pressure driving force created by steam, water, combustion gas into rotation energy (mechanical energy) that turns the generator rotor. • The generator rotor is connected to the turbine via a shaft.
Fossil Fired Steam Unit
Turbine Stage – The moving blade Æ “Buckets” – A set of stationary blade Æ “Nozzle Partition”
HP/IP turbine blading
HP & IP Rotor
LP Rotor
TYPE OF STEAM TURBINE
Straight Condensing Turbine CONTROL VALVE INITIAL PRESSURE
TO CONDENSER EXHAUST PRESSURE LESS THAN ATMOSPHERIC
Straight Non-condensing Turbine CONTROL VALVE INITIAL PRESSURE
EXHAUST PRESSURE GREATER THAN ATMOSPHERIC
Non automatic Extraction Turbine (Condensing or Non condensing) CONTROL VALVE INITIAL PRESSURE
EXCTRACTION ONE OR MORE
EXHAUST PRESSURE
Automatic Extraction Turbine (Condensing or Non condensing) CONTROL VALVE INITIAL PRESSURE
• Tandem compound turbine-generator – High press (HP), intermediate pressure
(IP), Low pressure (LP) and generator on a common shaft
From boiler
Cross over
MSV CV
HP
MSV Æ Main Stop Valve CV
Æ Control Valve
LP
LP
shaft
GEN
Condenser
Non-reheat tandem compound steam turbine
From boiler
Cross over
MSV CV
HP
IP
LP
LP
shaft
GEN
RSV IV
Condenser
RH RH
Æ Reheater
RSV
Æ Reheat Stop Valve
IV
Æ Intercept Valve
Single reheat tandem compound steam turbine
From boiler
Cross over
MSV CV
HP
IP
IP RSV IV
LP
LP
LP
LP
GEN
Condenser
RH RH
Æ Reheater
RSV
Æ Reheat Stop Valve
IV
Æ Intercept Valve
Single reheat tandem compound steam turbine
Steam Steam turbine turbine rotor rotor
• Cross compound turbine- generator – Commonly with HP, IP and one generator on one shaft , LP and another generator on a second shaft
• Greater capacity • Improved efficiency • More expensive
100 MW – 700 MW HE series
• H turbine - Single flow HP turbine module - one stop and control valve • E turbine - Single flow IP / LP section combined in one cylinder
Modular Design of the E-Turbine
250 MW – 700 MW KN series
• K turbine - combined HP/IP • N turbine - Double flow LP section
Modular Design of the K-Turbine
Stop and Control valve
LEFT Generator
sv cv HP stage LP stage
RIGHT
sv cv LP HEADER
HP HEADER
Process parameter control • • • •
MW output. Main steam Fuel / Air Feed water
Steam Turbine Controller
The tasks of steam turbine controller • • • • • • • • •
Starting up and shutting down the turbine Synchronizing with grid* Loading the turbine Influencing the grid regulator Pressure stabilization Limitation of load Control of Isolated operation Turbine interception during load rejection Monitoring function
Comparison between DEH governor and conventional hydraulic governor
Speed and Load Control Speed signal
+
TNH 2 out of 3 Voting Logic
-
1/S
+
Speed summer Speed setpoint
Load Setpoint
+ TNR
Hold
TNE
Intgrl Summer
Speed Gain
+ +
Speed /Load summer
PWR
Hard ware of turbine controller • Very fast response digital system - Microprocessor-based controller • Redundant structure – Dual, TMR
• Man machine interface with CRT • Standardize interface technique with other systems • Control panel* – Hard wired push buttons comply with minimum requirements for backup operation
SPEEDTRONIC TM Mark V Steam Turbine Controls
Mark V Control Simplex Configuration
Mark V Control TMR Configuration
Mark VI
Siemens AG, Power Generation Modern Automation Concepts
Alstom P400 Turbine Control
GE Fanuc PACSystem RX7i
TMR SYSTEM
Mark V TMR Control Sequence
Hardware voting for analog Outputs
Hardware voting of logic outputs
Servo Position Controller (SPC)
Block diagram of SPC
Single coil wiring - Integrating Servo Application
Over Speed Protection Device
Over views diagram of TurboSentry Application
Steam Turbine Operation
STARTING AND LOADING • Successful operation • Maintenance • Long life a turbine-generator
Main factors involved during starting and loading • • • •
1) Thermal Stress 2) Vibration 3) Shell and Rotor differential expansion 4) HP exhaust temperature
Thermal Stress • Operating Transients can be produce high thermal stresses in stem turbine rotor and shell – Start-ups – Load changes – Shutdowns
Turbine Stress Evaluation (TSE) • Limiting the acceleration during start-up • Load ramp gradients under normal loading operation
Differential expansion • Rotor temperature change faster than outer shells. • Lead to differential expansion large enough to cause internal rubbing
Oil and Hydraulic Fluid System Check lube oil temp. > 50 F°/ 70 F°
Starting AC lube oil pump
Check lube oil pressure & flow to bearing
A Check lube oil protection sequence
Return to normal configuration
Recheck lube oil pressure
Lube oil ready
Oil and Hydraulic Fluid System Check EH fluid reservoir level
Check EH fluid temp.
