Section 13 — Electrical

Induction Motor Repair

IPE Engineering Practice IPE-EP-13-23-1

Document number: IPE-EP-13-23-1 · Section: 13 — Electrical

Table 3 Shaft Vibration Limits Relative to Bearing Housing Using Noncontact Vibration Probes

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SCOPE

• This practice covers the requirements for the inspection, repair, and/or refurbishing of integral horsepower (HP), medium voltage, AC polyphase induction motors above 200 HP, and integral horsepower AC polyphase induction motors below 600 VAC, 250 HP or less NEMA frame motors.
• This Practice is appropriate for inquiry or attachment to a service purchase document.
• This Practice provides general information and deviation per EP 1–1–3 is not required.
• If other methods or types of work than those outlined in this Practice are recommended by the Contractor, the Contractor is encouraged to offer these to the Owner for consideration. The recommendation should include complete technical support, (analysis for the recommendation against that given or omitted in this Practice) and the cost impact for the recommendation.

2.0 REFERENCES

The latest edition of the following standards and publications are referred to herein.

STANDARDS AND PUBLICATIONS

STANDARDS AND PUBLICATIONS (CONT.)

DEFINITIONS

• Contractor – Company or business that agrees to furnish materials or perform specified services at a specified price and/or rate to the Owner.
• Explosion Proof Motors – Motors for use in Class I or II, Division I classified locations as defined by the National Electrical Code shall comply with UL 674 and bear the UL listing mark.
• Inspector – A Inflection Point Engineering, LLC appointed engineer or inspector.
• Manufacturer – The recipient of a direct or indirect purchase order for materials and/or equipment. In this context, a direct order is one issued to a Manufacturer by a Contractor or the Owner. An indirect order is one issued to a Manufacturer by a vendor (recipient of a direct order) for materials, fabricated components, or subassemblies.
• Owner – Inflection Point Engineering, LLC.
• Owner’s Engineer – A Inflection Point Engineering, LLC appointed engineer.
• Purchaser – The party placing a direct purchase order. The Purchaser is the Owner’s designated representative.

DAMAGE APPRAISAL

• General
• The status of the motor as a result of inspection and testing shall be made by the repair facility for the Owner’s review. This shall include, but not be limited to, the requirements of this Practice.
• Additional information, testing or procedures may be necessary to determine a motor’s deficiencies or to support a recommendation. These could include:
• Pre–repair photographs.
• Pre–repair load (Dynamometer) testing of a motor to verify vibration under load. This type of complex, costly testing shall only be done with the approval of the Owner.
• The Contractor shall not initiate any repairs without approval of the Owner.
• The depth of inspection for damage appraisal may not require a complete analysis/testing as outlined in this Practice because of obvious excessive damage. For this situation the Contractor should contact the Owner for guidance to continue with further inspection/testing.

• The Contractor shall be responsible for recording all inspection and testing information as required for each such item in this Practice. The Contractor may use their forms after review and approval by the Owner.
• Prior to proceeding with any repair work, the Contractor shall provide a detailed estimate of cost to repair/refurbish and a schedule for job progress and date of completion.
• Incoming Inspection and Testing
• Incoming initial inspection shall include but not be limited to:
• Record any observed physical damage.
• Verify that the shaft rotates freely.
• Record all nameplate data.
• Inspect the shaft and record condition and any specific problems.
• Inspect for lubrication leaks.
• Verify the bearings are lubricated.
• Incoming Testing

The following tests shall be performed as part of the incoming inspection and as part of the initial motor disassembly (Review this section prior to disassembly). The testing and order of disassembly shall be such as to aid in determining the motor quality and required repairs. A running test shall only be performed if in the judgment of the Contractor this is required and can be done without damage to the motor or the Contractor. Note: The tests below are not in any particular order of required performance. Specific information on testing is covered in Section

6.0 of this Practice. The incoming testing shall include but not be limited to:

• Perform an insulation and resistance test of the stator windings (paragraph 6.1.1 and 6.1.14).
• Perform a Polarization Index/ Dielectric Absorption (PI) of the stator windings (paragraph 6.1.2).
• Perform a DC high–potential test to ground (paragraph 6.1.4).
• Verify the continuity of the stator windings and turn–to–turn insulation quality via a surge comparison test with the rotor removed (paragraph 6.1.5).
• Perform tests on the rotor to check for loose rotor bars or bar discontinuities (paragraph 6.1.3).
• Perform a core loss test (paragraph 6.1.11). Note: This test is not required for motors only having bearings replaced. This test required as part of motor refurbishing, etc.
• Disassembly
• All damage or special re–assembly requirements shall be noted/documented in writing.
• Before any disassembly is begun, parts shall be marked (e.g. bearing brackets, fan orientation, etc.).
• Brackets and bearings (seals etc.) shall be identified/marked in pairs.
• Any wiring should be recorded and identified/tagged.
• Prior to removing the coupling (if attached) or other shaft–mounted components, measure and record their position with respect to the end of the shaft.
• Critical components shall be match marked for reassemble (e.g. bearing brackets, etc.).
• Disassembly Inspection/Verification

• Check the fan for damage and cracks.
• Check the fan shrouds or covers for cracks and serviceability.
• Visually check for evidence of rubbing (e.g. fan, fan shrouds/cover, seals, stator, rotor).
• Inspect the bearing grease or oil for serviceability, water or other foreign matter.
• Inspect the condition of ball or roller bearing housing or cartridges (wear, grooving, seal fits, fretting, etc.) or sleeve bearings, rings and housing.
• Check the tightness of the core on the shaft and stator to frame.
• Inspect the frame, end bells and bearing brackets for cracks and excessive corrosion.
• Inspect the shaft to include the following and record any defects:
• Keyways
• Bearing area (journal)
• Worn fits
• Shaft straightness
• Inspect the rotor for broken bars, arcing, cracking etc. The defective areas shall be marked/identified and recorded on the inspection report Data Sheets EP13–23–1DS.
• Bearing and bracket fits shall be measured and recorded.
• Shaft runout (mechanical) shall be measured and recorded.
• Inspection of Stator Leads
• Stator leads shall be examined for damage to the insulation and/or missing wire strands. Leads with insulation damage, wire damage or cut excessively short shall be replaced. See Section

5.4 for stator lead requirements.

• Stator leads that are determined to be serviceable shall be marked/tagged with easy to read sleeve markers or tags that have sufficient durability to withstand handling/terminating. Single layer type tape labels are not suitable. Sleeve labels shall be loose enough to be moved above termination taping.

