5 - Turbine Generator Upgrades & Maintenance

Presented by:

Daniel Sculley, Manager

Turbine, Generator & Piping

Systems Engineering

APP Site Visit

October 30 – November 4, 2006

Turbine/Generator Upgrades and Maintenance

Turbine/Generator Upgrades and Maintenance

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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 O&M 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

ResultsRestored 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) gainErosion minimized, reduced repairsExtended inspection intervals to 10-11 yearsRe-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.

ResultsBlading Efficiency > 92.0%, increase of 4.7%20 MW and 28.5 kcal/kWh (113Btu/kWh) Improved rotor stability against steam swirl3 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.

Results82.8% - 86.3% HP section efficiency11MW gained on 800MW Series600 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

Efficiency Degradation of HP Turbines

BS #2

ML#2BS#2CD#1

MR#5

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76

78

80

82

84

86

88

0 2 4 6 8 10 12

Time (Years)

Eff

icie

nc

y

ADSPOriginal DesignNormal OverhaulML#2BS#2CD#1MR#5BS #2

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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 IssuesEfficiency

Turn-around

(Pressure Loss)

Curtis Stage

(Poor Efficiency)

Conventional Cylindrical Airfoil

(Poor Efficiency)

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Existing Maintenance IssuesReliability

Large Blade Ring

(Distortion, Rubbing, Blade Leaning)

L-0 Blade Fatigue Life

(Blade Failure)

L-0 Shrunk-on Disc

(SCC Potential)

Large Dia. Inner Casing (CrMo casting)

(Distortion, Rubbing)

Stage 1 Blade Root Distortion

Stages 2-4 Blade Untwist

IP/SFLP Rotor

44 years Old

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New HP Section Design

Monoblock

No Bore Rotor

Separately supported blade rings and balancing ring

3-D Reaction Blades (ISB)

ACC Packing(Active Clearance Control) Integral Inner Casing

Rateau control stage

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New IP/LP Section DesignACC Packing

(Active Clearance Control)

Mono block no bore rotor

No Shrink-fit

Separately-Supported Blade Rings

3-D Reaction Blades (ISB)Integral Inner Casing

25in ISB

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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 O&M– Reduce pressure drop

1300MW SVCV Upgrade

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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

ResultsSmooth, rapid rollups to synchronous speedCV position and load ramping optimized by stress

probeCV stroke ramped according to test throttle pressure Improved reliability during protective device checksLower peak speeds reached during turbine tripReduction 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, repairsGoal: 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 – TG&PSE Manager

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Questions