BY TRAVIS GRIFFITH, AUSTIN H BONNETT, BILL LOCKLEY, CHUCK YUNG, & CYNTHIA NYBERG IEEE INDUSTRY APPLICATIONS MAGAZINE JAN j FEB 2011 WWW.IEEE.ORG/IAS © ARTVILLE 26 Improvements in repairing and rewinding of ac electric motors HIS ARTICLE DETAILS THE UPDATES for the entire standard A major change in the document and modifications to the 1996 revision of is its evolution to full standard status The IEEE Standards IEEE 1068, Recommended Practice for the Repair Association also granted the working group’s petition to and Rewinding of Motors in the Petroleum and broaden the scope and title to include process industries Chemical Industry It contains only selected topics present in general Such recognition acknowledges its value to those within the standard and should not be treated as a substitute employing machines in demanding services and severe envi- T Digital Object Identifier 10.1109/MIAS.2010.939428 Date of publication: 12 November 2010 ronments, such as the cement trade and pulp and paper processing IEEE Standard 1068–2010 was restructured 1077-2618/11/$26.00©2011 IEEE End Turns Coil Extensions Coils End Ring Stator Shroud Belly Band Eye Bolt Lifting Eye Grease Fitting Zerk Fitting Rabbet Fit Spigot Fit Axial Thrust Washer External Cooling Fan Air Deflector Air Baffle Shroud Bearing Cap Bearing Retainer Back Cap Clearance Fit Flame Path Shaft Opening Fan Cover Fan Shroud Keyway Grease Drain Shaft End Bracket End Bell Rotor Skew Foot Sator Laminations Satcked Stator Core Iron Core Plate Punchings Frame Stator Frame Horizontal electric motor nomenclature (Illustration courtesy of EASA.) IEEE INDUSTRY APPLICATIONS MAGAZINE JAN j FEB 2011 WWW.IEEE.ORG/IAS IEEE Industrial Application Society to better track the methodologies and (IAS) Petroleum and Chemical Indusprocesses employed in present-day IEEE STANDARD try Committee (PCIC) to establish a repair facilities Substantive improveworking group for the next revision ments include incorporation of cur1068 WAS cycle However, its potential within rently available technology, document the IEEE IAS indicated the need for specific testing, evaluation criteria, and RESTRUCTURED TO 1068 to become a standard This evoclarification of end user and service lution required large-scale changes In center responsibilities BETTER TRACK THE most cases, more emphatic wording It is commonly known that electric necessitated full rewriting rather than a motor drivers are the most significant METHODOLOGIES simple change of might/may wording user of electric energy within a process AND PROCESSES being replaced with will/shall facility Such machines often take prime During this revision effort, IEEE consideration in the plant’s critical path EMPLOYED IN Standard 1068–2010 was modified to of operation Even in spared or noncritimake clear common practices and was cal service, the cost or long delivery PRESENT DAY restructured to reflect the flow of a tycycle of a new unit makes refurbishpical machine through the repair process ment, repair, and rewinding an essential REPAIR FACILITIES Qualitative and quantitative test propart of plant reliability, uptime, and cedures were included and importance profitability When ac machines (Figure 1) placed on key aspects of each step require repair, an important relationship exists between the motor user and a repair facility In References were updated and expanded to reflect the large plants, orders for machine repair may be repeated most recent versions of relevant documents from the several times during a normal year of operation The original American Petroleum Institute (API), American Society 1068 recommended practice [1] provided basic guidance for for Testing Materials (ASTM), Electrical Apparatus and plants with few motors, personnel who were new to the Service Association (EASA), IEEE, International Elecindustry, and those less familiar with motor repair specifics trotechnical Committee (IEC), International Standards First published in 1990, it achieved acceptance in the petro- Organization (ISO), and National Electrical Manufacturleum and chemical industries and was then revised in 1996 ing Association (NEMA) Of note was the working group’s focus on ac machines IEEE guidelines advise that a recommended practice is, by and large, distinguished by the verb should This style and the decision to remove dc types that are quite dissimiof writing is critical to imply wording with more force than lar to ac units and are less prevalent in the petroleum, the use of “may” in a guide It is also differentiated from a chemical, and process industries In short, IEEE Standard 1068–2010 [2] provides detailed standard employing “shall,” which indicates a single-accepted method Consideration of 1068’s general use prompted the procedures for ac machine evaluation and data interpretation 27 IEEE INDUSTRY APPLICATIONS