The Care and Maintenance of Motors

Care and Maintenance of Electric Motors

Define Electric Motor

A device that converts electrical energy into rotational or linear motion

The electric motor is one type of prime mover in a mechanical system

Common Motor Applications Include

Pumps Fans Conveyors Extruders Agitators Crushers Mills Grinders Elevators Many, many more……………….

Electric Motors

Some Energy approximate facts:

Electric motors make up the largest end use of electricity in the United States

60 % of electrical consumption in Industrial Plants 70 % of electrical consumption in Process Industries Motor Systems – 60-70% of total electricity used in any

Industrial Facility 25 % of total electricity sales in the U.S.

Electric Motors

The annual energy cost to run a 100 HP Electric Motor continuously for 1 year is approximately - $ 30,000 at .05 KWH.

Electric MotorsCare and Maintenance

Why and when invest resources to maintain Electric Motors ?

What strategies can be implemented? What have other motor users done to

maintain their motors What support resources and tools are

available ?

Types of Electric Motors

AC Induction Motors DC Motors and Generators Synchronous Wound Rotor Single Phase Permanent Magnet AC - New

AC Induction – Nema Frame

Large AC Induction Motor

5500 HP 6600 volt

AC Induction – Nema Frame

Nema Frames – 145T – 449TLow voltage, 3 Phase/ up to 600 volts1-250 Hp900, 1200,1800, and 3600 rpmODP, TEFC, TENV, TEBCBall or roller bearingsAll mounting positions

Synchronous Motor

Synchronous

A synchronous motor is an ac motor in which the rotor revolves in step or in synchronism with the rotating magnetic field produced by the stator winding. . This action means that if the magnetic field of a 60-cycle, four-pole motor revolves at the rate of 1,800 rpm, the rotor will also turn at that speed.

Synchronous

Larger Ratings – 500 – 10,000 Hp Usually Medium Voltage – 2300/ 4160 volt Often slower speeds – 164 – 3600 rpm Often sleeve bearing Typically open frame designs

Wound Rotor

Wound Rotor

THREE-PHASE WOUND-ROTOR

The three-phase wound-rotor motor ranges in size from fractional to hundreds of horsepower. They are designed for variable speed operation, and accelerating large inertia loads. Typical use for this type of motor would be pumps, cranes, conveyors, and large air compressors.

Single Phase

AC Permanent Magnet

Motor Frame

Induction Rotor

Fan Cover

Motor End Bracket

Electric Motor Nomenclature

Conduit Box

Motor Bearings

Stator Winding

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AC Motor Nameplate

Voltage

Frequency

Temperature

RPMFrame

Horse Power

Amps

Phase

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Motor Enemies

Heat Time Power Supply Issues Humidity Improper Lubrication Unusual Mechanical Loads

Leading causes of Motor Failures

Bearings 51% Stator Winding 16% External 16% Unknown 10% Rotor Bar 5% Shaft/Coupling 2%

Common Causes For Motor Failures

Failure distribution statistics, like these from IEEE Petro-Chemical Paper PCIC-94-01, are helpful, but still necessary to conduct a thorough root cause analysis when determining modes of failure.

Focus on greatest opportunity to Improve

Bearings – 51% of motor failures

The largest percentage of these failures will be in Nema Frame Motors

The largest percentage of motors in most plants will be Nema Frame Motors

Factory Lubed

Factory lubed ball bearing

Factory Lube in housing

Typical lube after time

Contaminated Lube

Lack of lube

Bearing Failures in Motors


















Practical Maintenance Practice ?

Develop predictive and preventative plans to maximize motor reliability and to minimize major motor repairs

That’s easily said, however defining what that is will differ based on type of plant, operating philosophy, applications, environment, etc.

Practical Maintenance Practice ?

There are volumes of information, technical papers, publications, guidelines, and typical plans available

EPRI – Electric Motor Tiered Maintenance Program EASA- Recommended Practice for Repair of Rotating

Apparatus Electric Motors- Care and Maintenance – Exxon Mobil

Corp. IEEE – Electric Motor Predictive and Maintenance Guide

So what is practical ?

