Motor Trouble Shooting

7/29/2019 Motor Trouble Shooting

1/14

CHAPTER 2 - Troubleshooting AC MotorsProblem A - Motor won't start or motor accelerates too slowly

A1: Check input power to starter. Is therepower on all lines? (Three-phase motorswon't start on one-phase.) Restore power on all lines

A2: Check starter. Is overload protectiondevice opened? Replace or reset device. Does itopen again when starting?

A3: Is there power on all lines to motor? Repair starter

A4: Is voltage to motor more than 10%below nameplate voltage? Restore proper voltage.

A5: Check motor terminal connections. Areany loose or broken? Repair connections.

A6: May be wrong motor for application. Isstarting load too high? Install Design C or Design Dmotor. Install larger motor.

A7: Is driven machine jammed oroverloaded? Remove jam or overload.

A8: Are misalignments, bad bearings ordamaged components causing excessivefriction in driven machine or powertransmission system?

Repair or replace component.

A9: Are bad bearings, bent shaft, damagedend bells, rubbing fan or rotor or otherproblem causing excessive friction in the

motor?Repair or replace motor.


2/14

A10: Check stator. Are any coils open,shored or grounded? Repair coil or replace motor.

A11: Check commutator. Are any bars orrings broken? Replace rotor.

Problem B - Motor runs noisyB1: Are vibrations and noise from drivenmachine or power transmission system being

transmitted to motor?Locate source of noise andreduce. Isolate motor with belt

drive or elastomeric coupling.

B2: Is a hollow motor foundation acting as asounding board?

Redesign mounting. Coatfoundation underside with sounddampening material.

B3: Check motor mounting. Is it loose? Tighten. Be sure shaft is aligned.

B4: Is motor mounting even and shaftproperly aligned? Shim feet for even mounting andalign shaft.

B5: Is fan hitting or rubbing on stationarypart or is object caught in fan housing?

Repair damaged fan, end bell orpart causing contact. Removetrash from fan housing.

B6: Is air gap nonuniform or rotor rubbing onstator?

Recenter rotor rubbing on wornbearings or relocate pedestalbearings.

B7: Listen to bearings. Are they noisy? Lubricate bearings. If still noisy,replace.


3/14

B8: Is voltage between phases (three-phasemotors) unbalanced? Balance voltages.

B9: Is three-phase motor operating on one-phase? (Won't start on single-phase.) Restore power on three-phases.

Problem C - Motor overheatsC1: Is ambient temperature too high? Reduce ambient, increase

ventilation or install larger motor.

C2: Is motor too small for present operatingconditions? Install larger motor.

C3: Is motor started too frequently? Reduce starting cycle or uselarger motor.

C4: Check external frame. Is it covered with

dirt which acts as insulation and preventsproper cooling?

Wipe, scrape or vacuumaccumulated dirt from frame.

C5: Feel output from air exhaust openings.Is flow light or inconsistent indicating poorventilation?

Remove obstructions or dirtpreventing free circulation of airflow. If needed, clean internal airpassages.

C6: Check input current while driving load. Isit excessive indicating an overload? Go to Step C11.

C7: Is the driven equipment overload? Reduce load or install largermotor.

C8: Are misalignments, bad bearings ordamaged component causing excessivefriction in driven machine or power

Repair or replace badcomponents.


4/14

transmission system?

C9: Are motor bearings dry? Lubricate. Does motor still drawexcessive current?

C10: Are damaged end bells, rubbing fan,bent shaft or rubbing rotor causing excessiveinternal friction? Repair or replace motor.

C11: Are bad bearings causing excessive

friction? Determine cause of bad

bearings (See Problem D).

C12: Check phase voltage. Does it varybetween phases? Restore equal voltage on allphases.

C13: Is voltage more than 10% above or10% below nameplate? Restore proper voltage or installmotor built for the voltage.

C14: Check stator. Are any coils groundedor shorted? Repair coils or replace motor.

Problem D - Motor bearings run hot or noisyD1: Check loading. Is excessive sidepressure, end loading or vibration overloadingbearings?

Reduce overloading.* Installlarger motor.

D2: Is sleeve bearing motor mounted on aslant causing end thrust? Mount horizontally* or install ballbearing motor.

D3: Is bent or misaligned shaft overloading Replace bent shaft or align


5/14

bearings? shaft.*

D4: Is loose or damaged end bell

overloading shaft?Tighten or replace end bell.*

D5: Are bearings dry? Lubricate.*

D6: Is bearing lubricant dirty, contaminatedor of wrong grade? Clean bearings and lubricatewith proper grade*

D7: Remove end bells. Are bearingsmisaligned, worn or damaged? Replace.*Bearings may have been damaged. If motor still runs noisy or hot, replace bearings


6/14

CHAPTER 3 - Troubleshooting DC MotorsProblem E - Motor won't start

E1: Check main input power to controller. Isthere power on the lines? Are contactsclosed? Restore input power.

