Industrial Electric Motors

Electric Motors
An electric motor converts electrical energy into mechanical energy. Most electric motors operate through interacting magnetic fields and current-carrying conductors to generate force. The reverse process, producing electrical energy from mechanical energy, is done by generators such as an alternator or a dynamo. Electric motors and generators are commonly referred to as electric machines. ROMAC carries a large inventory of electric motors, including Toshiba, US Electric Motors, Baldor, Lincoln, Marathon, Leeson, and Weg.

Common types of electric motors include, but are not limited to, induction, brushed DC, brushless DC, stepper, linear, unipolar and reluctance.

Main Components of Industrial Electric Motors

Industrial electrical motor parts and assemblies include, but are not limited, to:
  • Shaft
  • Windings
  • Ball / Roller/ Sleeve/ Antifriction bearings
  • Armature
  • Stator
  • Commutator
  • Brushes
  • Terminals
  • Case

ROMAC's Electric Motor Reconditioning Process

Inspect exterior of motor for condition. Look for cracks in frame, shaft end bell or fan cover. Check for original factory nameplate. Check for third-party mark such as UL on hazardous location motors (ROMAC DOES NOT OPEN UL-SEALED MOTORS). Record all nameplate data including third-party listing labels onto test reports. Record motor inspection observations.

  • Check for correct fitting and sealed conduit box and or accessory boxes.
  • Remove fan cover. Check for cracks at bolt downs or vent slots. Check all frame bolt holes and bolt hole threads. Check motor feet for cracks. Check motor frame bolt down holes in feet and ensure holes have not been damaged.
  • Remove conduit box and check for proper rubber seal at motor frame. Check fan for cracks, chips, tightness to shaft and tightening bolt.
  • Examine shaft and fan side end bells for cracks, corrosion and excessive grease.
  • Examine motor leads for length and insulation integrity. Check leads where they exit motor, look for cracking in insulation. Look for signs of overheating and melting.
  • Remove and examine fan. Check fan shaft ID for cracks or chips. Examine tightening bolt and bolt hole threads. Replace fan and fan cover.
  • Examine shaft for dents, gouges, chips, cracks and indications of excess stress; check for oil slinger; check both ends for grease zerks or bearing oil fillers. Verify there is bearing grease or source of bearing oil available to motor.
Pre-run Testing

  • Open conduit box and check leads for general condition. Clean leads for pre-recon testing.
  • Apply 1000V megohm meter to motor lead and ground to check for winding moisture or winding fault. Perform on each lead.
  • If available, apply surge and hipot test according to test equipment manufacturer directions.
First Run Test

If Meggar and surge test results are favorable, we move on to motor run test. It is important to make sure the motor is on a flat, level surface. If a bolt-down platform is available, that is preferred. Connect or set up dust collector exhaust end of motor. Motors have fans and especially after sitting for any length of time, dust and debris are ejected from motors when started. This is a hazard to operators. Once motor is set up, make lead connections per pattern defined on nameplate for available test voltage.

Apply voltage gradually until desired operating voltage is reached. As this is a no-load test, starting motor at full voltage is acceptable if there is enough current available. Motor should accelerate to full speed quickly. Using tachometer, observe speed and record; record no-load current. Using a stethoscope or high-frequency listening device listen to bearing noise at each end of motor; record observations. Observe motor for vibration visually or employ vibration detection instruments; record observations. Looking at motor shaft, observe shaft for out-of-true conditions; record observations. It is our habit to run motors for at least 10 minutes. Upon completion of run test, turn power off to motor. Remove motor from power source. Remove dust collector.

Reconditioning


Once again, remove fan cover and fan. Remove conduit box. Wrap leads to protect them from damage during reconditioning of motor. Carefully punch corresponding reassembly marks at frame and end-bell joints on each side. Carefully remove end bells or end bell halves at shaft and fan ends. Remove rotor, being very careful not to drop or drag rotor on surface of stator iron.