MOTOR RECONDITIONING/REFURBISHING

• General
• Motors shall be reconditioned when authorized by the Owner in accordance with this Practice, EP13–23–1DS and Owner approved purchase order documents. If during the process of reconditioning a major defect is discovered, all work shall be suspended until directed to continue by the Owner.
• Motor refurbishing/reconditioning shall include, but not be limited to:
• Incoming inspection and testing per Section 4.0 and Section 6.0.
• Stator reconditioning per paragraphs 5.3.1, 5.3.2 and 5.5.
• Bearing replacement per paragraphs 5.2.1, 5.2.2, and 5.6.
• Mechanical reconditioning per Sections 5.2, 5.6, 5.7 5.8, 5.10 and 5.11.
• Balancing per paragraph 5.2.4.
• Final testing per paragraph 6.2.
• Mechanical Reconditioning
• Anti–Friction Bearings
• Unless directed otherwise on the Data Sheet (EP13–23–1DS) all anti–friction bearings shall be replaced with new bearings. Replacement bearings:

• Shall be new and free from rust and dirt.
• Shall have ball and roller bearing manufacturing tolerance limits in accordance with ANSI/AFBMA 20–1987, Table 4 (ABEC1–RBEC1).
• Shall have AFBMA C/3 clearances for ball bearings used in horizontal motors.
• Shall have the highest L10 life hour rating possible without having to re–machine for fit. In general, minimum hour life acceptable is 25,000 hours unadjusted, with the preferred value of 100,000 hours unadjusted at maximum service factor and 40°C ambient temperature.
• Shall not have filling slots.
• All damaged, unserviceable shields and seals shall be replaced with types that are exact equivalent to the original equipment and compatible with the installed bearings, unless specified otherwise by the Owner.
• The bearing housing internal diameter shall be measured for roundness. The Owner shall be notified if the housing is greater than 0.0005 inch out of round, or if the fit area is otherwise damaged.
• When approved by the Owner, the bearing housings for anti–friction bearings that have an enlarged bore caused by vibration or breakdowns may be repaired by having the housing fits repaired by sleeving as follows:
• Remove enough metal to allow a mild steel sleeve to be inserted. The sleeve must have a wall thickness of at least 1/8 to 3/16 inches.
• Finish the ID to the proper diameter.
• The OD is to be an interference fit in the overbored housing. Suggest 0.001 to 0.0015 inches per diametrical inch.
• The sleeve inboard OD edge shall be chamfered, to reduce galling while being pressed into place.
• Replicate any existing lubricant entry and exit holes etc. in the sleeve.
• Grease fittings and reliefs
• All motors shall have grease fill extensions and Zirk fittings added, if not already supplied.
• All motors shall have grease relief extensions with low pressure relief devices added, if not already supplied. The extension shall reach low enough to be observable by the Owner.
• Sealed non–regreasable bearings
• Motors with sealed bearings shall have bearings replaced with sealed bearings rated L10, 100,000 hours minimum for direct coupled application, unless specified otherwise by the Owner.
• Insure that any regrease ports on the bearing brackets are sealed with appropriate threaded plugs.
• Insure that the shaft journals, end bells and all re–grease and grease relief fittings and extensions are cleaned and free of all grease/dirt and rust.
• Replacement bearings shall only be those manufactured by SKF, FAG, MRC or FAFNIR.
• All sealed and pre–greased double shielded bearings, when required, shall be pre–greased with Chevron SR1–1 polyurea based grease; the grease shall be fresh, i.e., have been pre–greased less than three years prior to date of installation.
• Sleeve Bearings/Seals/Rings

Note: Sleeve bearings shall only be replaced when determined to be unserviceable/repairable and with specific approval by the Owner.

• Upon removal of the sleeve bearings, the Contractor shall inspect, measure and record bearing housing internal condition and diameter for out of round and taper. The Owner shall be notified if out of round exceeds 0.001 inches.
• The taper or inboard and outboard bearing shells shall be checked for proper fit in the bearing housing. Bearing shell to housing fits shall be –0.001 (L) to 0.002 (T).
• Measuring sleeve bearing babbitt fits (recommended method). This procedure details the recommended method for measuring sleeve bearing, to bearing housing fits.
• Remove both bearing housing upper half and bearing upper half. Clean and de–burr all bearing housing and bearing machined surfaces by stoning.
• Place a strip of 0.005 in. thickness shim on each of the bearing housing lower half splits. Install bearing upper half.
• Place a strip of 0.001–0.006 in. thickness Plasti–Gage between bearing and bearing housing upper half. Install bearing housing upper half. Bolt up bearing housing to crush Plasti–Gage.
• Remove bearing housing upper half and determine Plasti–Gage thickness.
• If Plasti–Gage thickness is greater than shim thickness, bearing is loose in bearing housing by difference in Plasti–Gage and shim thicknesses.
• If Plasti–Gage thickness is less than shim thickness, bearing is crushed in bearing housing by difference in Plasti–Gage and shim thicknesses.
• Normal practice is to set sleeve bearing, to bearing housing fits shall be –0.001 in (L) to

+0.002 (T).

• Sleeve bearing contact check. This procedure details the recommended method for checking sleeve bearing babbitt contact.
• Measure bearing housing oil seal labyrinths for correct clearance.
• Remove bearing housing upper half and bearing upper half. Clean bearing journals of oil.
• With sleeve bearing lower half installed, rub a thin film of Dykem Blue on shaft bearing journal. The film should be about 1/2 in. wide and as long as sleeve bearing length.
• Rotate shaft one full turn and clean excess Blue from the bearing journal.
• Lift shaft up enough to roll out sleeve bearing lower half for inspection (without allowing bearing to touch shaft). Check Blue contact on bearing babbitt. Contact should be 90% or better on load carrying portion of bearing. If contact is less than 90% correct cause of misalignment.
• Repeat babbitt Blue contact check until 90% or more contact is achieved.
• When babbitt contact is correct. Install sleeve bearing upper half and measure bearing clearance, per 5.2.2.5.
• Babbitt bearing shaft fit. This procedure details the recommended method for checking clearances between bearing and shaft.
• Remove bearing housing upper half. Clean shaft and top bearing contact surface.
• Place a strip of 0.004–0.009 inch thickness Plasti–Gage between the shaft bearing journal and bearing upper half. Reinstall the bearing housing upper half and tighten to crush the Plasti–Gage.
• Remove bearing housing upper half and determine Plasti–Gage thickness.

• Acceptable Babbitt bearing clearances are 0.0015 to 0.002 inch per inch shaft diameter.
• Bearings that exhibit no wiping or excessive shell to housing clearance and that are in compliance with 5.2.2.1 to 5.2.2.5 (including a bearing to shaft clearance between 0.0015 inches to 0.0020 inches per inch of shaft diameter +0.001 inches) shall be reinstalled.
• Bearings with excessively distorted shells shall be replaced.
• Re–Babbitting
• Shells are to be thoroughly degreased, fluxed and tinned before re–babbitting. New re– babbitting shall be by the centrifugal or “spin casting” process. The repairing of a sleeve bearing by puddling is unacceptable.
• Adhesion of Babbitt to bearing shell shall be at least 80% overall and 100% along the mating surface of a split bearing, as verified by ultrasound testing using the basic methods of ASTM E114.
• Babbitt alloy shall be a high–tin, either ASTM B23 No. 2 or No. 3 containing no lead.
• After finish machining of the replacement babbitt, horizontal split sleeve bearings shall be fitted to the shaft journals by scraping/blueing as outlined in 5.2.2 and 5.2.3 of this Practice.
• Oil distribution slots and oil distribution grooves shall be reproduced as original.
• Seals
• Labyrinth type seals must have the teeth pointed as original. Oversize seals shall be replaced or repaired by one of the following methods.
• Machine out tooth area and make a replaceable insert.
• Weld tips of teeth and re–machine points.
• Machine a complete new seal.
• Note: Seals shall not be repaired by metal, spraying to build up teeth.
• Oil drain backholes shall be adequate and free of blockage.
• Oil Rings
• Bearing oil rings shall be inspected for roundness and excessive inside surface wear.
• Removable type oil rings are to be checked to insure the locking devices are in good condition and all screws are tight.
• Anti–rotation pins shall be checked for looseness and correct length.
• Shaft
• The Contractor shall inspect the shaft for cracks, straightness, journal wear or scoring and record the inspection results along with serviceability recommendations.
• If required, the shaft shall be straightened by either peening or heating. The shaft shall not be undercut, unless approved in writing by the Owner. After straightening, the region of the bend/repair shall be NDT (NDT method shall require approval by the Owner) inspected for crack propagation. Final shaft runout shall be less than 0.001 TIR maximum.
• If the keyway is worn, the keyway shall be recut to dimensions approved by the Owner. Unless directed otherwise, keyways that are repaired shall have their dimensional tolerances in compliance with the limits given in NEMA MG–1 Section 4.15. The bottom corners of all keyways shall have a radii of at least one–eight of the keyway depth to reduce stress concentrations.

