motors | automation | energy | coatings basic electric motor maintenance ed robinson regional...

Motors | Automation | Energy | Coatings

Basic Electric Motor Basic Electric Motor MaintenanceMaintenance

Ed RobinsonEd Robinson

Regional Service MangerRegional Service Manger

[email protected]@weg.net


Eli Lilly Study Eli Lilly Study Primary causes of failure:Primary causes of failure:

• Misalignment of sheaves and couplingsMisalignment of sheaves and couplings

• Over/under lubrication of bearingsOver/under lubrication of bearings

• Improper tension in belted systemsImproper tension in belted systems

• Temperature: Readings taken on the drive-end bell housing Temperature: Readings taken on the drive-end bell housing within 1 in. of the drive shaft closely approximate the within 1 in. of the drive shaft closely approximate the internal internal winding and bearing temperatureswinding and bearing temperatures


Basic Maintenance Basic Maintenance

1.1. Bearing & Lubrication Bearing & Lubrication MaintenanceMaintenance

2.2. Coupling MaintenanceCoupling Maintenance

3.3. Electrical InspectionElectrical Inspection


Bearing Failures

• Bearing Failures are the #1 cause of motor failures. Over 60% of all motor failures are attributed to the bearings. However, many external factors contribute to the actual failure of the bearings. The bearing itself is not usually the culprit.

• So, let’s start by talking about the original design and what affect that has on the life.


Bearing Design Shape

Deep Groove Radial Ball Deep Groove Radial Ball Bearings are used for Bearings are used for “general purpose” “general purpose” applications. They work applications. They work with both radial and axial with both radial and axial type loading.type loading.

Ball Bearings Roller Bearings

Cylindrical Roller Cylindrical Roller Bearings are used for Bearings are used for heavy radial loaded heavy radial loaded applications, like a V-applications, like a V-belt drive. There is NO belt drive. There is NO axial loading.axial loading.


Bearing Design Size

200 Series

Ball Bearing

200 Series

Ball Bearing

300 SeriesBall Bearing

300 SeriesBall Bearing

Same Bore Size

And……Given the same load, the 300 Series will last twice as long as the 200 Series.

The 300 Series has larger diameter balls or rollers and a larger outside diameter which results in the heavier load carrying capacity


Bearing Design Size It’s very easy to see the difference in the

300 series bearing on the left, and the 200 series on

the right.


Bearing DesignFactors in the life of a bearingFactors in the life of a bearing

Load and Speed. Those are the two determining factors in designing a bearing for a particular application and the life expected from that bearing in that application.

The size of the bearing will help determine how much load, and for how long the bearing can handle that load. The size and type of the rolling element also plays an important part in the load rating.

Since you can’t change the design characteristics or the size of the bearings in your motors, it is a good idea to include these things in your analysis for selecting a new motor, in the beginning.


Bearing Design Life

L10 Life

Of 100 bearings Of 100 bearings tested, under tested, under the same load the same load and speed and speed conditions, the conditions, the L10 life is where L10 life is where 10% of the 10% of the bearings will fail bearings will fail (or 90% will (or 90% will survivesurvive).

Of 100 bearings Of 100 bearings tested, under tested, under the same load the same load and speed and speed conditions, the conditions, the L10 life is where L10 life is where 10% of the 10% of the bearings will fail bearings will fail (or 90% will (or 90% will survivesurvive).


Bearing Design Life

L50 Life

Of 100 bearings tested, under the same load and speed conditions, the L50 life is where 50% of the bearings will fail(and only 50% will survive).

Of 100 bearings tested, under the same load and speed conditions, the L50 life is where 50% of the bearings will fail(and only 50% will survive).


Bearing Design Life

L10 Life

L50 allows them to downsize the bearing and save money. But who

really pays?

Some Manufacturers use L10 life in engineering their motors.

And some use L50 life in engineering their motors.


Bearing MaintenanceBasic Inspection

Shaft “Feel”, without the motor running

Turn the shaft by hand … • Before 1st use to distribute grease.• Does it turn easily ?• Feel for flat spots, rubbing, stiffness, etc …

Bearing Noise while running (unloaded)

Listen to the motor bearings … • Listen for abnormal sounds, squealing,

squeaking, grinding, etc …• Unloaded roller bearings will definitely make a

“rattling” noise..


Bearing MaintenanceHi Tech Inspection

Vibration Analysis

RTD Thermal Analysis

Infrared Thermography


Bearing Failure Factors

Leading causes of bearing failure

Lack of lubrication

Too much lubrication

Incompatibility of greases

Contamination of lubrication

Internal Winding Temperatures


Bearing Lubrication

Re-lubrication IntervalsRe-lubrication Intervals

MOTOR BEARING GREASE RELUBRICATION INTERVALS (In Months)

8 hrs / day 8 hrs / day 24 hrs / day 24 hrs / day

RPM HP Range clean dirty clean dirty

0.5 - 7.5 12 6 8 3

3600 10 - 40 9 4 4 2

50 - 150 9 4 4 2

0.5 - 7.5 36 18 18 9

1800 10 - 40 24 9 12 4

50 - 150 18 9 9 4

0.5 - 7.5 48 24 24 12

1200 10 - 40 36 12 18 650 - 150 12 12 12 6

Believe it or not, too much lubrication in a ball bearing can have the same result as not enough lubrication


Nameplate Information

The nameplate tells you exactly what type, how much, and how often to add lubrication.