E2: Check controller. Is the overloadprotective device open? Reset or replace device. Does itopen again when starting motor?

E3: Check controller. Is there voltageavailable at output terminals?

Check controller for openstarting resistor, broken leadsand connections or othermalfunctions. Repair.

E4: Set the controller for full speed. Is thevoltage for field or armature circuits too low?

Check voltage from powersource. Correct if too low. Checkcontroller for malfunction.Repair.

E5: Check for weak or non-existent field. Ismotor field open? Has one field coil shorted?

Repair broken leads orconnections. Rewind or replaceopen or shorted coil.

E6: Check for open armature circuit. Isvoltage at motor armature terminals zerowhen starting?

Repair damaged armaturecircuit.

E7: Is driven machine jammed oroverloaded? Remove jam or overload orinstall larger motor.

E8: Are misalignments, bad bearings or worncomponents causing excessive friction indriven machine or power transmissionsystem?

Correct misalignment or repair orreplace worn component.


7/14

E9: Are bad bearings, bent shaft, rubbing fanor rotor, damaged end bells, or othermechanical problems causing excessivefriction in motor?

Repair or replace damagedmotor components or install new

motor

Problem F - Motor starts but stops and reverses directionF1: Check polarity of power source. Did itreverse? Determine why power supplyreversed polarity and repair.

F2: Shunt and series field may be buckingeach other. To check and correct:Reconnect the shunt or series field to correctpolarity. Connect armature for desiredrotation direction. Try fields separately todetermine rotation direction and connect soboth give the same rotation.

Problem G - Motor runs but overload protective device trips too often.G1: Is motor too small for load? Haveloading conditions changed? Reduce load or install largermotor.

G2: Check controller. Is overload device set

too low for application?Increase overload setting.NEVER exceed safe limits

specified by codes or equipmentmaker.

G3: Is motor overheating? See Problem H.

Problem H - Motor overheats


8/14

H1: Is ambient temperature too high? Reduce ambient, increaseventilation or install larger motor.

H2: Check external frame. Is it covered withlayer of dirt which acts as insulation andprevents proper cooling?

Wipe, scrape or vacuumaccumulated dirt from frame.

H3: Feel output from air exhaust openings.Is flow light or inconsistent indicating poorventilation?

Remove obstructions or dirtpreventing free of air flow. Ifneeded, clean internal airpassages.

H4: High load speed consumes extrahorsepower overloading motor. Is motoroperating above normal speed? See Problem J.

H5: Check for overload. See Steps E7 thru E9.

Problem I - Motor runs too slowly.I1: Is motor overloaded? See Steps E7 thru E9.

I2: Is the field resistance too low? Add proper resistance.

I3: Check for shorts in armature or betweencommutator bars. Are armature coils orwedges burned? Are any commutator barsburned?

Replace or replace coils or bars.

I4: Check brush holders. Are brushes setahead of neutral? Reset brushes to neutral.


9/14

I5: Voltage to armature too low. Setcontroller for full speed. Is voltage at output

terminals below nameplate voltage?Check power source outputvoltage. Raise if too low. Checkcontroller for malfunction.

Repair.

I6: DC motors may run 20% slower on lightloads when they don't heat up. Is motoroperating cold?

Increase load or reduceventilation to increase heating.Install new motor.

Problem J - Motor runs too fast.J1: Is driven load too light allowing motor torun fast? Increase load or install smallermotor.

J2: Check for a weak field per Steps J3through J6.

J3: Are shunt or series coils reversed? Reconnect reversed coils forproper polarity.

J4: Is there excessive resistance in shuntfield circuit? Remove excessive resistance.

J5: Is excessive heat causing higherresistance in shunt field circuit? Increase ventilation or correctother cause of overheating.

J6: No field causes unbalanced shunt motorto race. Is field circuit open? Repair broken lead orconnection. Replace open coil.

J7: Set controller for full speed. Is voltage atoutput terminals of controller abovenameplate voltage?

Reduce output voltage. Checkcontroller for malfunction.Repair.


10/14

J8: Check brush holders. Are brushes setbehind neutral? Reset brushes to neutral.

Problem K - Motor runs noisyK1: Are vibrations and noise from drivenmachine or power transmission system beingtransmitted to motor?

Locate source of noise andreduce. Isolate motor with beltdrive or elastomeric coupling.

K2: Is a hollow motor foundation acting as asounding board?

Redesign mounting. Coatfoundation underside with sounddampening material.

K3: Check motor mounting. Is it loose? Tighten. Be sure shaft is aligned.

