Post on 05-Aug-2020
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
BUILDING STRONG® PORTLAND DISTRICT 5
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
BUILDING STRONG® PORTLAND DISTRICT 6
Lashing and Cap Removal
BUILDING STRONG® PORTLAND DISTRICT 7
Bar Removal
BUILDING STRONG® PORTLAND DISTRICT 8
Slot Prep/Bar Test
BUILDING STRONG® PORTLAND DISTRICT 9
Bar Insertion
BUILDING STRONG® PORTLAND DISTRICT 10
Slot Wedging
BUILDING STRONG® PORTLAND DISTRICT 11
Brazing Mock-ups
BUILDING STRONG® PORTLAND DISTRICT 12
Lashing Bars and Brazing
BUILDING STRONG® PORTLAND DISTRICT 13
Bottom Cap Installation
BUILDING STRONG® PORTLAND DISTRICT 14
Taping Pole Group Jumpers
BUILDING STRONG® PORTLAND DISTRICT 15
Top Cap Installation
BUILDING STRONG® PORTLAND DISTRICT 16
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
BUILDING STRONG® PORTLAND DISTRICT 19
Questions?
BUILDING STRONG® PORTLAND DISTRICT 20
Cause of Fault
BUILDING STRONG® PORTLAND DISTRICT 21
Field Coil Removal
BUILDING STRONG® PORTLAND DISTRICT 22
Pole Body Insulation
BUILDING STRONG® PORTLAND DISTRICT 23
Re-assembling Coil