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May 11, 2006
Hydropower Refurbishment –
Alstom’s Methodology and Case Studies
Presented By
Naresh Patel ( Electrical)
Sreenivas.V ( Mechanical)
Introduction
Alstom Power – Hydro Products
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Descended from Neyrpic, ASEA, BBC, Alsthom
Over 100 years experience in hydro industry
Eng’g & Mfg’g in Americas, Europe & Asia
Presence in Asia Includes:
• Turbine, Generator, Hydro Mech, P&S, BoP
• Design & Mfg’g in Tianjin, China
• Design & Mfg’g in Vadodara, India
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The Need for Refurbishment
Repair, Modernize & Uprate
• Repair – Equipment failure results in units
out of service / operating at derated output
• Most compelling of refurbishment drivers
• Issue – Return to full service quickly
• Solution – Often a temporary “band-aid”
• If ‘quick fix’ not possible, modernize and
uprate options should be considered
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We should have done this last
year as a planned outage!
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The Need for Refurbishment
Repair, Modernize & Uprate
• Modernize – Apply new technology,
materials and calculation techniques
• Normally done in conjunction with other
refurbishment work
• Example – Uprate field-coil insulation
during a stator rewind
• Example - Install self-lubricating bushings
during runner replacement
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The Need for Refurbishment
Repair, Modernize & Uprate
• Uprate – Increase the output capability of the
generating unit
• Most economically feasible of drivers
• Typically 15 to 40% uprate without civil-works
modification
• Minimum scope usually involves runner
replacement and new stator core & winding
• BoP modifications have to be considered
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GENERATOR LIFE CYCLE
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Refurbishment Methodology
General Philosophy
• Refurbishment presents more challenging
design requirements than that of new units
• Interfaces between old & new equipment have
to be considered
• Existing unit must be synthesized
• Collection of reliable data for existing units is
absolutely necessary for a successful project
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Refurbishment Methodology
Data Collection
• Review of specification and data from spec
• Site visit absolutely necessary for:
• Measurements and visual inspection of unit
• Assess the installation environment & limitations
• Collection of additional data, eg maintenance records,
test & operational data, OEM drawings, etc.
• Discussion of refurbishment requirements and Q & A
with customer engineers
• Duration of site visit is scope dependent and can last from a
few hours to a few days
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Generator Specific Methodology
Proposal Design
• Refurbishment of the generator and turbine parts will be
presented here separately, but the shaft coupling is an
important interface for matching of capability and maximum
speed. Generator and turbine design are performed together
• Relatively short time for design
• Synthesis of existing design required with accurate model of
components to be kept
• Model of existing design is modified for refurbished parts
• Modeling is only rigorous enough to ensure the solution will
work and to guarantee performance
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Generator Specific Methodology
Basic and Detailed Design
• Continuation of the proposal design
• A second site visit is essential
• Additional generator testing may be required to
validate the model of existing unit
• Analysis is much more rigorous and can include
electromagnetic & mechanical FEM studies
• Interface issues are resolved during detailed design
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Generator Specific Methodology
Synthesis of Existing Generator
• Required data are rarely all available
• Physical model is created from dimensions given in spec
and from site visit
• Electromagnetic model, including excitation requirements
and reactances are correlated to test & operational data
• Thermal model, including ventilation configuration and
airflow are correlated to measured temperatures & losses
• Throughout the synthesis, measured data are used to
deduce unknown dimensions and material properties
• Additional tests may be required after award of contract
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Modeling of the Refurbishment
New Winding
• Small scope with very little design space
• Optimize temperature (output) and efficiency
• Slot dimensions are fixed so the only variables are:
• Insulation thickness (design for hipot or VET)
• Strand dimensions
• Typically a 15% uprate is possible if replacing
asphalt bars or coils
• Upgrade field insulation during outage
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Modeling of the Refurbishment
New Core & Winding
• This scope allows a change in winding configuration
• Important to identify core-replacement need at time of
tendering through inspection or El Cid test or by the age
of the core
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Allatoona Stator Core ~
45 Years Old
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Modeling of the Refurbishment
New Core & Winding
• This scope allows a change in winding configuration
• Important to identify core-replacement need at time of
tendering through inspection or El Cid test
• Possible to achieve large increase in efficiency
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STATOR-STEEL QUALITY
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Modeling of the Refurbishment
New Core & Winding
• This scope allows a change in winding configuration
• Important to identify core-replacement need at time of
tendering through inspection or El Cid test
• Possible to achieve large increase in efficiency
• Possible to eliminate noise problems
• Keying and clamping system should be replaced
• Effective soleplate modifications not usually possible
unless frame also replaced, i.e. new stator
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Modeling of the Refurbishment
New Poles and Field Coils
• In conjunction with a new stator & ventilation
modifications, can allow up to a 40% uprate
• Torque transmission of other components plus BoP has to
be checked explicitly for >15% uprate
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Modeling of the Refurbishment
Refurbishment with Larger Scope
• Begins to look like design for a new machine with fewer
interfaces, fewer dimensional and performance limits
• In these cases, the limits are given by the civil works and
balance-of-plant components
• Optimization of performance and output has much higher
opportunity
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Generator Case Studies
Rocky Reach, Units 1-7
• Customer – Chelan County PUD, Washington State
• Existing unit - 120 MVA, 15 kV, 90 rpm, 0.95 pf
• Airgap instability
• Stator-core buckling
• Increase of efficiency
• Some units noisy, > 95 dB