Bearing Lubrication Grease

Did you know you can’t mix just any grease with any other grease? It’s true - doing so can cause catastrophic damage to equipment. And it’s true even if the grease types are the same. Why is this?

Grease consists of two parts - the actual lubricant (normally oil) and a carrier, or base. Each has it’s own function. It’s the carriers that are not compatible. Always know the base of the grease you are adding and the base of the grease you are adding to. Once you know those things, you can use the chart on the next page to determine if you can add one grease to the other.

The grease compatibility chart will help ----


Bearing LubricationBearing Lubrication

Grease types Li

thiu

m

Com

plex

Lith

ium

Al

Com

plex

Ca

C

ompl

ex

Ba

Na

Ben

toni

te

Si G

el

Poly

urea

Lithium Complex

Yes Yes No Yes No No No Yes Yes

Lithium Yes Yes No Yes No No No Yes Yes

Al Complex

No No Yes No No No No Yes No

Ca Complex

Yes Yes No Yes Yes No No No No

Ba No No No Yes Yes No No Yes No

Na No No No No No Yes No No No

Bentonite No No No No No No Yes Yes No

Si Gel Yes Yes Yes No Yes No Yes Yes No

Polyurea Yes Yes No No No No No No Yes


Bearing LubricationHow does the grease get into the rolling element?How does the grease get into the rolling element?

PositivePressure

LubricationSystem


Basic Maintenance

1. Bearing & Lubrication Maintenance

2. Coupling Maintenance

3. Electrical Inspection





Belt Drives

Belt Over-Tension is a Primary Source of Bearing, Belt and Motor Shaft Failure.

Example

D - Large Sheave = 18”d - Small Sheave = 12”C - Ctr Dist = 36”

C2 = 1296”18 - 12 = 6” - - 6/2 =3”

32 = 9”1296 - 9 = 1287”

t 1287”Span = 35.8”

35.8 / 64 = .5”

1/2” Belt Deflection


Belt DrivesIf you have a V-belt tension gauge and want to tension by force, you can use a chart like this. This is a much more accurate method of tensioning.


Belt DrivesLife Expectancy

The load has a great deal of effect on the

life of the belt.

A 25% overload on the belt drive, will result in only 50% of the design belt life.

A 25% overload on the belt drive, will result in only 50% of the design belt life.



The tension also has a great deal of effect on the

life of the belt.

A 18% over-tension on the belt drive, will also result 50% of the design

belt life.

A 18% over-tension on the belt drive, will also result 50% of the design

belt life.



Heat is also a major factor. Designing good ventilation for the V-Drive can make a big difference.

A 20o temperature increase above ambient, will also result 40% loss in the design life of the belt.

A 20o temperature increase above ambient, will also result 40% loss in the design life of the belt.


Belt Drives Installation

Most of the belt problems begin with the original installation of the belts. Prying the belts on (as pictured below) can break the cords in the belt, not to mention external groove damage along the sides of the belts where they ride in the groove of the sheave.


Belt Drives Alignment

Another problem that is often overlooked is the sheave alignment. This type of misalignment can result is belt overheating, shortened life, as well as bearing overloading.


Belt Drives

Maintenance

Another much looked over issue is the sheave groove wear. When the sheave grooves wear, and dish out, as shown below, you lose belt contact on the sides of those grooves. Then, you have to over tension the belt to try and make it work. That puts excess overhung load on the bearing and shaft.


Belt DrivesMaintenance

As you can see, a great deal of cost effective maintenance can be done on a simple V-belt drive.

Critical Factors

Original DesignAlignment

TensionClean

Cool

Critical Factors

Original DesignAlignment

TensionClean

Cool


Direct CouplingShaft Alignment

TABLE.2 RULES FOR OFFSET MISALIGNMENT AND INBOARD BEARING LIFE

Maximum offset (direct measurament and percent of maximum for three expected bearing life)

Coupling Type 90% life expectancy 80% life expectancy 50% life expectancy

Maximum coupling offset

recommended by manufacturer

Link 3 mils (12% max)

5 mils (19% max)

20 mils (77% max) 26 mils

Elastomeric 8 mils (11% max)

21 mils (30 % max)


Grid 1 mil (8% max)

2 mils (17% max)


Gear 5 mils (10% max)

10 mils (20% max)


Using average offset values for various life expectancies, it can then be broadly stated for the couplings used in this study that: 1. If the motor is offset misaligned by 10 percent of the coupling manufacturer's allowable offset, then one can expect a 10 percent reduction in inboard bearing life. 2 . If the motor is offset misaligned by 20 percent of the coupling manufacturer's allowable offset, then one can expect a 20 percent reduction in inboard bearing life. 3. If the motor is offset misaligned by 70 percent of the coupling manufacturer's allowable offset, then one can expect a 50 percent reduction in inboard bearing life.