MAGAZINE JAN j FEB 2011 WWW.IEEE.ORG/IAS through a higher degree of engineering language and the establishment of a technical reasoning base 28 Description of IEEE 1068 To demonstrate the flow of a machine through the various individual or combined modification processes, a brief document outline is illustrated: n scope n qualification of service centers n define user and repair facilities responsibility n identify information to obtain before the machine is removed from service n incoming inspection (prior to dismantling the machine) n accessory device inspection n disassembly and inspection key points n electrical tests (stator and rotor) n mechanical inspection n rewind guidelines n balancing of rotating element n assembly and final test n post repair work In the scope, the first significant change was to focus on ac induction and/or synchronous machines (e.g., motors) and to add dc machines to the list of excluded apparatus Should consensus determine the need, a future dc repair standard might be developed As noted above, a midstream alteration broadened the usefulness of IEEE Standard 1068– 2010 to associated IAS constituents and other unrelated process industries The document is now titled Standard for the Repair and Rewinding of AC Electric Motors in the Petroleum, Chemical and Process Industries As with the original recommended practice, IEEE Standard 1068–2010 is a supplement to manufacturers’ designs, tests, and instructions It is not possible for the document to address all possible designs, construction methods, or materials having occurred over the previous century Thus, it does not supersede the manufacturer’s information, directives, or cautions To quote from the revised scope: “The standard covers recondition, repair, and rewind of horizontal and vertical induction motors and synchronous machines.” Recognizing that there are certain specialized niche categories of electric motors, each of which has unique repair requirements, the document specifically excludes dc, hermetic, nuclear, submersible, and hazardous (classified) area Example of a Level failure (Photo courtesy of EASA.) machines from coverage While large portions of Standard 1068 are still applicable to such repairs, those specialized machines require unique treatment It is self-evident that a working motor has no use for this document Aside from the few programs that require periodic cleaning of large motors, an operating machine is not likely to be sent to a repair facility until something breaks When a damaging event occurs, the usual preliminary focus is to return the unit to running condition Repair extends machine life at reduced cost and in less time than obtaining a new unit On some occasions additional goals arise subsequent to teardown and component evaluation A simple case is upgrading components to accommodate a manufacturer’s current design, but more likely are changes to mitigate the cause of the failure and, particularly, redesign of the winding to improve any one of several operating parameters Just as not all failures are equally severe, not all repairs are equally extensive The standard adopts a practical description of graduated levels of repair, ranging from Level (routine maintenance) through Level (machines that suffered catastrophic failure and would normally not be repaired) These levels of repair as in [3] are defined as follows: n Level 1: Basic Reconditioning: It includes replacing of antifriction bearings, or inspecting and verification of hydrodynamic bearings, cleaning all parts, and replacing lubricant Also, the repair includes addition of seals and other accessories as agreed with the customer n Level 2: This includes Level with the addition of varnish treatment of stator windings, repair of worn bearing fits, and straightening of bent shafts n Level 3: This includes Level as well as rewinding the stator (replacing windings and insulation) n Level 4: This includes rewinding of the stator plus major lamination repair or rotor rebar It may also include replacement of the stator laminations or restacking of laminations Shaft replacement would normally fall into this category In short, Level involves major repairs that are costly enough to justify examining the option of replacement n Level 5: Motors that would normally be replaced except for special circumstances faced by the customer (i.e., no spare or unacceptable lead time for a replacement) Level includes misapplied motors, inadequate enclosures, and pre U-frame motors A motor that should be replaced, if not for the owners’ inability to operate without it The standard recognizes that in cases where replacement new unit or replacement component delivery time is unacceptable, or where substitutions are not possible, it may be necessary to repair machines usually considered catastrophically failed (Figure 