Open pump Start number 1 suction valve fluid pump (if used)
B Adjust cooling water flow
Place backup fluid Check auto. EH fluid pump on auto. Start of ready backup pump
Oil and Hydraulic Fluid System Lube oil and hydraulic systems ready
A AND B
Turbine rotor prewarming • rotor warming (prewarm) prior to roll-off after the vacuum system is in operation. • rotor warming (heatsoak) be performed during turbine acceleration and involves a “part speed hold” • In either case the manufacturer ‘s specific recommendations should be followed
Valve trip testing • the main turbine valves should be tested to verify that the testable functions of the trip system are working properly. - verifying that all valves involved are in the proper position. - manually tripping the turbine from the control-room panel and observing that all valves return to the tripped status.
Turbine preroll • Energize the supervisory instruments. • Energize the EH (electro-hydraulic) electronic governor at least 2 h before admitting steam into the turbine. • If an electrical-trip system shall be energized prior to turbine roll-off. • Control & Stop valves are closed • resetting the turbine trip system and the status of the various valves when reset vary with manufacturers.
Energize supervisory instrument Energize electronic governor Energize electric trip system Check main stop valve closed Check control valve closed Check intercept valve closed Check generator ok Lube oil system ok
Unit on turning gear AND
Unit on turning gear Hydraulic fluid system ok
Turbine rotor prewarmed (if required)
Vacuum ok AND Steam seal ok Drain valve open Eccentricity ok Eccentricity ok
1
1
Reset turbine
All trip lockouts reset Ready to roll Deactivate initial pressure reg. Check main stream press. & Temp ok Water induction preroll checks
– Main steam pressure 24.22 MPa – Main steam temp. 538 °C – Reheat steam temp. 566 °C – Condenser vacuum 700 mm Hg – Number of Extraction 8
Unit Capability and Minimum Load • Unit capability refers to the maximum possible megawatt output that the generating unit can safely produce. • Minimum load is the smallest amount of generation that a unit can sustain for an extended period.
Stop Valves / Throttle Valves - Normally provide fast interruption of the main energy input to the turbine. A stop valve is defined as an open or closed valve A throttle valve have some portion of its opening through which it can modulate flow ( used for turbine control during startup)
DEHC Function • Control function – – – – – – –
Speed up control Valve transfer control Close all valves Load / Frequency control Load limiter IMP control (Impulse chamber pressure) Valve management
DEHC Function • Protection function – EOST (Electrical Over Speed Trip) – OPC (Over Speed Protection Control) – IPR (Initial Pressure Regulator)
DEHC Function • Test function – Valve closing test – OPC test – MOST test (Mechanic Over Speed Trip)
Start-up curve rpm 3000 2200
400 T/B reset Rub check Startup
Heat soak
Valve transfer
41E Synchronizing on
Speed control • Turbine speed is controlled by MSV from starting to rated speed. • GV full open
Speed control position
RSV GV (full open)
MSV
T/B reset
EH AUTO
Target speed Program select 400 rpm GO
Speed Control Speed reference
+
3000 Hz Speed A Speed B
>H
-
K
MSV control
• What is 3000 r.p.m. ? r.p.m. Æ round / minute ( r/min ) • Frequency of network = 50 Hz (Thailand) Hz
Æ round / second (r/sec)
50 HZ = 50 round / second In one minute = 60 Second Rotation in one minute = 50 x 60 = 3,000 round or 3000 round / minute = 3000 r.p.m.
