the effect of dc machine adjustment on loop unbalance papers/the effects of dc machine...

The Effect of DC Machine The Effect of DC Machine Adjustment onAdjustment on Loop UnbalanceLoop Unbalance

WMEA, Edmonton, Alberta, CanadaWMEA, Edmonton, Alberta, CanadaJune 11June 11--13, 200813, 2008

Rich Hall Rich Hall –– Morgan AM&TMorgan AM&T

Jim Shackelford Jim Shackelford –– Peabody EnergyPeabody Energy

Technical ContributorTechnical Contributor

Jason Conrad Jason Conrad –– GE Canada GE Canada

Peterborough, Ontario, CanadaPeterborough, Ontario, Canada

Dragline Generator LoopsDragline Generator Loops

Loop 1Loop 1 Loop 2Loop 2

HG1HG1

HM1HM1

HG3HG3

HM3HM3

HG2HG2

HM2HM2

HG4HG4

HM4HM4

Dragline Loops ContainDragline Loops Contain

•• Direct Current GeneratorsDirect Current Generators•• Direct Current MotorsDirect Current Motors•• Ammeter ShuntsAmmeter Shunts•• CablesCables•• ConnectionsConnections

Dragline Generator LoopsDragline Generator Loops Design BenefitsDesign Benefits

• Multiple units in each loop “average out” some of the variation in individual generators and motors, cabling, etc.

• Multiple motors and generators “average out” the effect of temperature variations around the house

• Multiple loops give some degree of control of the machine if one loop is lost

Loop BalanceLoop Balance

Ideally, the loops behave exactly the Ideally, the loops behave exactly the same as each other under all conditionssame as each other under all conditions

Visually, they would look like a Visually, they would look like a wellwell--choreographed synchronized choreographed synchronized

swim teamswim team

Loop BalanceLoop Balance cont.cont.

•• This means each generator behaves This means each generator behaves like every other generatorlike every other generator

•• Each motor behaves like every other Each motor behaves like every other motormotor

•• Each loopEach loop’’s cables and connections s cables and connections have the same resistance as each other have the same resistance as each other looploop

These loops act electrically in These loops act electrically in parallelparallel

•• If the generators in one loop produce If the generators in one loop produce more Voltage than the generators in other more Voltage than the generators in other loops, that loop will draw more currentloops, that loop will draw more current

•• If the motors in one loop If the motors in one loop ““trytry”” to run to run faster than the motors in other loops, they faster than the motors in other loops, they cannot because they are geared together, cannot because they are geared together, but that loop will draw more currentbut that loop will draw more current

These loops act electrically in These loops act electrically in parallelparallel

•• If the resistances of the cables and If the resistances of the cables and connections are lower in one loop than connections are lower in one loop than the other loops, that loop will draw the other loops, that loop will draw more currentmore current

So what??So what??•• Unbalanced loop currents may cause Unbalanced loop currents may cause

excessive torque in some loops, cause excessive torque in some loops, cause increased mechanical wear and take increased mechanical wear and take life out of couplings, gears, and life out of couplings, gears, and structural parts of the machinestructural parts of the machine

•• Unbalanced loop currents may result in Unbalanced loop currents may result in too little torque in some loops and too little torque in some loops and reduce the productivity of the draglinereduce the productivity of the dragline

Other ProblemsOther Problems

•• Unbalanced loop currents may result in Unbalanced loop currents may result in increased brush and commutator wearincreased brush and commutator wear

•• Unbalanced loop currents may result in Unbalanced loop currents may result in flashoversflashovers

•• Unbalanced loop currents may trip the Unbalanced loop currents may trip the loop overcurrentloop overcurrent

•• Unbalanced loop currents may cause Unbalanced loop currents may cause the generator field overcurrent to tripthe generator field overcurrent to trip

Bigger Problems!!!Bigger Problems!!!

