GE Industrial Control Systems GEEP-124-I These Instructions do not purport to cover all details or variations in equipment nor to provide for every possible contingency to be met in connection with installation, operation or maintenance. Should further information be desired or should particular problems arise which are not covered sufficiently for the purchaser’s purposes, the matter should be referred to GE Industrial Control Systems. Custom 8000 is a registered trademark of General Electric Company. GE Industrial Control Systems GEEP-124-I Copyright 1997,1998 The General Electric Company, USA 1 Instructions Custom 8000 Horizontal Induction Motor Weather Protected Type I Antifriction Bearing
Transcript
GE IndustrialControl Systems
GEEP-124-I
These Instructions do not purport to cover all details or variations in equipment nor to provide for every possible contingency to be met in connection withinstallation, operation or maintenance. Should further information be desired or should particular problems arise which are not covered sufficiently for thepurchaser’s purposes, the matter should be referred to GE Industrial Control Systems.Custom 8000 is a registered trademark of General Electric Company.
GE Industrial Control Systems GEEP-124-I Copyright 1997,1998 The General Electric Company, USA 1
Instructions
Custom 8000
HorizontalInduction Motor
Weather Protected Type I
Antifriction Bearing
GE Industrial Control Systems GEEP-124-I Copyright 1997,1998 The General Electric Company, USA2
The purpose of this instruction manual is toprovide a description of the product and to providehelpful suggestions for receiving, handling, storing,installing, operating, and maintaining the unit togetherwith useful general information. Although reasonablecare has been taken in the preparation of this instructionmanual to assure its technical accuracy, no responsibilityis assured in any manner by the General ElectricCompany for any consequences of its use. If furtherinformation is required, contact the nearest GeneralElectric office.
This instruction manual should be available to allpersonnel involved in installing and operating the unit.It should be reviewed before initiating any action on theunit.
Safety Precautions and Warnings
For equipment covered by this instructionmanual, it is important to observe safety precautions toprotect personnel from possible injury. Among the manyconsiderations, personnel should be instructed to:
• avoid contact with energized circuits or rotatingparts.
• avoid by-passing or rendering inoperative any
safeguards or protection devices. • avoid extended exposure in close proximity to
machinery with high noise levels. • use proper care and procedures in handling, lifting,
installing, operating, and maintaining theequipment.
• before operating, replace any covers that have been
removed for inspection.
Safe maintenance practices with qualifiedpersonnel are imperative. Before starting maintenanceprocedures, be positive that:
• equipment connected to the shaft will not causemechanical rotation.
• main machine windings and all accessory devices
associated with the work the area are de-energizedand will remain disconnected from electrical powersources for the duration of the maintenance period.
If high potential insulation testing is required,procedure and precautions outlined in NEMA StandardsMG-1 and MG-2 should be followed.
Failure to properly ground the frame of thismachine can cause serious injury to personnel.Grounding should be in accordance with the NationalElectrical Code and consistent with sound local practice.
WARNING: HIGH VOLTAGE AND ROTATINGPARTS CAN CAUSE SERIOUS INJURY. THEUSE OF ELECTRICAL MACHINERY, LIKE ALLOTHER UTILIZATION OF CONCENTRATEDPOWER AND ROTATING PARTS, CAN BEHAZARDOUS. INSTALLATION, OPERATION,AND MAINTENANCE OF ELECTRICALMACHINERY SHOULD BE PERFORMED BYQUALIFIED PERSONNEL. FAMILIARIZATIONWITH NEMA PUBLICATION MG-2, SAFETYSTANDARD FOR CONSTRUCTION ANDGUIDE FOR SELECTION, INSTALLATIONAND USE OF ELECTRIC MOTORS ANDGENERATORS, THE NATIONAL ELECTRICALCODE, AND SOUND LOCAL PRACTICES ISRECOMMENDED.
GE Industrial Control Systems GEEP-124-I Copyright 1997,1998 The General Electric Company, USA4
ANSI/NEMA MG-2 Safety Standards for constructionand Guide for Selection,installation and Use of ElectricMotors and Generators.
ANSI C50.10 General Requirements forSynchronous Machines.
IEEE 1 General Principles forTemperature Limits in Rating ofElectrical Equipment.
IEEE 85 Test Procedure for Air-borneNoise Measurements on RotatingMachinery.
IEEE 112 Test Procedure for PolyphaseInduction Motors and Generators.
IEEE 115 Test Procedures for SynchronousMachines.
Standards can be obtained by writing to the following:
National Electrical Manufacturers Association2101 Street, N.W.Washington, DC 20037
American National Standards Institute1430 BroadwayNew York, NY 10018Attention: Sales Department
The Institute of Electrical and Electronics Engineers,Inc.445 Hoes LanePiscataway, NJ 08854Attention: Publication Sales
Warranty considerations The warranty coverage applicable to the
equipment specified under “Identification of Unit” maybe found in the corresponding sales contract.
The equipment must be operated in accordancewith nameplate specifications, applicable standards andcodes, and in accordance with this instruction manualfor the warranty to remain in effect during the warrantyperiod.
If a question or circumstance not covered by theinstruction manual occurs, or should a problem occur,contact the nearest General Electric Technical Servicerepresentative.
GE Industrial Control Systems GEEP-124-I Copyright 1997,1998 The General Electric Company, USA 5
Whenever traffic clearance allows, the machine isshipped from the factory as an assembled unit ready forinstallation. Sole plates (or slide rails), if ordered, arebolted to machine feet. Occasionally some accessoryitems are shipped separately. All packing lists should becarefully checked to assure all items have been received,Each unit should be carefully inspected upon arrival.Any damage should be photographed, documented andthen reported immediately to the carrier and to thenearest General Electric office.
Handling
The machine should be lifted only by means ofthe four lifting lugs which have been provided on theframe. If couplings or other attachments unbalance theload, an additional sling should be used to preventtipping or rotation. Spreaders should be used with theslings attached to the lifting lugs to prevent damage tothe top cover while lifting the machine.
WARNING: LIFTING LUGS ON THE FRAMEARE DESIGNED FOR LIFTING THE MACHINEONLY. DO NOT USE FOR LIFTING COUPLEDEQUIPMENT SUCH AS PUMPS,COMPRESSORS, GEARS OR OTHEREQUIPMENT. DO NOT USE MACHINELIFTING LUGS FOR LIFTING EQUIPMENTON A COMMON BASE.LIFT THE ASSEMBLYWITH A SLING AROUND THE BASE OR BYOTHER LIFTING MEANS PROVIDED ON THEBASE. FOR UNBALANCED LOADS (SUCH ASCOUPLINGS OR OTHER ATTACHMENTS),ADDITIONAL SLINGS OR OTHER EFFECTIVEMEANS SHOULD BE USED TO PREVENTTIPPING.DO NOT ATTEMPT TO LIFT THE ENTIREMACHINE USING EYEBOLTS IN THE HOLESIN THE TOP COVER.FAILURE TO OBSERVE THESEPRECAUTIONS MAY RESULT IN DAMAGE TOTHE EQUIPMENT, INJURY TO PERSONNEL,OR BOTH.
Always lift or move the unit with all assemblybolts, screws and studs in place, secured with the shaftclamp in position when supplied (supplied on machineswith sleeve bearings only). Machines with oil-lubricatedbearings are shipped without oil.
Storage
If, at the time of purchase, it was specified thatthe motor be packaged for long-term storage, thepackage should be left intact during the period ofstorage.
If the machine is not put in service immediately,adequate precautions must be taken to protect it while instorage. The following instructions are provided as aguide for storage. Full compliance with theseinstructions is required to maintain the warranty.
During manufacturing, testing, and preparationfor shipment basic precautions are taken by the factoryto guard against corrosion of the bearing journals andshaft extension. The shaft extension is treated with aheavy coating of rust inhibitor. All machines with oil-lubricated bearings are operated and tested at the factorywith a rust-inhibiting oil in the lubrication system.Although the machines are shipped without oil , a rust-inhibiting film remains on the critical bearing surfacesduring transit and for up to three months of normalstorage. Nevertheless , when the machine is received, thebearing oil reservoirs should be filled to the proper oillevel with a good grade of rust-inhibiting oil. (Seesection entitled Lube Oil Recommendation on page 24).
Grease-lubricated machines have the bearingspacked at the factory and no further preventivemaintenance is required on the bearings during storage.
For clean, dry, indoor storage locations, rotate theshaft of all two-bearing machines at three-monthintervals so as to thoroughly coat journals with a freshoil film.
Machines equipped with brushes should have thebrushes lifted in the brush holders so they are not incontact with the collectors.
GE Industrial Control Systems GEEP-124-I Copyright 1997,1998 The General Electric Company, USA6
Outdoor storage is not recommended. Asidefrom all the possibilities of external weather conditions,erection conditions, environmental conditions etc.,which can affect an idle machine, variations intemperature and humidity can cause condensationthroughout the unit, producing rust and corrosion onmetal parts as well as deterioration of the electricalinsulation. If outdoor storage cannot be avoided, contactthe factory through the nearest General Electric officegiving full information on the circumstances andexplaining steps to be taken to protect the machine.Failure to protect the machine may invalidate thewarranty.
The storage facility must provide protection fromcontact with rain, hail, snow, blowing sand or dirt,accumulations of ground water, corrosive fumes andinfestation by vermin or insects. Continuous or severeintermittent floor vibration should be avoided. Electricalservice for space heater and illumination should beprovided. There should be fire detection and a firefighting plan. The machines must not be stored wherethey are liable to accidental damage or exposed to weldspatter, exhaust fumes or dirt. If necessary, erect suitableguards or separating walls to provide adequateprotection. Avoid storage in a atmosphere containingcorrosive gases, particularly chlorine, sulphur dioxideand nitrous oxides.
