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Generator Upgrades and ModernizationSolutions for an aging fleet

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GENERATOR UPGRADES AND MODERNIZATION

Presented byMichal GawronMarketing EngineerGenerator Major Services DepartmentSiemens AG, Mülheim / Ruhr, Germany

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Targeted LTE solutions forSiemens generators

Air-cooled replacementgenerator (Footprint™)

Introduction into generatormaintenance and upgrades

AGENDA

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Introduction Into Generator Maintenance and UpgradesActual Influence of Renewable Energies (e.g. Electricity Production in Germany in 2014)

Source: Fraunhofer-Institut für Solare Energiesysteme ISE Freiburg , 07.01.2015

• Peaks and valleys in output from renewable generation are compensated for by load variation in conventionalpower plants

• More load variation means increased MVAR cycling, more starts/stops, prolonged stand-by• Longevity of generator components is affected.

Winter Winds in Calendar Week 51 Sun and Winds in Spring at Calendar Week 11

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Introduction Into Generator Maintenance and UpgradesChanging duty cycles

§ New built units running in intermediate and peak load condition ( )§ Higher stresses in most generator components, e.g. windings§ Faster aging and wear à Improved design and maintenance concepts are required

Example: 32 Gas-Fired Power Plant Units

Service Factor (Operating hours / Period hours)

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Introduction Into Generator Maintenance and UpgradesTypical Sources of Failures

STATOR ROTOR

Source: VGB data base

Other9%

WindingDistortion

11%

WindingCracks

8%

RetainingRings

8%

Insulation39%

Damper winding /Wedges

15%

Shorted Turn13%

Other18%

Exciter3%

Slip ring7%

Ground Short8%

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AGENDA

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Targeted LTE Solutions for Siemens GeneratorsSummary of product improvements

Position in Rotor

Example ofFinding

Description ofSolution

• Laminated copper• Improved geometry

• “Omega”-shaped pole crossover

• Improved geometry

Main Lead Retaining Ring Shrink Fit Pole Cross Over Gas Baffle Teflon Coated Slotliners

• Modification of shrink fit onretaining rings

• Two piece blocks• Non-conducting & more flex.

material

• Reduced friction• Teflon coating of slot liners at

slot outlet

Position in Rotor

Example ofFinding

Description ofSolution

J-Lead Connection Retaining Ring Shrink Fit Pole Cross Over Gas Baffle

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J-Lead (or J-Strap)

§ Connects main lead viaradial bolt to the windingpole

§ Subject to cyclic stresses

Targeted LTE Solutions for Siemens GeneratorsJ-Lead Modification

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Axial loading on J-lead due toexpansion of Rotor windings• Highest loading at high VAR

loading• Load cycling increases cyclic

stresses on J-lead

Radial loading on windingdue to centrifugal loading atspeed• Frequent cycling of unit

increases cyclic stresseson J-lead

• Over-speed increaseloading on J-lead

Stress concentrations due togeometry

Material variations, assemblyvariations, and operation canaffect cyclic life of J-strap Deflection of J-Strap during standstill

and operation (exaggerated)

Targeted LTE Solutions for Siemens GeneratorsStresses / Loading on J-Lead

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Lam

inat

edTo

pC

onne

cted

J-S

trap

Lam

inat

edB

otto

mC

onne

cted

J-S

trap

Targeted LTE Solutions for Siemens GeneratorsJ-Lead Design Improvements

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Rotor tooth-tops

§ Support the retaining ringon the rotor body

§ Rotor teeth areasubjected to shrink fit ofretaining ring

§ Subject to cyclic stresses

Targeted LTE Solutions for Siemens GeneratorsRetaining Ring Shrink Fit Modification

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Compressive loads atstandstill from shrink fit

Tensile loads atrunning speed fromslot contentcentrifugal force

Axial loadsfrom lockingkey

Stress concentrationat fillet radii and holes

Targeted LTE Solutions for Siemens GeneratorsLoads and Stresses on Rotor Tooth Tops