The ideal plan would cost nothing, and motors would never fail

Mobile Recommendation

4 Part Improvement Plan to include:

Implement a Rebuild and New Motor Specification Guide

Implement a Motor Acceptance test for all new and rebuilt motors

Implement a Motor storage program Implement a Tiered Maintenance

Strategy for your motor population

Motor Specification Guide

New Motors Rebuilt Motors

Electric Motor Specifications - New

Inpro/seal on Drive end Only 25 HP & Above. Oversized J-Box per specifications. Blue Chip Quality. 100% cast iron construction for rigidity and reduced

vibration. Internal and external epoxy paint. MAX GUARD insulation system 1.15 Service Factor. Extended grease tubes, regreasable in service. Brass drain and breather Meets IEEE45 USCG Marine Duty IP54 Construction. Actual test and vibration data supplied with each motor CSA Certified Division 2 CSA certification nameplate, for hazardous locations, Class I Groups

A, B, C, and D. Temperature code T2B Three Year warranty.

Electric Motor Acceptance Test

All motors for a plant should go through an acceptance test prior to be put into service or storage

The purpose would be to insure:1. Not damaged during shipping and

handling2. No obvious manufacturing defects3. Motor has been repaired properly

Acceptance test may include:

Incoming visual inspection

Electrical – Megger – PDMA

Mechanical – Vibration Test

Required to perform acceptance tests

An appropriate test area:• Power supply to run motors at rated

voltage – 460 volt. 2300/4160 volt, 500 volts DC

• Test bed isolated from ambient vibration to mount horizontal and vertical motors

• Qualified personnel

Required to perform acceptance test

A complete testing facility is typically not practical in most industrial plants and environments

So what can you do ?

Back to Specifications

Adopt a specification for the purchase of new electric motors

Only allow purchases from Manufactures that meet or exceed your specification

Require a final test document for each motor that includes actual vibration data and electrical test results

Back to Specifications

Develop a specification for the repair of electric motors Closely evaluate and only utilize Motor Repair Service

Centers that meet your requirements Require repair and test reports indicating scope of

repair, failure analysis, recommendations, and complete test data• Electrical final tests• No load vibration and rotor balance data• Mechanical fits and shaft run out• Sleeve bearing clearance and end play

Evaluate Repair Providers

Make a point to spend time evaluating each potential provider’s service center

Look for indicators of a quality control program, such as evidence of participation in an ISO 9000 program, membership in EASA, & participation in EASA–Q program.

Inquire about staff morale, training, turnover, etc. Determine whether the service center has

sufficient facilities & materials to handle the size & type of motors you send them.

Note what test equipment the service center owns and routinely uses to verify successful repair. Examples:• Core loss tester• Surge comparison tester• Voltage regulated power supply for

running at rated voltage• Vibration testing equipment

Ask to see record-keeping system that the service center maintains for repaired motors

Inquire about method of insulation removal, burnoff, mechanical pulling, etc. • For burn off, ask about methods for preventing flames or

hotspots & ensuring uniform temperature when roasting multiple motors

Take note of the overall cleanliness of the service center



Become better informed about motor repair and maintenance Prequalify and select a quality electric motor repair facility

before you need it Aquire or write a set of motor rebuilding standards Establish a spare motor inventory system Request a completed motor repair report of each repaired

motor Test new and rebuilt motor when they are received at your

plant Maintain communication system and relationship with your

repair shop

Repair Warranty Rate

Electric Motor Storage Guidelines

Pick a location:

• Clean and dry area indoors if possible

• Avoid heat, humidity, and vibration

• Store in position for the intended use- horizontal – horizontal and vertical - vertical


Outdoor storage of large motors:• Cover – allow for breathing at the

bottom• Energize space heaters if they exist –

10–20 degrees F > ambient• Prevent rodents, snakes, birds, and

small animals from nesting inside


Apply rust preventative coating to shaft and other exposed machine surfaces

Bearing damage is possible in storage – avoid humidity and vibration• False brinelling of ball and race• Fretting from corrosion