The machine in storage must be protected frommoisture condensation on the windings and other criticalparts. To prevent condensation, energize the machine’sspace heaters to keep the machine temperature above theroom temperature by at least 3C. During the periods ofextreme cold or rapid temperature decrease, the spaceheaters may not be adequate to maintain thistemperature differential. Therefore, safe supplementaryspace heating may be required.
The machine in storage should be inspectedperiodically and inspection records maintained. Thefollowing tests and inspections are designed to revealdeterioration or failure of protective systems (shelter,coatings and temperature control), of the machinewithout delay. Inspect the storage area for compliance tothe above criteria and inspect the stored machine for thefollowing:
1. Physical damage.
2. Cleanliness.
3. Signs of condensation.
4. Integrity of protective coatings.
5. Condition of paint - discoloration.
6. Signs of vermin or insect activity.
7. Satisfactory space heater operation. It isrecommended that an alarm system be in place tooperate on interruption of power to the space heaters.Alarms should be responded to immediately.
8. Record the ambient temperature and relativehumidity adjacent to the machine, the windingtemperature (utilizing the RTD’s), the insulationresistance and the polarization index. Refer to thesection entitled Insulation Resistance on page 15 forinformation on determining the insulation resistance andpolarization index.
Experience has shown that adequate precautionsduring storage will avoid costly deterioration of partsand lengthy maintenance procedures at installation andstart-up
.
GE Industrial Control Systems GEEP-124-I Copyright 1997,1998 The General Electric Company, USA 7
The location of the connected equipmentdetermines the general location of the machine. Motorsand generators, however require large volumes of cleanair for cooling and these machines have environmentrequirements which must be considered. They are:
1. A clean, well-ventilated location. 2. The machine enclosure should be consistent
with the location, environment and ambient conditions. 3. If the location is not relatively free of dust and
particles, the machine should have air filters or, in moresevere cases, the machine should be enclosed.
4. Other equipment, walls, buildings, etc. should
not restrict machine ventilation or allow ventilating airto recirculate.
5. Adequate space around the machine for
normal maintenance 6. Adequate overhead space for removal of the
top cover. 7. An environment free of corrosive gases and
liquids (both acids and bases).
WARNING: INSTALLATION OF THEMACHINE WHERE HAZARDOUSFLAMMABLE OR COMBUSTIBLE VAPORSAND/OR DUSTS PRESENT A POSSIBILITY OFEXPLOSION OR FIRE SHOULD BE INACCORDANCE WITH THE NATIONALELECTRICAL CODE, ARTICLES 500-503, ANDCONSISTENT WITH SOUND LOCALPRACTICES. EXTREME CARE IS REQUIREDFOR MACHINES SUPPLIED WITH A DUST-IGNITION-PROOF COLLECTOR-RINGHOUSING, ACCESSORY DEVICE, ORCONDUIT BOX SINCE ANY NICKS OR BURRSDURING DISASSEMBLY AND REASSEMBLYMAY DESTROY THE EXPLOSION-PROOF ORDUST-IGNITION-PROOF FEATURES.
IF IGNITABLE DUST OR LINT IS PRESENT,THE SURFACE TEMPERATURE OF SPACEHEATERS, IF SUPPLIED, SHOULD NOTEXCEED 80 PERCENT OF THE IGNITIONTEMPERATURE. REFER TO FACTORY FORINFORMATION ON SURFACETEMPERATURE. DUST AND/OR LINTSHOULD NOT BE ALLOWED TO BUILD UPAROUND THE SURFACE OF THE SPACEHEATERS.FAILURE TO OBSERVE THESEPRECAUTIONS MAY RESULT IN DAMAGE TOEQUIPMENT, INJURY TO PERSONNEL, ORBOTH.
Foundation
The mounting dimensions of the machine and theminimum foundation stiffness required to adequatelysupport the machine are supplied on the outline. Acertified outline drawing is supplied by the factory soonafter receipt of the order, and the above information isessential for planning and constructing the foundation.
A properly constructed foundation is essential toinsure the correct horizontal and vertical alignment ofthe driving and the driven equipment, to carry theweight, to resist the reaction torque, to absorb anycyclical or dynamical forces generated by the drivenequipment and to prevent vibration amplification. Sincea suitable foundation is a basic requirement forsatisfactory operation, it is recommended that a persontechnically competent in foundation design be consulted.
Although adequacy of the foundation is theresponsibility of the owner, the following suggestions areprovided as a guide. A concrete foundation is preferableto any other type of foundation. It should be reinforcedas required and should extend downward to have a firmfooting. The top of the foundation should beapproximately one inch short of the bottom allow forgrout.
If the machine must be located on structural steelor on a building floor, the weight and minimum stiffnessrequirements stated on the outline drawing must be met.Also, the dynamics of the entire structural system fromthe machine to the structure footing must be considered.
GE Industrial Control Systems GEEP-124-I Copyright 1997,1998 The General Electric Company, USA8
The machine has two full-length mounting feet,one on each side, consisting of machined steel barsintegral with the frame. When foundation caps or soleplates are used, their function is to act as spacersbetween the actual foundation and the unit. They are tobe a part of the foundation. Accordingly, if they areused, it is important that they be firmly attached to thefoundation to withstand the applied torques and normalvibration forces. It is also imperative that they be
supported evenly on the foundation and be located in alevel plane.
Place the machine on the foundation (sole plates,if used) with its shaft approximately in line with and atproper distance from the shaft of the machine to becoupled. Use shims under the feet to adjust for thecorrect shaft height. Refer to the outline drawing forinformation covering the shim location and requiredshim and depth. When this preliminary alignment iscomplete, install the holdown bolts but do not tight themuntil final alignment has been made.
GE Industrial Control Systems GEEP-124-I Copyright 1997,1998 The General Electric Company, USA 9
GeneralMachines with antifriction bearings are designed
to have the outer race of the opposite drive end axiallyheld by the end shield and to allow the outer race of theother bearing to move axially to allow for the thermalexpansion and contraction of the-rotor relative to thestator. Because one bearing is held, the machine doesnot have any end play designed into the rotor shaft. Theshaft cannot carry any external thrust unless specified atthe design state and designed into the bearing system. Acoupling which allows independent axial movement ofthe driven equipment shaft relative to the motor shaft,such as a splined type (or other axially independent type)coupling, is recommended for all units with antifrictionbearings.
Parallel and Angular Alignment forFlexible Couplings
Flexible couplings should not be used tocompensate for inadequate initial alignment of the twocoupling halves. Refer to the instructions supplied by theflexible coupling manufacturer. Coupling parts, such aspins, links, buffers, and spacers should be removed(depending on the type of coupling) and the sleevesshould be axially moved over the shaft to expose theactive hub portions of the coupling halves. The spacingbetween coupling hubs should be that recommended bythe coupling manufacturer.
The parallel and angular alignment of the twocoupling halves may be accomplished using theprocedures outlined below, provided the procedures tonot conflict with requirements supplied by the couplingmanufacturer. If a machined, vertical surface is notaccessible on one or both coupling halves, feeler or blockgauges may be substituted for the two dial indicators inperforming the angular alignment check. The twocoupling halves should be aligned to within 0.001-inchparallel and 0.0015-inch angular misalignment. Afterthe flexible coupling halves are aligned, the couplingshould be lubricated and assembled in accordance withthe coupling manufacturer’s instructions.
Parallel Alignment for FlexibleCouplings
Position the motor or generator on the foundationwith the plane of its feet horizontal as discussedpreviously under Mounting. Axially position the motorwith respect to the machine as discussed in the sectionentitled “Installation.” Attach a dial indicator on onecoupling hub with the indicating button on themachined, circumferential surface of the other couplinghub. See Fig. 1.
Set the dial indicator to zero. Mark the location ofthe indicating button with a visible mark. Rotate each ofthe two shafts in 90 degree increments, and successivelyread and record the dial indications when the indicatoris at 3:00, 6:00, 9:00 and 12:00 o’clock angularpositions. The indicating button must be positioned onthe mark for each reading.
Adjust the shaft position such that the differencebetween the two side readings (3:00 and 9:00 o’clock)and between the top and bottom readings (12:00 and6:00 o’clock) is less than 0.001-inch. This may requireseveral iterations. Lateral (3:00 and 9:00 o’clock)differences are corrected by lateral movement of the unit.Vertical (12:00 and 6:00 o’clock) differences arecorrected by appropriately adding or removing mountingshims. The proper shim location is shown on the outlinedrawing. Note that the total number of shims in a given
Fig. 1. Arrangement of indicator for parallel alignment
GE Industrial Control Systems GEEP-124-I Copyright 1997,1998 The General Electric Company, USA10
shim pack under any one foot should not exceed five,because too many shims may provide a “soft” mount onthat foot. This condition could cause dynamic problems.
Drilled and tapped holes are provided in themotor or generator feet for jacking screws as aconvenience in alignment. Note that jacking screws mustnot be used for permanent support.
Angular Alignment for FlexibleCouplings
Axially separate the coupling halves to theirmaximum end float. Attach a dial indicator on onecoupling hub with the indicating button positionedagainst vertical, machined surface on the other couplinghub. Attach a second dial indicator hub 180 degreesapart. See Fig. 2. Mark the locations of the indicatingbutton with a visible mark.