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Remove tooth tops outboard of keyway• Removes majority of cracking & fatigued material at crack

tip• Transfer slot load from rotor to retaining ring• Removes centrifugal loading on vent holes

Machine fillet enlargement inboard of keyway• Removes shallow cracks & fatigued material• Relieve the outboard land surface of the end wedges

Modifiy shrink fit on retaining rings• Replace retaining rings as necessary• Improve shrink fit characteristics

Targeted LTE Solutions for Siemens GeneratorsShrinkfit Modification of Rotor Tooth Tops

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Rotor retaining rings

§ Subjected to StressCorrosion Cracking(SCC)

§ Periodic inspection of18-5 material isnecessary

§ Periodic inspection of18-18 material may berecommended,depending on operatingconditions

Targeted LTE Solutions for Siemens GeneratorsRetaining Ring Inspection

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Targeted LTE Solutions for Siemens GeneratorsAutomated Retatining Ring Inspection

In-Situ In the factory

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Rotor slot liner

§ Slot liner wears off due tothermal cycles

§ Slot liner wears off duringturning gear operation

§ Insulation between rotorcoils and rotor bodycompromised

Targeted LTE Solutions for Siemens GeneratorsSlot Liner Upgrade

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Signs of abrasion at slot channel insulation and slot cells at end of rotor body

Abrasion rate is correlated to:

• Deflection of the rotor (D² x L4 / I)• Time of turning-gear operation (HT)• Speed of turning-gear operation (NT)

Targeted LTE Solutions for Siemens GeneratorsReliability issue: Slot cell abrasion

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AGENDA

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Air Cooled Replacement GeneratorTypical auxiliary systems in a generator with Hydrogen / Water cooling

• Hydrogen gas systemProvides cooling medium (H2) inside the generator

• Seal oil systemKeeps the hydrogen gas inside stator frame

• Gas inertization systemRequired for de-gassing generator during stand-stills

• Stator winding cooling water system (> 200MW)Provides cooling medium (Water) for direct cooling ofstator winding

With the FootprintTM Generator these auxiliary systems are not required and can be eliminatedsaving life cycle costs

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Air Cooled Replacement GeneratorTypical age related problems in auxiliary systems

Porous Seal

Leaking ComponentsCorrosion

Lost Tagging Wear and Tear Vibration

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Air Cooled Replacement GeneratorOverview of design features

The use of different cooling zones in the activepart of the generator yields a more uniformtemperature profile.

Mechanically decoupled stator endwinding system with maximum rigidity towithstand transient system faults andmaximum flexibility for thermal expansion.

The maintenance-free stator core is flexibly mounted to the outer casingwith flex plates. This prevents vibrations at double rotational frequency fromimpacting the outer casing and thus the foundation tabletop.

Cooler cover with 4x25% drop in verticalcoolers, site installed for easy shipment of thecore generator and easy maintenance

.

The radially direct cooled stator core provides maximumheat transfer capability for the stator winding with minimumflow resistance for the overall cooling circuit.

Improved enclosure design makes theseair-cooled turbogenerators suitable foroutdoor installation, allows sound pressurelevels down to 85db(A) and provides easyaccess to all relevant components

The assembled winding is using the provenMICALASTIC® insulation system with globalvacuum-pressure impregnation technologyproviding maximum electrical endurance.

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Air Cooled Replacement GeneratorFootprintTM Approach

Adaptation of base frame• Customized base frame fits existing foundation

dimensions / No foundation mods requried• Generator can be installed more quickly

Adaptation of stator core and rotor shaft• Stator winding insulation with global vacuum

pressure impregnation (GVPI)• Rotor shaft and coupling are adapted• Plug-in or pedestal bearings• Rotor-dynamic calculation of shaft train

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Air Cooled Replacement GeneratorFootprintTM Approach

Adaptation of excitation• Excitation can be static or brushless• Reduced operating costs with new exciter

Adaptation of bushings• Downward• To the side• Or upward through the cover

Adaptation options for cooling• Location and configuration of the cooler can be

varied• Typically use Totally Enclosed Water to Air Cooling• Water demand no greater than for existing

Hydrogen coolers

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Air Cooled Replacement GeneratorCustomer benefits

Elimination of auxiliary systems• Increased safety by eliminating hydrogen• Reducing operation complexity and cost

Built-to-function design• Cyclic operation modes• Peaking mode operation• Multiple start/stop cycles

Highest Reliability/ Availability• Over 98% availability• Standard spare parts only, i.e. always stocked• Major inspection intervals can be spread over 12 years

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Air Cooled Replacement GeneratorCase study – South Africa

Unit Existing Units Replacement Foot-PrintTM Generator

Manufacturer AEG (1964) Siemens

Reactive Power [MVA] 139 139

Active Power [MW] 125,1 125,1

Power Factor 0,9 0,9

Rated Voltage [kV] 10,5 12,5

Primary Cooling Medium H2 Air

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CONTACT PAGE

Michal GawronMarketing EngineerGenerator Major ServicesEurope, Africa, Asia-Pacific

Phone: +49 (208) 456 8134Fax: +49 (208) 456 8137Mobile: +49 (173) 317 6546E-mail: [email protected]

mailto:[email protected]

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BACK-UP

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§ The Micalastic® is used in Siemens generators for more than 50 years.

§ In addition Siemens introduced the Global Vacuum Pressure Impregnation (GVPI) Technology in1988.

§ Since then Siemens has manufactured more than 1000 generators (air-, hydrogen- andhydrogen/water cooled) using GVPI technology in conjunction with the Micalastic insulation systemwith voltage levels up to 22 kV and rating up to 550 MVA.

§ Operational experience of these units without any stator insulation based failures since the beginningsin 1988 demonstrates the superior quality of GVPI technology.

Air Cooled Replacement GeneratorMicalastic® experience base

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Summary

The two J-Leads which connect the radial leads to the rotorwinding can suffer fatigue- induced cracking.

In order to avoid any forced outages and potential consequentialdamage resulting from such cracking, Siemens has developedimproved J-Lead assemblies as part of its ongoing productdevelopment process and in order to increase reliability.

Siemens recommends that the old type of J-Lead be replacedwith these improved J-Lead assemblies.

Please ask your Siemens representative or check on our servicecustomer portal if this product bulletin applies to a generator youhave in operation.

Targeted LTE Solutions for Siemens GeneratorsProduct Bulletin – New J-Lead

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Summary

The rotor tooth tops underneath the retaining rings are subject tocracking. In order to prevent the initiation of cracks and to reducethe impact of any existing cracks a “short ring modification” hasbeen developed by Siemens and it is recommended that thismeasure be implemented in order to increase reliability.

This modification also encompasses machining of the shrink fit ofthe retaining ring, the rotor tooth tops and the retaining ring itself.In order to perform this modification it is necessary to removeboth retaining rings and remove the rotor from the stator.

Please ask your Siemens representative or check on our servicecustomer portal if this product bulletin applies to a generator youhave in operation.

Targeted LTE Solutions for Siemens GeneratorsProduct Bulletin – Short Ring Modification

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Summary

A periodic inspection of 18Mn-18Cr1 retaining rings and a qualified Non-Destructive Examination (NDE) procedure are recommended on allgenerator rotors. This inspection is intended to evaluate the structuralintegrity of non-magnetic retaining rings and zone rings. Siemens mayrecommend replacement of retaining rings in cases of inspection findings orexceptional operating conditions.

Cases that might be considered “exceptional conditions” include:

• Stress corrosion cracking due to chemical conditions that should not bethe normal operating environment of large electrical generators. Theseinclude long-term exposure to saturated sodium chloride solution andexposure to bromine under electrical fault conditions.

• Grid interaction with the generator (such as disturbances from electric arcfurnaces), which can result in rotor torsional oscillations.

• Loss-of-control events, such as out-of phase synchronization, suddenshort circuit, motorization and similar severe abnormal operation.

Please ask your Siemens representative or check on our service customerportal if this product bulletin applies to a generator you have in operation.

Targeted LTE Solutions for Siemens GeneratorsProduct Bulletin – Inspection Recommendation for Retaining Rings

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