2) Summary of the Standard The importance of communication between the end user and the repair facility is recognized and emphasized If the repair is more complex, then more importance is placed on good communication Certainly, this is important not only to avoid misunderstandings but also to have a complete performance and repair history of critical machines This is, especially, necessary in identifying cases where previous changes have impacted performance or present modifications can increase reliability Negative results are to be avoided and positive ones considered as best practice User and repairer responsibilities are set forth in detail Where practical, the standard contains background information and guidance for the user There is a specific checklist useful for prequalifying a service center, material about in-plant machine diagnostics, and a section describing procedures for preinspection test runs, when warranted Importance of Machine History Aside from expanding the initial list of recommendations, the document includes practical courses of action to benefit the user, for example, reporting coupling damage so it can be replaced in a timely fashion and the mating half be inspected and replaced if necessary Noting the importance of root cause failure analysis, the standard now includes guidelines for evaluating less common failures, such as an open rotor or certain types of stator winding failures For example, when a rotor bar fractures because of fatigue-cycle life, the remaining bars are also likely near the end of their fatigue-cycle life The entire rotor should be rebarred, rather than a repair performed on the open bar [4] Airgap The physical airgap between stator and rotor is electrically and mechanically important Experience has shown that the airgap should be uniform within 10% of the average value Determining the status of the airgap during the incoming inspection is critical to determining the complete work scope This is necessary for several reasons, not the least of which are focusing on the correct components contributing to the problem, projecting a practical completion date, and establishing a realistic cost of the repairs When practical, one predisassembly inspection step is the performance of an uncoupled test run (Figure 4) to Squirrel cage rotor after dismantling for inspection (Photo courtesy of EASA.) Incoming test run can reveal some problems (Photo courtesy of Chuck Yung.) IEEE INDUSTRY APPLICATIONS MAGAZINE JAN j FEB 2011 WWW.IEEE.ORG/IAS For the repair facility, obtaining complete nameplate information can be critical Consider the example of a two-pole motor manufactured for 50-Hz operation, where the rotor resonant frequency is 20% above the operating r/min The machine is eventually moved to North America, where it operates on 60-Hz power Chronic vibration problems, not surprisingly, plague the machine Absent the original nameplate and/or knowledge of the machine’s history, the user would lose production attempting to correct the vibration Lacking knowledge of the machine’s history, a repair facility—and possibly a succession of repairers—would balance the rotor Yet, it is unlikely that the resonant frequency problem would be immediately revealed The user is in the best position to know the machine’s history and is, therefore, responsible for retaining documentation and, where practical, sharing repair and maintenance history with the repair facility This is one example where on-site diagnostics are invaluable to a complete root cause failure analysis A complete vibration spectrum, voltage and current records, and accurate description of the operating and environmental conditions are valuable aids in determining the repair requirements Presented with as much machine history as possible, and a good description of the reason the machine was removed from service, the repair facility has the opportunity to better evaluate the machine with attention toward those issues that might contribute to the user’s experience with the machine Unless otherwise agreed in advance with the user, the repair facility shall provide a detailed inspection report with estimated repair costs prior to proceeding with repairs Toward that end, IEEE Standard 1068 includes sample inspection and repair report forms Where possible, consensus approaches toward evaluating distinctive problem areas of rotating equipment are provided These include practical tests for squirrel cage induction rotors, insulation and winding tests, rotor thermal sensitivity tests, and evaluation of laminated stator cores for eddy-current losses Incoming inspection (Figure 3) is necessary to verify machine condition and detect items needing repair When there is no spare for the machine, a sense of urgency can cause routine items to be overlooked The new standard suggests best practice