Set the two dial indicators to zero. Then, witheach coupling a full end float, rotate the two couplinghalves in 90 degree increments. Read and record eachdial indicator at 3:00, 6:00, 9:00 and 12:00 o’clockangular positions of the shaft. Two dial indicator setups,180 degrees apart, are used to correct for possible, axialshift of one shaft with respect to the other. Use thedifference in readings between the two indicators to
Fig 2 Arrangement of indicators for angular alignment
determine the angular misalignment between the twocoupling halves. Add or remove shims under the feet asappropriate to correct for misalignment in the verticalplane. A lateral, angular movement of the unit isrequired to correct for misalignment in the horizontalplane. Continue the angular alignment procedure untilthe angular misalignment does not exceed 0.0015-inch.This may require several iterations.
GE Industrial Control Systems GEEP-124-I Copyright 1997,1998 The General Electric Company, USA 11
WARNING: MOTOR AND CONTROL WIRING,OVERLOAD PROTECTION AND GROUNDINGSHOULD BE IN ACCORDANCE WITH THENATIONAL ELECTRICAL CODE ANDCONSISTENT WITH SOUND LOCALPRACTICES.FAILURE TO OBSERVE THESE CAUTIONSMAY RESULT IN DAMAGE TO THEEQUIPMENT, INJURY TO PERSONNEL, ORBOTH.
Power connections
The stator winding is terminated in the powerterminal box. Connections to the stator wiring should bemade in accordance with the stator connection diagramfor the machine or with the connection diagram shownon the main nameplate. The stator is wound to produceclockwise rotation, facing opposite drive and when thephase sequence of the applied voltage is T1, T2, and T3(i.e. when the phases of the supply voltage connected tothe power leads reach positive maximum in that timeorder.). The direction of rotation can be changed byreversing any two of the connections. However, themachine should always rotate clockwise viewed from theopposite drive and unless it was specifically sold foropposite or dual rotation, since the fans, or otherdevices, may be directional. Machines Furnished with asingle direction of rotation have an arrow on the driveend. If the owner desires to operate the motor in oppositestandard rotation, first check the factory for suitabilitythrough the nearest General Electric office.
Before any electrical connections are madebetween the machine and the owner’s power oraccessory cable or wire, it is desirable to check theinsulation resistance of the winding to determine if thewinding is sufficiently dry for safe operation. See thesection entitled Insulation Resistance on page 15. Thischeck may prevent having to break the electricalconnections later.
The stator winding leads are terminated withconnectors for bolting to corresponding connectors onthe cable from the owner’s power supply. The boltedconnections should be adequately insulated, phase-to-phase and to ground.
The rotor winding of wound-rotor inductionmotors is terminated on the collector rings. Externalconnections to the brush rigging should be made inaccordance with the rotor connection diagram for themachine or with the connection diagram supplied on theinside of the collector cover. The rotor-winding amperesat rated horsepower with the slip rings shorted (i.e., noexternal impedance in the rotor circuit), is shown on thenameplate as Secondary Amperes. The ring-to-ringvoltage of the rotor winding at locked rotor, is shown onthe motor nameplate as Secondary Volts. Note that themachine should not be plugged for braking or otherreasons, by control external to the motor unless themachine has been ordered as suitable for such duty.Plugging will increase the ring-to-ring voltage to twicethat on the nameplate. Therefore, the rotor insulationmust be designed for this higher level. Questionsconcerning this should be referred to the nearest GeneralElectric office. Care should be taken to assure thatinsulation containing silicon is not used for thesecondary conductors. A small amount of silicon in thearea will greatly accelerate brush wear.
Accessory connections
Depending upon the specific equipmentfurnished, (see outline nameplate) the machine mayinclude any of the following accessories:
• Stator winding resistance temperature
detectors, 2 per phase • Bearing resistance temperature detectors. • Copper-constantan bearing thermocouples • Bearing temperature readout capability • Bearing temperature alarm and shutdown
contact capability
• Space heaters, with either 220C or 120Cmaximum surface temperature
• Stator winding thermostat
GE Industrial Control Systems GEEP-124-I Copyright 1997,1998 The General Electric Company, USA12
• Heaters for the bearing oil reservoir. Switch for excess pressure drop across air filters
• Proximity type vibration pickup for shaftvibration with or without proximeters (sleevebearings only)
• Velocity vibration pickup for end shield
vibration (antifriction bearings only) withalarm light and contacts
When supplied, all of the above accessories willhave electrical terminations in the accessory terminalbox, except for the seismic vibration pickup which hasits electrical termination for the contacts at the devicelocated on the endshield.
For all of the accessories that have electricalterminations in the accessory terminal box, a SchematicDiagram and an Accessory Lead Connection Diagramwill be provided on the inside of the accessory terminalbox cover. This gasketed cover should be kept closed toprevent the entrance of moisture, dust and conductingparticles. The gasketed cover should be kept closed toprevent the entrance of moisture, dust, and conductingparticules. The gasketed cover should also be closed forelectrical safety, except when required to performconnection work inside the box.
Grounding
Two stainless-steel, grounding pads are suppliedon the frame. One at each end near the foot. A pair ofdrilled and tapped holes, with NEMA spacing and size1/2-13, are provided in each grounding pad. Oneadditional stainless-steel, grounding pads are suppliedinside the power terminal box in the region of the throatconnection between the power terminal box and theframe. These pads are used for connection of groundleads, cable shield, etc., as may be required. Thesegrounding pads are also drilled and tapped as describedabove. The machine should be grounded in accordancewith the National Electric and consistent with soundlocal practices.
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Variations of applied stator voltage and frequencyfrom the rated nameplate values will result variation ofmachine performance. Torque, efficiency, power factor,heating and stator current will change. Also, noise andvibration levels may change. The torque varies as thesquare of the voltage; therefore, a 10 percent decrease involtage will decrease the torque by 19 percent. For bestoperating performance, nameplate voltage and frequencyshould be maintained.
The machine will operate successfully, underrunning conditions and at rated load. with variations involtage or frequency up to the limits indicated below:
1. Plus or minus 10 percent of rated voltage, atrated frequency.
2. Plus or minus 5 percent of rated frequency, at
rated voltage. 3. A combination of variation in voltage and
frequency of 10 percent (sum of the absolute quantities)of the rated values, provided that the variation infrequency does not exceed plus or minus 5 percent of itsrated value.
Performance of the machine within these voltageand frequency variations will not be in accordance withthe values established for operation at rated nameplatevoltage and frequency.
Line-to-line Voltage Balance
Polyphase machines are sensitive to unbalance inthe applied line voltages. If unbalances exist in theapplied line voltage, unbalance in phase currents willresult. The resulting unbalance in currents will, ingeneral, be significant. For example, the locked-rotorcurrent will be unbalanced by the same percentage as thevoltage, but at operating speed the percentage unbalanceof the current will be 6 to 10 times the percent unbalanceof the voltage. Percent Voltage Unbalance is defined asfollows:
PercentVoltage = x 100Unbalance
Where Average Voltage is arithmetic average ofthe three line voltages and Maximum VoltageDerivation is the greatest line voltage deviation from theaverage.
Unbalanced line voltages result the production ofnegative sequence currents in the machine that producefields which rotate in a direction counter to the normalfield. This results in an increase in current, losses andheating with reduction in torque, efficiency and powerfactor. Accordingly, line voltages should be as closelybalanced as can be determined on a voltmeter.
If line voltage unbalance exists, the machinemay be damaged and should be derated in accordancewith Figure 20-2 of NEMA Standard MG-20.55, inorder to reduce the possibility of such damage. Deratingfactors, for several values of line voltage unbalance, aregiven below.
Percent Voltage Unbalance 1 2 3 4 5
Operating Factor 0.99 0.95 0.89 0.82 0.75
In addition, the selection and setting of themachine overload-protective device must consider thederating factor and the increase in current, resultingfrom line voltage unbalance. This is a difficult procedurewhich must be done by a person familiar with settingprotective devices to adequately protect the machine. Itis recommend that the nearest General Electric office becontacted if assistance is required.
Maximum Voltage DerivationAverage Voltage
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WARNING: BEFORE MEASURINGINSULATION RESISTANCE, THE MACHINEMUST BE AT STANDSTILL AND ALLWINDINGS BEING TESTED MUST BECONNECTED TO THE FRAME AND TOGROUND FOR A TIME TO REMOVE ALLRESIDUAL ELECTROSTATIC CHARGE.GROUND SURGE CAPACITORS, IFFURNISHED, BEFORE DISCONNECTING ANDISOLATE FROM LEADS BEFOREMEGGERING.FAILURE TO OBSERVE THESEPRECAUTIONS MAY RESULT IN INJURY TOPERSONNEL.
Insulation resistance is determined by applying a dcvoltage, typically 500 or 1000 Volts, across insulation,measuring the current flow after the voltage has beenapplied for a specific length of time and thendetermining the ratio of voltage to current. Because thecurrent flow is low, the value of insulation resistancewill be great in terms of ohms. Accordingly, megohmsare used as a practical unit.
Factors affecting insulation resistance are asfollows:
1. Moisture2. Surface cleanliness of the insulation3. Temperature4. Length of time of applying the dc test voltage5. Magnitude of the applied dc test voltage
Fig. 1. Temperature correction factor curve
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The magnitude of the applied dc test voltageonly slightly affects the value of the insulation resistanceand the use of a 500 Volt or 1000 Volt megger for statorwindings (and a 500 Volt megger for rotor windings) issuitable for machines covered by this InstructionManual. The environmental conditions of moisture andsurface cleanliness, together with the ambienttemperature, largely determine the value of insulationresistance. The insulation must be clean and dry and themeasured value must be corrected to 40C. This value isthen compared to a minimum acceptance criteria.Moisture and dirt will decrease the insulation resistanceof a winding and these conditions must be corrected inorder to increase it.