Rotor


Place rotor in rotor stand to protect from possible damage. Remove sleeve (babbit) or antifriction bearings from rotor shaft. Check rotor for visible damage. Examine rotor bars, looking for cracks. Examine end rings or rotor bar retainers for dents, gouges and cracks. Examine rotor laminations for separating or other obvious damage. Check rotor shaft at bearing points for damage. If shaft surface is not pristine, measure shaft diameter with micrometer or vernier calipers. Compare shaft diameter to bearing ID. Inspect key slot for straight and true. Look for gouges. Thoroughly clean, degreasing entire rotor assembly. Coat all rotor surfaces other than shaft with glyptol or epoxy specific for the application.

End Bells


Examine each end bell for cracks or other obvious damage. Pay special attention to bearing cavities. Look for rust, debris and corrosion. Examine bearing races, looking for damage. Thoroughly clean and degrease end bells. Treat end bell interior with glyptol or epoxy specific for the application. Apply grease to races of antifriction bearing cavities.

Stator


Stator is made of motor frame, stator lamination stack, windings and winding slot insulation. Examine the frame for cracks, gouges or creases at machined fitments. Examine condition of the laminations. Look for separations, burns or indications of heat and crush indications. Examine slot insulation for burns or indications of heat or deterioration. Examine windings for insulation integrity and any damage to the wire. Check lead connections to windings. Look for deterioration of connections. Thoroughly clean and degrease all parts of stator.

If motor meggered low at first test, place stator in bake oven for drying. Remove from oven and allow motor to cool to just warm. If varnish dipping is available, this is the time to dip the stator. Allow excess varnish to drain from stator before replacing in oven for curing.

Recheck leads for damage and that they are free of debris and excess varnish. Be sure terminal is clean and clear of debris. If lead has no terminal installed, be sure that there is adequate exposed wire for proper connection.

Bearings

Whatever type of bearings are present in the motor, they must be examined carefully for condition. In the case of antifriction bearings, check inner and outer races for signs of poor fit, corrosion or rust. Both surfaces should be very clean and smooth. The inner and outer bearing casements should fit tightly with no looseness or play in the assembly.

Sleeve bearings should be examined for signs of wear. Oil grooves should be clear of debris. There should be no obvious wear points on the babbit or oil rings.

Bearings should be thoroughly cleaned and degreased and dried. Antifriction bearings should be repacked if not sealed.

External Parts

Fan, fan cover, conduit box and auxiliary box (for RTDs and space heater wires) should be examined thoroughly, cleaned and painted.

Assembly

Replace bearings on motor rotor shaft ends. Lift rotor from rotor stand and carefully insert through stator opening. With rotor still supported by lifting device, slide fan side end bell over shaft and fit bearing into bearing cavity. Allow rotor to settle gently onto stator and slip shaft side end bell over shaft, sliding bearing into bearing cavity on that side. Both end bells should be rotated so that reassembly punch marks align at each end bell frame fitment. Insert and finger tighten each assembly bolt. Applying gentle torque manually, tighten bolts on each end bell until each fitment is drawn tight. Complete tightening with torque wrench to manufacturer-prescribed torque value.

Install fan (if fan cooled motor), fan cover, conduit box and auxiliary box; verify lead numbering is clearly legible.

Final Retest

Open conduit box; apply 1000V megohm meter to motor lead and ground to check for winding moisture or winding fault. Perform on each lead. Record observations on motor test data sheet. If available, apply surge and hipot test according to test equipment manufacturer directions.

Final Run Test


If megger and surge test results are favorable, we move on to motor final run test. Once motor is set up, make lead connections per pattern defined on nameplate for available test voltage.

Apply voltage gradually until desired operating voltage is reached. As this is a no load test, starting motor at full voltage is acceptable if there is enough current available. Motor should accelerate to full speed quickly. Using tachometer observe speed and record; record no-load current. Using a stethoscope or high-frequency listening device, listen to bearing noise at each end of motor; record observations. Observe motor for vibration visually or employ vibration detection instruments; record observations. Looking at motor shaft, observe shaft for out-of-true conditions; record observations. It is our habit to run motors for at least 10 minutes. Apply fine emery paper to turning shaft to expose clean surface. Shaft bluing may be applied at this point. Upon completion of run test, turn power off to motor. Remove motor from power source. Install shaft key and apply retainer tape.

Apply test sticker showing date, job or service order number and/or inventory number.

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