procedures for those initial steps, with emphasis on those which experience has shown to cause later delays These procedures include details such as lead markings, the location and position of critical electrical and mechanical components, and the presence, arrangement, and condition of accessories, such as filters, surge capacitors, lightning arrestors, and space heaters User Guidance 29 evaluate vibration, bearing temperature, and thermal stability There are instances where operation of a machine in dangerous electrical or mechanical condition carries sufficient risk that could preclude running Good communication between user and repair facility can avoid this risk to the machine, test equipment, and personnel Where the user advises the reason the machine was removed from service, a predisassembly test run can aid in evaluation of the machine and justify a more lengthy examination into specific phenomena or a component When vibration is the concern, it is often possible to duplicate operating thermal conditions The new standard provides detailed instructions for this step as well as acceptance criteria to aid in evaluation of the results Inspection During the disassembly process, the mutual experience of users and repair shops illustrates that there are common key areas where problems can develop Identifying these enables a directed approach to problem resolution The standard describes these in the sequence in which they are encountered during the disassembly and inspection process For the stator, these include presence and condition of air baffles, evidence of a core loose in the frame, damage to (or loose) stator wedges, condition of winding ties, blocking, evidence of arcing, or partial discharge IEEE INDUSTRY APPLICATIONS MAGAZINE JAN j FEB 2011 WWW.IEEE.ORG/IAS TABLE MECHANICAL INSPECTION TOLERANCES 30 Foot flatness 0.0127 mm Shaft bearing journal diameter 0.005 mm Sleeve bearing inside diameter (ID) 0.005 mm Sleeve bearing outside diameter 0.01 mm Bearing housing ID 0.01 mm Bearing cartridge 0.01 mm Bracket to stator fit 0.03 mm Shaft extension runout (total indicated runout) Manufacturer’s values or Table (by r/min) For those users without a comprehensive document to assure quality repairs, IEEE Standard 1068 includes specifics as to which components should be measured and to what degree of accuracy A partial list is included in Table Organization The material in IEEE 1068 is separated into electrical and mechanical sections, with subparagraph identification for stator, rotor, shaft, and bearing information Electrical Repair Topics Insulation Evaluation Important through the evaluation, repair, and final test phases of a repair, recommended voltages for measuring insulation resistance (IR) are noted in Table Core Evaluation and Repair Significant areas of the rewind process are described and control guidelines provided Removal of the failed winding is an area where improper procedures can be detrimental not only to the duration and cost of the repair but also extended to permanent or nonrepairable damage The three methods for winding removal (burnout oven, water blasting, and mechanical removal) are described, with procedural tips to control and evaluate the results for each method When inspection and testing reveals that a stator core has lamination damage (Figure 5), the corrective measures are dictated by the extent and nature of the damage IEEE Standard 1068 provides descriptive paragraphs to detail these methods The methods described are n pneumatic vibration of the core to separate fused laminations n use of a die grinder to remove small areas of fused laminations n a complete or partial restack of the core, cleaning, and reinsulating the individual laminations n installation (or adjustment of) pressure plates, banding, undercutting, and lamination stiffening Rewind The rewind section is divided into random- and formwound machines See Figure for a representative illustration used in IEEE 1068 relating to coil types Most random TABLE INSULATION RESISTANCE TEST VOLTAGE Winding Rated Voltage (V)* 12,000 5,000–10,000 *: Rated line-to-line voltage for three-phase ac machines Ground failure that may result in core damage (Photo courtesy of EASA.) windings are rated 600 V or lower, with an increasing portion of these machines being operated from an adjustable speed drive (ASD) The most commonly applied ASD is the pulse width modulated (PWM) type, which may subject the winding to fast rise times and voltage overshoots The insulation shall be capable of continually operating at rated temperature with repetitive spikes having a 0.1-ls rise time and a magnitude of 1,600-V peak for motors operating on a 480-V system and 1,900-V peak for motors operating on a 600-V system Enhanced insulation additives (spike resistance), mechanically robust insulation, and