The insulation resistance of a winding measuredby a 500 Volt or a 1000 Volt megger, with the testapplied for 1 minute, should not be less than.
R = KV + 1where : R = Insulation Resistance in megahoms,
corrected to 40C baseKV = rated voltage of the winding in kilovolts
To convert the actual insulation resistancereading of the megger, Rt, taken at an ambient windingtemperature in degree Celsius, to R, make the followingconversion.
R = KtRt
The temperature correction factor, Kt, can bedetermined for any specific winding or a reasonableapproximation can be used. Both methods will bedescribed.
To determine the temperature correction factorfor a specific winding, make several measurements (atleast five) at several different temperatures, all of whichare above the dew point. Then plot the results, withmeasured insulation resistance on a log scale andwinding temperature on a linear scale. The resultsshould approximate a straight line, from which the valueof insulation resistance at 40C can be determined.
A more general method, with reasonableaccuracy, is to use the curve, Fig. 1, to determine Kt as afunction of the winding temperature at the time ofmeasurement. It is based on doubling the insulationresistance for each 10C reduction in temperature, forconditions above the dew point. It has been found to bereasonable for new windings.
The polarization index is frequently helpful inevaluating the cleanliness and freedom from moisture ofa winding. The polarization index is a measure of thechange is insulation resistance with the time duration forwhich the test is applied. It is conducted by applying themegger for 10 minutes and determining the insulationresistance at 1 minute and 10 minutes. The polarizationindex in the ratio of the 10-minute insulation resistancereading to the 1-minute insulation resistance reading,both readings haven been corrected to a 10C temperaturebase. Clean, dry windings should exhibit a polarizationindex of 2 or more.
Each winding of each unit will have its owninsulation resistance history which is unique to it. It isrecommended that the insulation resistance be measuredand recorded at least every six months, and more often iffeasible, and that the polarization index be measured andrecorded at least once a year. This accumulatedinformation will provide a data base which will behelpful in managing preventative maintenance.
The user is referred to IEEE Standard 43, IEEERecommended Practices for Testing InsulationResistance of Rotating Machinery, for a morecomplete discussion of the complete subject of InsulationResistance.
Pre-start inspection
Before the machine is started for the first time, apre-start inspection should be made. The following aresome of the items frequently overlooked.
1. Measure the insulation resistance of thewindings. For machines located in or near salt air orother corrosive environments, a polarization indexshould also be taken.
2. Verify that the voltage and frequency
corresponds to the nameplate. 3. Verify that the phase sequence of the applied
voltage is correct for the desired direction of rotation.Verify that the desired direction of rotation agrees withthe nameplate.
4. For totally-enclosed. water-cooled machines,
verify that the cooling-water temperature does notexceed the value on the nameplate.
5. The lubricant used should agree with the
nameplate and this instruction book.
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6. Verify that the bearing housings on machines withself-lubricated bearings have been filled to the properlevel. 7. The oil flow to each bearing housing on flood orforced lubricated machines should be adjusted so the oillevel in each bearing housing is maintained. 8. All accessory devices should be connected andoperational. 9. All protective and control equipment should beinstalled and operational. 10. The machine hold down bolts should be tightenedand the foot doweling completed. 11. The coupling alignment should be in accordancewith previous instructions. 12. The interior of the motor frame, top cover, terminalboxes and fan casings (for Totally-enclosed Air-to-AirCooled Machines) should be free of tool, waste and otherforeign materials. 13. The air gap of the machine should be free of foreignmaterial. 14. Guards should be in position to protect personnelfrom moving parts such as coupling, etc. 15. Walls, baffles, other equipment, coupling guards,etc., should not obstruct the necessary movement of airrequired to adequately ventilate the machine. 16. Any load condition of the drives equipment whichcontributes its load torque, at low speed, should be setcompatible with the starting torque specified for themotor (i.e., if it is necessary to start the drivenequipment in an unloaded condition, in order tocorrespond to the starting torque specified for the motor,then verify that the driven equipment is appropriatelyunloaded).
17. All covers should be in place and properly secured.The cover on the power terminal box and the accessoryterminal box should be properly secured.
Initial test run
The starting current of a motor is several timesthe rated current. This starting current causes thewindings to heat at a much higher rate than normal andcauses the windings to heat at a much higher rate thannormal and causes magnetic forces on the end turns tobe many times normal. The section of this publicationentitled “Frequency of Starts and Load Inertia” shouldbe read, since the user may also be considering checkoutand adjustment of some of the control and protectionequipment at this time. The limitations on startingmust be observed at all times to prevent damage tothe machine.
After verifying that the machine and the rest ofthe system is ready for operation, a controlled initialstart should be made and a test run performed to verifythat the unit is properly installed and is operational. Forthis run, it is recommended that several people beappropriately located in order to observe any problems.The following are the minimum steps to be taken on theinitial test run. Note that the machine must be shutdown immediately if any problem occurs.
1. If so equipped (See Outline Drawing), startauxiliary lubrication system and verify oil flows. Alsocheck interlocking to make sure machine is preventedfrom starting unless the lubrication system is functioningand the machine will be shut down on the loss oflubrication.
2. Start the machine. (For a generator, bring upto speed with prime mover.)
3. Listen for any unusual noise duringacceleration and running.
Machines with oil-lubricated bearings only.
4. Observe oil flow and/or oil ring action foreach bearing.
5. Verify that the rotor runs at the magneticcenter.
6. Observe and record each bearingtemperature and the rate at which it is increasing foreach bearing. Initially temperatures will rise rapidly andthen should level off.
NOTE: Bearing temperatures should notexceed 95C for a sleeve bearing.
GE Industrial Control Systems GEEP-124-I Copyright 1997,1998 The General Electric Company, USA 17
7. Observe the temperature of windings(Resistance Temperature Detectors (RTD’s) are providedon all machines). In no case should the windings exceedthe sum of the rated rise on the nameplate plus themaximum design ambient.
8. Determine that the amplitude of vibration is
not excessive (see the section entitled “Vibration” in thispublication). Misalignment should be the first item tocheck if there is unacceptable vibration.
9. Verify that all accessories supplied with themachine are functioning normally and are performingconsistent with the load on the machine and system.
10. Verify that all control and protectivedevices are functioning normally and are performingconsistent with the load on the machine and system.
11. The machine should be operated and fullyobserved for not less than two hours and should be freeof any problems before it is released for normal duty.
12. As stated earlier, the machine must beshut down immediately if any problem occurs. Shouldany problem occur, it source should be determined andcorrected, and then the initial test run should berepeated.
Vibration
General Electric motors and generators, coveredby this Instruction Manual, are balanced at the factory,in accordance with NEMA Standard MG 1-20.52 andMG 1-20.53, to be within the following limits (unlessotherwise specified in the sales contract).
Speed (RPM) Maximum Peak-toPeak Amplitude
(Inches) on BearingHousing
MaximumVelocity
Inches/sec, zero-peak
3600 0.0005 .0941800 0.0016 .151200 0.0024 .15
900 and below 0.0025 .12
Vibration amplitude measurements are made onthe bearing housing and are taken in the vertical,horizontal and axial directions.
If the owner’s half coupling was sent to thefactory to be mounted onto the machine shaft extension,the rotor is balanced with the half coupling installed.Otherwise, the rotor is balanced with a half key (i.e., thekeyway is filled with a steel bar equal in length to thekey length shown on the outline and flush with the topof the keyway). The shaft key furnished with themachines of 1500 rpm and higher is a full-length, fullkey with a three-inch long half key extension on oneend. To maintain factory balance, cut the key to lengthas follows. See Fig. 2.
1. Measure the coupling hub length (H) and cutthe full key to length H by cutting the excess from thefull key end.
2. Cut the half key end so that the overall key
length equals the key length shown on the outlinedrawing.
3. Full key must fill coupling/keyway. Half keymust fill shaft/keyway.
WARNING: TO AVOID EXCESSIVE STRESSESIN THE KEY, THE MAXIMUM LENGTH OFTHE HALF KEY SHOULD NOT EXCEED 3.0INCHES.FAILURE TO OBSERVE THIS PRECAUTIONMAY RESULT IN DAMAGE TO THEEQUIPMENT, INJURY TO PERSONNEL, ORBOTH.
Fig. 2. Key alignment
GE Industrial Control Systems GEEP-124-I Copyright 1997,1998 The General Electric Company, USA18
The foundation should be constructed inaccordance with the requirements in the sectionentitled “Foundation” on page 7. If the unit has beenproperly aligned, the amplitude of the vibration ofthe installed motor should be as stated in the abovetable. If vibration amplitudes are significantlygreater than these values, the instruction referencedabove should be reviewed. Misalignment is the mostprobable cause of excessive vibration. Other possiblecauses are “soft” shim packs under one or more feet,loose foot bolts or an inadequate foundation.Contributions to vibration from the driven equipmentshould not be overlooked.
Do not operate the machine with excessivevibration. If the cause cannot be found andcorrected, contact the nearest General Electric office.
Frequency of starts and loadinertia
When a motor starts, it must accelerate therotational inertia of its own rotor and that of thedriven equipment from standstill to full speed.Accordingly, it must transfer and store a largeramount of energy into the rotating parts in a shorttime. An equal amount of energy is dissipated in therotor windings in the same short period of time.
