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There are two significant ways to extend the life of an electric motor: proper care and maintenance. Creating and following care and maintenance programs consistently will increase productivity, reduce costs, and increase profits.
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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
22
AC Motor Nameplate
Voltage
Frequency
Temperature
RPMFrame
Horse Power
Amps
Phase
19
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
Bearing Failures in Motors
Bearing Failures in Motors
Bearing Failures in Motors
Bearing Failures in Motors
Bearing Failures in Motors
Bearing Failures in Motors
Bearing Failures in Motors
Bearing Failures in Motors
Bearing Failures in Motors
Bearing Failures in Motors
Bearing Failures in Motors
Bearing Failures in Motors
Bearing Failures in Motors
Bearing Failures in Motors
Bearing Failures in Motors
Bearing Failures in Motors
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
Evaluate Repair Providers
Evaluate Repair Providers
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
Electric Motor Storage Guidelines
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
Electric Motor Storage Guidelines
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
Electric Motor Storage Guidelines
Recommend to rotate shafts at regular intervals – Monthly
• Redistributes lubrication to prevent corrosion
• Minimize brinelling by relocating the balls within the races
Electric Motor Storage Guidelines
Tip
Leave all keyways the same, and in a different position each time
This provides an easy visual indication
Electric Motor Storage Guidelines
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
Electric Motor Storage Guidelines
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
23
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
23
Tests for Winding Condition
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
23
Tests for Winding Condition
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
23
Tests for Winding Condition
Surge Comparison Test•Normally not performed in the field• Indicates presence of phase to
phase and turn to turn shorts within a winding
23
Tests for Winding Condition
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
23
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
Bearing Size Ounces Strokes
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
Bearing Size Ounces Strokes
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
Bearing Size Ounces Strokes
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 !!