refined rewind procedures are employed to resolve waveform damage issues IEEE 1068–2010 standard expands this area of discussion by providing further particulars 25 6 3 (a) (b) Coil types: (a) random wound and (b) form wound (Reprinted with permission from the EASA, Mechanical Repair Fundamentals of Electric Motors, 2003.) Electrical Testing TABLE SINGLE-COIL SURGE TEST VOLTAGES Rated Voltage At 0.1 ls At 0.5 ls At 1.2 ls 460 V 650 V 760 V 945 V 2.3 kV 3.3 kV 3.8 kV 4.7 kV kV 5.7 kV 6.6 kV 8.2 kV 6.6 kV 9.4 kV 10.9 kV 13.5 kV 13.2 kV 18.8 kV 21.8 kV 27 kV Lacing and bracing methods are described, with some general description of coil spacing, brazing, vacuum pressure impregnation (VPI), and resin-filled insulation methods Figure illustrates an in-process rewind of a form coil stator The tape on each coil comprises the groundwall insulation IEEE INDUSTRY APPLICATIONS MAGAZINE JAN j FEB 2011 WWW.IEEE.ORG/IAS Electrical testing methods for ac and dc high potential, and surge testing, draw on the IEEE Standards 432-1992 [5], 43-2000 [6], and 112-2004 [7], as well as API 5412003 [8], and ANSI/EASA AR100-2006 [9] For form coil windings, surge test voltages, and rise times (based on phase–phase voltage) are specified in Table As with the random winding section, the standard provides specific information on how to attain the requirements where the “as found” materials and thicknesses are shown to be insufficient Table indicates the types of turn insulation required to provide proper protection for the noted steady-state volts per turn levels Recommended groundwall insulation thicknesses [10], based on standard voltage ratings, are provided in Table TABLE RECOMMENDED GROUNDWALL INSULATION THICKNESS FOR COMMON VOLTAGE RATINGS Groundwall (kV) Total (mm) Per Side (mm) 2.3 1.5 3.56 1.78 6.6 4.57 2.29 TABLE TURN INSULATION RECOMMENDED VALUES Volts/Turn Turn Insulation Up to 30 Film coating of wire Up to 60 Fiberglass over film >60 Mica turn tape Form coil insertion in process (Photo courtesy of EASA.) 31 nature of rotor bar failure If one or more broken bars are revealed, it is The widely accepted polarization index JUST AS NOT ALL highly probable that the remaining (PI) test has long been recognized as usebars are at or near the end of their ful for evaluating insulation condition FAILURES ARE fatigue-cycle life For this reason, parPrior to improved insulation materials tial repairs are discouraged and VPI methods, interpretation of the EQUALLY SEVERE, PI test was straightforward: the IR to ground is measured at time and again Synchronous Machines NOT ALL REPAIRS at intervals for 10 min; the 10-min As synchronous machine stators are the ARE EQUALLY resistance value is divided by the 1-min same as those in induction units, Secresistance value and the resulting ratio tion 6.3.3 continues to address windEXTENSIVE used to assess insulation condition ings located on the rotor Procedural A ratio between two and five was instructions are provided for the inspecgenerally deemed acceptable with a ratio tion, testing, removal, and connection below two indicating poor insulation, and a ratio above five of rotating poles Slip rings and the more common methoften interpreted as indicating a dry winding in need of var- ods of excitation are also addressed nish treatment Improvements in insulation systems have resulted in Mechanical Repair Topics initial IR values measured in gigaohms (1 billion X or 109 X) It is unrealistic to expect such a high IR value Cleaning Methods to double over the course of the PI test IEEE 1068 adopts Machines are routinely cleaned of oil, grease, dirt, as well the caveat that states “If the initial resistance is 5,000 MX as environmental and biological contaminants as part of a (5 GX) or higher, the PI ratio may not be meaningful.” routine repair, while larger machines are sometimes cleaned Standard 1068 further stipulates that a PI ratio of 1.5 or in place as part of a preventive maintenance program The lower requires the repairer to notify the user standard covers steam cleaning, pressure washing, and dryFor random windings, a dielectric absorption ratio ice blasting of motor components, with particular cautions (DAR) of the 1-min value divided by the 30-s value is used for windings instead This is due to the differences in the insulation system design: insulation thickness, surface capacitance, and Mechanical Repairs other factors For machines equipped with antifriction (i.e., ball or roller) bearings (Figure 9), removal of bearings should be accomplished by the use of a hydraulic or screw-type puller to Rotor Test Rotor inspection should include a single-phase rotational prevent possible shaft damage The disassembly and removal test, or growler test, to aid in the detection of open rotor of babbitt bearings is also dealt with, for the benefit of those bars It is