•• Unbalanced loop currents may result in Unbalanced loop currents may result in overheating some generators or motorsoverheating some generators or motors

•• Badly unbalanced loop currents may Badly unbalanced loop currents may cause the sync motors to pull out of cause the sync motors to pull out of synchronization, especially on weak synchronization, especially on weak power systemspower systems

ResultsResults

•• This may cause damage to equipment, This may cause damage to equipment, loss of productivity, increased loss of productivity, increased downtime and increased repair costsdowntime and increased repair costs

•• Rule of thumb in the business loss Rule of thumb in the business loss insurance industry: the cost of the insurance industry: the cost of the repair is 10% of the business lossrepair is 10% of the business loss

How much voltage does it take to How much voltage does it take to drive rated current?drive rated current?

•• The rating of a GE 1045 KW generator The rating of a GE 1045 KW generator is 475 Volts and 2200 Amperes.is 475 Volts and 2200 Amperes.

•• It does not take 475 Volts to drive rated It does not take 475 Volts to drive rated current in the loop, however.current in the loop, however.


•• The answer The answer –– about 20 Volts per about 20 Volts per generator!!!generator!!!


•• When the machines are in a When the machines are in a ““motoringmotoring”” quadrant, the generators are generating quadrant, the generators are generating an electro motive force (EMF), but the an electro motive force (EMF), but the motors are motors are also generating an generating an electromotive force that opposes the electromotive force that opposes the generator EMF and it is called a counter generator EMF and it is called a counter EMF (CEMF).EMF (CEMF).


•• It is the sum of the generator Voltages It is the sum of the generator Voltages minus the sum of the motor Voltages in minus the sum of the motor Voltages in the loop that drives loop current.the loop that drives loop current.

•• This Voltage divided by the loop This Voltage divided by the loop resistance gives the loop current.resistance gives the loop current.

Dragline Generator LoopDragline Generator Loop

Loop 1Loop 1

HG1HG1

HM1HM1

HG3HG3

HM3HM3

++

++

++

++__

__

__

__Loop Loop CurrentCurrent


•• The loop resistance is most easily The loop resistance is most easily determined at stall when the motors are determined at stall when the motors are not rotating or generating any CEMF.not rotating or generating any CEMF.

•• For a 1045 KW generator, about 40 Volts For a 1045 KW generator, about 40 Volts per generator drives stall current (2X rated per generator drives stall current (2X rated current or 4400 Amperes).current or 4400 Amperes).

•• Loop Resistance = Loop Resistance = (40V + 40V (40V + 40V –– 0V 0V -- 0V) 0V) = = 0.0181 Ohm0.0181 Ohm 4400 Amperes4400 Amperes


•• It does not take a large Voltage It does not take a large Voltage imbalance to drive a lot of current when imbalance to drive a lot of current when you divide it by 0.0181!!!you divide it by 0.0181!!!

Standards for Loop Balance

•• 5% of stall current at stall conditions5% of stall current at stall conditions

•• 5% of stall current while running steady 5% of stall current while running steady (even at peak power)(even at peak power)

•• 10% of stall current during transient 10% of stall current during transient load changesload changes

How much voltage difference How much voltage difference does it take to be at the does it take to be at the recommended limits?recommended limits?

•• 5% of 4400 Amperes = 220 Amperes5% of 4400 Amperes = 220 Amperes

•• V = IR = 220 Amperes x 0.0181 Ohms V = IR = 220 Amperes x 0.0181 Ohms

V = 3.9 VoltsV = 3.9 Volts

•• So a 4 Volt difference between loops is So a 4 Volt difference between loops is all it takes to be at 5% of stall current! all it takes to be at 5% of stall current!