Recommend to rotate shafts at regular intervals – Monthly

• Redistributes lubrication to prevent corrosion

• Minimize brinelling by relocating the balls within the races


Tip

Leave all keyways the same, and in a different position each time

This provides an easy visual indication


Periodic shaft rotation is more critical on:

•Larger 2 pole (3600 rpm) machines•Machines with long shafts and heavy rotors

Critical to avoid shaft distortion due to rotor sag


Oil Lubed Bearings These motors are always shipped without oil

Fill to capacity as soon as set into storage

Do not move motor with oil in the reservoirs

Drain it – Move it – Refill it

Tiered Maintenance

Define motor population

Apply appropriate maintenance and predictive tools according to criticality, safety significance , and economic significance of each motor

Categorize level of Maintence

Minimum MaintenanceModerate MaintenanceTrendable MaintenanceExtensive Maintenance

Minimum Maintenance Category

Non-critical motors less than 50 HP Motors having low safety and economic

significance Motors not of special design and

normally readily available Unexpected failures are tolerable Typically not repaired, but replaced with

new

Moderate Maintenance Category

Motors that may run to electrical failure, but not mechanical failure

Maintenance may focus on the mechanical health of the motor

Trendable Maintenance Category

Mid sized low and medium voltage motors

50 -200 Hp – 460 volt 200 – 1000 Hp – 2300/4160

volt Larger DC motors - > 50 hp

Extensive Maintenance Category

Mission Critical Motors Require comprehensive electrical and

mechanical monitoring Usually the larger and medium voltage

motors Motors that have highest safety and

economic significance

Testing Motor Windings

Motor Winding Failures Grounded winding Turn to turn short Single phased condition Roasted winding due to overload Locked rotor condition Shorted connection Winding damaged by voltage surge

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Tests for Winding Condition

Insulation Resistance – megger test• Spot Check and Trendable• Indicates condition between the

conductors and ground• Low readings indicate moisture, dirt, or

damaged insulation• Minimum 1 meg ohm/1000 volts

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Polarization Index• Further indicates condition between the conductors

and ground• It’s the ratio of 10 min/1 min reading• A PI > 2 or 1 min reading > 5 giga ohms indicates

motor is suitable for service• PI > 7 could indicate brittle or aged insulation• PI can also help determine if a winding is wet or

contaminated

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DC Hipot• DC test voltage is applied to entire winding to

verify the insulation to ground• [ (2 x nameplate volts + 1000) x 1.7 x .60• Common on motors rated 4000 volts and higher• Done on low voltage motors to verify that its safe

to perform a surge comparison test

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Surge Comparison Test•Normally not performed in the field• Indicates presence of phase to

phase and turn to turn shorts within a winding

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Rotor Current Analysis•Indicates the presence of cracked

and broken rotor bars or voids in cast rotors

• These could be the cause for vibration especially under load

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Electric Motor Lubrication

According to EASA the motor component with the highest failure rate is the bearing.

51% of all motor failures are due a bearing failure.

Bearing lubrication is one of the many aspects of motor care and one of major importance to the life of a motor.

Preventive/Predictive Maintenance

The establishment of an effective predictive maintenance system will significantly affect the life of a motor.

Lubricating bearings at arbitrary intervals can result in bearings that are under lubricated or over lubricated. Either of these conditions can reduce the expected life of a bearing.

Is this enough grease ?

Unique Lubrication Coating

Moisture in Lubricant

Moisture in Grease

Bearing Protection

Shaft slinger Inpro/Seal Bearing Isolator

Bearing Types

Motor bearings are manufactured in various types of configurations.

Shielded (2Z), shielded bearings have a metallic shield on both sides of the bearing that is open on the ID or inner race side.

Single Shield (1Z), same as above except one side of the bearing is open.

Bearing Types

Sealed (2RS) sealed bearings have a seal arrangement on both sides of the bearing that will not allow any contaminants to enter the bearing. These bearings are lubricated at the factory and do not require any additional grease.

Single Seal (RS) same as above, but sealed on one side only.

Determining Frequency of Lubrication

Determining what frequency at which a particular bearing needs to be lubricated requires consideration of many criteria.

