Tuning Up DC Motors and Generators for Commutation and Performance

(1)

Tuning Up DC Motors and

Generators for Commutation

and Performance

Rich Hall

Rich Hall-- National Electrical CarbonNational Electrical Carbon Western Mining Electrical

Western Mining Electrical Association

Association

June 8, 2007, Billings Montana June 8, 2007, Billings Montana

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Sometimes your machine may not

run just like it should

(3)

That is an indication

that it might be time for

a

(4)

Spark Plugs

Breaker Points

Condenser

(5)

Distributor Cap

Spark Plug Wires

(6)

But even with all new

parts, the machine may

not run right!

(7)

Unless

you make the

_{you make the}

“

(8)

That

includes

setting

the

spark

plug

gap, the

ignition

point

gap or

dwell,

and the

ignition

timing

(9)

DC machines need tune

-

-up adjustments to run

up adjustments to run

properly, too!

(10)

DC machines tune

-

_-

up

_up

adjustments to run

properly, too!

These adjustments include

setting neutral and adjusting

the commutating field

(

(11)

Electrical Neutral Methods

•

• Black Band

_{Black Band}

•

• Kick Inductive Neutral

_{Kick Inductive Neutral}

•

• AC Neutral

_{AC Neutral}

•

• Speed Reversibility

_{Speed Reversibility}

•

• DC Current In Armature

_{DC Current In Armature}

•

• Pencil Volt Neutral

_{Pencil Volt Neutral}

•

(12)

Electrical Neutral Methods

•

• Also see

Also see

“

Setting Neutral by AC

Curve Method for DC Machines

”

by

Rick Scherer, Flanders, WMEA,

November 2005 (WMEA Web Site,

www.wmea.net

(13)

Electrical Neutral

Setting Neutral on an electric motor or Setting Neutral on an electric motor or

generator is similar to setting timing generator is similar to setting timing

on an engine. on an engine.

The brushes are basically electrically The brushes are basically electrically

positioned on the commutator between positioned on the commutator between

the areas of main pole flux so commutation the areas of main pole flux so commutation

can take place at the right time and in an can take place at the right time and in an

area where no electrical work ( torque ) is area where no electrical work ( torque ) is

being produced. being produced.

(14)

Neutral

Usually it is best to look for

Usually it is best to look for “_“factory markfactory mark”_” and set brush yoke to this position after and set brush yoke to this position after

reassembling the motor. reassembling the motor.

The OEM has the benefit of knowing the The OEM has the benefit of knowing the

electrical design and how previous motors electrical design and how previous motors

were adjusted. They also have more test were adjusted. They also have more test

equipment than the typical motor repair equipment than the typical motor repair

shop, for running the motor under load at shop, for running the motor under load at

various speeds. various speeds.

(15)

Factory Neutral Mark

(16)

Shifted off the factory mark Shifted off the factory mark

(17)

If armature has been changed, or brush

arms moved on yoke, correct setting may

not be on

(18)

Methods For Adjusting

DC Machines

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Adjustments

1. Brush Position

2. Commutating Field Strength

(20)

Factory Method

Field Method

(21)

Excavator MG Set

(22)

Black Band

A test where you intentionally misadjust

the magnetic strength of

interpole

(

comm

field ) by adding or subtracting

current to find the limits of sparking.

Also use this data to adjust neutral setting

and

interpole

shimming for good

commutation over the range of speeds

and loads.

(23)

Black Band

•

• ProcedureProcedure –

– Connect buckConnect buck--boost power supply (low boost power supply (low Voltage high current) in parallel with the

Voltage high current) in parallel with the

commutating fields

–

– Operate the machine at various loads (0% to Operate the machine at various loads (0% to 150%), apply buck

150%), apply buck--boost current and observe boost current and observe sparking

sparking

–

– Adjust brush rigging position or shim Adjust brush rigging position or shim

commutating poles as shown from recorded

and plotted data

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(25)

DC Machine and Load

ARM

ARM LoadLoad

Comm Comm Field Field Field Field

(26)

Black Band Set Up

ARM

Buck Boost Gen

(27)

Buck Amps Buck Amps Boost Amps Boost Amps 0 0 Load Amps (%) Load Amps (%)

Buck Boost Curve

50

(28)

No Load

ARM

Buck Boost Gen

I

(29)

