Directing the o & m of Motors

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Note: The source of the technical material in this volume is the ProfessionalEngineering Development Program (PEDP) of Engineering Services.

Warning: The material contained in this document was developed for SaudiAramco and is intended for the exclusive use of Saudi Aramcos

employees. Any material contained in this document which is notalready in the public domain may not be copied, reproduced, sold, given,

or disclosed to third parties, or otherwise used in whole, or in part,

without the written permission of the Vice President, Engineering

Services, Saudi Aramco.

Chapter : Electrical For additional information on this subject, contact

File Reference: EEX20305 W.A Roussel on 874-1320

Engineering EncyclopediaSaudi Aramco DeskTop Standards

Directing The Operation And Maintenance

Of Electric Motors


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Engineering Encyclopedia Electrical

Directing the Operation and Maintenance

of Electric Motors

Saudi Aramco DeskTop Standards

CONTENTS PAGES

PREVENTIVE MAINTENANCE REQUIREMENTS....................................................1

Minimum Annual Requirements................................................................................2Visual Inspection..................................................................................................2

Bearing Inspection ...............................................................................................4

Vibration Level Testing........................................................................................9

Insulation Resistance (IR) and Polarization Index (PI) Testing .........................11

Additional Requirements .........................................................................................13

Motor Alignment................................................................................................13

Motor Lubrication ..............................................................................................19

Oil Lubricant Testing .........................................................................................20

Inspection of RTDs ............................................................................................22

Insulation Cleaning and Drying .........................................................................22

Measure Bearing Insulation ...............................................................................25DETERMINING WHETHER MOTORS ARE FUNCTIONING PROPERLY ............29

Motor Maintenance Record and Interpretation ........................................................29

Insulation Resistance Data and Data Interpretation............................................31

Vibration Level Data and Data Interpretation ....................................................32

Maintenance History of Motors .........................................................................35

DETERMINING THE CORRECTIVE ACTIONS FOR COMMON MOTOR

PROBLEMS ..................................................................................................................37

Vibration Alarms......................................................................................................37

Temperature Alarms ................................................................................................39

Winding Alarms.......................................................................................................40Bearing Alarms ..................................................................................................41

Motor Trips ..............................................................................................................42

Faults..................................................................................................................42

Process Interlocks...............................................................................................43

WORK AID 1: PROCEDURE AND ACCEPTABLE TEST VALUES

(PERFORMED DURING MOTOR MAINTENANCE AND COMPILED

FROM SADP-P-113, NFPA 70B, AND ESTABLISHED ENGINEERING

PRACTICES) FOR DETERMINING WHETHER MOTORS ARE

FUNCTIONING PROPERLY .......................................................................................44

WORK AID 2: PROCEDURE FOR DETERMINING CORRECTIVE

ACTIONS FOR COMMON MOTOR PROBLEMS (BASED ONESTABLISHED ENGINEERING PRACTICES) .........................................................48

ADDENDUM ................................................................................................................56


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Saudi Aramco DeskTop Standards 1

PREVENTIVE MAINTENANCE REQUIREMENTS

Electrical preventive maintenance consists of routine inspections, tests, and service on

electrical equipment. The purposes of electrical preventive maintenance are:

To reduce the hazards to life and property that can result from a failure of

electrical equipment.

To detect impending equipment trouble and to reduce or to eliminate

unscheduled downtime of equipment and systems.

The performance and the extent of an EPM program must be determined through a cost

analysis of the performance of the EPM program versus the cost of nonperformance of the

EPM program. An EPM program that will collectively cost more than the replacement of the

equipment would not be cost-effective. The determination of the EPM programs content andof the frequency of program performance must consider the following items:

The impact of the program on personnel safety.

The potential for equipment loss or damage.

The impact of the maintenance schedule on production.

This section of the Module will present information on the following preventive maintenance

requirements:

Minimum Annual Requirements

Additional Requirements


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The first part of the annual visual inspection is performed while the motor is in operation.

The inspection should be performed through use of a look-listen-feel approach. The

maintenance person should look at the motor to ensure that there is no physical damage to the

motor or to the connected equipment. The operational parameters of the motor (amperes,

voltage, and power factors) also should be observed to be within the established limits that are

listed on the motors nameplate. The maintenance person should listen carefully to the

sounds that the motor makes while it is in operation. A motor that is operating correctly will

make a smooth, steady sound. Oscillations or unusual sounds can indicate a pending

electrical or mechanical failure. The maintenance personnel also should feel the motor for

excessive heat in the vicinity of the motor stator and the motor bearings (e.g., feel the stator

case and end bells).

The second part of the annual visual inspection is performed while the motor is deenergized.

The following is a list of the general items to inspect while the motor is deenergized. (The

manufacturers technical information should be consulted for specific requirements.)

Inspect for water and for condensation on or in the motor.

Inspect for rust and for corrosion on the connection boxes and seal points.

Inspect for dirt, for dust, and for foreign objects on or around the motors

ventilation ports.

Inspect for proper anchors, mounts, grounds, and ground connections.

Check the air gap at eight radial locations or at all poles of a synchronousmotor. Record this information. Excessive variation of the air gaps may

suggest misalignment or excessive wear of the motors bearings.

Inspect for signs of excessive heat such as charred or cracked insulation and

discolored or blistered paint and varnish.

Inspect the integrity of the electrical terminals.

Inspect for frayed or worn insulation.

Inspect the stator and the rotor coil insulation for thermal aging, cleanliness,and tightness of bracing.


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Ensure that all fasteners are properly secured.

Inspect for clogged rotor and stator ventilation ducts.

If possible, inspect the end windings of the motor for dirt, dust, grease, oil, or

other foreign material.

DC motors require the following additional inspection items:

Inspect the commutator surface for indications of faulty commutation and for

high mica insulation between commutator segments..

Inspect all brushes for satisfactory operation, for proper length, and for proper

brush holder compression.