Four Quadrant OperationFour Quadrant Operation

1122

33 44

+ Vo

lts+

Volts

-- Vol

tsVo

lts

+ Amps+ Amps-- AmpsAmps

First QuadrantFirst QuadrantA

rmat

ure

Volts

Arm

atur

e Vo

lts

Armature AmpsArmature Amps

Commutation LimitsCommutation Limits

Loop 1Loop 1

Loop 2Loop 2

Unbalanced Loop Unbalanced Loop CurrentCurrent


•• Loop 1 is the control loop and is inside Loop 1 is the control loop and is inside the commutation limits, so it is OK.the commutation limits, so it is OK.

•• Loop 2 is the slave loop and is inside Loop 2 is the slave loop and is inside the commutation limits, so the the commutation limits, so the equipment is OK. It is equipment is OK. It is ““loafingloafing””, , however, so the dragline is working at however, so the dragline is working at less than capacity.less than capacity.

First QuadrantFirst QuadrantA

rmat

ure

Volts

Arm

atur

e Vo

lts


Commutation LimitsCommutation Limits

Loop 1Loop 1

Loop 2Loop 2

Unbalanced Loop Unbalanced Loop Current Current


•• Loop 1 is the control loop and is inside Loop 1 is the control loop and is inside the commutation limits, so it is OK.the commutation limits, so it is OK.

•• Loop 2 is the slave loop and is outside Loop 2 is the slave loop and is outside the commutation limits. This may lead the commutation limits. This may lead to commutation distress, flashovers, to commutation distress, flashovers, excessive wear of couplings and gears, excessive wear of couplings and gears, tripping of the machine, etc. tripping of the machine, etc.

Assembling DC MachinesAssembling DC Machines

•• To work properly together and to To work properly together and to commutate well, machines must be commutate well, machines must be built or rebuilt properly.built or rebuilt properly.

•• Following are GE factory tolerances Following are GE factory tolerances provided by GE Canada, Peterborough, provided by GE Canada, Peterborough, Ontario.Ontario.

GeneratorsGenerators

•• Pole centerline to pole centerline chord Pole centerline to pole centerline chord –– measured at both ends of machinemeasured at both ends of machine–– minimum to maximum values must not minimum to maximum values must not

differ by more than 0.125differ by more than 0.125”” (3.2 mm)(3.2 mm)

Pole Tip SpacingPole Tip Spacing

Difference Between A and B is Difference Between A and B is 1/81/8”” (3.2 mm) Maximum(3.2 mm) Maximum

AA BB

FrameFrame


•• Brush Holder AssemblyBrush Holder Assembly–– holders to be set 0.070holders to be set 0.070”” to 0.080to 0.080”” from from

commutator surface (1.8 to 2.0 mm)commutator surface (1.8 to 2.0 mm)–– axial skew must not exceed one mica axial skew must not exceed one mica

thickness over the length of the thickness over the length of the commutatorcommutator

0.070 – 0.080” (1.8 – 2.0 mm)

Brush Box HeightBrush Box Height


•• Circumferential brush spacing (paper Circumferential brush spacing (paper tape on commutator)tape on commutator)–– arcs measured from one brush toe to the arcs measured from one brush toe to the

next must be within 3/64next must be within 3/64”” (0.047(0.047”” or or 1.2 mm) 1.2 mm) (MAXIMUM)(MAXIMUM)

Commutator

Commutator

A

F

E

D

C

B

A = ______B = ______C = ______D = ______E = ______F = ______

Max. SpacingDiff. = ______

Target is .030”

On WestinghouseEquipment

Brush Spacing

Max. Spacing diff = .050” on GE equip.