No Load Boost

ARM

Buck Boost Gen

I I_A_A= 0= 0 i i i i

(30)

No Load Buck

ARM

Buck Boost Gen

I I_A_A= 0= 0 i i i i

(31)

Buck Boost Curve

X X X X 50 50 100100 150150 Band at No Load Band at No Load

(32)

Buck Boost Curve

X X X X 50 50 100100 150150 X

X No Load Band No Load Band

Center on Buck

Side (Strong)

Corrective action

Corrective action –– shift shift brush rigging with rotation

brush rigging with rotation

(motor) or against rotation

(generator)

(33)

Buck Boost Curve

X X X X 50 50 100100 150150 X

X No Load Band _{Center on Boost}No Load Band _{Center on Boost}

Side (Weak)

Corrective action

Corrective action –– shift shift brush rigging against

brush rigging against

rotation (motor) or with

rotation (generator)

(34)

Buck Boost Curve

X X X X 50 50 100100 150150 X X No Load Band No Load Band Centered Centered OK

OK –– Proceed with load Proceed with load test

(35)

Loaded Boost

ARM

Buck Boost Gen

I I_A_A i i I I_A_A + i+ i I I_A_A

(36)

Loaded Buck

ARM

Buck Boost Gen

I I_A_A i i I I_A_A -- ii I I_A_A

(37)

Buck Boost Curve

X X X X 50 50 100100 150150 x x x x

Take data with machine

loaded, beginning at 50%

load

(38)

Buck Boost Curve

X X X X 50 50 100100 150150 x x x x x x x x x x x x Band Center Band Center

Band Center on Boost Side

(Weak)

Corrective Action

Corrective Action –– Remove Remove

nonmagnetic shims, add magnetic

shims shims No sparking in black area, sparking outside black area

(39)

Buck Boost Curve

x

Load Amps (%)

Corrective Action

Corrective Action –– Remove Remove

magnetic shims, add non magnetic

shims shims Buck Amps Buck Amps Boost Amps Boost Amps 0 0 X X X X 50 50 100100 150150 x x x x x x x x x x Band Center Band Center Band Center on Band Center on Buck Side

Buck Side (Strong)(Strong)

Sparking with no buck or boost

(40)

Buck Boost Curve

X X X X 50 50 100100 150150 x x x x x x x x x x x x

Near perfect black band

Near perfect black band ––centered at centered at all loads

(41)

Black Band

• Advantages

– Adjusts both neutral and commutating

pole shimming

– Tests over complete load range or can

(42)

Black Band

• Advantages

– Adjusts both neutral and commutating pole shimming

– Tests over complete load range or can adjust for specific load

and speed

• Disadvantages

– Requires field supply and armature

supply capable of 1.5 to 2 times rated armature Amperes

– Need control of loading, voltages,

speeds,etc.

– Need buck-boost power supply (low

(43)

Kick Inductive Neutral

•

• Procedure

_Procedure

–

– Connect an analog DC voltmeter Connect an analog DC voltmeter

between shunts of brushes on adjacent between shunts of brushes on adjacent arms (brushes need to be well seated) arms (brushes need to be well seated)

–

– Repeatedly apply and remove DC Repeatedly apply and remove DC voltage from shunt fields

voltage from shunt fields

–

– Shift brush yoke for minimum deflection Shift brush yoke for minimum deflection (kick) if meter needle

(44)

+

-Switch Switch A1 A1 A2 A2 Analog

Analog DC VoltmeterDC Voltmeter

0 0 + +

-Shift brushes for minimum needle deflection

Shift brushes for minimum needle deflection

Shunt Shunt

Field Field

(45)

Kick Inductive Neutral

•

• Advantages

_Advantages

–

– Static TestStatic Test

–

(46)

Kick Inductive Neutral

•

• AdvantagesAdvantages

–

– Static TestStatic Test

–

– Little equipment requiredLittle equipment required •

• DisadvantagesDisadvantages

–

– Best compromise neutral for reversible Best compromise neutral for reversible machines. Best for motors that could machines. Best for motors that could run either rotation.

