Comparison of Peak Armature and Field Winding Currents for ...
B.C. Hydro Brushgear Testing and Monitoring...Commutator ( armature winding) Megger Test. IR and PI...
Transcript of B.C. Hydro Brushgear Testing and Monitoring...Commutator ( armature winding) Megger Test. IR and PI...
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Hydro and Turbine Machines
Rotating Exciters Testing and
Repair
Presentation By Igor Chichkin, P.Eng
Generation Maintenance (GM) –Electrical Group
BC Hydro, British Columbia,Canada
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Fundamentals of DC Machine Operation
Four-pole DC
machine
Two -pole DC
machine
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Fundamentals of DC Machine Operation( by EASA)
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Fundamentals of DC Machine Operation( by EASA)
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Fundamentals of DC
Machine
Operation( by EASA)
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DC machine Interpoles
Output Voltage < Input Voltage
Typical Voutput = ¼ to 2/3 Vinput
if interpoles polarity is correct.
if Voutput > Vinput
reverse interpoles polarity
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Fundamentals of DC Machine Operation( EASA)
Electrical Neutral set up …
what
does this mean ?
Why it is necessary ?!
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Brush Potential Test
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Rotating Exciter
Refurbishment /rewind
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Rotating exciter refurbishment/rewind
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Armature core after winding removal.
Commutator has been replaced.
Rotating Exciter refurbishment/rewind
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Rotating Exciter refurbishment/rewind
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Armature Core Loss Test
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Rotating Exciter refurbishment/rewind
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Rotating Exciter refurbishment/rewind
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Rotating Exciter refurbishment/rewind
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Rotating Exciter refurbishment/rewind
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Rotating Exciter refurbishment/rewind
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Rotating Exciter refurbishment/rewind
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Exciter armature ( half coil winding)
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Rotating Exciter refurbishment/rewind
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Exciter armature ( half coil winding)
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Commutator Profile Test
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Commutator Profile Test Plot
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Commutator ( armature winding) Megger Test
IR and PI measured at 1000 Vdc.
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Commutator ( armature winding) Surge Test
Commutator Surge test equipment
Surge test is being performed with 16 commutator segments span.
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Commutator ( armature winding) Surge test
Surge test voltage shall not exceed the AC Hipot test voltage level
Surge comparison test wave form
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WORK PERFORMED ON FIELD FRAME ASSEMBLY
12) INSTALL NEW COILS 13) CHECK FINAL AIR GAP MEASUREMENTS( indicate where ) 14) ADJUST SHIMS ON ONE INTERPOLE 15) TORQUE ALL BOLTS AND CONNECTIONS 16) FULL ELECTRICAL TESTS AS PER SPECIFICATIONS 17) POLARITY TESTS 18) RESISTANCE CHECKS 19) 400 HZ DROP TESTS and SURGE TESTS 20) VARNISH AND BAKE WINDINGS, 2 CYCLES 21) PAINT ASSEMBLY ASA70 ENAMEL 22) PALLETIZE AND SHRINK WRAP AND SHIP
1) INCOMING TESTS, REMOVE AND ROAST COILS 2) RECORD INCOMING DIAMETRICAL IRON MEASUREMENTS AND SHIMS 3) RECORD WINDING DATA 4) REWIND ALL SIX MAIN POLE COILS, U300 THERMO SETTIN EPOXY 5) BOLTED CONNECTIONS ON SHUNT COILS 6) ROAST, CLEAN AND RE-INSULAT SERIES WINDINGS 7) ROAST CLEAN AND RE-INSULATE INTERPOLE WINDINGS 8) REPLACE ALL COIL BLOCKING & SPACERS 9) CLEAN AND RE-INSULATE ALL JUMPERS 10) SILVER PLATE CONNECTIONS 11) CORN COB FRAME AND POLE PIECES
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G1 Field Frame Windings ( were in bad condition before rewind)
All (6) Main Field winding removed
Six (6) Interpole windings with shims removed.
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G1 Field Frame Windings ( were in bad condition before rewind)
Main Field winding with shims removed.
Interpole winding and Series winding jumpers.
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Rotating exciter ( Field Frame windings)
Main Field ,Series Field and Interpole windings
Series Field and Interpole windings ( have a few turns) and Main Field winding ( has many turns).
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Commutator ( armature winding) Megger Test
Exciter Field Frame with Interpoles removed
Blocking and lashing of the Series Field winding to prevent it from moving.
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Rotating Exciter ( Field Frame windings )
Interpoles winding
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Rotating Exciter ( Field Frame windings )
Main Field winding with shims
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Main Shunt Field Winding Surge Test
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Rotating Exciter ( Brush gear )
The number of brush holder arms (6) is equal to the number of exciter field poles.
Brush gear yoke is in place.
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Rotating exciter ( Field windings) Interconnection
Hence, to improve brush gear performance modification has been made to the brush holders position. Brush holders have been 180º reversed to make brushes running with 15º trailing rather than with 15º leading angle.
Modification has been also made to brush holders interconnection with the windings and flexible connectors have been installed.
G1 commutator spins clockwise.
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Rotating exciter adjustments and testing at site
G2 exciter .
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Rotating exciter adjustments and testing at site
G2 exciter spins CW ( note : brush holder is set to TRAILING position because of its angle 15 Deg.
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Rotating exciter adjustments & testing
Brush holders spacing adjustment
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Rotating exciter adjustments and testing at site
G2 exciter set up for PVN (Pencil Voltage Neutral) Test
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Rotating exciter adjustments and testing at site
G2 exciter Pencil Voltage Neutral PVN test on spinning machine .
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Rotating exciter adjustments and testing at site
G2 exciter Pencil Voltage Neutral PVN test .
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Rotating exciter adjustments & testing
Pencil Voltage Neutral ( PVN) Test
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Importance of armature resistance
test
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Bar-to-Bar (“Span of Bars”) Resistance Test method
Before repair
Graph below : Note variations in resistance
measurements > 20%
RULE for Span method : The span should be less than one
pole-pitch.
Suggested span = ¼ of bar pole-
pitch. The fewer number of bars
spanned the more accurate the
results.
Bar per pole = Bars/Poles
126 bars/6 poles=21 bars
Bar pole Pitch= 1 & 22
Acceptance criteria :
Deviation “ Span of Bars” < 1 %
Deviation “Bar-to-Bar” < 5 %
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Bar-to-Bar (“Span of Bars”) Resistance Test method
After repair
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Bar-to-Bar Resistance Test
( armature winding with Equalizers)
Expect repeatable pattern
on good commutator and armature winding
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Slip Ring Film Makeup
Carbon
Brush
Grains of
Moisture
Airborne
Contaminants
5%
Metal
Oxide
75%
Carbon Graphite
from the brush
15 - 20%
Steel Ring
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Why Brushes Wear so fast ?
Carbon rubbing on bare copper/steel
- high friction
Comm/slipring surface with good film
- low friction
Rule of thumb : brush wear 0.003 to 0.006 inch/day
or about 5 mm / 1000 hours
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Humidity Units
Relative Humidity ( RH) - %
Absolute Humidity – grains / lb dry air
1 grain = 0.000143 lbs
Two critical thresholds : 2 and 25 g of water / m 3 of air
less than 2– brush wear
above 25 – commutator deterioration
Rapid Brush Wear : about 20 % RH at 75 F, 24°C or
about 40% RH at 55 F, 13°C
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What is Good Commutator Film ?
Commutator filming is a continuous process ! ( formed and stripped and formed and ………maintained )
Commutator COLOR
Chocolate brown or burnished bronze to dark brown
It is not bright copper or burned black copper color
Uniform in color
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Requirements For Good Film
In General :
Brush Current density : 55-85 Amps/in²
Commutator Surface Temperature : 60-90°C
Water Vapor ( optimum): 8-15 g of water/ m3air
Brush Pressure : 2 to 4 lbs/in²
Commutator Surface Speed ( D, rpm) < 8,000 fpm
Brush Material or Grade no MAGIC brush
Lack of Contamination ( vapors) Silic.,Sulf.,Chl.
Mechanical Integrity and Setup El neutr,alignm.
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Brush angle
Trailing : at least 5° ( 5-15° common use)
Reaction : 30-35° ( with 22 ° minimum safe)
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Jig to seat the brushes in the shop
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Questions ?