Inspect for cleanliness in the commutator area. An excessive runout or an

irregular commutator surface can generate excessive amounts of carbon dust in

the commutator area. An excessive accumulation of carbon dust can contribute

to flashovers.

Inspect the brush fit in the brush box to ensure ease of movement of the

brushes in the brushbox.

The value that is obtained through performance of an annual visual inspection often is

dependent on the mental approach that the inspector uses to perform the inspection. If the

annual visual inspection is performed under the mental assumption that no problems exist, theinspector often will miss the subtle signs of potential problems; however, if the annual visual

inspection is performed under the mental assumption that a problem does exist and that the

purpose of the inspection is to identify the problem, the inspector is more likely to locate the

signs of potential and existing problems.

Bearing Inspection

The complexity of the bearing inspection will depend upon the actual type of bearing and

lubrication system that is installed. Anti-friction bearings that use a grease lubrication system

require the least amount of maintenance of all the types of bearings that are used in SaudiAramco installations. Sleeve bearings that use an oil transfer system require the greatest

amount of maintenance. The exact bearing inspection requirements should be in accordance

with the manufacturers technical manual.


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The first portion of an anti-friction bearing inspection is performed while the motor is in

operation. This portion of the inspection involves listening for sounds such as squeals,

screeches, and clicks that emanate from the bearings. Such sounds are usually a sign of

improper lubrication or of a dirty bearing.

After the motor is shut down, the bearing housing should be opened, and the bearing should

be checked for proper lubrication (grease), signs of excessive heat, and indications of high

currents across the bearing. On relatively small motors, the shaft should be checked for

excessive endplay or for freeplay while the shaft is manipulated by hand. On motors that

have shafts that are less than five inches in diameter, the shafts also should be rotated by

hand. While the shafts on the motors are rotated, the inspector should feel for any hard points

on the bearings.

Anti-friction bearings that use grease for lubrication should have the bearing cleaned and

should have the grease changed during the annual bearing inspection. Anti-friction bearingsthat use oil for lubrication should be inspected to ensure that the oil is clean and that the oil is

at the proper level. If necessary, oil should be added to the bearing. The manufacturers

technical manual should be consulted to ensure that the proper amount and the correct type of

grease or oil is used.

Sleeve bearings require more maintenance than anti-friction bearings because these bearings

must be disassembled to allow an adequate inspection. The exact procedure for disassembly

and for inspection of motor sleeve bearings should be in accordance with the motor

manufacturers technical manual.

After the bearing is disassembled, the bearing should be checked for unusual signs of wearand for signs of excessive heat. An exact check of bearing wear can be performed through

measurement of the air gap around the rotor and through comparison of these measurements

to the manufacturers specifications and to previous air gap measurements. The bearing also

should be checked for signs of circulating currents that are evidenced by localized pitting or

heating on the soft metal inner surface of the bearing. Large motors are provided with

bearing pedestal insulation to prevent circulating currents; therefore, excessive bearing current

would indicate a failure of the bearing insulation. The oil lubrication system also should be

inspected to ensure that there is adequate oil flow to the bearing and to ensure that bearing

temperatures are within specifications.

The Electrical Engineer should be able to inspect the bearing and to identify the type ofbearing damage. This identification of damage is especially useful in cases of chronic

(repetitive) bearing failures.


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The babbitt surfaces must be examined for evidence of the following unusual conditions:

Rub marks in the top half of the bearing usually are a result of machine

misalignment.

Rub marks on the babbitted thrust faces are an indication of axial thrust loads.

These rub marks usually result from improper axial alignment or from

excessive shaft end play.

The bearing should be checked for evidence of wiping or of pulling of the

babbitt metal. This bearing wiping generally is the result of the bearing

overload due to machine misalignment or due to machine vibration.

The wear pattern on the babbitt surface of the bottom half of the bearing should

be noted. The wear pattern should extend axially along the lower half of thebearing and should be centered on the bottom of the babbitt surface. The width

of the wear pattern should be uniform from one end of the bearing to the other.

Uneven wear patterns typically are due to improperly fitted bearings or are due

to a bent shaft.

The lower bearing babbitt should be checked for circumferential scratches.

These scratches run perpendicular to the bearing wear marks and commonly

are caused by foreign particles that pass through the oil film.

The upper and lower halves of the bearing should be checked for general

surface roughness. This roughness may be caused by abrasive particles in theoil.

The journal surface should be checked for protruding sharp edges.

The bearing surface should be checked for pitting. This pitting is normally due

to corrosion, to careless handling, or to bearing currents.

After the bearing surface inspection has been conducted, the bearing oil reservoirs should be

drained and flushed.


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Split Sections of a Sleeve Bearing

Figure 1


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Vibration Level Testing

Vibration level tests are performed to check for excessive vibration or for changes in vibration

that are above the established limits. All equipment that rotates will vibrate to some degree;however, changes in the vibration levels can be a sign of a pending malfunction. These

abnormal vibration levels, if left unattended, can cause damage to the motor shaft, to the

motor rotor, to the motor endbells, to the motor bearings, and to the other equipment that is

connected to the motor.

Different types of vibration must be considered when a vibration level test is performed.

Because motors rotate in the radial plane and the axial plane, a complete vibration analysis

must consider both vibrational planes. The number of test points that should be checked on a

specific motor application should be based on the manufacturers recommendations, motor

history, and instructions for technical services.

The source of vibration can be identified through performance of a frequency analysis. The

frequency analysis will identify the frequency at which the excessive vibrations occur. This

frequency can then be used to determine the cause of the excessive vibration. The amplitude

of the frequency will indicate the severity of the problem. The following is a list of the

typical sources of vibration:

Imbalance

Misalignment

Resonance

Bearings

Gears

Vane Passing

Fans

Air gap eccentricity

Cavitation

Oil whirl

Pipig

Bent shaft and bowed rotor

Looseness

Belts and pulleys


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Figure 2 shows a sketch of a motor and illustrates where the vibration measurements should

be made. The axial plane of vibration is measured at two locations, the front end (AF) of the

motor and the rear end (AR) of the motor. The radial plane of vibration is divided into two

components: vertical and horizontal. The vertical component consists of VRand VFand thehorizontal component consists of HR and HF. Four vibration level measurements must be

made in the radial plane: one at VR, one at VF, one at HR, and one at HF.