During the starting period, current in thewindings are several times the rated value. Thiscauses heating of the windings at a significantlygreater rate than occurs at full-speed operation.Also, because magnetic forces are proportional to thesquare of the current, forces on the winding endturns are many times greater than the normalcondition.
For the above reasons, the frequency of starts andthe magnitude of rotational inertia of the connected load,must be limited for squirrel-cage induction and synchronousmotors. The motors covered by this Instruction Book (unlessotherwise stated in the, sales contract), are suitable foraccelerating the rotational inertia of the driven equipment inaccordance with Standard MG 1-21.42. The motors aresuitable for the following frequency of starts.
1. With the motor initially at ambient temperature,two starts in succession, coasting to rest between starts.
2. With the motor initially at a temperature not
exceeding its rated temperature, one start.
It is recommended that the total number of startsmade in the life of the machine be controlled, with an effortto minimizing them, since the life of the machine is affectedby the total number of starts.
Wound rotor induction motors have the capability toaccelerate high inertia loads with limited stator currentthrough the use of external resistance inserted in the rotorcircuit. The motor characteristic is changed by adjusting theresistance. Most of the energy dissipated in the rotor circuitduring the acceleration is dissipated in the resistor externalto the motor.
Oil level
Sleeve bearing machines are furnished with an oillevel gauge in each bearing housing. Refer to the PartsIdentification Instruction for this model to locate the oillevel gauge. The gauges are either bulls eye type, with acircular glass window, or column type.
With the bulls eye type gauge, the centerline of thegauge indicates maximum oil level and the bottom of thegauge indicates minimum oil level
.
GE Industrial Control Systems GEEP-124-I Copyright 1997,1998 The General Electric Company, USA 19
The machine covered by this Instruction Manualhas been designed with reliability and utility as goals. Itis constructed of high quality materials. If it is installed,operated and maintained in accordance with theinstructions in this manual, it can be expected to givemany years of trouble-free service.
Importance of a MaintenanceProgram
The purchase and installation of a large electricmachine represents a significant capital investmentwhich should be protected by a thorough maintenanceprogram. This program should include the machine aswell as the protective and control equipment.
A maintenance program is based on fourconcepts: (1) maintaining cleanliness, (2) periodicinspection, (3) keeping adequate records, and (4) takingcorrective action on a timely basis. Periodic inspectionprovides the system and discipline for maintainingcleanliness as well as assuring that parts are functioningproperly. The frequency of periodic inspections can varyfrom several per day for such items as windingtemperature readout (if printout and/or automaticshutdown control is not provided) to once per month fora general inspection on the interior of the unit. Thekeeping of accurate records is necessary to maintain ahistory of the unit and to provide a procedure forcheckoff and verification of the various items. If aproblem is encountered, whether it be a minor and afrequently encountered problem, such a cleaning, or asignificant problem such as increased vibration levels, itshould be corrected as quickly as possible afterdetermining its need. If the unit should requiresignificant repairs in the course of its life, it isrecommended that they be done in a General ElectricService Shop.
WARNING: BEFORE INITIATINGMAINTENANCE PROCEDURES, DISCONNECTALL POWER SOURCES TO MACHINES ANDACCESSORIES. FOR MACHINES EQUIPPEDWITH SURGE CAPACITORS, DO NOTHANDLE CAPACITOR UNTIL DISCHARGEDBY A CONDUCTOR SIMULTANEOUSLYTOUCHING ALL TERMINAL AND LEADS,INCLUDING GROUND. THIS DISCHARGECONDUCTOR SHOULD BE INSULATED FORHANDLING.REPLACE ALL GROUNDING CONNECTIONSPRIOR TO OPERATING.FAILURE TO OBSERVE THESEPRECAUTIONS MAY RESULT IN INJURY TOPERSONNEL.
Importance of Cleanliness
The location of the connected equipment willnecessarily determine the location of the machine.Accordingly, considerable variation between differentapplications and between different sites will beencountered. To a significant degree, the choice of theenclosure will compensate for variations in environment,particularly for moisture and weather conditions.However, the preservation of cleanliness of theventilating inlet and outlet openings, air ducts, winding,space heaters, accessory connection blocks, etc., isessential.
Ventilating air will bring environmentalcontamination to the active parts of an ambientventilated machine. Properly maintained air filters willsignificantly reduce the amount of particles in the air,but cannot totally eliminate them. Totally-enclosed typeenclosures will greatly, but not completely, reduce theinterchange of external environmental air and internalrecirculating air.
Dirt particles, entrained in the ventilating air,tend to accumulate in air ducts and on the surface of thewindings. This accumulation will have adverse effectssuch as an increase in operating temperature, decrease ininsulation resistance and more rapid deterioration of theinsulation. Dirt particles in the lubricating oil or greasesupply will cause more rapid bearing wear and evenbearing failure. Acid and alkali vapors can, over a
GE Industrial Control Systems GEEP-124-I Copyright 1997,1998 The General Electric Company, USA20
period of time, cause corrosive deposits to develop whichfurther contribute to deterioration.
Keep metal particles such as copper, iron or steelaway from the machine. This is especially important foriron and steel since such particles will adheremagnetically and are extremely difficult to remove. Theymay be agitated by magnetic fields present duringoperation causing abrasion and eventual failure ofinsulation. If for any reason sawing, drilling, machining,etc., of ferrous materials must be done in the generalvicinity of the unit, such work should be done asremotely as possible. The unit should not be in operationat that time. All filings, chips, etc., should be completelyremoved prior to starting the unit. The same precautionsshould be observed for copper chips or other conductingmaterials.
In removing dirt and contamination from themachine, a vacuum is much preferred to positive airpressure. Air pressure does not remove, but onlyrelocates, the objectionable material. It frequently drivesand embeds foreign material into the sides of insulationas well as into natural crevices inside the machine. Asuction hose from an industrial-type vacuum cleaner
should be used for cleaning. The hose wand or nozzle,which comes into direct contact wit the machine parts,should be small enough in cross-section as to produce areasonably high air velocity at the entrance to the wand.This is necessary to accelerate and move the foreignmaterial into the vacuum hose.
Frequency of Inspection
Frequency of inspection will vary with the itembeing inspected and with the severity of localenvironmental conditions.
Certain items, such as winding temperature,bearing temperature and vibration amplitude should bemonitored on a conditions basis. If local provision hasbeen made for readout or printout of these parameters,and if contacts and relays are provided to shut down theunit in case of above-normal temperatures, then all thatis required for inspection is to assure that the protectiveequipment is operational and set to detect abnormaloperation. Conversely, if no provision has been made to
Item Frequency of InspectionClean Conditions Severe Conditions
Stator winding (including bracing and support structures, coilend connections, insulation resistance check)
Yearly Quarterly
Rotor end ring (or end turns) Yearly Yearly
Rotor removal (rotor and stator bore) Every Five Years Every Five Years
Stator core (with rotor removed) Every Five Years Every Five Years
Brushes and collector rings Quarterly Monthly
Bearing inspection Every Three Years Yearly
Bearing lubrication Twice Yearly Bi-Monthly
Separate lube system (if supplied) Quarterly Monthly
Top cover (filters) Quarterly Monthly
protect the winding and bearings from over temperaturesby means of protective relays, then the maintenanceprogram must discharge the local operator with beingaware of the winding and bearing temperatures on acontinuous basis. This also applies to vibrationmonitoring and protective equipment.
Routine inspection and maintenance of the statorwinding, rotor winding, core, brushless exciter,brushless and collector rings (for machines suppliedwith this equipment), bearings and top covers should bedone on a scheduled basis. However, the frequency willdepend upon the severity of local environmentalconditions. Installations located in clean environments
GE Industrial Control Systems GEEP-124-I Copyright 1997,1998 The General Electric Company, USA 21
will require only occasional routine inspections. Otherinstallations located in severe environments, such aspaper mills, cement mills, steel mills, power stations,etc., will require routine inspections more frequently.The accompanying tabulation is suggested as a basis fora maintenance program for these two cases. There willbe may installations falling between then, as well asinstallations with extremely severe conditions. Goodjudgment and common sense should be exercised whenstructuring the maintenance program. Impropermaintenance and inspection can result in prematurefailure.
Stator Winding Inspectionand Maintenance
For special applications, such as belt drives, or onsmaller machines, a one piece solid end shield andbearing may be supplied. Generally, direct-drivemachines are arranged to permit the removal of theupper half of the end shield from either end forinspection purposes without disturbing the motor line-up.
To gain access to the stator winding, first removethe end shield upper half on each end of the unit. Toaccomplish this, remove the screws which secure it tothe frame and to the bottom half of the end shield. Notethat a gasket is located between the mating surfaces forsealing against moisture and dirt. This gasket should bekept free of dirt for use during reassembly. On smallerframe sizes, one or two men can lift the cover. On largerframe sizes a hoist or crane is required.
Removal of the upper half of the end shieldexposes the top-half or a large opening in the end of theframe. The air deflector or baffle can be seen inboard ofthis semi-circular opening. Remove the top-half of theair deflector on each end of the unit. To accomplish this,remove the screws which secure it to the internal ringand disconnect the L-clamps joining the upper and lowerair deflectors. If further accessibility is desired, rotate thering and lower the deflector. Remove the screws holdingthe lower deflector to the ring. The lower air deflectorcan now be removed. Note that reassembly of the airdeflector and end shield cover is the reverse of thedisassembly steps. This disassembly will provide accessto the entire top-half and some portion of the bottom-half of the stator end turns, end turn bracing and ends ofstator wedges. For a routine inspection, this providessufficient view of the winding to indicate its generalcondition and allows room for cleaning with a flexible
vacuum hose. When the rotor is removed on a lessfrequent schedule, more of the winding is accessible.