noted that all tests are indicative, some containing unfamiliar with them There is emphasis on identifying the hard information, and others providing subjective data and location and orientation of the bearings, as well as inspection requiring personal interpretation Here, current signature and bearing fits With the prevalence of ASDs (particularly PWM drives) analysis results obtained before the machine is removed from in process industries, material has been included to diagservice can be of high value in evaluating rotor condition The standard includes guidance for recognizing many nose, evaluate, and understand various corrective measures symptoms of rotor cage faults (Figure 8), such as burned or It is necessary to be familiar with capacitively generated discolored laminations, evidence of arcing, electrical noise circulating currents, know how to interpret symptoms under loaded conditions, and more obvious signs such as found during the inspection process (Figure 10), and initivisibly broken bars or lamination rubbing On a practical ate effective repair processes note, the document directs attention to the fatigue-cycle IEEE INDUSTRY APPLICATIONS MAGAZINE JAN j FEB 2011 WWW.IEEE.ORG/IAS Insulative Quality 32 Balancing Failure of the upper cage of this dual-cage rotor indicates a starting issue (Photo courtesy of EASA.) Rotor balance procedures are described, with reference to NEMA MG1 Part [11], ISO 1940 [12], and API 541 [8] There are specific procedural details, such as where and how weight can be safely added or removed The use of proximity probes to monitor vibration when a machine is in service requires special consideration Not all users or repair facilities are familiar with this technology, so tutorial information was added Included are the difference between mechanical runout and electrical runout, the need to burnish the area of the shaft beneath the probe(s) tip, and avoidance of invasive repair methods, such as welding or metalizing In addition to the standard machine vibration limits established in NEMA MG1 [11], a table designated for special machines is included (Table 6) These are for unfiltered maximum relative shaft displacement Deep Groove Ball Bearing Tapered Roller Bearing Outer Ring Outer Ring Roler (Tapered) Inner Ring Cage (Pressed Cage) Bore Surface Roller Small End Face Inner Ring Raceway Surface Small Rib (Raceway Groove) Ball Inner Ring Cage (Pressed Cage) Inner Ring (Cone) Rivet Outer Ring Outer Diameter Surface Side Surface Inner Ring Front Face Outer Ring Back Face Cylindrical Roller Bearing Rolling Surface Roller Large End Face Center Rib Inner Ring Raceway Surface Inner Ring Rib Rivet Inner Ring Raceway Surface Spherical Roller Bearing-Self-Aligning Outer Ring Cage (Machined Cage with Rivet) Guide Rib Face Outer Ring Cylindrical Roller Inner Ring Outer Ring Front Face Large Rib Inner Ring Back Face Guide Rib Face Guide Rib Face Roller (Spherical) Roller Surface Cage (Machined Cage with Rivet) Roller Large End Face Inner Ring Raceway Surface Roller Filling Slot Small Rib Rolling Surface Roller Large End Face Types of antifriction bearings (Reprinted with permission from the EASA, Mechanical Repair Fundamentals of Electric Motors, 2003.) Electrical Connections The standard includes gasket and minimum spacing requirements as well as torque values for electrical fasteners in both standard and metric bolt sizes Because there are many connection variations dictated by machine size and type, plus the many possible user instrumentation requirements, this section was limited to general guidance Accessories The handling of auxiliary components, devices such as space heaters, pressure sensors, and vibration probes, is addressed Also included are temperature sensors, such as resistance temperature detectors (RTDs), thermocouples, and bimetallic thermal elements Practical guidance is provided for both incoming inspection and final assembly, including device location, verification of proper operation, and correct lead marking The associated issue of lead characteristics is important for other stator, rotor, and other line leads Observance of original markings and comparison with NEMA and industry standard labels shall be observed Final assembly must also consider wires or cables that are connected by terminal lugs, which were installed with a compression or crimping tool This includes verifying that all strands are held within the lug barrel, insuring the barrel is properly crimped with the correct tool and the strands are securely held so as to avoid a high-resistance connection, which could overheat and fail TABLE UNFILTERED SHAFT DISPLACEMENT LIMITS Max r/min 10 Fluting resulting from shaft currents (Photo courtesy of EASA.) Relative Displacement (Peak-to-Peak) of Shaft 1,8013,600 50 lm (0.002000 ) 1,2011,800 70 lm (0.002800 ) Up to 1,200 76 lm (0.003000 ) IEEE INDUSTRY APPLICATIONS MAGAZINE JAN j FEB 2011 WWW.IEEE.ORG/IAS Additional Topics 33 Acceptance Testing Final Test and Documentation THE PHYSICAL AIRGAP BETWEEN STATOR AND ROTOR IS ELECTRICALLY AND MECHANICALLY IMPORTANT IEEE INDUSTRY APPLICATIONS MAGAZINE JAN j FEB 2011 WWW.IEEE.ORG/IAS An adage states “If it is important enough to measure, it is important enough to record.” Proper final testing includes documentation—lots of documentation Shaft runout, vibration levels, IR, voltage, and current on each phase during the test are extremely important These readings must dovetail with expected values and approach or equal original manufacturer performance data Also, establishing this repaired/ refurbished baseline data is crucial to the comparison of historical data Significant differences between the in-shop (Figure 11) and on-site values for any of these items should trigger an investigation to determine the cause For users with duplicates of the same machine, a comparison of like units is helpful There are many times when prompt inspection of apparent deviations reveals a problem, which, untended, would have resulted in another machine failure The authors attest to many cases where a machine was connected to the wrong voltage, reversed rotation, misaligned, incorrect end float, or otherwise misapplied Such obvious items as bearing temperature should also be monitored and recorded Bearing temperature should be allowed to stabilize, which is defined to be no more than a °C increase over a 30-min time frame 34 Winding Resistance Winding resistance between phases should not vary by more than 3% [9] High-resistance connections, broken strands, and incorrect winding connections are some of the more common causes of excessive variation in resistance However, the root cause must be considered Especially for smaller machines, the cause could be no more than the use of a concentric winding Machine-wound 11 Acceptance testing after repair establishes baseline information for vibration levels and no load current (Photo courtesy of EASA.) concentric windings rarely have the same mean length of turn (MLT), so the resistance may differ as much as 5% Bearing End Float for Sleeve Bearing Machines NEMA MG1 [11] prescribes that a machine fitted with babbitt bearings have a minimum total end float of 1/2 in (or Æ0.25 in) Often overlooked is the fact that it also stipulates a maximum coupling end float of 0.190 in Thus, when a machine operates on its magnetic center on the test bed and the user complains that a machine is running against the thrust face as illustrated in Figure 12, it is a self-indictment of the alignment practices used We note here that the IEC-based machines have a total end float of mm (Æ3 mm), which would cause problems if not observed prior to installation Figure 13 shows a representative illustration used in IEEE 1068 relating to sleeve bearings Quality Assurance Measures Comparison of in-shop performance criteria to those same items measured after the machine’s installation is important in the last step of total quality management Reinstallation of a repaired machine into an unsatisfactory mechanical or electrical environment can quickly repeat the failure Attention to issues such as power quality, precision alignment, belt tensioning, and piping stresses is critical to future machine operability and life Quality assurance at every step, including final installation and operation, is necessary to obtain full value from a first-class repair Toward that end, the repair report should be suitably detailed to inform the reader as to the probable cause of failure, the method(s) of repair, the repaired condition, and final test results The user also has the responsibility to appropriately protect the machine This means that a motor placed into storage should be kept in a clean area, 12 Sleeve bearing thrust face damage is the result of improper coupling practices (Photo courtesy of EASA.) ideally in a temperature- and humiditycontrolled environment Space heaters (or some other means) should be used to maintain the winding temperature above the dew point When the motor is placed into service, IR should be measured, alignment to driven equipment must be precise, and vibration and bearing temperatures ought to be monitored for an appropriate time to assure there are no problems Poor installation practices could necessitate the next repair Bottom Half of Bearing Housing/Oil Chamber/Bracket Oil Ring Assembled Flange-Mounted Sleeve Bearing Oil Ring Bearing Shell Bottom Half of Babbitt Informative Annexes Babbitt Bearing Labyrinth This IEEE standard would not be comBearing Saddle Bearing Seal plete without supportive documentaShell Top Half of Bearing tion or extra information To this end, Top Half of Bearing Annex A provides a list of useful