K4: Is motor mounting even and shaftproperly aligned? Shim feet for even mounting andalign shaft.

K5: Is fan hitting or rubbing on stationarypart or is object caught in fan housing?

Repair damaged fan, end bell orpart causing contact. Removetrash from fan housing.

K6: Is air gap nonuniform or armature rotorrubbing on pole pieces?

Tighten loose pole piece.Recenter armature by replacingworn bearings or relocatingpedestal bearings.

K7: Listen to bearings. Are they noisy? Lubricate bearings. If still noisy,replace.

K8: Are bearings noisy or running hot? See Problem L.


11/14

K9: Are the brushes developing high or lowfrequency chatter? See Problem M.

Problem L - Motor bearings run hot or noisyL1: Check loading. Is excessive sidepressure, end loading or vibration overloadingbearings?

Reduce overloading.* Installlarge motor.

L2: Is sleeve bearing motor mounted on aslant causing end thrust? Mount horizontally* or install ballbearing motor.

L3: Is bent or misaligned shaft overloadingbearings? Replace bent shaft or alignshaft.*

L4: Is loose or damaged end belloverloading shaft? Tighten or replace end bell.*

L5: Are bearings dry? Lubricate.*

L6: Is bearing lubricant dirty, contaminatedor of wrong grade?

Clean bearings and lubricate

with proper grade.*

L7: Remove end bells. Are bearingsmisaligned, worn or damaged? Replace.*Bearings may have been damaged. If motor still runs noisy or hot, replace bearings.


12/14

Problem M - Brushes sparking excessively; may be accompanied by brushchatter

and/or excessive wear and chipping.

M1: Is motor overloaded? Reduce overload or install largermotor.

M2: Is vibration from driven machine ormotor present? Locate source of vibration andreduce.

M3: Check brushes and brush holders. Arebrushes worn too short? Replace brushes.

M4: Does each brush fit commutator asindicated by polished surface over entirebrush face. Refit brushes to commutator.

M5: Are brushes hanging up in holders? Clean brushes and holders.Remove rough surfaces thatcause extra friction.

M6: Are brush springs broken or is springpressure too light?

Replace spring or increasepressure. Be sure pressure isequal on all brushes.

M7: Is spring pressure to high? (May alsocause brush chipping) Reduce pressure or replace withlighter spring.

M8: Are brush holders set off neutral? (Mayalso cause brush chipping) Reset holders at neutral.

M9: Are brushes set a wrong angle? (Mayalso cause brush chipping)

Reset holders for brush anglerecommended by motormanufacturer.


13/14

M10: Is brush holder set for more than 1/8"clearance above commutator? (May alsocause brush chipping) Reset holder for 1/8" clearance.

M11: Chipping brushes may also indicatewrong brush material. Are brushes too weakfor duty?

Consult motor manufacturer forrecommendations.

M12: Check commutator. Is commutatorsurface under brushes polished brown color? Normal condition. Go toStep M18.

M13: Is commutator surface black (generallycaused by sparking)?

Check for overloads, low springtension, poorly undercut mica,loose commutator bars, etc.Correct sparking. Dresscommutator.

M14: Is there thick film on commutator - mayappear black? Use more abrasive brushes.

M15: Is commutator surface bright andbrassy looking?

If humidity is below 2 grams percu. ft., increase humidityORreduce spring pressure, use lowfriction brushes or use lessabrasive brushes.

M16: Is commutator surface contaminatedfrom paint spray, oil or chemical fumes? Isthere excessive moisture in air?

Clean commutator and brushesand protect motor fromcontamination. Install motor withproper enclosure to protectcommutator.

M17: Is commutator streaked or grooved

under one or more brushes?Be sure all brushes same grade.Replace if some are too

abrasive. Check for faulty shuntconnections causing unbalanced


14/14

load; repair.

M18: Is commutator rough or eccentric? Grind commutator roundUndercut mica

M19: Is mica above bar surface? Undercut mica.

M20: Are some commutator bars too high,too low or loose?

Replace commutator or tightenV-ring bolts to tensionrecommended by manufacturerand grind commutator.

M21: Are there flat or burned spots oncommutator bars caused by unbalanced loadin armature circuit?

Balanced load. Grindcommutator.

M22: Is conductive film carbon dust orcopper flaking causing shorts between

armature bars?Undercut mica.

M23: Are there any shorts or opens inarmature circuits? Locate and repair.

M24: Are there any grounds, shorts oropens in the field wiring circuits? Locate and repair.

M25: Are connections to brush holder pooror broken? Locate and repair.

M26: Is the interpole current weak or the airgap too great? Increase interpole current orreduce gap.

Motor Trouble Shooting

Documents

Transcript of Motor Trouble Shooting