For a routine inspection clean the accessibleportions of the winding with a vacuum hose equippedwith an appropriate non-metallic wand or nozzle. Referto the “Importance of Cleanliness” section of thispublication.. (Note that, if this is an emergencyinspection instead of a routine one, the first step is tolook for the fault, before disturbing the existing status ofthe winding by cleaning.)
Inspect the stator coil bracing and supportstructure. Look for evidence of looseness, movement orchafing of the coil ends relative to the support structure.Small “tails” and other similar surface irregularities ofthe epoxy varnish on, and around, the surface geometryof the coil bracing system is not significant and resultsfrom the curing of the vacuum-pressure impregnation ofthe prewound core. Check for tightness of the bracinggussets to the core plate.
Inspect the stator coils end turns, connections andwedge ends. All dirt or other foreign materialaccumulations between coil sides should be removedwhile exercising care not to damage the integrity of thecoil insulation. The surface of the coils should be free oflocalized areas of damaged insulation resulting fromimpact, such as would occur from being struck by anedge of the rotor during a previous disassembly andreassembly of the rotor assembly.
Because of the large volume of ambient air whichpasses through ambient ventilated machines, certainairborne, abrasive particles can wear away some of thecoil insulation over a period of time. Accordingly forsteel mill, coal mine, taconite and certain otherapplications, considerable attention should be given toobserve this condition.
If cracks are evident in the varnish and areassociated with evidence of movement and chafing of thebracing system, they should be investigated.With the end shield cover and top air deflector coverremoved, access to the stator slot wedges is some whatlimited. However, it is possible to obtain a reasonableimpression of wedge conditions from an inspection ofthe ends. On a less frequently scheduled basis, when therotor is removed, the entire length of the wedge may beviewed. The wedges should be tightly secured. Theyshould show no evidence of movement or migration. Theends of the wedge should be free of fraying. Again asindicated above for coil insulation,abrasiveenvironmental contaminates can wear away wedges.However, such an affect may not be visible on thewedges except at inspection in which the rotor isremoved.
GE Industrial Control Systems GEEP-124-I Copyright 1997,1998 The General Electric Company, USA22
The insulation resistance should be measured andrecorded during each inspection of the winding. Refer tothe section entitled Insulation Resistance on page 15. Ifthe measured value of insulation resistance in megohmsis less than (KV + 1), when corrected to 40C, themachine should not be put back into service until stepshave been successfully taken on the winding to restoreits insulation resistance to that value, or more. At thispoint, a polarization index measurement may also behelpful as additional data on the condition of thewinding. See the information on page 16 - PolarizationIndex.
Moisture and dirt are the two primary causes oflow insulation resistance of a winding. Accordingly, thefirst two steps in correcting such a condition are to drythe winding and to remove all possible dirt andcontamination. Space heaters should always be turnedon when the machine is shut down. If this is not done,the insulation resistance will usually decrease because ofcondensation on the windings. Space heaters may beused to dry out a winding, but adequate time must beallowed to accomplish it. Also, low voltage may beapplied across the winding terminals (ac or dc) tocirculate a fraction of must be monitored in order to keepthe temperature below rated during the drying outprocess. Six to eight hours, depending upon the size ofthe unit, are required for drying a winding withcirculating current. The winding should be thoroughlycleaned, in order to remove dirt and contamination, asan important part of the program to increase theinsulation resistance value.
A thorough cleaning and drying program willusually restore the winding insulation resistance to(KV + 1) megohms, or more, corrected to 40C. If it doesnot, it is probable that some additional factor, beyondmoisture and dirt, exists. If the incoming cable was notdisconnected from the motor leads in the conduit box,the additional cable could significantly affect theinsulation resistance. Surge capacitors which are directlyconnect to the stator winding could procedure a similaraffect. In both cases, the connection with the statorwinding should be opened and the insulation resistancetest repeated.
If all the above corrective actions fail to restorethe insulation resistance value, it is highly probable thatexpert Assistance will be required. It is recommendedthat a General Electric Service Shop be contacted forassistance.
There are additional tests which are available foruse on stator windings, particularly on older windings,to determine their present condition and serviceability.Among these are high potential dc and ac testing. It isimportant that such testing be done only by peopletrained in conducting the tests, to avoid unnecessarilydamaging the winding, to correctly interpret the resultsand to observe all the safety precautions necessary toprotect personnel. If it is desired to do such testing atsome point in the history of the unit, it is recommendedthat a General Electric Service Shop be contacted.
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Bearings must carry the weight of the rotor;normal magnetic forces between the rotor and stator; anylateral belt pull; and still maintain the rotor in accuratelocation relative to the stator bore. Accordingly, theyconstitute a very important part of the unit and havebeen selected to give long life on a unit which has beencorrectly installed, aligned and maintained.
The antifriction bearings used on this unit aregrease lubricated. The grease consists of a lithium basesoap impregnated with a suitable lubricating oil. It isplaced in close proximity to the bearing and the oil seepsout of the soap structure and lubricates the balls orrollers as they move relative to the inner and outer race.Although the amount of grease required to lubricateantifriction bearings is not great, it is essential thatgrease always be present, that the grease be of thecorrect type and that it be clean and free ofcontamination. The correct grease viscosity, specified inSSU units at 100F, is given on the nameplate. Theantifriction bearings used are specified on thenameplate.
Bearings should be lubricated once every sixmonths for normal, applications associated withmoderate to average environmental conditions of dirt,moisture and heat. For more severe conditions of anyone or more of the above environmental conditions, thelubrication frequency should be increased to every twomonths.
To lubricate the bearings, first stop the unit andremove voltage from all circuits. Remove the greaseplug, located on the outboard side of the end shield, atthe bottom of the bearing housing, and make certain thatthe grease-relief hole is free of hardened grease. Thegrease fitting is located at the end of the pipe below thehorizontal split. (on totally-enclosed, air-to-air cooledmachines the grease fittings are located on the side ofthe external fan casing. The grease relief plug isconnected to a spiral rod which assists in purging greasefrom the bearing cavity). Wipe the grease fitting clean.
Using a hand-operated grease gun, apply thespecified grease. Continue to apply grease until oldgrease cases to purge from the grease-relief hole and it isa apparent that new grease is purging. Make certain thatthe purged grease is captured and removed from the sidearea. Leave the grease-relief hole plug temporarily off.Start the unit and operate for about 30 minutes. Anyexcess grease will be expelled from the grease-reliefhole. Again, stop the unit and remove voltage from allcircuits. Then, replace the grease plug and remove theexcess grease which was just purged.
It is important that end shield vibration andbearing noise be monitored.
Some conditions which can cause bearing failuresto occur are:
1. Insufficient grease, or too much grease. 2. Incorrect grease specification. 3. Ambient temperature conditions either too
hot or too cold for the viscosity of the grease being used. 4. Contaminated grease. 5. Misalignment of unit and driven equipment(in parallel, angular or axial misalignment). 6. Seals too tight. 7. Bearing operated longer than design life (L10
130.000 hours for direct drive) (L10 40.000 hours forbelted drive) will have an increased risk of failure.
If one or both bearings exhibit an increase invibration, noise or temperature, above the normaloperating conditions, the unit should be shut down andthe cause determined and corrected.
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Since the method of greasing anti-frictionbearings tends to purge the hosing of used grease,removal of all grease should be required infrequently.
Whenever the motor is disassembled for generalcleaning, however, the bearings and housings should becleaned of old grease by washing with a grease-dissolving solvent.
If so desired, the ball bearing may be cleanedwithout disassembling the machine. Follow thisprocedure:
1. Remove the alemite fitting and the reliefplug.
2. Free both holes of any hardened grease.
3. Pass flushing liquid through the housingwhile the machine is operating. Flush until no greasecomes out with the liquid. For flushing use hot mineraloil (not more than 100 C or 212 F).
4. Continue the cleaning by alternately injectingsmall amounts of flushing liquid while the relief plug isin place and drawing off the liquid by removing thedrain plug.
5. Regrease the bearing and then insert therelief plug.
Grease Recommendation
In order to assure proper relubrication of themotor, regrease with Shell Alvania R2 or a greasemeeting the following specifications:
Worked penetration 265-296Oil viscosity, SSU at 100F 400-550Soap type Sodium or lithiumN-H bomb, minimumhours for 30 psi drop at210F
750
Bleeding, maximumweight % in 500 hours212F
10
Rust inhibiting Yes
Grease for Low Temperature: Esso Beacon 315Grease for High Temperature: Rycon #2
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One of the most important features in thesuccessful operation of an induction motor are thebearings.
The machines covered by these instructions aresupplied with anti-friction bearings.
A conscientiously applied program of preventivemaintenance will add years of useful life to the bearings.In order to assure proper operating conditions, seesection entitled Grease Recommendation.
Bearing Repair and Replacement
Even though high-quality design and workman-ship are incorporated in a bearing, it sometimes becomesnecessary to remove if for maintenance. It is for thisreason that the following instructions are included.
Care must be taken to avoid scratching or nickingthe critical surfaces of the balls or rollers.
Bearing Disassembly
Extreme care is required in the disassembly of amachine for bearing removal. In addition, the surfaces ofthe shaft bearing fit and the bearing itself must beprotected during and after disassembly operations.