Motor Vibration Measurements

Figure 2


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The following steps can be used as a guide to insulation resistance testing:

All leads of the motor should be connected together, and the insulation

resistance should be recorded from the leads to ground. If the individual

winding phase connections are accessible, each phase winding should be

disconnected, and phase-to-phase measurements also should be taken.

The insulation resistance check should be performed as soon as the motor is

turned off and the motor windings are still hot.

The insulation resistance test voltage should be determined by the voltage of

the motor. A 500 volt handcrank instrument can be used for motors that are

less than 600 volts. A 1000 volt or 2500 volt motor driven or rectifier type

instrument should be used for motors of 2300 and 4000 volts. A 5000 volt

megger should be used for 13.2 kV motors.

Spot measurements should be conducted for 60 seconds.

Ambient temperature and moisture should be recorded.

All resistance values should be corrected to 50oC.

The results of the 60 second spot measurement should be recorded on the

maintenance form and should be compared to previous measurements.

The Polarization Index (PI) is a ratio of the ten minute insulation resistance to the one minuteinsulation resistance. The following equation can be used to determine the Polarization Index

(PI) of a motor.

The value of the PI should be equal to or greater than two to be considered satisfactory.


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Additional Requirements

In some instances, the Electrical Engineer may determine that the minimum annual

requirements do not provide sufficient data to determine if a motor is operating properly.This section provides additional tests that can be performed to obtain more specific data on

motors. Prior to the performance of these preventive maintenance items, the Electrical

Engineer must consider if the benefits that are derived from this maintenance are worth the

additional cost. Sound engineering practices dictate that the following are advisable

preventive maintenance items to be considered when extra maintenance data are desired:

Motor Alignment

Motor Lubrication

Oil Lubricant Testing

Inspection of RTDs

Insulation Cleaning and Drying Measure Bearing Insulation

Motor Alignment

Many failures of motors and motor bearings can be attributed to a motor alignment problem.

Motor misalignments often appear as other motor problems, such as bearing overheating,

excessive bearing wear, motor overheating, excessive noise, and excessive motor vibration.

Motor misalignment also can appear as problems with the connected load such as overheating

of connected equipment and connected equipment bearing damage.

The motor alignment should be checked whenever the following indications are present:

The bearing temperature (of the motor or of the connected equipment)

increases with no lubrication system problems.

The motor air gap increases/decreases.

The noise that is generated by the bearing (motor or connected equipment)

increases.

Motor or connected equipment vibration increases.


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A straight edge, a feeler gauge, or a dial indicator can be used to check motor alignment

through comparison of the motor shaft position to the load shaft position. Each instrument

will check for a different type of motor misalignment. The straight edge will ensure that the

motor shaft and the load shaft line up axially and will ensure that no lateral displacement has

occurred. This method is especially useful for alignment of belt drives because the straight

edge will contact the motor sheave and load sheave squarely when the motor and the load are

properly aligned. Figure 3 illustrates the use of a straight edge for alignment of belt drives.

Figure 3 shows one correct alignment of a belt drive and two incorrect alignments of belt

drives. In the correct alignment, the straight edge is used to line up the sheaves of the motor

and of the load. In the first incorrect alignment, the motor and the motor sheave are cocked in

relation to the load sheave. The installation that is shown would produce rapid belt wear and

would place an unnecessary combination load on the shaft of the motor.

The second incorrect alignment shows that the motor and the load are not lined up in the axial

direction. This type of installation would also produce rapid belt wear and would develop anunnecessary combination load on the shaft of the motor and the shaft of the load.


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Alignment of Belt DrivesFigure 3


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A feeler gauge can be used to check for an angular displacement between the motor shaft and

the load shaft (the face of both shafts should meet). The dial indicator can be used to check

for any type of rotational misalignment of the motor shaft and the load shaft. A rotational

misalignment will usually be caused by a bend in one of the shafts.

The most accurate method to use to check motor alignment is the dial indicator method. The

dial indicator can be used to check angular misalignment and to check run out. Figure 4

shows a motor shaft and a load shaft with the coupling hubs installed.

The following steps can be used as a guide to check angular misalignment:

The alignment of the motor and the load should be checked after the coupling

hubs have been installed.

The dial indictor base should be mounted to the side of one coupling hub (Hub1).

The button of the dial indicator should be placed against the finished face of the

other hub (Hub 2).

A reference mark should be inscribed on Hub 2 to mark the position of the dial

indicator button.

Both shafts should be rotated simultaneously while the indicator button is kept

on the reference mark on Hub 2.

The dial indicator reading should be noted at each quarter revolution.

The angular misalignment of the shafts will be indicated by a deflection of the

dial indicator dial. The misalignment of the shafts should not exceed a total

dial indicator reading of .001 for each one inch of radius of the coupling hub.


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Angular Alignment

Figure 4

After the shafts have been checked for angular misalignment and are parallel within the limits

that are specified, the shafts should be checked for run out to ensure concentricity of the

shafts.


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The following steps, in reference to Figure 5, can be used as a guide to check run out of the

shafts:

The dial indicator base should be mounted to one coupling hub (Hub 1).

The dial indicator button should be placed on the machined diameter of the

other hub (Hub 2). A reference mark (not shown in Figure 5) should be scribed

on Hub 2 to mark the location of the indicator button.

Both shafts should be rotated simultaneously while the indicator button is kept

at the reference mark on Hub 2.

The dial indicator reading should be noted at each quarter revolution.

The run out between the hubs will be indicated by a deflection of the dialindicator dial. The total run out between the hubs should not exceed .002 inch.

