Turbine/Generator Upgrades and Maintenance

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Turbine/Generator Upgrades and Maintenance
Presented by Daniel Sculley, Manager Turbine, Generator Piping Systems Engineering APP Site Visit October 30 November 4, 2006
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Topics

• Turbine Blading Steam Path Upgrades
• Turbine Stop / Control Valve Upgrades
• Turbine Control System Modernization
• Generator Improvements

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Steam Path Improvements

• More than 20 units in plan for upgrade
• Efficiency gain
• Aerodynamic blade profiles
• Improved inter-stage sealing
• Reduction of sidewall secondary flow losses
• Reduction in future OM costs
• Extend time between overhauls
• Reduction of solid particle erosion damage
• Less coal burned

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Glen Lyn 6 Series 235MW (GE) HP/IP

• Nine (9) Units (Subcritical, 1957 - 1961)
• Integral control valve chest girth weld creep
• Purchased complete spare in 1990
• Exchanged on other 8 units (1991 2004)
• New rotors replaced C grade materials
• New nozzles, diaphragms (Rows 1,9,10,12)
• Reassemble non-outage 4-week reduction
• Cost 8 Million (US) first unit installed,
  approx.
• Cost 4 Million (US) subsequent units, approx.

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Glen Lyn 6 Series 235MW (GE) HP/IP

• Results
• Restored CV chest with improved girth weld
• Improved HP efficiency by 1.5 - 2.0
• 2.5 MW and 35.28 kcal/kWh (140 Btu/kWh) gain
• Erosion minimized, reduced repairs
• Extended inspection intervals to 10-11 years
• Re-inspections begun in 2001 confirm benefit

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1300 MW Series (Alstom) HP

• Six (6) Units (Supercritical, 1973 1989)
• Use of spare rotor/inner casing assembly
• Replaced all stationary/rotating rows (28)
• Reuse rotor and re-round inner casing
• Modified seal strips for steam swirl stability
• Cost 6 Million (US) per unit installed,
  approx.
• Results
• Blading Efficiency gt 92.0, increase of 4.7
• 20 MW and 28.5 kcal/kWh (113Btu/kWh)
• Improved rotor stability against steam swirl
• 3 Units completed - - 1 with premature
  degradation

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600,800 MW Series (GE) HP/IP

• Eight (8) Units (Supercritical, 1967 1972)
• To date, four have been converted
• New nozzles, diaphragms, seals
• Reblade spare rotor reuse shells
• Cost 6.5 Million (US) per unit installed,
  approx.
• Results
• 82.8 - 86.3 HP section efficiency
• 11MW gained on 800MW Series
• 600 MW Series HP fell short of expectations by up
  to 3.5 due to overstated recoverable losses by
  OEM.

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Effect of Advanced Design Steam Path
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Big Sandy Unit 1 HP-IP/SFLP

• One (1) unit, W design (Subcritical, 1963)
• HP turbine complete and IP/SFLP turbine rotor and
  inner casing install 2008
• Inefficient original design
• Internal components subjected to erosion and
  distortion
• Creep damage evident
• No spare blade rings or rotors

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Original Design Issues

• Efficiency

Turn-around (Pressure Loss)
Curtis Stage (Poor Efficiency)
Conventional Cylindrical Airfoil (Poor Efficiency)
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Existing Maintenance Issues

• Reliability

Large Dia. Inner Casing (CrMo casting) (Distortion
, Rubbing)
L-0 Shrunk-on Disc (SCC Potential)
Stage 1 Blade Root Distortion Stages 2-4 Blade
Untwist
IP/SFLP Rotor 44 years Old
L-0 Blade Fatigue Life (Blade Failure)
Large Blade Ring (Distortion, Rubbing, Blade
Leaning)
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New HP Section Design
Separately supported blade rings and balancing
ring
ACC Packing (Active Clearance Control)
Integral Inner Casing
Monoblock No Bore Rotor
3-D Reaction Blades (ISB)
Rateau control stage
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New IP/LP Section Design
ACC Packing (Active Clearance Control)
Separately-Supported Blade Rings
25in ISB
Mono block no bore rotor No Shrink-fit
3-D Reaction Blades (ISB)
Integral Inner Casing
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Big Sandy Unit 1 Expectations

• Anticipated Results
• Improved reliability and design efficiency
• HP efficiency 4.1 to 88.9
• IP efficiency 3.1 to 94.6
• Expect 18 MW at original design steam flow
• Includes replacement throttle/governor valves
• Installed cost 18Million (US), approx.