1. End-Shield Bolt2. Upper-Half End Shield3. End-Shield Bearing Cap Screws4. End-Shield Gasket (when used)5. Grease Fitting6. Slinger Set Screw (when used)7. Shaft8. Slinger (when used)9. Bearing Locknut Assembly10. Antifriction Bearing11. Drain Plug12. Inner Bearing Cap13. Lower-Half End Shield
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NOTE: On motors with accessible or split endshields, it is not necessary to remove the upper-half endshield from the lower-half end shield.
Bearings may be recommended for cleaning orreplacement by using the following procedure:
1. Remove the hex head bolts (3) holding theinner bearing cap (12).
2. Remove the hex head bolts (1) holding the
end shields (2 and 13) to the frame. 3. Remove the end shields.
NOTE: On motors with an outboard slinger (8),it is necessary to remove the slinger before removing theend shield.
4. Remove the bearing lock-nut assembly (9). 5. Remove the bearing (10 by using a puller or
by tapping against the bearing cap 12).
Bearing Reassembly
Cleanliness is important when working withbearings. Before reassembling a bearing, all bearing andmachined surfaces should be thoroughly cleaned with asuitable solvent. Examine the machined lifts of the endshield, cartridge, slinger, and grease cap for burrs. It isimportant that these surfaces be smooth.
Reassembly of the bearing should be performed inthe following manner:
1. Inspect the bearing housing and related partsfor foreign material. Clean if necessary.
2. The machined fits and critical surfaces of the
end shield, bearing housing, bearing cap and bearingsshould be free of all nicks, scratches or burrs. If anypolishing is done, care should be taken to avoid a depositof metal dust in and around the bearing assembly.
3. The internal surface of the bearing housing
should be coated with a thin film of the recommendedgrease. The shaft and the shaft fit of the grease housingand grease cap should also receive a very light coating ofthe recommended grease. These precautions, althoughnot absolutely essential, will guard against corrosion ofthe critical surfaces.
4. Heat the bearing in oil to a temperature
between 50 C and 125 C (122 F to 257 F) and place it onthe shaft. Hold it against the shaft shoulder until thebearing cools.
5. Replace the bearing nut and washer. 6. Procure a stud, 8 inches long, threaded on
one end (3/8-16 thread). Screw the stud into one of theholes in the inner bearing cap to facilitate lining up thebearing-cap holes with the holes in the end shield.
7. All subsequent reassembly steps will be a
reversal of the disassembly procedure.
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One of the most important features in thesuccessful operation of an induction motor is thebearings.
The machines covered by these instructions aresupplied with anti-friction bearings.
A conscientiously applied program of preventivemaintenance will add years of useful life to the bearings.In order to assure proper operating conditions, seesection entitled Grease Recommendation.
Bearing Repair and Replacement
Even though high-quality design and workman-ship are incorporated in a bearing, it sometimes becomesnecessary to remove if for maintenance. It is for thisreason that the following instructions are included.
Care must be taken to avoid scratching or nickingthe critical surfaces of the balls or rollers.
Bearing Disassembly
Extreme care is required in the disassembly of amachine for bearing removal. In addition, the surfaces ofthe shaft bearing fit and the bearing itself must beprotected during and after disassembly operations.
NOTE: On motors with accessible or split endshields, it is not necessary to remove the upper-half endshield from the lower-half end shield.
Bearings may be recommended for cleaning orreplacement by using the following procedure:
1. Remove the hex head bolts (3) holding theinner bearing cap (12).
2. Remove the hex head bolts (1) holding the
end shields (2 and 13) to the frame. 3. Remove the end shields.
4. Remove the bearing lock-nut assembly (9). 5. Remove the bearing (10 by using a puller or
by tapping against the bearing cap 12).
NOTE: Care must be taken with bearinginsulation (14).
Bearing Reassembly
Cleanliness is important when working withbearings. Before reassembling a bearing, all bearing andmachined surfaces should be thoroughly cleaned with asuitable solvent. Examine the machined lifts of the endshield, cartridge, slinger, and grease cap for burrs. It isimportant that these surfaces be smooth.
Reassembly of the bearing should be performed inthe following manner:
1. Inspect the bearing housing and related partsfor foreign material. Clean if necessary.
2. The machined fits and critical surfaces of the
end shield, bearing housing, bearing cap and bearingsshould be free of all nicks, scratches or burrs. If anypolishing is done, care should be taken to avoid a depositof metal dust in and around the bearing assembly.
3. The internal surface of the bearing housing
should be coated with a thin film of the recommendedgrease. The shaft and the shaft fit of the grease housingand grease cap should also receive a very light coating ofthe recommended grease. These precautions, althoughnot absolutely essential, will guard against corrosion ofthe critical surfaces.
4. Heat the bearing in oil to a temperature
between 50 C and 125 C (122 F to 257 F) and place it onthe shaft. Hold it against the shaft shoulder until thebearing cools.
5. Replace the bearing nut and washer. 6. Procure a stud, 8 inches long, threaded on
one end (3/8-16 thread). Screw the stud into one of theholes in the inner bearing cap to facilitate lining up thebearing-cap holes with the holes in the end shield.
7. All subsequent reassembly steps will be a
reversal of the disassembly procedure.
GE Industrial Control Systems GEEP-124-I Copyright 1997,1998 The General Electric Company, USA 29
ROTATING PARTS CAN CAUSE SERIOUS INJURY.THE USE OF ELECTRIC MACHINERY, LIKE ALLOTHER UTILIZATION OF CONCENTRATED POWERAND ROTATING PARTS, CAN BE HAZARDOUS.MAKE CERTAIN THAT THE VOLTAGE IS REMOVEDFROM ALL CIRCUITS AND THAT NO MECHANICALPARTS ARE ROTATING. INSTALLATION,OPERATION AND MAINTENANCE OF ELECTRIC
MACHINERY SHOULD BE PERFORMED BYQUALIFIED PERSONNEL. FAMILIARIZATION WITHNEMA PUBLICATION MG-2, SAFETY STANDARDSFOR CONSTRUCTION AND GUIDE FORSELECTION, INSTALLATION AND USE OFELECTRIC MOTORS AND GENERATORS, THENATIONAL ELECTRICAL CODE AND SOUNDLOCAL PRACTICES IS RECOMMENDED.
TROUBLE - SHOOTING CHARTTrouble Possible Cause Action
Motor will not start Power not connected Connect power to control, and controlto motor. Check contacts.
Low Voltage Check motor nameplate value with busvoltage.
Wrong control connections Check connections with control wiringdiagram.
Driven machine locked Disconnect motor from load. If motorstarts satisfactorily, check drivenmachine.
Open circuit in stator or rotorwinding
Measure/compare winding resistanceof each phase.
Winding grounded Test for grounded winding.
Excessive load torque Check motor capability.
Overload control trip Wait for motor to cool. Try startingagain.
Noise or vibration Motor running single phase Stop motor. Then try to start. It willnot start on single phase. Check for“Open” in one of the lines or circuits.
Supply bus unbalanced Check balance by measuring currentand voltage in each phase. Correct thepower supply to obtain balancedvoltages.
GE Industrial Control Systems GEEP-124-I Copyright 1997,1998 The General Electric Company, USA30
The machines covered by this Instruction havebeen designed and manufactured to provide excellentreliability and quality. If properly handled, stored,installed, operated and maintained, and if the site isequipped with adequate protective equipment, the unitwill give many years of reliable service. However, aswith all power equipment, certain parts are subject tonormal wear. In addition, there is great variationbetween sites in severity of environmental conditions.
For these reasons an adequate stock of spare partsis important, as insurance, in order to minimize downtime of the unit. The correct number of spare parts tocarry in stock depends upon how critical the installationis to the owner. This decision must be weighed with anevaluation of the severity of environmental conditions atthe site and of the effectiveness of the local maintenanceprogram.
Parts subject to wear
Two parts which are in physical contact in whichthere is relative motion between the two members willexperience wear. Sleeve bearings and oil rings are incontact with the shaft and move relative to the shaft. Theballs or rollers of antifriction bearings are in contactwith, and move relative to the inner and outer race.Brushes are in contact with, and move relative tocollector rings and brush holders. Oil seals are in contactwith and move relative to the shaft.
All of the mentioned parts are subject to wear.The rate of wear, in each case, is determined by factorsdiscussed previously. It is recommended that these partsbe regularly stocked as spare parts.
Other parts
There are other essential parts which maydeteriorate at an unpredictable rate, over a period oftime, for which the mode of failure is more subtle. Airfilters used to remove dirt should be inspected andcleaned periodically, over a period of time, corrosive andother types of chemical contaminants, as well as certaintypes of physical contaminants, will cause air filters todeteriorate. This may cause throttling of cooling air and
an undesired increase in operating temperature of theunit.
The insulation of all the electrical windings willgive long life if operated within temperature ratings, ifcleaned in accordance with instructions and if notdamaged. Lightning surges, switching surges, generalsystem disturbances and other abnormal voltageconditions have the potential to cause dielectric damagethat can result in turn and ground insulation breakdownover a period of time. The large magnitude of ambientair which passes through the machine and over the coilsfor ambient breathing machines can cause the windinginsulation to be abraded and even penetrated by abrasiveparticles, conducting particles, moisture and normal dirt.
Criticality of the application
The owner should evaluate the critical nature ofthis machine’s application at it relates to the economy ofpotential downtime and loss of production.
Three categories are listed below underRecommended Spare Parts.