• Sleeve bearing journals
• If sleeve bearing journal surfaces require reconditioning, the Contractor shall contact the Owner and receive authorization for the work procedure and to perform the reconditioning.
• The Contractor shall recondition sleeve bearing journals by chrome plating only. Chrome plating shall not be deposited over metal sprayed surfaces.
• The Owner shall be contacted if the journal area to be reconditioned is metal sprayed or if over 0.060 diameter inches are required for journal reconditioning. See paragraphs 5.2.2 and 5.2.3 for proper journal to bearing clearance.
• Rotor Inspection and Balancing
• If opens, cracks, overheating, bar melting or other major damage is found on an aluminum cast rotor it shall not be repaired. Approval for replacement shall be by the Owner. Repair of fabricated rotors shall be by written authorization of the Owner after review and approval of the Contractor’s written repair procedure.
• Rotor serviceability must be checked and acceptable prior to decisions on motor refurbishing.
• The rotor shall be steam cleaned. Blast cleaning shall not be used without approval of the Owner.
• Rotor outer diameter shall be measured and recorded for concentricity. The Owner shall be notified if runout exceeds 0.003 inch total indicated reading (runout).
• Using a dynamic precision balancing machine, the rotor shall be balanced to 4 W/N oz. inch per Plane, unstacked using fully crowned half keyway in exposed keyways.

Where: W= Journal Static weight Load ( Pounds )

N = Maximum Continuous Running Speed (RPM)

• The rotor/shaft assembly should be dynamically balanced at the largest fraction of maximum operating speed possible on the repair center precision balancing machine.
• The use of solder or similar deposits for balancing is not acceptable. The use of balance washers is acceptable provided they are corrosion resistant stainless steel, zinc plated or Owner approved equal. Parent metal removed to achieve dynamic or static balance shall be removed so as not to affect structural strength of the rotating element nor reduce cooling (reduction of cooling fins is not permitted).
• After a rotor is balanced a residual unbalance determination test shall be performed to verify the quality of the balance and accuracy of the balance machine. The residual unbalance determination shall follow the procedure in Appendix C of API Standard 541, Third Edition, April 1995.
• Repair of Fabricated Rotors
• This procedure does not include repair of floating cage rotor design, such as that used by the Reliance Electric Company. Floating cage rotors shall only be repaired using a Reliance Electric Company approved procedure and written authorization from the Owner.

• All rotor repairs shall require a complete written work procedure from the Contractor that is reviewed and approved in writing by the Owner.
• The following are specific requirements for fabricated rotor repair.
• Rotor bar fitup: Replacement bars shall meet the following criteria.
• Electrical conductivity and chemical composition of the replacement bars shall be the same as the original bars. If bars are not supplied as exact replacement parts by the original motor Manufacturer, the repair center shall furnish the Owner with a supplier’s “Certificate of Compliance” defining the metallurgy of the bar material, and confirming that it is of the same metallurgy as the originally manufactured bar.
• Cross–sectional dimensions shall be equal to the original bar. Should it be necessary to machine finished bars from some larger cross–section, the finished dimensions shall be within plus or minus 0.002 inch of the original values.
• Overall bar length shall not be reduced, with or without compensating shift in end ring position, without written approval from the Owner.
• No aluminum bar shall be replaced by a copper bar of smaller cross–section or different shape.
• In some rotors, bars of two or more different copper alloys may be intermingled in some pattern. For example, every other slot may contain a copper bar, the alternate bars being brass. Any such pattern shall be repeated exactly when any bars are replaced.
• All bars shall be tight in their slots in both directions; widthwise or side to side, and top to bottom. Tightness shall be considered adequate if any bar can be driven back and forth in the slot by manual application of hammer blows to one end, but cannot be moved “by hand” alone. With copper or copper alloy bars, this result may be achieved in either both of two ways, depending upon the slot design, bar shape, and bar material.
• Slight interference or “scraping” between bar and slot, so that the bar can be installed only by “driving it in”.
• Intentional looseness in width in the design fitup between bar and slot (typically 0.015 to 0.020 inch), so the bar is placed in the slot by hand, then tightened by “swaging” or displacing bar metal through indentation in the top surface of the bar at various points along its length.
• If the original bar was installed with shims the replacement bar shall also be shimmed using shims of the same metallurgy, thickness and dimensions.
• Only the first method given in the first bullet above shall be used with aluminum bars.
• Vacuum Pressure Impregnation (VPI) treatment or other resin or varnish dipping or coating processes shall not be used to make rotor bars tight in slots.
• Rotor End Ring Attachment
• If new rings are needed, and are not obtained directly from the original motor Manufacturer, the material proposed and the method of fabrication shall be reviewed by the Owner before work is done. The cross–sectional area of the finished ring, after all machining, shall match the original construction, unless changes are approved by the Owner to suit a change in material conductivity.
• Copper or copper alloy bars and end rings shall be joined only by brazing. The methods and materials used shall completely fill the joint between abutting surfaces of the parts being joined. Bars shall be in sufficiently close contact with rings that feeler gages placed between shall not exceed 0.010 inch thickness at any point.

• The brazing process shall create a complete fillet throughout the visible circumference of each joint. Procedures recommended by the original motor Manufacturer shall be followed in the brazing process. These may include the nature of the torch flame (which shall be neutral or slightly oxidizing unless otherwise specified), the sequence of bar brazing around the periphery of the rotor, the nature of the brazing alloy used (which shall be silver–based rather than phosphorous–based), and any requirements associated with uniform heating of the end ring to avoid stress.
• For aluminum fabricated rotors, bars and rings shall be joined by metal inert gas (MIG) welding. Sufficient passes shall be made to build up a weld cross–section equal to that originally present. Preheating or “soaking” temperature, and the welding wire composition, shall be as prescribed by the motor Manufacturer. The welding procedure shall be submitted to the Owner for review prior to any work.
• Steel “retention caps” or “shrink rings”, often applied to large 2 pole rotors, shall be non– magnetic stainless steel. No other material (including plastic banding) shall be substituted. If the repair center can show written recommendation from the original motor Manufacturer for a change in material, dimensions, or fitup of these rings, such change shall be considered by the Owner, but is not to be made without written approval. In any event, unless the rings are supplied as exact replacement parts by the original motor Manufacturer, the repair center shall furnish the Owner with a “Certificate of Compliance” defining the ring metallurgy.
• Stator Reconditioning
• General

After all initial inspection and testing is complete and the rotor and bearings are declared serviceable, stator reconditioning may proceed as detailed below. Stator reconditioning shall only be applicable to stators that exhibit satisfactory serviceability without the need for a re– wind.

• Stator Reconditioning Process
• The stator, housing and end bells shall be steam cleaned with non–polar, non–ionic detergents and solvents that are compatible with the stator insulation (including slot liners and caps), the enamel on the stator iron and any paint on the surfaces of the motor. The temperature of the cleaning solution shall not exceed 250°F.
• The stator shall be dried out in a temperature controlled oven where the winding temperature does not exceed 80ºC as measured by thermometer.
• After cleaning and drying out, but before varnish coating, the stator insulation resistance to ground shall be tested (paragraph 6.1.1) and compared to the original incoming inspection tests. In no case shall the insulation resistance be less than 2.5 Megohms, for a one minute test with 500 VDC applied. The polarization index (paragraph 6.1.2) shall be verified prior to varnish coating and shall be greater than 2.0. Polarization Index’s (PI) less than 2.0 shall require notification and approval of the Owner before proceeding with varnish coating.
• The stator may be reheated in an attempt to improve the resistance to ground or PI, however, the temperature constraint of 80ºC still must be followed.

• Motors with acceptable Insulation Resistance and PI shall be given a surge comparison test prior to the dip and bake process.
• Inspect all bracing wedges, ties and slot sticks, etc. for damage. Repair/replace damaged materials using the techniques and materials outlined in the applicable sections in paragraph 5.4 of this Practice.
• After acceptable insulation resistance to ground, PI, and surge comparison tests are achieved the stator shall be dipped in, or sprayed with, (spray only for very large frame medium voltage motors) a high performance polyester resin or solventless epoxy and baked. The Contractor shall insure that the new material used is compatible with the existing varnish/epoxy.
• The Contractor shall inform the Owner as to the type of polyester or solventless epoxy to be used and obtain the Owners approval of the material prior to application.
• Typically the bake temperature shall be 300°F or less for a minimum of 8 hours. The bake temperature and time may vary depending on the polyester resin or solventless epoxy manufacturer’s recommendation. However, the bake temperature must not exceed the temperature limits of the stator lamination insulation thermal limit.
• Stator Rewind

If the stator winding is determined to be unserviceable and the other critical motor parts serviceable, and in the Contractor’s judgment a motor rewind is justified, the motor may be rewound only if approved in writing by the Owner.

• Winding Removal (Form Wound and Random Wound)
• Form wound stator windings shall be removed by either oven burn off or cold (mechanical) stripping methods. The Contractor may recommend alternate methods for review and approval by the Owner.
• Oven Burn off Method
• Stators with iron or steel frames may have windings burned out in a temperature controlled, uniformly heated oven. Oven temperature shall be controlled to limit stator core lamination temperature to 650°F or less depending on the core lamination insulation material.
• Motors may have laminations that require lower than 650°F to limit damage to lamination insulation (coating) and/or to avoid impairment of magnetic qualities of the core.
• Caution shall be exercised when burning out windings because the core temperature can exceed the oven temperature (thermal runaway). This is especially true of some epoxy insulations that will release large amounts of heat as they breakdown. For this reason, bake ovens shall have automatic temperature control that is responsive to a monitor measuring lamination temperature as will as oven temperature.
• Bake ovens shall have calibrated temperature recorders that measure and record both the oven temperature and the stator lamination temperature.
• The bake oven shall be equipped with some method to control thermal runaway (see paragraph 5.4.1.2.3 above). Acceptable thermal runaway suppression systems include use of steam or water injection.
• The use of hand held torches or direct flame is not acceptable.
• The stator core shall be vertically positioned in the burn out oven.
• After burnout the core and frame shall be allowed to cool by natural convection without forced air.

• Mechanical (Cold Strip) Method
• Extra care should be taken to insure lamination separation does not occur while pulling out windings.
• When heat is applied to soften the insulation (not burnout), the flame must not be allowed to impinge on the motor stator iron, frame or winding.
• Post Winding Removal, Cleanup, Inspection and Testing
• The stator slots shall be clean of old insulation material. If “blast” cleaning methods are used, soft abrasives shall be used to avoid peening of the iron laminations. No Alkali or Acid liquids shall be used.
• After slot cleaning the core shall be inspected and a core loss test performed. All defective/damaged areas shall be identified and recorded on test forms.
• Stator Lamination Repair
• Damaged laminations shall be repaired only after approval of the Owner based on a review of the damage amount and assessment of reparability by the Contractor.
• Actual repair technique shall be based on the Contractor’s experience and judgment as to which repair method will eliminate core hot spots.
• Repair method one is for lamination edge fusion that generally occurs when the rotor has wiped the stator. The fused laminations may be vibrated apart with an air hammer. While vibrating the laminations spray a high quality insulating varnish in the damaged area. The varnish should penetrate the air gaps caused by the vibration and re–insulate the laminations. An alternate method is to separate the laminations with restoration of the inter–laminar insulation via the insertion of varnished mica splittings.
• Method two covers slot melting caused by winding faults or the stator has suffered minor rotor wipe and where the total damage area is less than 10% of the total core area. To repair these areas, use a small high speed grinder to grind away fused metal until a definition of core laminations can be seen. Do not grind an area that will reduce the mechanical integrity of the slot.
• Method three covers lamination damage in excess of 10% of core–surface area or areas repaired via method two still exhibiting hot spots. If the damaged area is extensive in size and depth and/or cannot be repaired by methods one and two above then partial or total re–stacking of the core area must be considered. The Owner shall be informed of the need for major core repair and must authorize this type of repair before the Contractor proceeds with this type of core repair. The repair will generally consist of replacing and/or repairing individual core laminations. Repair can be accomplished by hammering and sanding away damaged areas and re–insulating the entire lamination with a high quality organic insulation material rated greater than 300ºC.
• After all repairs are completed, a core loss test shall be performed to verify the quality of repairs. See Section 6.0 of this Practice for details on core loss test procedures and acceptance criteria.
• Replacement Coil Installation (Random Wound Stators)

• Prior to making coils and starting the rewind, the stator core shall be tested, repaired and declared serviceable per the applicable testing and acceptance criteria in Section 6.0 and the recommended repair methods detailed in paragraph 5.4.2.
• Inspect the core slots for cleanliness and to insure they are free of burrs and sharp edges before rewinding.
• All materials in the insulation system shall be compatible and, as a minimum, suitable for operation at Class F, 155ºC temperature per NEMA MG–1.
• Magnet wire used in the coils shall be copper, insulated with a heavy enamel build and rated 180ºC based on testing per ASTM 2307. The wire shall have the proper current carrying capability equal to or greater than the original Manufacturer’s specifications.
• All slots are to be insulated as a minimum with Class F rated slot liners, midsticks and topsticks. The recommended minimum slot liner thickness is 0.015 inches.
• The ends of the slot liners shall be extended and reinforced.
• Sleeving used on jumpers, stubs and connections shall be acrylic (FA–1 Grade) coated fiberglass or equivalent motor rated volts or higher.
• Stator winding phases shall be separated with phase paper, dacron/mylar or nomex phase paper.
• Phase insulation in the winding end turns shall be resin treated class cloth or equivalent to provide positive separation between phases in the event of varnish degradation caused by excessive temperatures above the motor rating.
• Wedges shall be Nomex, Class H (180ºC).
• Tie cord used to secure the wires in the end turns shall be primarily glass fiber material with adequate thermal and physical capability. End turns shall be fully compacted such that no loose wires are present. Both ends of the winding shall be laced or tied in the end turn region such that each coil is secured at some point to one or more others.
• All connections shall be brazed or welded with materials that will be mechanically and electrically strong enough to withstand normal operating conditions. Any fluxes, inhibitors or other compounds employed during installation shall be neutralized.
• All connections and splices shall be so constructed as to have a cross–sectional resistance equal to or less than the conductors of the winding.
• Prior to stator winding dip and bake or VPI process, the stator winding shall be given a surge comparison test to verify correctness of winding connections and winding turn–to–turn insulation quality. This test result shall be recorded on the motor test Data Sheets.
• The completed stator shall be given, as a minimum, two complete dip and bake or VPI cycles with a high performance polyester resin or solventless epoxy.