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LP Turbine Performance Retrofits

• AEP experience driven by reliability issues
• Stress Corrosion Cracking on blades, disks and
  Low Cycle Fatigue on blade attachments
• Flow limit for L-1 rotating blade causes
  curtailment
• LP turbine exhaust limit 140 mm HgA (5.5 in
  HgA)
• Frequently caused summer time curtailments
• Solution LP Turbine Upgrade

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LP Turbine Performance Retrofits

• Four (4) BB73 W LP steam paths ruggedized
• Improved material properties to resist SCC and
  LCF
• Aerodynamic improvements to blades and inlet /
  exhaust flow guides
• Improved seal design to reduce leakage
• Full load capable to 203 mm HgA (8 in HgA)
  backpressure
• Improved performance 3.4MW, 22.4 kcal/kWh (89
  Btu/kWh)

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Stop/Control Valve Upgrades

• Material Damage
• Thermal fatigue, creep
• Reliability
• Tight shutoff, leaks
• Maintenance
• Weld repair to valve body, seats, bolt holes
• Design Improvement
• Improve OM
• Reduce pressure drop

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1300 MW Series SV/CV Upgrades

• Original Design
• Pressure drop across combined valves 5.1
• Limited steam flow at VWO 5 overpressure
• Significant solid particle erosion damage
• Expensive repairs performed every 2-3 years

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1300 MW Series SV/CV Upgrades

• New Design
• Separate stop and control valve chambers
• Actual pressure drop across valves 2.08
• Achieved 32 MW increased generation capability
  without changing boiler conditions
• Updating valve actuators to digital controls

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Turbine Control System Upgrades

• Converting original MH and analog EH controls to
  digital
• Integrated into plant Distributed Control System
• Reuse or modify hydraulic systems
• Use fire resistant fluids
• Expectations
• Enhanced control
• Fewer unit trips
• Faster startup/ramp rates
• Online testing of turbine valves and protective
  devices

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Turbine Control System Upgrades

• Results
• Smooth, rapid rollups to synchronous speed
• CV position and load ramping optimized by stress
  probe
• CV stroke ramped according to test throttle
  pressure
• Improved reliability during protective device
  checks
• Lower peak speeds reached during turbine trip
• Reduction in boiler tube leaks due to soft
  trips
• All contribute to improved reliability and
  performance

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Generator Improvements

• Inspection Intervals (typical)
• Field in-place ( 5 years)
• Field removed (10 years)
• Perform routine cleaning, testing, repairs
• Goal Achieve high reliability through design
  life of insulation systems

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Generator Rewinds

• Rewinds Offer Opportunity for Improvement
• Required for reliability and maintenance purposes
• Efficiency improvements are small added benefit
• Stator Windings
• Asphalt stator bar insulation replaced with
  modern epoxy-mica insulation
• Potential for increased copper cross-section in
  original slots
• Improved cooling gas or water flows reduce
  operating temperature and extend design life
• Stator Cores
• Inspect and test for looseness, hot spots,
  resonance
• Several cores replaced (full, partial)
• Reference papers available in Breakout Session

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Generator Rewinds

• Fields
• Replace retaining rings with 18Mn 18Cr material
• Improve end turn blocking design and materials
• Restore/replace copper and replace all insulation
• Optimize cooling gas flow

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Summary

• AEP has been retrofitting turbine generator
  equipment with efficiency improvements for more
  than 15 years.
• Experience with OEM and non-OEM solutions.
• Economic benefit drives the HP and IP turbine
  retrofits.
• Must consider design improvement vs. restoration
  improvement.
• Turbine valve design could provide upgrade
  potential.
• Turbine control integration can produce thermal
  benefits.
• Reliability benefit drives the LP turbine and
  generator retrofits (typically). Some small
  efficiency improvements are possible.

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Breakout Session

• Two Sessions on Tuesday Afternoon
• Expert Attendees
• Steve Molick Turbine Services Manager
• Jim Michalec Staff Engineer, Generators
• Alex Manukian Sr. Engineer, Turbines
• Jim Cable Sr. Engineer, Turbines, Controls
• Dan Sculley TGPSE Manager

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Questions