* University of Tennessee, College of Engineering

Laser Alignment


Basic Maintenance








Electrical Inspection

There are a lot of items included in this area, but it

starts with good wiring practices, including good clean

connections, and good grounding procedures. Many

electrical failures involving motors happen during the

initial connections. If your electrician doesn’t

understand the wiring diagram, get some outside help.

Don’t use the trial and error method. Most electrical

failures that happen because of miss-connection, will

do so quickly. This is an expensive mistake.


Preventative Electrical Maintenance

Checking the initial

wiring procedures, before starting the motor the first time.


Motor ProtectionProtecting the motor from Protecting the motor from overloadsoverloads

Thermocouple / Thermostat

Bi-metal construction (dual expansion rate) Alarm (or) Overheat Inexpensive

Thermistor: Solid State Switch Increase in temperature causes additional

resistance in sensor , energizing the external relay.

Alarm (or) Overheat Inexpensive

Thermocouple

Thermistor Relay


Motor ProtectionProtecting the motor from overloadsProtecting the motor from overloads

RTD’s: Resistance Temperature Detectors

Resistance change fed to external instruments allow for :

Alarm Signal

Temperature Readout

Automatic Shutdown

Continuous trend chart recording


Motor ProtectionProtecting the motor from overloadsProtecting the motor from overloads

RTD’s: Resistance Temperature Detectors

Change in resistance proportional to temperature Linear signal allows for exact temperature reportMore expensive than Thermistors or Thermostats

RTD - Resistance vs. Temperature

100

150

200

250

300

0

10

20

30

40

50

60

70

80

90

10

0

11

0

12

0

13

0

14

0

15

0

Temperature (ºC)

Re

sis

tan

ce

(o

hm

s)



PROTECTION AS A FUNCTION OF CURRENT

PROTECTION WITH MOTOR THERMAL

SENSORS OVEHEATING CAUSES FUSE FUSE AND

THERMAL PROTECTION

1. Overload with 1.2 x Rated Current

2. Duty Cycle S1 to S8 EB 120

3. Braking, reversals and operation with constant starts

4. Operation with more than 15 starts per hour

5. Locked rotor

6.Phase Failure

7. High voltage oscillation

8. Frequency oscillation

9. High ambient temperature

10. External heating caused by bearings, belts, pulleys, etc.

11. Cooling obstruction

LEGEND: UNPROTECTED PARTIALLY PROTECTED TOTALLY PROTECTED



Effects of voltage variationEffects of voltage variation

Periodic checks of Voltage and Current measurements might save some real problems down the road.



Unbalanced Voltage supply lines are responsible for a lot more failures than are usually thought of

A motor with a good service factor and low temperature rise might cover for the 3% unbalance, but not for 5%.


Application vs. Design IssuesApplication vs. Design IssuesCustomers Control Customers Control

(Preventable)

Correct Correct Electrical Electrical Connections Connections

Bearing Bearing Lubrication Lubrication

V- Drive V- Drive MaintenanceMaintenance

Shaft Shaft AlignmentAlignment

Thermal Thermal Overload ProtOverload Prot

Connections – Connections – loose bolts, loose bolts, nuts, and nuts, and screwsscrews

Manufacturers ControlManufacturers Control

(Warranty)

Short Circuit Between Turns

Short Circuit in Stator Slot

Phase to Ground Short

Rotor Failures

Rotor Bar Breakage

Excessive Rotor Heating


Preventative Maintenance

Preventative Maintenance compares to Reactive Preventative Maintenance compares to Reactive

Maintenance as a checkup or physical compares to Maintenance as a checkup or physical compares to

emergency room treatment.emergency room treatment.


Equipment Life/Cost Curve

Cost of FailureCost of FailureCorrective

MaintenanceCorrective

Maintenance

Predictive Maintenance


Preventative

Maintenance

Preventative

Maintenance

Cost Cost Time or Life Time or Life



Differs from Preventative Maintenance by using scheduled analysis of:

Shaft Misalignment

Relubrication

Balancing

Vibration

And then using that analysis to predict the longest period of life you can get from your equipment, BEFORE it fails.


Predictive TechnologiesVibration Analysis:

Couplings Bearings Gears

Infrared Thermography:Infrared Thermography:

Electrical Connections

Insulation Deterioration

Mechanical Considerations



Motor Starter Overload



Heat pattern caused by an improperly aligned motor


Conclusions

You can get more for your maintenance dollars with Preventive and Predictive maintenance routines. The old days of “Don’t fix it if it ain’t broke” are going by the way. Downtime and lost production is simply too expensive to let it run ‘til it quits. Identifying the critical applications, and starting a routine to log the failures, their causes and repairs is the first step.


Conclusions

Also, identifying the right motor in the first place is a great place to start. Some of the most important features to look for are:

Motor Insulation and Temperature Rise Service Factor Bearing Sizes and Load Capacities Construction Materials Efficiency ( Not only does the efficiency of the motor save you operating costs, but it helps to ensure the quality of materials the motor is built with )

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