• VPI processed motors shall have all lead and accessory cables/wires suitably treated/covered as necessary prior to impregnation so that resin does not wick into the insulation and or cable strands such as to solidify them during cure and also cause a reduction in insulation stability/value.
• Replacement Coil Installation (Form Wound Stators)
• Prior to making coils and starting the rewind, the stator core shall be tested, repaired and declared serviceable per the applicable testing and acceptance criteria in Section 6.0 and recommended repair methods detailed in Paragraph 5.4.2.
• Inspect the core slots for cleanliness and to insure they are free of burrs and sharp edges before rewinding.
• All materials in the insulation system shall be compatible and as a minimum suitable for operation at Class F, 155ºC temperature per NEMA MG–1, regardless of whether the original motor design was made for Class “A”, Class “B” or Class “F”.
• The copper conductors in the replacement form wound coil shall have circular mills of copper equal to or greater than the original winding.
• Wire sizes, turns per coil, coil pitch/span and winding connections (including lead cable/bus arrangement) shall be as originally specified and used by the motor Manufacturer, unless specified otherwise on the Data Sheet or purchase order.
• Upgrades to the original winding system, including increase to Class F insulation, shall include necessary upgrades in the blocking, tying and surge ring capability. The upgrade may also influence heat dissipation in winding slots and end turns. All these and other issues with a winding upgrade shall be evaluated by the Contractor and presented to the Owner for written approval before proceeding with an upgrade rewind.
• Strand insulation/turn insulation

Note: Tapes utilizing one or more layers of polyethyelen terephthalate (PET) are unacceptable.

• Strand insulation shall be a minimum of 1/2 lap layer of double dacron–glass wrap with either epoxy or polyester resin applied over copper windings with either Class “F” wire enamel or over windings with Kapton insulation as required by machine voltage, speed and size. The type of strand insulation is influenced by the surge or high frequency test requirement.
• Turn insulation of 1/2 lap 5 mil (minimum) mica tape shall be used on stators with a core length greater than 25 inches. Extra turn–to–turn insulation, conducting semi–conducting paints or tapes, and phase to phase insulation shall be applied as specified by the motor Manufacturer.
• Glass or polyester glass armor tape shall be put on the outside of the coil for mechanical protection.
• Each completed/insulated coil shall be high potential tested to ground to test levels recommended by IEEE Standard 95, prior to coil insertion into the stator core.
• Ground Wall Insulation

Note: Tapes utilizing one or more layers of polyethylene terephathalate (PET) are unacceptable.

• Ground wall (phase to ground) insulations shall be glass or dacron backed mica paper, or an equivalent glass or dacron backed mica–flake tape. The number of layers of tape and insulation thickness shall be determined from the voltage, speed and size of the motor (see Table 1).
• When a slot wrapper is used it shall be of the same type materials specified in paragraph

5.4.5.1 above, and is to be scarfed or tapered to permit the joining of end turn insulation to the cell portion of the coil in a smooth manner. Cell wrappers are not permitted on any coil with a core length exceeding 25 inches, unless required by the motor Manufacturer.

• Connections
• All connections shall be brazed or welded with materials that will be mechanically strong enough to withstand normal operating conditions.
• All connections and splices shall be so constructed as to have a resistance equal to or less than the conductors of the winding.
• Any fluxes, inhibitors or other compounds that were employed shall be neutralized after using.
• All connections shall be completely sealed with full ground wall insulation or better. This shall include a 1/2 lap layer of 5 mil glass armor or dacron tape for all coil jumpers.
• Neutrals and jumpers will be sleeved with Class “F” or better glass reinforced sleeving or taped with mica/paper and glass woven tape.
• RTD’s and Coil Inertion
• Coils shall be inserted in slots with side filler, bottom and mid sticks as required for a tight fit. If a slot liner is used, it must be semi–conducting material, rated 5 KV and above.
• RTD’s shall be provided in the quantity and ohmic value approved by the Owner. Note: Verify with the Owner exactly what type and quantity of RTD’s to be used in the rewound stator and bearings.
• Surge Ring
• All machines rated over 500 HP are to be returned with surge rings even if not originally equipped.
• Nonconductive materials are preferred such as “B stage” glass rope laced to the coils.
• Lacings and ties are to be glass roping, tape or cord. All coils (coil head) are to be individually tied to the surge ring and to adjacent coils. Shrink tapes of dacron–glass blend are permitted.
• Tapes of 100% dacron are not permitted.
• When steel rings are used the following methods for insulating and tie down shall be used:
• All surge rings shall be completely insulated, including support arms, and taped with paper mica tape or Nomex–M and glass armor tape.
• The rings and supports will be built up with glass mat and padded with felt tape for maximum resin penetration.
• The entire ring structure will then be taped with woven glass armor tape.

• Follow the lacing/tie instructions in paragraph 5.4.8.2.1.
• Bracing, Blocking and Tying
• Stubs, coil heads, jumpers and neutrals must be lashed together.
• Wedges, fillers, blocking materials shall be suitable for Class “F” operation. Dacron felt saturated with resin is the preferred blocking method. Spacer/blocks cut from flat, pre–cured sheet material shall not be used.
• All coil heads must be blocked with felt. Depending on the head extension, one or two blocks may be used.
• The following is a list of acceptable (recommended) materials that should be used for rewinds for 2400 volt and 4160 volt motors.

• Replacement Coil Testing Pre–VPI
• Prior to impregnation/cure, before all intercoil connections are complete, perform megger, high potential and surge comparison tests to identify turn–to–turn faults, turn to core faults reversed coils or groups, etc. Correct any such winding defects before proceeding.
• When the stator coil is completed and ready for impregnation, take a one minute insulation resistant measurement with a 1000 VDC instrument. The reading shall be greater than 1 megohm per 1000 volts of nameplate, plus 1 megohm.
• VPI Treatment and Post VPI Coil Testing
• Stator windings shall be sealed using a vacuum pressure impregnation (VPI) system of the entire rewound stator, in a high performance polyester resin or solventless epoxy.
• Two complete VPI oven cure cycles shall be applied to the rewound stator core/coil.