• Life extension / increased availability
• Scope – new stators & rotors - everything except shaft,
brackets & bearings
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Rocky Reach, Units 1-7
Design Requirements
• High efficiency – main design driver
• US$55k / kW evaluation, US$70k / kW penalty
• Airgap shape tolerances one half of IEC/CEA
standard
• Low audible noise, <80 dB 1 m from housing
• High evaluation for short outage
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Rocky Reach, Units 1-7
Design Solutions – High Efficiency
• 30% more active material than benchmark,
• Increase frame OD to accommodate larger core &
frame – radial clearance in housing reduced to limit
• Losses & temperatures very low, so ventilation
system can be optimized for efficiency not cooling
• Airgap reduced to allowable SCR limit of 0.8
• Relative to existing machine, the efficiency was
increased by 0.5% to almost 99%
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Rocky Reach, Units 1-7
Design Solutions – Airgap Stability & Shape
• Rim shrunk for full, off-cam runaway speed
• Oblique elements used on spider and frame
• Double dovetail design used for precise setting of
stator keybars
• Rotor poles individually shimmed to high circularity
tolerance
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Rocky Reach, Units 1-7
Design Solutions – Noise & Outage Time
• Frame & stator core stiffened with radial depth and
higher core clamping pressure
• Outage reduced by constructing both rotor and stator
in erection bay
• Last (fourth) unit had only 45 days between
commercial service of existing and refurbished units
• All guaranteed performance requirements were met
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Generator Case Studies
Crystal Power Plant, Unit 1
• Customer – US Bureau of Reclamation, Colorado
• Existing unit - 28 MVA, 11.0 kV, 257 rpm, 1.0 pf
• Realize uprate potential
• Increase reactive capability for black-start, line
charging
• Generator and turbine refurbishment for reduced
maintenance costs
• New rating – 35 MVA, 0.9 pf
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Crystal Power Plant, Unit 1
Design Requirement
• Contract requirement for 80 K field-temperature rise
• Existing unit had 75 K limit, which it could not meet
• 25% increase in MVA
• Power factor change from unity to 0.9 over excited
• 12.5% increase in MW
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Crystal Power Plant, Unit 1
Interface Requirements / Design Space Restrictions
• Existing soleplates
• Housing diameter
• Rotor outer diameter and axial length
• Upper bracket and deck plates
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Crystal Power Plant, Unit 1
Design Solutions – Field Temperature-Rise Limit
• Do all possible to reduce excitation requirements
• Re-insulate field with Class F material
• Increase series turns by 20% - tooth x-section
reduction more than compensated
• Increase radial depth of stator core
• Reduce airgap length
• Performance testing last year measured a fieldtemperature rise of 78 K
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Turbine
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Turbine methodology
Tender stage
– Simplified analysis of main components (Spiral case,
stay vanes, distributor, runner and draft tube);
– Geometrical comparison between existing design and
manufacturing references;
– Hydraulic transient calculation;
– Cavitation studies;
– Search solutions for specifics problems (frequent
mechanical failures, silt abrasion, operational
instability and others)
– Define the future turbine performance (guarantees)
Short term analysis (Basic studies with simple tools)
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Turbine methodology
Design stage
– Measurement of existing performance
– Deeply inspection of all components of machine
– Fluid Dynamic analysis of the static components
(Spiral Case, Stay Vane, Distributor and Draft tube)
– Design of some new profiles to improve the flow
behavior (stay vane, wicket gates and draft tube)
– Comparison of existing and new design (CFD)
– Development of new runner (genetic algorithm)
– Model test to validate the results
Deeply analysis and experience of specialist to reach
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Turbine methodology
Stay vane and Wicket Gate Optimization
CFD remain the main tool for analysis
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Turbine methodology
Draft tube study
Stream Line analysis
Existing
Modified
Flow velocity in a sectional
elevation view of the
existing draft tube elbow.
When technically available modification in Draft tube
- 34 provide good results
Turbine methodology
Runner development
“Classical” runner
“Final” runner
Blade profile is developed using an evolutionary
algoritm and the experience of a hydraulic engineer
Good Accuracy between CFD calculation and model -test
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St-Lawrence Rehab Project
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St-Lawrence Power Project
– 32 propeller units (16 NYPA and 16 OPG)
Two turbine designs :
BLH : 8 runners Ø5.8m (229 in.) 77.5  85 kHp
(63.4MW)
AC : 8 runners Ø6.1m (240 in.) 79 kHp
Targets:
- Increase overall efficiency
- Translation of the peak efficiency to higher
load
- Reduction of erosion by cavitation
- Increase of the stability of the turbine
Ambitious targets
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St-Lawrence Rehab Project
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Main modification  New Runner
• Development using the Alstom
methodology
• Twisted blade shape
Runner developed to reach targets and solve the old
- 37 design problems
St-Lawrence Rehab Project
Sigma break curve at full load up to the maximal flow allowed
by contract near the rated net head for the refurbishment of
ST. LAWRENCE Power Plant.
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St-Lawrence Rehab Project
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Acceptance model test : cavitation
New runner
Old runner
New & Existing runner for St. LAWRENCE power plant at
the rated net head, full load and plant sigma value
(model runner manufactured by ASTRÖ).
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St-Lawrence Rehab Project
Accurate manufacturing the reach the results
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St-Lawrence Rehab Project
New rated output :
63.4 MW
Cavitation behavior
improved
Better stability
Best efficiency in
the higher load
After commissioning confirmation of targets
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Conclusion
• Refurbishment is required to extend life of aging
equipments and increase the value of equipment to
the owner in terms of performance (higher output
and efficiency, greater availability)
• Presented Alstom case studies demonstrate the
methodology success
• Integration between Generator and Turbine is
essential for good results in refurbishment projects
• Alstom methodology has been efficient for projects
in all the corners of the world
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