Run-Out

Figure 5


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The lubrication of antifriction bearings and sleeve bearings with oil is a continuous function;

therefore, only a periodic inspection of the oil system is required. The inspection of the oil

system depends on the complexity of the oil system. As a minimum, however, the following

items should be checked:

That the oil level in the oil level indicators is in the normal range. If the oil is

out of the normal range, the proper type of oil should be added.

That the oil flow indicators on circulating oil systems indicate proper oil flow.

If improper oil flow is noticed, the circulating oil system should be investigated

to determine the cause of the lack of oil or of the loss of oil flow.

Oil pressure indicators on forced-flood oil lubrication systems should be

checked to verify that the oil pressure to the bearing is in the normal range.

Under normal operating conditions, the lubricating oil will not need to be changed over a two

year period. However, if the annual oil lubricant tests identify foreign particles in the oil or

contamination of the oil, the oil system needs to be drained, flushed, and refilled with the

proper lubricant.

Oil Lubricant Testing

Oil lubricant testing is performed to ensure that the oil is free from contamination and that the

oil still performs as a lubrication agent. Over time, all lubricants will chemically break down

and will eventually cease to effectively lubricate. A test of the oil will help to identify any

potential lubrication problems prior to failure.

Two types of tests are performed on oil lubricants: a simple foreign material contamination

test and a complex chemical analysis of the lubricant. The foreign material contamination test

is performed to ensure that contaminants such as water, sand, or other foreign material have

not entered the lubricant. The presence of any foreign material could cause damage to the

bearing. The chemical analysis checks for a breakdown of the lubricant on a molecular level

and includes an analysis of viscosity and of viscosity index to determine if there have been

any changes in the performance of the lubricant. The chemical analysis should be performed

in a laboratory.


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The foreign material contamination test is easy to perform in the field. A sample is drawn

from the oil lubrication system and then the lubricant is allowed to settle. Once the oil has

settled, it should be inspected for any foreign material. This test should also include a check

of the level of the oil in the oil reservoir or in the bearing to verify that the level is correct.

Because the chemical analysis is performed in a laboratory environment, the exact procedures

for the chemical analysis are beyond the scope of this module. The oil lubricant sample

should be obtained from the motor and then the sample should be sent to a laboratory facility

for testing.

The foreign material contamination test should be done on a quarterly basis or more often if

experience shows that the motor has a history of contamination problems. The oil lubrication

chemical analysis is done less often but should be done at least every six months. The oil in a

oil lubrication system should be changed every one or two years.

The periodicities of the oil tests can be changed based on the history of the motor. Prior toany change in oil lubrication test frequencies, the following items should be considered:

The average temperature of the lubricant.

The likelihood and the severity of bearing overloads.

The likelihood that contaminants will enter the system.

If the temperature of the bearing lubricant has been operating in the upper portion of the

lubricants temperature range, the lubricant should be tested more often. If the temperature of

the lubricant has exceeded its normal operational range, the lubricant should be immediately

tested. Follow-up testing of the oil should occur weekly for the next month.

If the bearing is subjected to periodic overloads or to cyclic overloads, the periodicity of the

oil tests should be reduced.

If there is a high likelihood that contaminants will enter the oil system, or if the oil system has

a history of contamination, the oil tests should be scheduled on a more frequent basis.

Decreased oil test periodicity does not remove the responsibility for determination of the

cause of contamination or for elimination of the source of the contaminants.


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Several methods can be used to clean motor insulation. The most effective method depends

upon the type of dirt and upon the amount of dirt that are lodged on the insulation. The

methods that can be used to clean motor insulation are listed below in the order of preference:

Dry wiping

Brush or suction cleaning

Blowing

Solvent cleaning

Water, emulsion, and alkali cleaning

Shell blasting

Dry wiping should be used to remove dry dirt from the surfaces of insulation that are located

in accessible areas. Dry wiping is performed through use of clean, dry, lint free cloths. Non-

lint free cloths should not be used because the lint will adhere to the insulation and will

increase the dirt collection. Lint is particularly objectionable on high-voltage insulationbecause the lint tends to cause a concentration of corona discharge.

Brush or suction cleaning also should be used to remove dry dust and dirt from the surfaces of

insulation that are located in accessible areas. The dry dust and dirt should be removed by

brushing with bristle brushes and then vacuum suction cleaning. Wire brushes should not be

used. Brush or suction cleaning is a desirable method to clean insulation because the dirt is

not scattered and the dirt does not settle on other apparatus. The use of this cleaning method

is limited to accessible areas that can be reached by the brush and the vacuum.

Blowing out dirt with a jet of air only should be done to remove dirt from inaccessible

crevices and only when the motor is dry. Blowing is performed through use of drycompressed air (30 psi or less) and vacuum suction. A vacuum suction is connected to one

end of the motor, and the compressed air is directed into the other end of the motor. The air

should be directed in a manner that will dislodge the dirt from the insulation and will allow

the vacuum suction to draw the dirt out of the motor.

Solvent cleaning is particularly effective for removal of tar, grease, wax, and oil from

electrical apparatus. The surfaces should be wiped with a cloth that is wet with the solvent,

and then the surfaces should be wiped with a dry cloth. To avoid lint deposits on the

insulation, non lint free rags should not be used. If solvents are used on windings with

silicone rubber or with an abrasion resistant coating, severe damage to the coating can occur.

The manufacturers technical manual should be consulted for the solvent that should be usedfor insulation cleaning.


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Motors can be cleaned by hose washing or by pressure spray from a steam generator. Steam

from a shop line or a spray of hot water and compressed air may be used. When insulation is

cleaned through use of this method, the jet pressure and temperature should not exceed 30 psi

and 80C (176F), respectively. To remove tar, wax, grease, or oil from insulation, a

nonconductive detergent compound must be added to the water. These detergent compounds

contain non-ionic emulsifying agents.