• Note: The motor leads insulation and wire ends must be sealed to prevent the entrance of VPI resin/epoxy into the insulation and/or wire lead ends.
• In no case will a “green” winding be transported to another facility for VPI processing, without written authorization from the Owner.
• The Contractor shall maintain a procedure of not performing VPI on any stator that is not new or rewound. This is to reduce the possibility of contamination. If the Contractor does VPI on non– rewound motors, an independent lab analysis of the resin to be used on the Owner’s motor shall be supplied to the Owner showing that the resin is not contaminated prior to VPI treatment of any Owner motor.
• When the VPI/bake process is complete, the coil/core assembly shall be given the following tests: insulation resistance/PI, DC high potential test, and coil (winding) resistance test.
• Stator Lead Replacement
• Stator leads shall be replaced when determined to be unserviceable as part of refurbishing or stator coil re–wind.
• Stator lead wire shall be stranded, extra flexible copper wire sized to carry the full load current capacity of the motor rating including service factor.
• Leads shall have double crimp barrel type lugs specifically designed for extra flexible cable (belled end on lug). In no case shall more than one wire be installed in a single lug nor shall strands be removed to allow insertion into the lug. The wire size and type shall be compatible with the design of the lug.
• Stator lead wire shall have non–hygrospic, non–wicking insulation material with a minimum rating equivalent to that of Class “F” (the lead wire insulation shall have the same or higher temperature rating/capability as the overall temperature rating of the stator insulating system).
• Lead wire insulation shall be suitable for use in contact with oil and/or other typical petro– chemical substances. EPR or other rubber wire insulation must have an oil protective jacket such as PVC. Motors used with oil mist systems shall use teflon insulation or other insulation impervious to oil and oil additives.
• A motor lead epoxy seal (or equivalent sealing material/method) gasket shall be provided between the motor frame and the terminal box. The motor leads/frame seal shall be designed and installed to minimize moisture entrance into the motor and to prevent lead wire insulation damage.
• Motors with bus bar leads shall have the bar insulated. The recommended insulation shall be the appropriate voltage rated Raychem heat shrinkable insulation.
• Lubrication
• Anti–Friction Bearings
• Unless recommended otherwise on the Data Sheet, all motor anti–friction bearings (including double shielded and sealed bearings) shall be lubricated with Chevron SRI (NLGI2) or compatible equivalent.

• If bearings are to be re–used, all existing grease shall be removed from the bearing and bearing holder and re–packed with new grease.
• All motors with anti–friction bearings shall be run for a minimum of 15 minutes after greasing, with the grease drain open before replacing the grease relief hardware.
• Motors with bearings requiring oil lubrication shall have all oil drained, reservoirs and bearings cleaned and oil replaced with original Manufacturer’s specified oil.
• Sleeve Bearings
• All oil sumps, reservoirs, oil sight glasses, constant level oilers and oil piping shall be cleaned and inspected for serviceability.
• Teflon ribbon (tape) shall not be used as a seal agent.
• Replacement of oil lines, if required, shall be with stainless tubing or pipe only. Copper pipe tubing is not acceptable.
• Replace oil with new, clean oil with SUS rating recommended by the motor Manufacturer. The oil as a minimum shall be a good grade of turbine type oil, with rust, foam and oxidation inhibitors.
• Other Components and Final Assembly
• Conduit boxes and other mechanical parts shall be inspected for damage and repaired or replaced as required. Gaskets shall be replaced with materials suitable for the motors in– service petrochemical environment.
• Before assembly, all machine surfaces shall be inspected to assure that they are free of paint, sealant, varnish or other material that would prevent metal contact. Particular care must be given to assure insulating varnish/epoxy is cleaned from all machined fits and from the stator bore.
• All mounting surfaces must be clean and free of burrs and other materials.
• All hardware shall be of appropriate strength corrosion resistant stainless steel. All existing non–corrosion resistant steel hardware shall be replaced with stainless steel hardware. Note: NEMA motors may use corrosion resistant zinc plated hardware.
• All hardware shall be lubricated with an anti–sieze compound such as “Never–Seez” prior to installation.
• All tapped holes shall be completely free of sand, rust, paint etc. Broken screws or bolts shall be removed.
• Tapped holes shall be chased with a bottom tap to assure threads are clean and in good condition.
• Holes with threads stripped shall be repaired to original hole size and threaded.
• All damaged bolts, screws and studs shall be replaced.
• All assembled machined parts, especially machined fits, shall be drawn up evenly with the diagonal tightening method. All bolts and studs shall be tightened to the stress levels recognized as good practice or to the Manufacturer’s requirements, when available. Air wrenches shall not be used on assembly.

• Non–NEMA frame motor rotor alignment within the stator shall be checked by measuring and recording the rotor to stator air gap as detailed in paragraph 6.1.12 of this Practice.
• Sleeve bearing motor rotors shall have 1/2 + 1/16 inch total internal axial float, unless the original design dictated otherwise.
• Babbitted bearings shall be aligned for good journal to babbitt contact. Bearings shall be blued. Minimum contact areas shall be 90% of journal surface. See paragraph 5.2.2 of this Practice.
• UL Listed/Labeled “Explosion Proof” Motors
• Any repair of an “Explosion Proof” motor involving disassembly and re–assembly beyond opening the terminal box, regardless of whether or not specific parts are replaced, shall be performed only by a repair center authorized by Underwriters Laboratories to participate in the UL motor “repair and re–listing” program. Before the repaired motor is returned to the Owner, the original UL “explosion proof” listed mark or label shall be removed and replaced with a new one properly identifying the repair location and re–listing the motor as “Explosion Proof”.
• If the Contractor anticipates being unable to make the needed repairs because of parts identification or procedures that either UL or the motor Manufacturer cannot or will not supply, the Contractor shall so advise the Owner at the earliest possible time for a disposition decision by the Owner.
• Nameplates
• Original nameplates shall be used and only replaced when it is considered unreadable. If a new nameplate is required (e.g. motor re–rate, unreadable) it shall have as a minimum, all the information provided on the original nameplate (including the original motor Manufacturer name and model) and shall be made of stainless steel.
• Painting of nameplates will not be tolerated. Motors with painted nameplates will not be accepted and returned to the Contractor, at Contractor’s expense, for paint removal and nameplate refurbishing.
• If the nameplate is missing, the Contractor shall make a new nameplate using information provided by the Owner.
• Space Heaters
• Space heater wiring shall be inspected for serviceability. Wiring with insulation that is frayed, cracked, brittle or otherwise unserviceable shall be replaced. The replacement wire shall be stranded copper the same AWG as the existing wire and have XHHW, XHHW 2 or SIS insulation.
• Space heaters shall be checked for serviceability. All damaged, defective space heaters shall be replaced with heaters having the exact ratings and surface temperatures as the existing heaters. Space heater surface temperature ratings are critical since most of the motors are installed in classified areas.
• Painting
• The Contractor shall clean all painted surfaces to remove grease and dirt as preparation for painting.
• All rusted and bare metal surfaces requiring paint shall be cleaned and prime painted.

• All exterior and interior frame metal, including accessory box interiors shall be finish painted with a quality severe duty epoxy paint of the Contractor’s standard color, unless specified otherwise on the Data Sheet.
• Paint color shall be as specified by the Owner’s Engineer.

TESTING

• General

The following are descriptions of specific tests, test methods and acceptance criteria as referred to and/or referenced in this Practice.

