Motor Types and Introduction

Motors convert electrical energy into mechanical energy by the interaction between the magnetic fields set up in the stator and rotor windings. Industrial electric motors can be broadly classified as induction motors, direct current motors or synchronous motors. All motor types have the same four operating components: stator (stationary windings), rotor (rotating windings), bearings, and frame (enclosure).

Motor Solo Run or No Load test

Motor Solo Run or the commonly called “no load test” will be performed in all of the motors installed in the industrires for efficient process requirement. The simplest of these techniques is no-load testing. As the name implies, “no-load” consists of applying rated voltage and/or frequency to the motor with “no load”(nothing) coupled to the shaft. The resulting current and power are measured and compared to limits derived from “master motors” for acceptance. Additional major external checkout is to determine the speed, direction of rotation and vibration. Field test for determining motor efficiency and reliability is beyond of this scope as it is factory tested at manufacturer or vendor`s workshop.

Purpose of Solo Run

The primary purpose of this procedure is to verify the following;

To determine by functional testing that all components and devices operate, control, and perform in accordance with approved design documents.

To verify, during operation, that the motor is suitable for the service intended and installed properly.

To provide baseline data for future evaluation of AC motors tested during routine maintenance.

Test Equipment Used for Solo Run test

  • Clamp-on Ammeter
  • Insulation Resistance Tester
  • Multi-meter
  • Stopwatch
  • Surface Pyrometer or applicable temperature measuring device (Where automatic measuring equipment is available it should be used.)
  • Vibration Analyzer (Where automatic measuring equipment is available it should be used.)
  • Noise Meter
  • Tachometer


Prior to performing this test, verify that all circuit breakers, fuses, starters, and overload devices have been properly sized, installed, and tested, as required.

A functional test of the motor control circuit has been completed.

  • Check that Start and Stop pushbuttons on the switchgear cause the contactor to be energized and de-energized respectively;
  • Check that the remote control circuits (start and stop) also cause the contactor to operate;
  • Check that all the motor protection relays cause the contactor to be de-energized.

Communications shall be established between control and monitoring areas during the performance of this test.


  1. Work Permit shall be prepared prior to start any activities. All safety materials   and equipment (warning signs, barricades, fire extinguisher, etc.) must be in place at work area.
  2. Initial and date the results of the following instructions and tests on attachments to this procedure.
  3. Inspect the foundation and ensure that the motor is properly secured.
  4. Visually inspect the motor for proper grounding.
  5. If it is not feasible to uncouple the motor and driven equipment, note so in the remarks section and state why and how the motor was tested.
  6. Prior to uncoupled operation, coupling halves shall be tied back to prevent the coupling halves from contacting any rotating members (if necessary).
  7. Verify by visual inspection or record check that the motor has been lubricated.
  8. If possible, manually rotate the shaft and check for free rotation. Note any unusual noise or drag effects.
  9. Where applicable, verify that the bearing cooling water system is operating properly.
  10. Where grease is used for lubricant, remove grease plug from one side of each bearing to allow for initial grease expansion.
  11. Positively confirm that the motor to be energized is connected to the correct controlling device (switch, starter, or breaker) by verifying the cable tags and by one of the following methods:
    1. For motors that can be manually rotated:
    • Connect a multi-meter (low DC volt scale) at controller and observe while turning motor.
    1. For motors that cannot be manually rotated:
    • Motor with terminal strip (example: MOV): Check continuity of circuit to motor termination.
    • Motor without terminal strip (example: Chem. Feed Pump): Energize circuit with single-phase 120 VAC and check by “tic-tracer” or multi-meter
  1. Measure motor winding and feeder circuit resistance, exciter resistance if synchronous motor and record results, if applicable.
  2. Perform and evaluate an insulation resistance test in accordance with project test procedures.
  3. Verify that the motor space heater (when installed) is energized when motor is de-energized.
  4. Verify proper rotation of motor shaft by “bumping” the motor ON/OFF. Correct rotation if necessary by exchanging two phases of the motor feed.

NOTE: Rotation may also be checked using a phase rotation meter, but if bumping is used verify that incorrect rotation will not damage the motor. Before restarting, make sure that the shaft has stopped rotating.

Start the motor and check for proper operation. Let the motor to run for a period of (4) hours. During the test, check the motor for excessive vibration or temperature.  Record current and voltage readings.

  • Motor no-load test shall be stopped if any abnormalities occurred which may damage the motor.
  • Where applicable, visually verify that the oil rings are properly distributing oil to the bearings.
  • Record and evaluate all the required data on attachments.
  • During operational testing, note any unusual noises or physical changes in the remarks section of the data sheet.
  • Monitor and evaluate all bearing temperatures. Operate the motor until the bearing temperatures have stabilized and record the readings.

NOTE: Where winding temperatures detecting devices are provided, they should also be monitored and the results recorded in the remarks section.

  • For motors 25 HP or greater, record motor vibration measurements in accordance with the test equipment manufacturer’s instruction manual. Record results on Attachment 3 of this procedure.
  • Verify scribe on the rotor shaft is correct to indicate the magnetic center of the motor (as applicable).
  • Stop the motor.
  • Restore motor control circuits to pretest conditions.


  • Motor controls shall correctly respond to control and actuation signals, and the associated indications shall properly reflect circuit status.
  • Motors must rotate in the proper direction as required by the driven equipment and as indicated in the manufacturer’s instruction manual.
  • All recorded data for uncoupled runs shall be evaluated by the test engineer and be compatible with the nameplate data and the design data for the system.
  • Vibration measurement readings shall be compared to vendor manual. If readings are below the fair band, they shall generally be considered acceptable. The test engineer or designee will evaluate equipment that has questionable vibration readings on an individual basis.

NOTE:Uncoupled motors that exhibit questionable vibration reading should also be compared with the vibration requirements or NEMA Standard MG-1 reproduced below.

The vibration limits prescribed by NEMA MG-1-20.52 are:

Speed: RPM Amplitude: Inches-Peak to Peak

    • 3000 RPM and above 0.001
    • 1500 – 2999  0.002
    • 1000 – 1499  0.0025
    • 999 and below  0.003
  • Motor insulation resistance shall be acceptable in accordance with the project technical specifications.
  • The running current of each phase of the motor shall not vary by more than 8% from the arithmetic average of all the phases. Where variance is greater than 8%, an evaluation should be made by engineering as to the causes.

NOTE:   The 8 percent limit in phase current variance is imposed to avoid excessive heating effects at full load current. This requirement is not for running currents more than 8 percent below the full load rating as the heating effects are different.


It must be positively confirmed that the motor to be run is connected to the correct controlling device (switch, starter, or breaker).

  • Do not “MEGGER” equipment with solid -state components.
  • Applicable project tagging procedures shall be followed when performing test.
  • Coupling guards shall be installed as soon as practical.
  • Do not exceed manufacturer’s starting limitations.
  • AC motors are generally tested uncoupled, where possible, and then coupled. Coupled testing should be with the system conditions as near normal or design as possible. When circumstances are such that normal operating conditions cannot be attained, the highest load possible shall be placed on the motor so that meaningful test data may be obtained and evaluated, and a reasonable evaluation of the motor’s adequacy for the intended service may be made.
  • AC motors should be completed perfectly preparation to start mechanically, electrically, and instrumentally.

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3 Responses

  1. Hairstyles says:

    I feel that is among the such a lot vital info for me. And i am happy reading your article. But should statement on some normal issues, The site style is perfect, the articles is actually excellent : D. Excellent task, cheers

  2. amit Kumar vishwakarma says:

    Info is good, I have one question this 4 hour no load run of motor is been mention in any standard?

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