Emulsion cleaners also contain solvents to soften hard deposits so that these deposits can

more easily be removed. These detergent compounds are not electrical conductors and are

safe for use on insulation. After the deposits have been removed, the motor windings should

be thoroughly rinsed with water to remove all traces of the cleaning compound. The water

should then be promptly removed from the motor windings through use of air pressure and

lint free rags.

Shell blasting is the process of air blasting with ground nut shells to remove hard dirt depositsfrom insulation. Shell blasting may abrade the insulation and should only be performed under

the direction and supervision of the manufacturer.

In Saudi Aramco, solvent cleaning, water/emulsion/alkali cleaning, and shell blasting are not

recommended for field maintenance. Motor windings with heavy oil and dirt contamination

must be sent to Dhahran shops for cleaning.

The best method for use in cleaning a given motors insulation should achieve the following

objectives:

The method should be able to remove the type of dirt that is present.

The method should cause the least amount of insulation damage.

The manufacturer should be consulted when there is a doubt as to the best method of

insulation cleaning.

The motor windings can be dried after they are cleaned through the use of external heat or

through the circulation of current through the windings. The use of resistance heaters or

steam coils is advisable when external heat is to be applied to the motor. Because the space

heaters that are located inside of the motor are not of sufficient capacity for use in drying the

motor windings, additional heaters are required. The additional heaters should be placed nearthe bottom of the motor, and care must be taken to protect the windings against direct heat

radiation from the heaters.


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A dc welding set can be used to heat the motor windings through use of the circulation of

current in the windings. The current that is circulated in any part of the winding should not

exceed the rated current value of the motor.

Motor windings cannot effectively be dried unless means are provided to circulate air through

the motor to remove the moisture. Openings must be provided near the bottom of the motor

for the entry of fresh air, and openings must be provided near the top for the discharge of the

heated moist air. A small fan might be necessary to provide assistance in the circulation of

air.

Regardless of the method that is chosen to dry the motor windings, the heat to dry the motor

windings must be applied gradually to allow the water vapor that is produced to travel out

through the insulation. A rapid application of heat could cause steam pressure to rupture the

insulation; such as a rupture would permanently damage the insulation.

Measure Bearing Insulation

The bearing insulation is tested to ensure that the bearing pedestal has sufficient dielectric

strength to resist the flow of current through the bearing to ground. Bearing insulation that

does not have sufficient dielectric strength will allow current to flow in the bearing; such

current flow has a destructive effect on the shaft journals and the bearings.

Bearing insulation consists of placement of a non-conductive sheet barrier between the

bottom of the bearing pedestals and the sole plates. Care must be taken to ensure that all

hold-down bolts, dowels, and oil piping are insulated from the pedestal. Figure 6 shows an

insulated bearing pedestal. The bearing pedestal rests on the sole plate and is insulated from

the sole plate through use of a micarta insulation strip. All dowel pins and hold-down bolts

are insulated with micarta tubes to prevent a short circuit between the pedestal and the sole

plate.


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Ball-type bearings also can be insulated through placement of an insulating material between

the outer race of the motor bearing and the motor housing end shield. Figure 7 shows an

expanded view of an end-shield type bearing with a sleeve insulator. When the bearing is

constructed, a non-conductive insulating sleeve is molded to the motor bearing. After the

insulating sleeve is molded, the sleeve is machined into the motor housing end shield. The

combination bearing/insulating sleeve is press-fitted into the motor housing end shield. The

insulating sleeve that is bonded to the motor bearing electrically isolates the rotor

shaft/bearing from the motor housing end shield. Such electrical isolation prevents the flow

of current through the bearing to ground.

Bearing insulation is tested through use of a megger. The megger is connected between the

motor shaft and ground. After the megger is connected, a test voltage of 500V is applied

between the motor shaft and ground. The test voltage is applied for one minute, and at the

end of one minute, the bearing insulation resistance is read from the meter that is on the face

of the megger.

End Shield Type Bearing with Sleeve Insulator

Figure 7

The bearing insulation test is performed to ensure that the insulation material has not been

damaged or short circuited. The test will also verify that no external or control device has

bridged the bearing insulation. It is possible to bridge the insulation gap when external

equipment such as metal oil ports or supports are attached to the motor.


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The following are the general steps that are necessary to verify the integrity of the bearing

insulation:

Uncouple the shaft from connected equipment.

Disconnect the ground strap at the base of the pedestal.

Disconnect all temperature monitoring equipment.

Megger the insulation that is between the bearing housing and ground.

The test results are considered unsatisfactory if the insulation measures less than 200k ohms;

however, the desired insulation value is one megohm. Before the pedestal insulation is

considered defective, all other sources of a short circuit must be eliminated. These sources

include but are not limited to the following items:

Uninsulated pipes that touch both the pedestal and sole plate.

Guard rails in contact with the pedestal.

Tools, ladders, or other equipment in contact with the pedestal.

Pumps or other equipment that are geared or coupled to the motor.

Other items that should not be overlooked are good housekeeping measures. Tools or other

miscellaneous items are often the cause of low insulation measurements.


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DETERMINING WHETHER MOTORS ARE FUNCTIONING PROPERLY

Determining whether motors are functioning properly is one of the major tasks involved in

equipment management. The Electrical Engineer must be able to evaluate motor maintenancerecords to determine if the motor is functioning properly. To determine if the motor is

functioning properly, the Electrical Engineer must compare motor maintenance values against

the acceptable limits and against the normal operational values. More importantly, the

Engineer must be able to recognize trends that indicate a deterioration of the motors

operation. Many times a motor will show early signs of a pending failure through trends, and

if the Electrical Engineer learns to recognize these trends, major equipment failures can be

averted.