• Insulation Resistance Testing

Insulation resistance to ground testing shall be performed in accordance with the latest issue of IEEE 43. The test voltage shall be 1000 VDC (500 VDC for NEMA motors), with the test voltage applied for one minute prior to taking a reading. The minimum acceptable resistance to ground value is 2.0 Megohms for old windings and 10.0 Megohms for new windings. All readings shall be corrected to 40ºC. Motors that do not meet the above acceptance criteria may have windings that are wet. The windings may be dried out and the insulation resistance re–tested. The dry out temperature should not exceed 80 °C by thermometer and care must be taken to correct the winding resistance to 40°C since the core may be at a temperature much higher than ambient.

• Polarization Index (PI)

PI is the ratio of a ten minute to one minute insulation resistance reading to ground. As described above, the testing shall be done at 1000 VDC (500 VDC for NEMA motors) in accordance with latest issue of IEEE43. The minimum acceptable ratio is 2.0 for old windings and 3.0 for new windings. Temperature correction is not required for this test provided the stator core is at ambient temperature at time of test start and does not change appreciably during the test.

• Rotor Testing
• Single Phase Test – If the stator and bearings are in usable condition, a “single phase test” may be performed. Apply less then rated voltage, typically 10% of rated voltage, to only two leads of the stator winding and turn the rotor slowly by hand. Wide current variations in the single phase source supply suggest possible cage defects.
• Perform a “Growler” test to check for open rotor bars or shorting ring breaks.
• Note: Broken rotor bars may be difficult to detect because the break may only separate when the rotor is hot. Oven heating the rotor prior to a Growler test may help in detection of a defect.
• DC High Potential Testing
• DC High Potential testing shall be done in accordance with the latest issue of IEEE 428 and IEEE 95.

• DC High Potential testing on new motors that have acceptable values for Insulation Resistance and PI shall have a maximum test voltage of 3300 VDC for 480 volt motors and 15,300 VDC for 4000 volt motors applied for one minute, or that voltage level recommended by IEEE 432 and IEEE 95, whichever voltage level is lower. This test voltage should only be applied to the new winding once. Subsequent tests shall be a maximum of 85% of the new winding test voltage.
• DC High Potential Testing on used/in–service motors that have not been cleaned and dried but have acceptable values for Insulation Resistance and PI, shall have a maximum of 215% of rated voltage applied for one minute, or that voltage level recommended by IEEE 432 and IEEE 95, whichever voltage level is lower.
• Motors with re–conditoned windings shall be DC high potential tested to a voltage level that is 60% of the new motor test voltage level.
• Surge Comparison Testing

Surge comparison testing shall be performed to verify correctness of winding connections and to detect turn–to–turn insulation damage. Test voltage and test procedures shall be as recommended by the surge comparison test instrument Manufacturer. Surge comparison tests shall be done with the rotor removed.

• Rotor Balancing

Rotor balancing shall be accomplished as outlined in Section 5.2.4.

• Anti–Friction Bearing Fits
• Bearing housing ID shall be less than 0.0005 inch out of round.
• Minimum rotor end play shall be 0.00075 inches per inch between bearing shoulders, unless specified otherwise by the motor manufacturer.
• Shaft Runout

Maximum permissible shaft runout on standard length shaft extensions shall be as specified in NEMA MG–1, as follows:

• For 0.1875 to 1.625 inch diameter shafts (inclusive), 0.002 inch indicator readings.
• For over 1.625 to 6.50 inch diameter shafts (inclusive), 0.003 inch indicator reading.
• Vibration Testing (Large Frame Medium Voltage Motors)
• The radial vibration levels measured on a bearing housing with the machine operating at rated voltage and frequency at any load shall not exceed the limits presented in Table 2.
• The maximum unfiltered and filtered shaft displacement relative to the bearing housing, with the machine operating at rated voltage and frequency at any load, shall not exceed the limits given in Table 3.

• For motors that do not have non–contact vibration probes or provisions for probes, the bearing housing vibration limits (measured using velocity transducers) are as given above in Table 2. A shaft–rider is not an acceptable substitute for non–contact vibration probes when non–contact vibration probes or provisions for vibration probes are available. When non–contact vibration probes are mounted on the motor, they shall be used for certified test data. When provisions for non–contact probes are provided, shop probes shall be used for vibration measurements and shall meet the accuracy requirements of API 670.
• During the running test, the mechanical operation of all equipment being tested and test instrumentation shall be satisfactory. Unfiltered and filtered radial and axial vibration measurements shall not exceed the limits specified in Table 2 and Table 3 and shall be recorded throughout the operating speed range.
• When radial vibration readings are taken directly on the bearing caps, they shall be taken in both the x and y planes.
• Radial and axial vibration readings shall be recorded at 15–minute intervals for a minimum of one hour after temperature stabilization.
• If replacement or modification of bearings or seals or dismantling to replace or modify other parts is required to correct mechanical or performance deficiencies, the initial test will not be acceptable, and the final specified shop tests shall be run after these replacements or corrections are made. During this run, rated voltage, stator amps, watts, and vibration shall be measured to confirm the correction.
• Facilities to ensure against entrance of oil into the motor shall be in operation throughout the test. Any violation of this condition requires termination of the test until correction is made.
• The Contractor shall maintain a complete detailed log and plots of all final tests and shall submit a minimum of two copies to the Owner, including data for bearing temperatures, rotor balancing, and vibration measurements taken over the operating speed range and the spectrum analysis. A description of the test instrumentation and certified copies of the instrument calibrations shall be available for the Owner’s review.
• The Owner shall be permitted to use their monitoring and/or recording equipment in conjunction with the vibration tranducers mounted on the machine to record the dynamic behavior of the machine during testing.
• All existing mounted vibration probes, transducers, oscillator–demodulators, and accelerometers shall be in use during the test. For motors without provisions for non– contacting probes, vibration measurements shall be made using bearing housing mounted velocity transducers.
• Shop test facilities shall include instrumentation with the capability of continuously monitoring and plotting revolutions per minute, peak–to peak displacement, velocity, and phase angle (x– y–y). Presentation and recording of vibration displacement and phase marker shall also be by spectrum analyzer including 10 orders of running speed as a minimum.
• Current, voltage and power in all three phases shall be measured and recorded, for all running tests. All required data shall be take at cold start continuing throughout the test.