•• Air GapsAir Gaps–– all air gaps to be within +/all air gaps to be within +/--0.0070.007”” (0.18 mm)(0.18 mm)–– commutating pole air gaps may be commutating pole air gaps may be

different than main pole air gapsdifferent than main pole air gaps

Uneven And Tapered Air GapsUneven And Tapered Air Gaps

FrameFrame

PolePole

PolePole

FrameFrame

ArmatureArmature

Air Gap Taper GaugeAir Gap Taper Gauge

Air Gap MeasurementAir Gap Measurement

MotorsMotors

•• Pole centerline to pole centerline chord Pole centerline to pole centerline chord –– measured at both ends of machinemeasured at both ends of machine–– minimum to maximum values must not minimum to maximum values must not

differ by more than 0.125differ by more than 0.125”” (3.2 mm)(3.2 mm)

MotorsMotors

•• Brush Holder AssemblyBrush Holder Assembly–– holders to be set 0.070holders to be set 0.070”” to 0.080to 0.080”” from from

commutator surface (1.8 to 2.0 mm)commutator surface (1.8 to 2.0 mm)–– axial skew must not exceed one mica axial skew must not exceed one mica

thickness over the length of the thickness over the length of the commutatorcommutator

MotorsMotors

•• Circumferential brush spacing (paper Circumferential brush spacing (paper tape on commutator)tape on commutator)–– arcs measured from one brush toe to the arcs measured from one brush toe to the

next must be within 3/64next must be within 3/64”” (0.047(0.047”” or or 1.2 mm)1.2 mm)

MotorsMotors

•• Air GapsAir Gaps–– all air gaps to be within +/all air gaps to be within +/--0.0070.007”” (0.18 mm)(0.18 mm)–– commutating pole air gaps may be commutating pole air gaps may be

different than main pole air gapsdifferent than main pole air gaps

N = Number of TurnsN = Number of Turnsg = Air Gapg = Air Gap

NN

gg

φφ αα

N x N x ii

NN

eeii

φφ FluxFlux

SATURATION CURVESATURATION CURVE

FluxFluxin in

Air GapAir Gap

N x N x IIFF (Ampere Turns)(Ampere Turns)

Iron Saturation RegionIron Saturation Region

Air Gap Region

Air Gap Region

φφ

NN

ee

0 24

24

++--

Generated VoltsGenerated Volts

LLVV

Volts = E. M. F. = B x L Volts = E. M. F. = B x L xxVVwherewhere

B = Flux Density ( B = Flux Density ( φφ / area) / area) L= Length of the conductorL= Length of the conductorVV = Velocity of the conductor= Velocity of the conductor

IIFF

GeneratorGenerator

V V αα

B x L x B x L x VV

V (EMF) V (EMF) αα

B B αα

IIFieldField

MotorMotorV V ==

B x L x B x L x VV

V V αα

B x RPMB x RPM

RPM RPM αα VoltsVolts α α VoltsVoltsBB IIFieldField

SpeedSpeed

TorqueTorqueF F α α B x IB x IAA x x LLTorque = Force x RadiusTorque = Force x RadiusTorque Torque αα

B x IB x IAA

BB

LL

rr( Flux Density )( Flux Density )

MotorMotor

V V αα

B x L x B x L x VV

V V α α B x L x RPM B x L x RPM

V (CEMF) V (CEMF) αα

B x RPM B x RPM

αα

IIFieldField x RPMx RPM

Generator Generator Data SheetData Sheet

00

Arm

atur

e Vo

ltsA

rmat

ure

Volts

100100

200200

300300

400400

500500

600600

Field AmpsField Amps22 44 66 88 1010 1212 1414 1616 1818 2020

..

..

No Load Saturation No Load Saturation CurveCurve

MCF866B, 836 KW, 475 Volt, MCF866B, 836 KW, 475 Volt, 1760 Ampere, 1200 RPM1760 Ampere, 1200 RPM

Load Curve Load Curve –– 836 KW Gen.836 KW Gen.Armature VoltsArmature Volts Arm. AmpsArm. Amps Field AmpsField Amps

600600 00 18.918.9575575 11201120 18.618.6550550 22302230 18.618.6450450 25002500 13.513.5350350 27702770 11.211.2250250 30303030 9.49.44040 36003600 6.26.2

Adjusting DC Machines Adjusting DC Machines -- FactoryFactory

•• Black Band MethodBlack Band Method

•• See the paper See the paper ““NECP NECP –– Tuning DC Tuning DC Motors and Generators Motors and Generators –– Jun 07Jun 07”” on on the WMEA web site the WMEA web site wmea.netwmea.net for other for other methods of tuning DC machinesmethods of tuning DC machines

Buc

k A

mps

Buc

k A

mps

Boo

st A

mps

Boo

st A

mps

00

Load Amps (%)Load Amps (%)

Buck Boost CurveBuck Boost Curve

XX

XX

5050 100100 150150

XX No Load Band No Load Band Center on Buck Center on Buck Side (Strong)Side (Strong) Corrective action Corrective action –– shift shift

brush rigging with rotation brush rigging with rotation (motor) or against rotation (motor) or against rotation (generator)(generator)

Buc

k A

mps

Buc

k A

mps

Boo

st A

mps

Boo

st A

mps

00



XX

XX

5050 100100 150150

XXNo Load Band No Load Band Center on Boost Center on Boost Side (Weak)Side (Weak)

Corrective action Corrective action –– shift shift brush rigging against brush rigging against rotation (motor) or with rotation (motor) or with rotation (generator)rotation (generator)

Buc

k A

mps

Buc

k A

mps

Boo

st A

mps

Boo

st A

mps

00



XX

XX

5050 100100 150150

xx

xx

xx

xx

xx

xx

Band CenterBand Center

Band Center on Boost Side Band Center on Boost Side (Weak)(Weak)

Corrective Action Corrective Action –– Remove Remove nonmagnetic shims, add magnetic nonmagnetic shims, add magnetic shimsshims

No sparking in black area, sparking outside black area


xxLoad Amps (%)Load Amps (%)

Corrective Action Corrective Action –– Remove Remove magnetic shims, add non magnetic magnetic shims, add non magnetic shimsshims

Buc

k A

mps

Buc

k A

mps

Boo

st A

mps

Boo

st A

mps

00

XX

XX

5050 100100 150150

xx

xx

xx

xx

xx

Band CenterBand Center

Band Center on Band Center on Buck Side Buck Side (Strong)(Strong)

Sparking with no buck or boostSparking with no buck or boost

Voltage or RPM Regulation DefinedVoltage or RPM Regulation Defined


Volts

or R

PMVo

lts o

r RPM

Increased Voltage or RPM RegulationIncreased Voltage or RPM Regulation

Decreased Voltage or RPM RegulationDecreased Voltage or RPM Regulation

Generator Generator –– increased main pole air gapincreased main pole air gap

Saturation CurveSaturation Curve

Volts

Volts

Field AmpsField Amps Armature AmpsArmature Amps

RegulationRegulation

Volts

Volts

BeforeBefore

AfterAfter

Regulation decreasesRegulation decreases

Generator Generator –– decreased main pole air gapdecreased main pole air gap


Volts

Volts



Volts

Volts

BeforeBefore

AfterAfter

Regulation increasesRegulation increases

Generator Generator –– increased comm pole air gap increased comm pole air gap or add nonmagnetic shimsor add nonmagnetic shims


Volts

Volts



Volts

Volts

BeforeBefore

AfterAfter

No EffectNo EffectRegulation increasesRegulation increases

Generator Generator –– decreased comm pole air gap decreased comm pole air gap or remove nonmagnetic shimsor remove nonmagnetic shims