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AC Neutral

•

• ProcedureProcedure

–

– Connect an AC voltmeter between the Connect an AC voltmeter between the shunts of brushes of adjacent arms shunts of brushes of adjacent arms (brushes well seated)

(brushes well seated)

–

– Apply 120 Volt AC to the shunt fields, Apply 120 Volt AC to the shunt fields, connected where the DC field supply connected where the DC field supply would normally connect

would normally connect

–

– Shift the brush yoke to get minimum AC Shift the brush yoke to get minimum AC voltage on the voltmeter

(48)

A1

A2

Analog or Digital AC Voltmeter

0 0 120 120 Volt Volt AC AC

Shift brushes for minimum AC Voltage

Shunt Shunt

Field Field

(49)

AC Neutral

•

–

– Static testStatic test

–

(50)

AC Neutral

•

–

– Static testStatic test

–

– Little equipment requiredLittle equipment required •

• DisadvantagesDisadvantages –

– Best compromise neutral for reversible Best compromise neutral for reversible machines. Not as good for single rotation

machines. Not as good for single rotation

machines. Really only gets you in the ball park

for large machines with pole face windings.

(51)

Speed Reversibility

•

– Apply known DC field Apply known DC field currentcurrent

–

– Apply known DC armature Apply known DC armature voltagevoltage

–

– Measure rotational speed (RPM)Measure rotational speed (RPM)

–

– Keep field Keep field currentcurrent the same, but reverse the the same, but reverse the armature

armature voltagevoltage polarity and measure RPMpolarity and measure RPM

–

– Shift brush yoke as required to equalize speed Shift brush yoke as required to equalize speed in both directions within 1%

(52)

A1 A1 A2 A2 DC Voltmeter DC Voltmeter DC DC Power Power Supply Supply DC DC Field Field Supply Supply 0 0 DC Ammeter DC Ammeter V V_A_A I I_f_f RPM RPM 0 Set I

Set I_f_f, Set V, Set V_A, Measure RPM. Reverse Polarity of V_A. Measure RPM. Shift until RPMs agee within 1%.

(53)

Speed Reversibility

•

• AdvantagesAdvantages –

– Good technique for reversible machinesGood technique for reversible machines

–

– Armature supply does not need to supply very Armature supply does not need to supply very much current

(54)

Speed Reversibility

•

–

– Good technique for reversible machinesGood technique for reversible machines

–

– Armature supply does not need to supply very much currentArmature supply does not need to supply very much current •

– Requires both field and armature DC supplyRequires both field and armature DC supply

–

– Machine must be uncoupled or able to rotate Machine must be uncoupled or able to rotate unloaded or with controlled load

unloaded or with controlled load

–

– Best compromise neutral for reversible Best compromise neutral for reversible machines. Best for motors that could run

machines. Best for motors that could run

either rotation.

(55)

•

– Apply DC current through armature and Apply DC current through armature and commutation fields only

commutation fields only

–

– If on neutral, machine will not rotate. If off If on neutral, machine will not rotate. If off

neutral, machine will rotate in one direction or

the other depending on which way it is off

neutral

–

– Shift brush yoke as required so motor does Shift brush yoke as required so motor does not rotate

not rotate

•

• WarningWarning --Do not use this method on Do not use this method on series motors as they will over

series motors as they will over--speed!!speed!!

DC Current In Armature

Circuit

(56)

DC Voltmeter DC Voltmeter A1 A1 A2 A2 DC DC Power Power Supply Supply V V_A_A I I_A Comm Comm Field Field

Armature Will Not Turn Armature Will Not Turn

on Neutral on Neutral

0 0

(57)

•

• Advantages

_Advantages

–

– Only armature supply is requiredOnly armature supply is required

DC Current In Armature

Circuit (Shunt Machines

Only)

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•

• AdvantagesAdvantages –

– Only armature supply is requiredOnly armature supply is required

•

• DisadvantagesDisadvantages

–

– Limited to smaller antiLimited to smaller anti--friction bearing friction bearing machines

machines

–

– Limited to shunt machines (series or Limited to shunt machines (series or compound machines will over

compound machines will over--speed)speed)

–

– Best compromise neutral for reversible Best compromise neutral for reversible machines. Best for motors that could run machines. Best for motors that could run either rotation.

either rotation.