• All windings and bearing temperature measurements shall be made using permanently installed detectors, when available. For cases where detectors are not supplied on the motor, the method must be approved by the Owner.
• Unless specified otherwise, measurements of items in paragraphs 6.1.9.12 (vibration), 6.1.9.13 and 6.1.9.14 shall be recorded every 15 minutes.
• For motors with uninsulated bearings, a measurement of end–to–end shaft voltage shall be made with the motor operating at no load and rated voltage. Shaft voltage shall not exceed 0.2 V rms.
• All tests shall be made with the shaft axis in the normal running position. The motor shall be mounted on a massive foundation having a natural frequency of at least 25% removed from the motor rotational–speed frequency. Note: A massive foundation is one whose vibration is limited to 0.02 inch per second velocity (peak, unfiltered) on test (in the vertical, horizontal and axial planes) above any background vibrations. The motor feet shall be firmly clamped and properly shimmed. A check for soft feet shall be made. When each hold–down bolt is loosened, the respective foot movement shall not exceed 0.001 inch.
• Vibration Testing (NEMA Frame Motors)
• Motor vibration readings shall be taken while the motor is bolted on a rigid, massive, baseplate/foundation and no “soft foot” is present.
• Vibration readings shall be taken with fan and coupling installed. If the coupling is not available use a fully crowned half key.
• Velocity vibration readings shall be taken during the run test in the following locations:
• Horizontally and vertically on the inboard and outboard bearing housing.
• Axially at inboard and outboard end.
• Motor unfiltered vibration at rated voltage and frequency shall not exceed 0.08 in/s peak velocity for 2–, 4–, and 6– pole machines, and 0.06 in/s peak velocity for 8–pole machines, when measured in any direction on the bearing housing and tested uncoupled with 1/2 height key in the shaft extension key way.
• Motor filtered vibration at rated voltage and frequency shall not exceed 0.05 in/s peak velocity at frequencies of 2n (twice speed) or 2f (twice frequency).
• Motor unfiltered axial vibration shall not exceed 0.06 in/s peak on bearing housings. This limit shall not apply to roller bearings.
• The Contractor shall provide hard copy of vibration readings including a spectral analysis with chart recording.
• Vibration readings shall be taken at the start of the test and repeated throughout the test at a minimum of every 15 minutes. The motor shall be run at least 30 minutes after reaching temperature stabilization with vibration readings continuing at 15 minute intervals. Bearing temperatures are considered stable when bearing temperatures change less than 1 °C in two successive 15 minute intervals.

• Insulated bearings shall have the insulation quality verified by testing per IEEE 112 with resistance to ground values recorded.
• Core Loss Testing
• All motors shall have a core loss test after the core is cleaned, prior to any other work being performed on the stator. The core loss testing shall be done by using a core loss tester, or loop test in accordance with IEEE 432. Stators with greater than a 10 °C difference between core lamination areas across the stator iron is an indication of a hot spot.
• Stators/motors that are in for refurbishing that have stator hot spots shall not be worked on further until the stator quality is reviewed with the Owner. Work shall not continue on the motor until approved in writing by the Owner.
• Stators to be rewound shall be core loss tested after winding removal. The extent of the core damage, if any, will be reviewed with the Owner before continuing with repair of the hot spots. Recommended methods for stator lamination damage repair is outlined in Section 5.0 of this Practice.
• Stators with hot spot areas with less than 10ºC difference between core lamination areas are generally considered acceptable.
• Air Gap

Air gap measurements shall be taken at three locations (9, 12 and 3 o’clock) at both ends of the motor between the exterior of the rotor and interior of the stator. The percentage deviation (D) obtained from the formula below shall not exceed 10 percent at each end.

D  H  L 100

Where:

D = Percent deviation

H = Highest of the three readings at one end L = Lowest of the three readings at that end

A = The average of the three readings at that end

• Bearing Oil Inspection

After the test run, both the inboard and outboard bearing oil shall be drained and inspected for discoloration. If discolored, sleeve bearings shall be inspected for damage. If bearings are replaced or reworked/fitted, a retest of the motor vibration and bearing temperature rise shall be accomplished.

• Winding Resistance

Winding resistance shall be made with a low power, four lead resistance measurement device. Care should be taken not to apply high test current for long time periods that result in winding heat and incorrect comparative winding resistance values. Take readings between all leads, with a maximum 5% difference on OHMS allowed between any two pairs.

• Final Testing

• Final testing to be given to all motors after repairs and balancing are completed and the motor is fully assembled shall include, but not be limited to:
• Insulation Resistance Testing (paragraph 6.1.1)
• Winding resistance determination (para 6.1.13)
• Determine the stator PI (paragraph 6.1.2)
• DC High Potential Testing (paragraph 6.1.4)
• Vibration Testing (paragraph 6.1.9 or 6.1.10)
• Air Gap Measurements (para 6.1.12) (not on TEFC motors).
• Special Tests (Special tests shall only be performed when specified on the Data Sheet) Rated temperature vibration testing
• Vibration measurements per paragraph 6.1.9 shall be taken with the motor at rated temperature.
• Acceptable temperature test loading methods are as follows:
• Shaft load the motor with dynamometer
• Connect two machines back–to–back in a motor generator configuration.
• The dual frequency superposed method per IEEE Standard 112.
• Warming up of the machine by blocking ventilation openings or shutting off the cooling water on water–cooled machines is not acceptable.
• Motors shall have shaft and bearing housing vibration verified with the motor at rated temperature. Vibration acceptance for induction machines can be based on a procedure which allows for quickly disconnecting the motor from a dynamometer, or removal of the superposed frequency source at the end of the dual–frequency test, and recording the no–load vibration with the machine hot.
• The magnitude of vibration vector changes from no load to rated temperature shall not exceed 50 percent of the values specified in Table 2 and 3. For motors that do not comply with this vector change allowance, while remaining within the specified limits of Tables 2 and 3, the Manufacturer shall demonstrate the structural stability of the motor. The vibration test shall be repeated by letting the motor cool down and then reheating it to achieve a stable temperature while recording the vibration data. The magnitude of vector change in succeeding vibration amplitudes, for the cold motor under no load and for the hot motor at rated temperature, shall be within 10 percent of the allowable limits shown in Table 3.

7.0 DATA/REPORT REQUIREMENTS

• Upon completion of motor refurbishing/repair the Contractor shall submit a written report including the following:
• Condition of the motor upon receipt.
• A detailed description of the work performed.
• Condition of the motor when returned.
• Copies of all testing and balancing data.
• The Motor Repair Report and Test Data Sheets are intended to demonstrate the status of the motor and should include appropriate comments/analysis by the Contractor as to their assessment of the motor condition as delivered to the Owner.

8.0 PREPARATION FOR SHIPMENT

• When specified on the Data Sheets the motor shaft shall be coated with a rust inhibiting agent to prevent corrosion during extended storage.
• Motors shall have their rotors blocked. However, motors with anti–friction bearings and vertical motors generally do not require blocking, but in some cases the motor may require that one bearing is “locked”.
• Motors with blocked rotors, locked bearings, or shipped without oil shall be prominently tagged indicating the shipping status with appropriate caution information for corrective action prior to starting the motor.

9.0 TABLES

TABLE 1

MINIMUM RECOMMENDED GROUND WALL INSULATION THICKNESS

TABLE 2

BEARING HOUSING VIBRATION LIMITS FOR COMMON OPERATING SPEEDS

NOTES:

• Measured with a velocity sensor or accelerometer integrated to velocity.
• Filtered (”1 Hz) discrete–frequency velocity at 1X and 2X running–speed frequency and 1X and 2X line frequency not to exceed 0.08 inch per second, zero–to–peak.

TABLE 3

SHAFT VIBRATION LIMITS RELATIVE TO BEARING HOUSING USING NONCONTACT VIBRATION PROBES (1)

NOTES:

• The motor is fastened to a massive foundation.
• Vibration displacement at any frequency below running–speed frequency shall not exceed 0.1 mil or 20% of the unfiltered vibration displacement, whichever is greater.
• Vibration displacement at any frequency above running–speed frequency shall not exceed 0.5 mil peak–to–peak.
• Vibration displacement filtered at running–speed frequency shall not exceed 80% of the filtered limit (runout compensated).

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