Motor Maintenance Record and Interpretation

Motor maintenance record forms contain the information and the data that are obtained from

motor testing. The Motor Maintenance Record is a two-part form. Part I of this form

contains the motor identification data and a record of the insulation resistance test data and the

vibration test data. Part II of this form is a record of the work that was performed on the

motor over the motors life. As Figure 8 shows, Part I of the Motor Maintenance Record is

divided into the following four areas:

The Motor Identification Data

The 60 Second Insulation Resistance Graph

The Insulation Resistance Data

The Vibration Level Data

The first section of the Record Motor Maintenance Record contains the following data for

motor identification:

Make

Type

Serial No.

Voltage

Amps

Frequency

Speed Rating (hp/kW)

S.F.

Insulation Class

Location

Date Installed

Description of Duty


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Motor Maintenance Record (Part I)

Figure 8


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The temperature of the motor windings also should be measured and recorded in the

appropriate block on the form. The temperature of the motor windings can be measured

through use of the RTDs that are installed in the motor If the motor does not have installed

RTDs, temporary temperature probes that are inserted into the motor housing are used. The

temperature of the motor windings is then used to calculate the temperature corrected, 60

second phase-to-ground IR measurement. The equation for use in temperature correction of

IR measurements is located in Work Aid 1.

The temperature corrected, 60 second phase-to-ground IR measurement and the calculated

phase-to-ground polarization index should be compared to the minimum acceptable values

and to the previously recorded values to determine whether these values are acceptable.

Work Aid 1 contains the minimum acceptable values for IR and for PI.

On motors that have accessible phase connections, the phase-to-phase insulation resistance

should be measured and should be recorded for all possible phase combinations. A one-minute and a ten-minute insulation resistance measurement should be recorded for each phase

combination. Through use of the one-minute and the ten-minute phase-to-phase insulation

resistance measurements, the phase-to-phase Polarization Index (PI) can be calculated. The

one-minute, the ten-minute, and the PI measurements should be compared to the minimum

acceptable values and to the previous readings to ensure that the values are acceptable. Work

Aid 1 provides the minimum acceptable values for IR and for PI.

Vibration Level Data and Data Interpretation

The vibration level of the motor should be determined through use of installed probes or

through use of temporary vibration probes, and the vibration level data should be recorded in

the Vibration Levels Data section of the form. The vibration level for both the drive end

bearing and for the non-drive end bearing should be recorded. The level of vibration should

be compared to the minimum acceptable values and to the previous values. Any changes in

the vibration level could be a signal of pending trouble and should be investigated. A trend of

an increase vibration could indicate wear on the motor bearings and would warrant further

investigation.


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Figure 9 is a typical vibration level trend chart that shows a graph of vibration level (in in/sec)

with time (in months). This graph shows a relatively constant vibration level from January of

1986 to November of 1986. Such a graph is consistent with normal motor operation. The

graph also shows a sharp rise in the vibration levels for two consecutive months: December

of 1986 and January of 1987. Such a rise indicates that a problem has developed and that the

problem is getting worse. If this problem is not corrected, it eventually will lead to a

breakdown as shown by the dotted line on the graph. Warning time and repair level, also

shown in Figure 9, illustrate the use of trend analysis in directing the operation and

maintenance of electric motors. Through establishment of a repair level that is below the

breakdown level, a sufficient amount of warning can be provided to schedule corrective

maintenance before a failure occurs.

The point at which a breakdown will occur can be predicted from experience with a similar

machine or from vibration standards. Work Aid 1 contains the maximum acceptable vibration

levels for Saudi Aramco motors. The value that is displayed on the graph in Figure 9 is anoverall value that represents the energy content of all the vibration frequencies.

Trend Chart

Figure 9


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Vibration level measurements indicate the magnitude of the vibration, but these

measurements do not indicate the source or the cause of the vibration. A narrow band

frequency analysis should be performed through use of a vibration spectrum, shown in Figure

10, to determine the exact source of the vibration. Figure 10 shows a frequency spectrum

graph of acceleration (in gs) versus frequency. The graph shows low values of acceleration

at the lower frequency ranges and higher values of acceleration at the higher frequency

ranges. These higher values indicate problem areas, and these frequencies can be pin-pointed

to specific sources of vibration.

The analysis of the vibration spectrum is beyond the scope of this Module. If a problem is

identified through use of trend analysis, a narrow band frequency analysis should be

performed by the appropriate personnel.

Typical Vibration Spectrum

Figure 10


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Maintenance History of Motors

As Figure 11 shows, Part II of the Motor Maintenance Record is divided into the following

sections:

Motor Identification Data

Description of Preventive and Corrective Maintenance Performed

The Motor Identification Data for Part II of the Motor Maintenance Record are the same as

previously discussed for Part I of the Motor Maintenance Record. The identification data are

duplicated so that the motor to which the information pertains can be identified if the forms

become separated. Part II of the Motor Maintenance Record is a narrative of the preventive

and corrective maintenance that is performed on the motor. The results of all inspections and

tests that are performed on the motor should be recorded in this section.

The information that is recorded in this section will allow others to better understand themaintenance history of the motor. The following are examples of the types of information

that are placed in the Description of Preventive and Corrective Maintenance Performed

section:

Results of the visual inspection.

Results of the bearing inspection.

Results of the RTD inspection.

Motor alignment data.

Dates and methods of insulation cleaning and drying.

Signs of abnormal operation.

Corrective troubleshooting.

Corrective maintenance.

A list of parts that were replaced or that were refurbished.

Any pertinent data that will help in future maintenance activities.


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Motor Maintenance Record (Part II)

Figure 11


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DETERMINING THE CORRECTIVE ACTIONS FOR COMMON MOTORPROBLEMS

In addition to being able to identify motor problems, the Electrical Engineer must be able todetermine the proper corrective actions for the identified problems. If the wrong corrective

actions were taken, the problem could be compounded, and the damage to the motor could

escalate. This section of the module will discuss common motor problems and the corrective

action for each problem. The corrective actions that are presented are by no means the only

method to solve the problem. Determination of the appropriate corrective actions for a

specific problem must be accomplished through use of manufacturers troubleshooting guides

and the Electrical Engineers knowledge and experience. The following common motor

problems and their corrective actions are discussed in this section:

Vibration Alarms

Temperature Alarms Motor Trips

Vibration Alarms

A sudden and significant increase in vibration amplitude is a very apparent indicator that

something is wrong with a motor. A gradual increase in vibration amplitude may not be

noted until damage occurs. Vibration monitoring equipment is installed on motors above 185

kW

(250 Hp) to alert personnel to abnormal vibration levels so that action can be taken to correct

the problem before damage occurs. The vibration limits of motors are set so that the motoralarms or shuts down prior to serious damage to the motor. Motors below 185 kW (250 hp)

are not equipped with vibration monitoring equipment and must be monitored by experienced

personnel to judge changes in vibration levels.

The vibration alarm and shutdown setpoints depend on the speed of the motor and the type of

vibration probe that is installed. Figure 12 shows the recommended vibration alarm and

shutdown setpoints for motors with various speeds and vibration monitoring probes.

The variations in alarm and shutdown levels occur because different speed motors will

naturally vibrate at different levels. The changes in alarm and shutdown levels for different

types of vibration probes occur because of the difference in the accuracy of the probes.


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Vibration Alarm and Shutdown SetpointsFigure 12


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Vibration alarms are symptoms for a variety of motor problems. The following are examples

of problems that can cause vibration alarms:

Loose mounting bolts

Loose coupling

Motor and load misalignment

Worn motor bearings

Mechanically unbalanced load

Mechanically unbalanced rotor

Bent or cracked shaft

Excessively pulsating load

Out of synchronism (synchronous motor only)

The corrective action for a vibration alarm will depend on the root cause of the vibration

alarm. In the case of an alarm, the motor should be stopped immediately to prevent excessivedamage to the motor or to the surrounding equipment. The possible causes of a vibration

alarm should be investigated one at a time. The most common problems should be

investigated first. Common problems can be found through a review of the Motor

Maintenance Record form. Items such as loose bolts, loose couplings, or misalignments also

are considered common problems. Work Aid 2 contains a procedure for troubleshooting a

vibration alarm. Possible corrective actions for some of the possible causes also are provided

in Work Aid 2.

Temperature Alarms

The goal of a temperature alarm is to stop a motor when a motor-related high temperature

condition exists. When properly applied, the high temperature alarm will trip a motor before

the high temperature condition can cause damage. The following types of temperature alarms

are associated with motors:

Winding Alarms

Bearing Alarms


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The temperature alarm or the trip settings will be dictated by the insulation class of the motor.

The alarm or the trip setting will always be lower than the maximum allowable insulation

temperature to ensure that no damage occurs to the winding insulation. The motor alarm/trip

setpoints should be in accordance with the following:

Motor Alarm or Maximum Allowable

Insulation Class Trip Setting Insulation Temperature

degrees C degrees C

B 120 130

F 145 155

H 170 180

Work Aid 2 contains common winding temperature problems and a course of corrective

actions for each problem. The corrective actions for each of the possible causes of windingtemperature alarms are different. The proper action to be taken to correct the problem will

depend upon the root cause of the winding temperature alarm.

Bearing Alarms

Bearing alarms are provided to protect the bearings from damage that can be caused by

excessive temperatures. Excessive heating of a bearing will cause a rapid deterioration of the

bearing and the bearing lubrication, and such deterioration can lead to a rapid failure of the

motor.

Excessive bearing temperatures, although detrimental to the bearings, are generally only a

symptom of a larger problem. An investigation must be performed to correct the root cause

of the bearing alarm as well as to repair the bearing, if necessary. The following are some of

the causes of bearing alarms:

Loss of lubrication flow

Motor out of alignment

Dirt in lubrication system

Overlubrication of grease lubricated bearings

Overload on motor

Old bearings Incorrect bearings

Bearing alarms must be set to respond at a temperature that is lower than the temperature at

which bearing damage will occur. The maximum temperature that a bearing can withstand

without damage will depend on the type of bearing that is installed.


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The maximum temperature and bearing alarm setpoints should be as follows:

Maximum Allowable Bearing

Alarm and Temperature ino

C based onBearing Type Trip Setting in oC a 40oC rise above ambient

Anti-Friction 82 92

Sleeve 80 90

The proper corrective action for bearing alarms will depend on the root cause of the bearing

alarm. In general, the first priority is to stop further heating of the bearing. The next step is to

cool the bearing. The bearings will start to cool as soon as the motor is tripped or as soon as

the load is removed from the motor. Motors will automatically trip on a bearing alarm to help

prevent further heating of the bearings. After the immediate corrective actions have been

taken, the next step is to determine the cause of the problem and to correct the situation. Afterthe root cause of the problem has been corrected, the bearing and motor shaft should be

inspected. Work Aid 2 presents some of the possible causes of bearing alarms and a course of

corrective action for each possible cause.

Motor Trips

Motor trips are installed to prevent damage to the motor or to the system due to undesirable

motor or system conditions. Motor trips are divided into two main categories:

Faults Process Interlocks

Faults

Motor trips are installed to protect against electrical system faults and against mechanical

faults. The type of motor trip that is provided depends on the specific motor installation. The

following is a list of the possible motor trips:

Motor overload

Phase overcurrent

Ground fault Current unbalanced

Vibration

Temperature alarm

Phase-to-phase fault


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If a motor trip occurs, the Electrical Engineer must use all available indications to analyze the

cause of the motor trip. On very large motors, alarm panels are provided that make the

troubleshooting procedure much easier. Smaller motors or motors without alarm panels

require more thought and troubleshooting skills. Ground faults and phase-to-phase faults

quickly can result in motor winding insulation break down. Lockout relays (86 devices) are

used in conjunction with the relays that detect ground faults and phase-to-phase faults to limit

the motor damage that can be caused by these faults. Because lockout relays must be

manually reset after they operate, these relays force maintenance personnel to investigate the

cause of the problem prior to re-energization of the motor. Correct determination of the cause

of the motor trip is vital in the recovery of the motor. An Electrical Engineer must use his

knowledge and common sense to analyze the cause of a motor trip. Many times, the obvious

signs can be overlooked because they seem too simple. Work Aid 2 provides a procedure

to guide the Engineer in troubleshooting. Work Aid 2 also provides a list of the common

motor problems and their possible causes. In addition to the troubleshooting guides, the

Engineer should also obtain the maintenance records and the manufacturers troubleshootingguides for the motor.

The corrective actions that must be taken for a motor trip will depend on what causes the relay

to actuate. Different corrective actions must be performed for the different causes of relay

trips. The wrong actions could cause more harm than good. Each set of corrective actions is

different, but all corrective actions have the same goal. The goal of corrective actions is to

prevent further damage to the motor until the motor fault is cleared and the motor is repaired.

The first step in any motor trip corrective action will be to turn off the motor to ensure that the

motor will not accidentally restart if the relay resets. Work Aid 2 contains the possible

courses of action for each possible cause of a motor trip.

Process Interlocks

The second category of motor trips is process interlocks. Process interlocks are provided to

control a system and are not provided to protect the motor; therefore, when a motor trips or

fails to start due a process interlock, the motor control circuit is operating properly. In some

instances, these process interlocks are confused with a motor problem and delay the recovery

process. The Engineer must be fully aware of the motors start and stop permissives prior to

troubleshooting the motor circuit.

Process interlock trips are varied and depend on the different systems in which motors areinstalled. Process interlocks can be associated with system pressure, temperature, level, or a

multitude of other parameters. When a motor trips or fails to start, the process interlocks

should be the first step of the troubleshooting process. Indications of all these parameters

should be readily available. An example of a process interlock that operates during normal

operation is a motor that trips after the pump that is driven by the motor fills a storage tank.

Although the motor tripped, the trip was an expected event, and no further investigation is

required.


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WORK AID 1: PROCEDURE AND ACCEPTABLE TEST VALUES (PERFORMEDDURING MOTOR MAINTENANCE AND COMPILED FROMSADP-P-113, NFPA 70B, AND ESTABLISHED ENGINEERING

PRACTICES) FOR DETERMINING WHETHER MOTORS AREFUNCTIONING PROPERLY

Use this Work Ai d to complete Exercise 1.

Procedure

Perform the following steps to determine if the motor is operating properly.

1. Temperature correct the insulation resistance values.

2. Compare the insulation resistance values to the minimum acceptable insulationresistance values and to the previously measured insulation resistance values to

determine whether the current insulation resistance values are acceptable.

3. Calculate the polarization index (PI) and compare this PI to the minimum acceptable

PI to determine whether the current value is acceptable.

4. Compare the current vibration level measurements to the maximum allowable

vibration levels to determine whether the current motor vibration levels are acceptable.

5. Review the narrative portion of the Motor Maintenance Record to determine whether

the motor has other discrepancies that require corrective action.

Technical Requirements

Insulation Resistance Test - If IR is below the minimum acceptable level, the motor insulation

should be cleaned and dried.

The minimum acceptable insulation resistance value is determined from the following

equation:

RM = 1 megohm per kV of motor rated voltage plus 1 megohm

where: RM = Minimum insulation resistance in megohms at 50oC

kV = Rated voltage of the motor in kilovolts

Any rapid drop in the IR value, even if the IR is still above the minimum value, is considered

unacceptable.


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Polar ization Index

Minimum acceptable polarization index - 2:

Temperature Correction of IR

Use the following equation to temperature correct insulation resistance values:

RC= KTx RT

where: R C = Insulation resistance in megohms, corrected to 40oC

RT = Measured insulation resistance, in megohms, at winding temperature T

KT = Insulation resistance temperature correction factor

To find KT, use Figure 14, Insulation Resistance Variation with Temperature.


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Insulation Resistance Variation with TemperatureFigure 14


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Vibration Level Measurement

The maximum allowable vibration levels for motors with seismic velocity transducers is 4.6

mm/s (0.18 in/s) zero to peak.

The maximum allowable vibration levels for horizontal motors with proximity probes are as

follows:

3600 rpm - 2 mils

1800 rpm - 2.5 mils

1200 rpm - 3 mils

or less

If the maximum vibration level is exceeded, the cause should be investigated and should be

corrected.


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Troubleshooting Chart for Common Motor Problems


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anti friction bearing A bearing that employs an assembly of balls or rollers forrotation

babbitt Soft metallic lining material of a sleeve bearing.

bearing race The portion of an antifriction bearing that is connected to theshaft or bearing housing and that allows the ball bearing to

rotate.

corrective maintenance The maintenance that is carried out after a failure has occurred.This maintenance is intended to restore an item to a state in

which it can perform its required function.

endplay The amount by which the shaft of a motor can move in the axial

direction.

freeplay The amount by which the shaft of a motor can move in the radialdirection.

gs Acceleration that is due to the force of gravity.

Insulation Resistance (IR) The resistance that is offered by an insulation to the flow ofcurrent that results from an impressed direct voltage.

Polarization Index (PI) The ratio of the ten-minute insulation resistance measurement to

the one-minute insulation resistance measurement.

preventive maintenance The maintenance that is intended to prevent or to reduce theprobability of failure or the performance degradation of an item.

This maintenance is carried out at predetermined intervals,

according to prescribed criteria.

resistance temperature A temperature monitoring device that works on the principle ofa change in resistance as the temperature changes.

service factor (SF) A multiplier that, when applied to the rated power, indicates thepermissible power loads that can be carried by a motor.

sleeve bearing A bearing with a cylindrical inner surface in which the journal ofa rotor shaft rotates


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ADDENDUM

Topographic Map of McCamey North, Texas

Topographic Map of Mc Elroy Ranch, Texas

Topographic Map of Tatum, New Mexico - Texas

Design Basis Scoping Paper

Directing the o & m of Motors

Documents

Transcript of Directing the o & m of Motors