Volts

Volts



Volts

Volts

BeforeBefore

AfterAfter

No EffectNo Effect

Regulation deceasesRegulation deceases

Generator Generator –– brush shift with rotationbrush shift with rotation


Volts

Volts



Volts

Volts

BeforeBefore

AfterAfter

No EffectNo EffectRegulation increasesRegulation increases

Generator Generator –– brush shift against rotationbrush shift against rotation


Volts

Volts



Volts

Volts

BeforeBefore

AfterAfter

No EffectNo EffectRegulation decreases Regulation decreases

Motor Motor –– increased main pole air gapincreased main pole air gap


Volts

/ R

PMVo

lts /

RPM



RPMRPM

BeforeBefore

AfterAfter

Regulation increasesRegulation increases

Motor Motor –– decreased main pole air gapdecreased main pole air gap


Volts

/ R

PMVo

lts /

RPM



RPMRPM

BeforeBefore

AfterAfter

Regulation decreasesRegulation decreases

Motor Motor –– increased comm pole air gap or increased comm pole air gap or add nonmagnetic shimsadd nonmagnetic shims


Volts

/ R

PMVo

lts /

RPM



RPMRPM

BeforeBefore

AfterAfter

Regulation increasesRegulation increasesNo EffectNo Effect

Motor Motor –– decreased comm pole air gap or decreased comm pole air gap or remove nonmagnetic shimsremove nonmagnetic shims


Volts

/ R

PMVo

lts /

RPM



RPMRPM

BeforeBefore

AfterAfter

Regulation decreasesRegulation decreasesNo EffectNo Effect

Motor Motor –– Brush shift with rotationBrush shift with rotation


Volts

/ R

PMVo

lts /

RPM



RPMRPM

BeforeBefore

AfterAfter

Regulation increasesRegulation increasesNo EffectNo Effect

Motor Motor –– Brush shift against rotationBrush shift against rotation


Volts

/ R

PMVo

lts /

RPM



RPMRPM

BeforeBefore

AfterAfter

Regulation decreasesRegulation decreasesNo EffectNo Effect

Voltage Regulation Voltage Regulation –– Shunt GeneratorShunt Generator


Volts

Volts

Low Voltage RegulationLow Voltage Regulation

Voltage Regulation Voltage Regulation –– Shunt GeneratorShunt Generator


Volts

Volts

Low Voltage RegulationLow Voltage Regulation

Delta AmpsDelta Amps

Delta Delta VoltsVolts

Voltage Regulation Voltage Regulation –– Differential Differential Compound GeneratorCompound Generator


Volts

Volts

Higher Voltage RegulationHigher Voltage Regulation

Delta AmpsDelta Amps

Delta Delta VoltsVolts

Differentially Compound Differentially Compound GeneratorsGenerators

•• Differentially compound generators Differentially compound generators limit loop current unbalances, as limit loop current unbalances, as generators that are more heavily loaded generators that are more heavily loaded (loop unbalance) will drop in voltage (loop unbalance) will drop in voltage and shed some load.and shed some load.

•• This helps, of course, but does not This helps, of course, but does not ““curecure”” loop unbalance.loop unbalance.

Machine Adjustments and Loop Machine Adjustments and Loop Balance SummaryBalance Summary

•• DC machines must be built to accepted DC machines must be built to accepted tolerances of air gaps, brush spacing, brush tolerances of air gaps, brush spacing, brush box heights, pole spacing, box heights, pole spacing, commcomm pole bolt pole bolt material, etc. to be as much alike as possible material, etc. to be as much alike as possible for the machines to commutate well and for the machines to commutate well and share load.share load.

•• Connections within the machines must be Connections within the machines must be tight to minimize variation in excitation tight to minimize variation in excitation currents and loop resistance.currents and loop resistance.

Machine Adjustments and Loop Machine Adjustments and Loop Balance Summary cont.Balance Summary cont.

•• When machines are disassembled and When machines are disassembled and reassembled, it is important to keep reassembled, it is important to keep track of shims, especially commutating track of shims, especially commutating pole shims. Both the thickness and pole shims. Both the thickness and order of shims are important! There is order of shims are important! There is not an easy way to correct interpole not an easy way to correct interpole shimming in the field, so care with the shimming in the field, so care with the machines when working on them in machines when working on them in shops is critical.shops is critical.