DC Current In Armature

Circuit (Shunt Machines

Only)

(59)

Pencil Volt Neutral

•

• Procedure

_Procedure

–

– Place special template on the Place special template on the commutator

commutator

–

– Run machine at 100 Volts, no loadRun machine at 100 Volts, no load

–

– Measure voltage through holes in the Measure voltage through holes in the template with a special probe

template with a special probe

–

– Plot readings on graph paper and adjust Plot readings on graph paper and adjust yoke accordingly

(60)

PVN Template

(61)

Installing PVN Template

(62)

PVN Test

Points

(63)

PVN

Anchoring

Point

(64)

PVN Voltmeter

(65)

Pencil Volt Neutral

Rotation Rotation Voltmeter Voltmeter Pencil Pencil Probe Probe Brush Stud Brush Stud Brush Brush Box Box Template Template

(66)

Warning!!

Working around rotating electrical machinery

can cause serious or fatal injury due to

electrical shock hazards or contact with

rotating parts. Contact the manufacturer

’

s

service engineers for performing adjustments

on electrical motors and generators. These

people have the necessary training and

information available to properly adjusting

DC machines.

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Typical Data

Pencil Volt Neutral

836 KW Generator

Taken at 100 volts

Taken at 100 volts -- No LoadNo Load

Lead Voltage

Lead Voltage _{Hole No.}_{Hole No.} _{Trail Voltage}_{Trail Voltage}

19.9 19.9 21.5 21.5 23.3 23.3 25.0 25.0 26.8 26.8 16.4 16.4 17.9 17.9 19.6 19.6 21.3 21.3 23.0 23.0 4 4 5 5 6 6 7 7 8 8

Note: Lead Volts Higher Than Trail Volts For Single

Rotation Machine. For a Reversible Machine,

Lead Volts Equals Trail Volts.

(68)

Neutral Adjustments

•

• To lower trail volts

To lower trail volts

shift brush rigging

against rotation

•

• To raise trail volts

To raise trail volts

shift brush rigging

with rotation

•

• To raise trail volts

To raise trail volts

shift brush rigging

against rotation

•

• To lower trail volts

To lower trail volts

shift brush rigging

with rotation

Generator

(69)

Pencil Volt Neutral

•

• Advantages

_Advantages

–

– Repeatable, accurate way to set neutralRepeatable, accurate way to set neutral

–

(70)

Pencil Volt Neutral

•

–

– Repeatable, accurate way to set neutralRepeatable, accurate way to set neutral

–

– Can adjust single rotation machinesCan adjust single rotation machines •

– Requires working closely with energized Requires working closely with energized rotating machinery

rotating machinery

–

– Motors must be mechanically uncoupled or Motors must be mechanically uncoupled or able to operate with little load

(71)

Other Methods Of Setting

Neutral

There are other methods of setting neutral. There are other methods of setting neutral.

It is important that neutral be set by

It is important that neutral be set by somesome method as commutation or motor or

method as commutation or motor or generator performance may suffer. generator performance may suffer.

(72)

Using Static Neutral Setting

Methods for Single Rotation

Machines

From experience, excavator generators

can be shifted about

½

bar against

rotation from symmetrical neutral to

approximate black band or pencil Volt

neutral

(73)

Adjusting Commutating

Field (

Interpole

_Interpole

) Strength

_{) Strength}

Adjusting

Adjusting commcomm field strength in the field is field strength in the field is difficult to impossible.

difficult to impossible.

The machine voltage, speed and load must The machine voltage, speed and load must be controlled, which is usually impossible, be controlled, which is usually impossible,

and some of the methods available, such as and some of the methods available, such as

brush potential measurements, have safety brush potential measurements, have safety

issues. issues.

(74)

Adjusting Commutating

Field (

Interpole

_Interpole

) Strength

_{) Strength}

Some manufacturers ( GE ) use non Some manufacturers ( GE ) use non-

-magnetic

magnetic interpoleinterpole bolts. These can be bolts. These can be same size as main pole bolts. Do Not mix same size as main pole bolts. Do Not mix

these up. Look at bolt head markings. these up. Look at bolt head markings.

Magnetic bolts will have 3 (grade 5) or 6 Magnetic bolts will have 3 (grade 5) or 6

(grade 8) radial marks. (grade 8) radial marks.

The order of the shims is also important, The order of the shims is also important,

make sure to put them back like you make sure to put them back like you

found them! Best to put tape around the found them! Best to put tape around the

whole

whole “shim pack“shim pack”” and mark similar to:and mark similar to: