US Army Corps of Engineers

BUILDING STRONG®

In-house Repair of Hydro-generator Stator Winding

May 17, 2017 by Scott Cotner, P.E. Senior Electrical Engineer Hydroelectric Design Center

BUILDING STRONG® PORTLAND DISTRICT 2

John Day Lock and Dam Multi-purpose facility on Columbia River on

Washington-Oregon border Powerhouse has sixteen 164MVA generators

BUILDING STRONG® PORTLAND DISTRICT 3

Fault and Damage

Placing Unit in-line, generator at rated speed and voltage

LL Fault occurred: ► >13kA in A and B

phase ► Tripped by multiple

elements of DMFR relay

BUILDING STRONG® PORTLAND DISTRICT 4

Repair Decisions

Contract or in-house forces? ► Contracting difficulty encountered ► In-house with technical direction

With rotor in or out? ► In – remove 2-3 poles

• shorter duration, cramped workspace

► Out – disassemble machine • much longer duration, easier access

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Materials and Tooling On-hand at project

► Spare top and bottom stator bars, insulating caps, polyester roving, spare pole collars

On-hand at nearby projects ► Slot closing wedges, fillers, polyester felt, field coil

lifting jig ► Test equipment, induction brazing equipment

To be ordered ► Mica tape, insulating, semiconducting, and weeping

epoxies, brazing filler metal, copper for pole group connections

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Lashing and Cap Removal

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Bar Removal

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Slot Prep/Bar Test

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Bar Insertion

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Slot Wedging

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Brazing Mock-ups

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Lashing Bars and Brazing

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Bottom Cap Installation

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Taping Pole Group Jumpers

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Top Cap Installation

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Testing – In-process and Final Overpotential (hipot) spare bars Slot paint resistance to ground Top bar side resistance to ground Ripple spring compression Overpotential (hipot) bars after wedging Resistance of all brazed joints Field winding pole drop Both Rotor and Stator - winding resistance,

insulation resistance/polarization index, final overpotential (ac)

BUILDING STRONG® PORTLAND DISTRICT 17

Lessons Learned

Rotor in or rotor out? ► Out: allowed more work space but much longer

outage ► In: cramped but could pull and push bars against rim

Careful Spare Bar measurements ► Checked width but not depth, spare bars were slightly

shallower than old ones resulting in lots of top filler to wedge slot tightly.

BUILDING STRONG® PORTLAND DISTRICT 18

Lessons Learned (cont’d)

Material orders ► Order early and notify team of supply problems

Technical Direction ► More emphasis on what not to do

• Collateral damage expands repair scope

► Clear descriptions of work • Sketches, photos, and mock-ups help ensure all parties have

clear understanding of work

Crew consistency and craftsmanship

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Questions?

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Cause of Fault

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Field Coil Removal

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Pole Body Insulation

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Re-assembling Coil