Machine Adjustments and Loop Machine Adjustments and Loop Balance Summary cont.Balance Summary cont.

•• There are many things that can contribute to There are many things that can contribute to commutation issues: rough commutators, commutation issues: rough commutators, symmetry of assembly, brush grades and symmetry of assembly, brush grades and construction, faulty machine components construction, faulty machine components and electrical connections. Sometimes and electrical connections. Sometimes people try to people try to ““fixfix”” machines by tuning them machines by tuning them up with neutral adjustments. Remember up with neutral adjustments. Remember –– this affects machine output and loop this affects machine output and loop balance, and you cannot balance, and you cannot ““adjust outadjust out”” these these underlying causes of commutation distress.underlying causes of commutation distress.

Field Process to Address Field Process to Address Loop UnbalancesLoop Unbalances

• Take Time versus: Drive Reference, Armature Volts and Amps, and Motor Field Current

• Make Stud to Stud Spacing Correct• Set Neutral (on GE Generator 1/8” with Rotation)• Adjust Generator Air Gaps to Ensure that the Sum of

the Volts in Each Loop are Equal within 2.5 Volts per Generator in the Loop ( 4 Generators in the Loop – 10 Volts)

• Trim Motor Fields “As Necessary”• Adjust Motor Neutral As “Last Resort” (Should be at

Neutral – Not with or Against Rotation)• If Possible Re-wire the Motion to Two Loops

Oversize HoleOversize HoleUse Use ½”½” Thin WallThin WallConduit to CenterConduit to CenterStud on YokeStud on Yoke

Lot 8 2570WLot 8 2570WHoist Unbalance Hoist Unbalance ““As FoundAs Found””485 Amps 485 Amps –– 12.2%12.2%

Lot 8 2570WLot 8 2570WDrag Unbalance Drag Unbalance ““As FoundAs Found””988 Amps 988 Amps –– 24.9%24.9%

Lot 8 2570WLot 8 2570WHoist and Drag Unbalances Hoist and Drag Unbalances ““As LeftAs Left””After Adjustments and Making Both Motions into Two LoopsAfter Adjustments and Making Both Motions into Two LoopsHoist Unbalance 53 Amps Hoist Unbalance 53 Amps –– 1.3% Drag Unbalance 95 Amps 1.3% Drag Unbalance 95 Amps –– 2.4%2.4%

Key 2 8750Key 2 8750Drag Unbalance Drag Unbalance ““As FoundAs Found””1800 Amps 1800 Amps –– 50%50%

Key 2 8750Key 2 8750Drag Unbalance Drag Unbalance ““As LeftAs Left””59 Amps 59 Amps –– 1.6%1.6%

Key 2 8750Key 2 8750Hoist Unbalance Hoist Unbalance ““As FoundAs Found””616 Amps 616 Amps --15.6%15.6%

Key 2 8750 Key 2 8750 Hoist Loop Unbalance Hoist Loop Unbalance ““As LeftAs Left””139 Amps 139 Amps –– 3.5%3.5%

Related WMEA Papers Related WMEA Papers –– available on available on wmea.netwmea.net

•• National Carbon National Carbon –– Successful Brush Successful Brush Performance Performance –– Jun 05Jun 05

•• NECP NECP –– Tuning DC Motors and Tuning DC Motors and Generators Generators –– Jun 07Jun 07

Reference MaterialsReference Materials

• “Loop Unbalance Guidelines” – GE Benchmark, January 1997, Steve Baade

• “Loop Unbalance Guidelines” – GE Benchmark, April 1997, Steve Baade

• GE “DC Machine Adjustments and Operating Characteristics”

Reference Web SitesReference Web Sites

•• Morgan AM&T Morgan AM&T –– National Electrical National Electrical Carbon Carbon –– www.morganAMT.comwww.morganAMT.com

•• GE Motors GE Motors -- www.GEMotors.comwww.GEMotors.com

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