2. Semi-Critical Application - AdequateProtection (one set of each item, as originally supplied)
First Seven Items in (1) (as applicable)Prewound Stator CoreSynchronous Rotor Wound PolesExciter RotorExciter Stator Synchronous Machines onlyRectifier Assembly
2. Critical Application or Multiple Units - FullProtection (one set of each item, as originally supplied)
First Seven Items in (1) (as applicable)RotorStatorExciter RotorExciter Stator Synchronous Machines onlyRectifier Assembly
Ordering Parts
A general view of the machine is given in theinstruction section entitled “Parts Identification”. Whenordering parts or seeking additional information fromyour General Electric Company contact, include theserial number and model number of the machine as wellas the rating and the part number reference from theParts Identification section.
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GE Industrial Control Systems GEEP-124-I Copyright 1997,1998 The General Electric Company, USA36
A belt or chain drive delivers torque by virtue ofan unbalance in tension between the two sections of thebelt or chain. Thus, there is an unbalanced, lateral forceon the belt sheave or chain sprocket. The lateral force istransmitted to the bearing of the drive motor and is asignificant component in the magnitude and direction ofthe bearing loading.
The capability of a motor to deliver torque by or achain drive is a function of the motor horsepower, speed,and bearings. Unless the motor was specifically orderedsuitable for this type of drive, it should not be employedwithout first consulting the factory, through the nearestGeneral Electric office.
Belt and chain drive motors can be furnished withthe slide rails for adjusting belt tension. Such slide railsshould be levered and adjusted as discussed forfoundation caps and sole plates, under Mounting. Theslide rails should be positioned such that the axis of thedrive motor shaft and the axis of the driven equipmentshaft are parallel and that the centerline of the beltsheave or chain sprocket on the drive motor is in thesame vertical plane as the sheave or sprocket of thedriven equipment. The relative location of the drivemotor and driven equipment should permit belt or chaintightening or loosening. The belt sheave gear sprocketshould be mounted as close to the motor end shield asreasonably possible.
For V-belt drives, align the sheave or pulley withconsiderable care to avoid axial thrust on the bearings.The belt tension should be such as to just preventslippage at full load. Too great a belt tension will causegreater bearing loading than is necessary resulting inadditional bearing heating and wear. It is incorrect toovertighten the belt tension on high-inertia loads inorder to prevent belt slippage and “squealing” during theacceleration period. The belt tension should be set to justprevent slippage at full load, full speed conditions and toallow slip during acceleration.
The tension ratio, the pulling ratio and theperipheral belt speed should not exceed the followingvalues:
Type ofBelt
TensionRatio
PullingRatio
Peripheral BeltSpeed*
V-belt 7/1 8/1 5000 feet/minute
*Unless otherwise recommended by the beltmanufacturer.
For chain drives, adjust the chain length relativeto the distance between sprocket centerlines to permit aslight sag of the chain on its slack span or side. Thedistance between sprocket centerlines should not be lessthan the diameter of the larger sprocket, plus the radiusof the smaller one. The maximum acceptable chainmanufacturer. The lubrication and maintenance of thechain should be in accordance with the chainmanufacturer’s instructions.
GE Industrial Control Systems GEEP-124-I Copyright 1997,1998 The General Electric Company, USA 37
GE Motors horizontal, weather-protected type Imotor enclosures can be used in confidence in manyoutdoor locations where increased protection againstmoisture and/or other contaminants is required.
Custom Polyseal insulation systems, specialbearing seals, conduit box gaskets, sealed terminalplates, and moisture-resistant finished are standard withthese enclosures to assure extended life in adverseambient.
Enclosure
Fabricated steel construction is used in theframe section to withstand the severe shocks normallyexperienced in heavy-duty applications. Flat end shieldsprovide support for the machine bearings with alightweight construction which permits easymaintenance without sacrificing strength or rigidity.
These motors have received special inspectionduring the manufacturing and assembly operations toassure that all parts have been manufactured inaccordance with strict quality-assurance standards.
Ventilation
These motors are designed with a self-ventilationsystem which circulates ambient air through the motor.Louvered openings in the end shields provide anentrance for cooling air at both ends of the motor. Theair passes through air deflectors to the rotor fans. Thefans blow a portion of the air radially across the endturns of the stator coils. The remainder enters the largeventilation openings in the rotor body and passesthrough the rotor ducts. At this point it rejoins the aircirculated across the coil end turns and is directed out ofthe air exhaust passages at the side of the frame.
Weather-protected Type I motors are equippedwith removable screens over all air openings.
GE Industrial Control Systems GEEP-124-I Copyright 1997,1998 The General Electric Company, USA38
1. Stator Frame2. Stator Laminations3. Rotor Laminations4. Stator Windings5. Fan6. Air Deflector7. Upper Half End Shield8. Inner Bearing Cap9. End Shield Gasket (when used)10. Slinger Set Screw (when used)11. Shaft12. Bearing Locknut Assembly13. Antifriction Bearing14. Lower Half End Shield
15. Conduit Box16. Exhaust Port Screen17. Lower Half End Shield18. Inner Bearing Cap19. Bearing Insulation20. Antifriction Bearing21. Cover22. Bearing Locknut Assembly23. End Shield Gasket (when used)24. Upper Half End Shield25. Air Deflector26. Fan27. Dowel Pin28. Heater
Fig. 1 General view -Antifriction Bearing
General
To assist in identifying the machine parts, andgeneral view Fig. 1 is presented in this page. Each partsis marked by a reference number for identification. Thislisting is generated from the parts list for this machine.
Use of the general view and the list permits easyidentification of each machine part by its actual number.When ordering spare or renewal parts, include this partnumber in addition to the model and serial number ofthe machine.
GE Industrial Control Systems GEEP-124-I Copyright 1997,1998 The General Electric Company, USA 39
The machine assembly consists of the frame, endshields, end-shield covers, air deflectors, stator core andcoils, rotor, power terminal box, accessory terminal box,and bearings.
The frame fabrication has been designed todeliver the weight of the unit and the reaction torque tothe foundation.
The assembly also directs the cooling air throughthe active parts of the machine.
In a top-cover machine, cooling air from the topcover enters the top of the frame at the two ends. The airis then directed by the air deflectors into the two fans oneach end of the rotor, where the pressure is increased.This causes the air to flow through the air passages inthe rotor and stator. The cool air removes the heat fromthe core and coils as it passes over the surface of theseactive parts. Finally, the heated air is discharged aroundthe periphery of the stator core, where it is directedupward into the top cover.
In a dripproofmachine, cooling airenters the frame throughopenings in the endshields. The air is thendirected by the airdeflectors into the twofans on each end of therotor, where the pressureis increased. This causesthe air to flow through theair passages in the rotorand stator. The cool airremoves the heat from thecore and coils as it passesover the surface of theseactive parts. Finally, theheated air is dischargedaround the periphery of the stator core, and then throughthe side frame openings.
Frame
The fabricated rectangular frame holds the othervarious parts of the unit in proper position duringoperation and positions the drive and in the correctvertical ad axial alignment with the driven equipment.
The frame includes:
4 lifting lugs - 2 on each side - near the ends ofthe frame.
4 ground pads - 2 on each lower side - near theends of the frame.
On top-cover enclosures: 2 gasketed access-coverplates, one on each lower-side of the frame. Theplates run the full length of the frame and coverthe access holes to the foundation bolts, dowelsand space heaters.
Fig. 1 Dripproof Machine Assembly
GE Industrial Control Systems GEEP-124-I Copyright 1997,1998 The General Electric Company, USA40
An end shield is provided on each end of theframe to support and position the rotor relative to thestator assembly. The end shields carry the weight of therotor and position or center the rotor in the statorminimizing the unbalanced magnetic forces.
The end shield is machined with a rabbet fit tomate with shield frame and to mount the bearingassembly.
Air Deflector
The air deflector is secured with screws to avertical frame plate near each end of frame. Itcircumferentially shrouds the fan and directs theentering cooling air to the vortex of the fan and preventsthe pressurized air from recirculating back through thefan. The air deflector is made of glass-fiber, reinforced,molded thermosetting resins and is split at the horizontalcerterline in order to facilitate assembly anddisassembly.
Fig. 2 Prewound stator core
Stator Core and Coils
The stator core and coils (along with theequivalent rotor parts) constitute the activeelectromagnetic parts of the machine. The stator core isprewound, i.e. the stator coils are wound into the coreprior to installing the core in the frame.
The core is made from segmental laminationspunched from magnetic silicon steel. The punchings areaccurately positioned and stacked to maintain a truestator bore. The core is build up axially with packets ofpunchings separated by radial air ducts.
Stator flanges are located at each end of the statorcore to hold the punchings together in compression. Theinterlaminar pressure is maintained by steel straps whichrun axially along the outside diameter of the stackedcore, from the annular plate on one end of the core tothat on the other end. These steel straps are welded tothe end plates while the core is under heavy axialcompression.
The stator coils are formed from insulated,rectangular copper wire. The wire insulation consists ofan enamel, glass, and/or corona-resistant materials. Thewire insulation is over-wrapped with mica tape foradditional surge voltage protection, if necessary. Theformed coils are insulated to ground with mica tape,which is over-taped with glass tape for physicalprotection.
For machines rated 6000 volts and above, a semi-conducting material is applied to the slot portion of thecoils and graded beyond the core to provide coronaprotection.
The coils are wound into the stator core andwedged into the slots with fiber glass-reinforced wedges.Bracing is then added to the coil extensions, beyond theends of the stator core. The entire prewound stator coreis vacuum-pressure impregnated with epoxy resin andthen cured by baking.