IEEE Housing PCIC technical papers and the obliga13 tory catalog of other IEEE standards Sleeve bearing component nomenclature (Reprinted with permission from the and recommended practices Informative Annex B provides an evaluation EASA, Mechanical Repair Fundamentals of Electric Motors, 2003.) form that equipment owners can use in the process of screening repair facilities [3] A Bonnett and C Yung, “A repair-replace decision model for petroBasic capabilities included in the questionnaire are electrical chemical industry electric motors,” in Proc 2002 Petroleum and Chemiand mechanical repair, lifting, technical and backup resources, cal Industry Conf., pp 55–66 test facilities, housekeeping, and quality assurance [4] “Root cause failure analysis,” Electrical Apparatus Service Association, References [1] Recommended Practice for the Repair and Rewinding of Electric Motors for the Petroleum and Chemical Industry, IEEE Std 1068-1990 [2] Standard for the Repair and Rewinding of AC Electric Motors in the Petroleum, Chemical and Process Industries, IEEE Std 1068-2009 Inc., St Louis, MO, 2002 [5] IEEE Guide for Insulation Maintenance for Rotating Electric Machinery (5 hp to less than 10 000 hp), IEEE 432-1992 [6] IEEE Recommended Practice for Testing Insulation Resistance of Rotating Machinery, IEEE Std 43-2000 [7] Standard Test Procedure for Polyphase Induction Motors and Generators, IEEE Std 112-2004 [8] Form-Wound Squirrel-Cage Induction Motors—500 Horsepower and Larger, 4th ed., ANSI/API Standard 541-2003, June 2004 [9] Recommended Practice for the Repair of Rotating Electrical Apparatus, ANSI/EASA AR100-2006 [10] C Yung, “Opportunities to improve reliability and efficiency of existing medium-voltage electric motors,” in Proc 2005 Petroleum and Chemical Industry Conf., pp 199–208 [11] Motors and Generators, NEMA MG1, 2006 [12] Mechanical Vibration—Balance Quality Requirements for Rotors in a Constant (Rigid) State—Part 1: Specification and Verification of Balance Tolerances, ISO 1940-1, 2003 [13] T Griffith, C Yung, and C Nyberg, “Recent revisions of IEEE 1068 standard for the repair and rewinding of AC electric motors in the petroleum, chemical and process industries,” in Proc 2007 Pulp and Paper Industry Technical Conf., pp 191–196 Travis Griffith (t.griffith@ieee.org) is with GE Oil and Gas in Houston, Texas Austin H Bonnett (retired) was with Emerson Electric in Gallitin, Missouri Bill Lockley is with Lockley Engineering in Calgary, Alberta, Canada Chuck Yung is with EASA in St Louis, Missouri Griffith, Yung, and Nyberg are Senior Members of the IEEE Bonnett is a Life Fellow of the IEEE Lockley is a Fellow of the IEEE This article first appeared as “Revisions to IEEE 1068: Standard for the Repair of AC Electric Motors in Process Industries” at the 2009 Petroleum and Chemical Industry Conference IEEE INDUSTRY APPLICATIONS MAGAZINE JAN j FEB 2011 WWW.IEEE.ORG/IAS Conclusions The repair process is important to both the repair facility and the user Accepted high-quality procedures and materials must be used so as to maximize the machine’s usefulness and reduce mean time between failures For process industries, the repair cost is typically a small portion of the total cost of a machine failure Process industries, such as pulp and paper, petroleum companies, and chemical operations, recognize that downtime is measured in the tens or hundreds of thousands of dollars It has long been recognized that higher quality workmanship and materials increase the life of both new and repaired machines By making sure that repairs meet stringent requirements and pass tests designed to provide quality assurance, the user and repairer can increase machine life IEEE Standard 1068 is designed to aid both repairer and user toward that goal Given that most manufacturers (process industries in particular) recognize the relationship between quality control and machine life, the extension of 1068 to include process industries is a logical way to expand the benefits of this standard A key element of this standard deals with the importance of doing a root cause failure analysis to assure that repeat failure not occur Also, this analysis may suggest modifications to prevent future failures 35 ... Recommended Practice for the Repair and Rewinding of Electric Motors for the Petroleum and Chemical Industry, IEEE Std 106 8- 1990 [2] Standard for the Repair and Rewinding of AC Electric Motors in the... Bearing Rolling Surface Roller Large End Face Center Rib Inner Ring Raceway Surface Inner Ring Rib Rivet Inner Ring Raceway Surface Spherical Roller Bearing-Self-Aligning Outer Ring Cage (Machined Cage... This includes Level as well as rewinding the stator (replacing windings and insulation) n Level 4: This includes rewinding of the stator plus major lamination repair or rotor rebar It may also include