• • • •
Turbine speed = 3000 rpm. No. of gear teeth = 60 Pulse / min = 60 x 3000 Pulse / sec. = 60 x 3000 = 3000 Hz 60
Taget speed & Speed change rate • Taget Speed – 400 rpm – 2,200 rpm – 3,000 rpm
Valve transfer • After turbine has reached the rated speed. • Speed control change from MSV to GV
Valve transfer GV
Full open Bias 0%
GV position demand
(No load valve position) Full open
MSV Valve transfer
Valve transfer complete
41E permit
GV
MSV
Start-up
Full open
Speed control
Transfer
Speed Control
Full open
Synchronize
Load Control
Full open
Close all valves • For turbine stop and rub check • MSV, GV and ICV are fully Closed by the sevo valve. • RSV still open.
Load control • Load frequency control • Load limiter – limit steam flow
Load control DCS
Load setter
GV control
+
3000 rpm
+ -
Actual speed
droop
Load limiter Comparator
Response Rate • Response rate is the rate of load change that a generating unit can achieve for normal operating purposes in MW/min.
Position Controller Position demand +
K
+20 mA E/H
LVDT
Electrohydraulic Servovalve
Voltage vs Range of Travel Curve
Partial Arc Admission ( a nozzle governing system) • Two or more regulation valve are opened one after another • The Load being control by varying a nozzle area and a constant rated pressure • Lower throttling Loss • Better heat rate
Partial Arc Admission
Full Arc Admission ( a throttling governing system) • Two or more regulating valve are opened and closed at a time • The Load being control by varying a pressure at a constant nozzle area
• Preferred during start-up turbine • Lower stress
100%
STEAM FLOW
LOAD
100%
100%
VALVE AREA
STEAM FLOW
100%
100%
VALVE AREA
VALVE LIFT
100%
100%
STEAM DEMAND
VALVE LIFT
100%
IMP (Impulse chamber pressure) control • For valve closing test • Keep the power of turbine
IMP (Impulse chamber pressure) control Boiler MSV
GV
HP MSV
IP
LP LP LP LP
GEN
GV
Px
HP turbine 1 st steam pressure
EOST (Electrical Overspeed Trip) 3300 rpm speed
>111%
speed
>111%
speed
>111%
2/3
Turbine Trip
MOST (Mechanical Overspeed Trip) test • To confirm mechanical overspeed protection device (before synchronization) • EOST setting 111% Æ 115% • OPC is blocked
MOST setting
+ 15 rpm - 15 rpm
MOST 110% (+ 0.5%)
OPC (Overspeed Protection Control) • Power-load imbalance • To avoid overspeed trip when load rejection • Speed up to 107.5% OPC valve solenoid are energized.
• Power output Æ IP Turbine inlet pressure (Mechanical) • Power output Æ CT (current transformer) (Electrical)
OPC (Overspeed Protection Control) Boiler MSV
GV
HP MSV
IP turbine inlet pressure
Px
IP
LP LP LP LP
GV
Gen.Current
GEN
IPR (Initial Pressure Regulator) • Protect against excessive decrease of the initial (main) steam pressure • Main steam deviate from main steam pressure reference > 25 bar • Turbine water damage prevention • Load reference runback rate 200%/min.
IPR (Initial Pressure Regulator) Load setter 100%
200% / min
GV = 25%
Time (sec)
Valve Closing Test • Confirm the safety function – GV & MSV valve test (RH, LH) – RSV & ICV valve test (RH, LH)
GV – MSV Valve test MSV IMP IN GV
Test
ICV – RSV Valve test RSV
energized
ICV
De-energized
Close
OPC Test energized GV De-energized ICV
1 Sec.
Overall unit control • Boiler following mode (Turbine leading) • Turbine following mode (Boiler leading) • The integrated or coordinated boiler turbine control • Sliding pressure mode
Boiler following mode (Turbine leading) • Change in generation are initiated by turbine control valves. • The boiler controls respond to the resulting changes in steam flow and pressure by changing steam productions.
Turbine following mode (Boiler leading) • Change in generation are initiated by change input to the boiler. • The MW demand signal is applied to the combustion control. • The turbine control valves regulate the boiler pressure.
The integrated or coordinated boiler- turbine control • Provides an adjustable blend of both boilerfollowing and turbine-following mode of control. • The improvement in unit response achieved through integrated control. • The integrated control strikes a compromise between fast response a boiler safety.
The sliding pressure mode • The control valves are left wide open. • The turbine power output is controlled by controlling the throttling pressure through manipulation of the boiler control.