1. Type of grease2. Type of bearing3. Motor operating temperature4. Motor speed5. Environmental conditions6. Duty Cycle

Lubricant Compatibility

If two lubricants that are incompatible are mixed they will lose their lubrication ability.

If in doubt check with your motor manufacturer or lubrication supplier.

The majority of motor manufacturers use a polyurea based grease that meets EP-2 standards such as Mobil Polyrex-EM

Motor Operating Temperature

Motors that operate in elevated ambient temperatures need to be lubricated more frequently.

Motors operating in a temperature controlled environment can be lubricated less frequently.

Motor Speed

Motors operating at 3600 RPM need to be lubricated more frequently.

Motors operating at 900 RPM need to be lubricated less frequently.

Roller bearings require more frequent lubrication than ball bearings.

Environmental Conditions

Motors operating in a cement plant need to be lubricated more frequently.

Motors operating in a clean room need to be lubricated less frequently.

Duty Cycle

Motors operating 24/7 need to be lubricated more frequently.

Motors operating 8 hours/day 5 days/week need to be lubricated less frequently.

Bearing Size

The size of a particular bearing will determine the amount of lubricant the bearing needs.

Most motor manufacturers provide instruction manuals detailing the correct procedures and the amount of lubricant required to re-lubricate a bearing.

Amount of Lubricant

Deep Groove

Ball Bearings6200 Series

6200 Series

Bearing Size Ounces Strokes

6204 0.10 3

6205 0.12 4

6206 0.15 5

6207 0.19 6

6208 0.23 8

6209 0.25 8

6210 0.28 9

6211 0.33 11

6212 0.38 13

6213 0.43 14

6214 0.47 16

6215 0.50 17

6216 0.55 18

6217 0.65 21

6218 0.74 24

6219 0.84 28

6220 0.95 31

Amount of Lubricant

Deep Groove

Ball Bearings6300 Series

6300 Series


6304 0.12 4

6305 0.16 5

6306 0.21 7

6307 0.26 9

6308 0.32 11

6309 0.39 13

6310 0.46 15

6311 0.54 18

6312 0.63 21

6313 0.72 24

6314 0.81 27

6315 0.92 30

6316 1.03 34

6317 1.14 38

6318 1.26 42

6319 1.40 46

6320 1.57 52

Amount of Lubricant

Cylindrical RollerBearings200 Series

200 Series


204 0.10 3

205 0.12 4

206 0.15 5

207 0.19 6

208 0.23 8

209 0.25 8

210 0.28 9

211 0.33 11

212 0.38 13

213 0.43 14

214 0.47 16

215 0.50 17

216 0.55 18

217 0.65 21

218 0.74 24

219 0.84 28

220 0.95 31

Amount of Lubricant

Cylindrical RollerBearings300 Series

300 Series


304 0.12 4

305 0.16 5

306 0.21 7

307 0.26 9

308 0.32 11

309 0.39 13

310 0.46 15

311 0.54 18

312 0.63 21

313 0.72 24

314 0.81 27

315 0.92 30

316 1.03 34

317 1.14 38

318 1.26 42

319 1.40 46

320 1.57 52

Lubricant Storage

Lubricants need to be stored properly to avoid contamination.

Keep lubricants stored in a storage locker if possible.

Keep lids on oil drums, grease containers etc. to avoid contamination.

Priority Equipment

Some equipment is vital to the operation of your facility.

Some equipment can be replaced for a minimal amount of cost.

It is not economical to spend $100/month lubricating a $300 motor.

Vibration Analysis

Vibration analysis can be used as a tool to determine when a particular bearing requires lubrication.

A baseline vibration reading should be taken shortly after a motor is put into service.

Subsequent vibration readings can be compared to the base line to determine the need for additional lubrication.

Conclusion

Proper care and maintenance of the motor and its bearings, can significantly increase the life of the motor,increase productivity, reduce costs and improve profits.

Take care of your bearings and they’ll take care of you!

That’s all folks

Questions ?

Thank you !!

Business

The Care and Maintenance of Motors