How To Test A Three Phase Electric Motor (Easy Guide)

Three-phase motors are widely used in the commercial sector due to their high operational capacity, longevity, and energy efficiency. Do you know three-phase electric motors are responsible for about 40% of industrial energy use, declared by the U.S. Department of Energy? How to test a three phase electric motor?

Figure 1 How to Test a Three Phase Electric Motor

Figure 1: How to test a three phase electric motor

However, if operated with negligence, it can cause shorted or burnt winding. Therefore, it is important to test a three phase electric motor if you want to avoid any significant damage. 

Let’s discuss the primary steps to inspect the health of a three-phase electric motor.

How to test a three phase electric motor:

Figure 2 Three-phase motor Testing with Multimeter

Figure 2: Three-phase motor testing with multimeter

These steps are important to test an electric motor’s performance and health with simple tools such as a multimeter or ohmmeter;

1. Voltages and Current measurement:

Measure the applied voltages and currents (FLA) using a multimeter. The expected voltages for three-phase between phase and neutral is 230V and 400V between the phases.

Record the result and check if the FLA is equivalent to the nameplate or not. Variance in the motor’s current and amperes indicates active malfunction or failure.

2. Winding test:

Three-phase motor winding tests are crucial to signify any defects and damage in the windings. These tests can help to detect if your winding is shorted or burnt.

  • Winding Continuity:

Check the continuity of motor winding from phase to phase ( U to V, V to W , W to U ). If all phases have satisfactory continuity, your motor winding is error-free. 

  • Winding Resistance:

Inspect the winding resistance from phase to phase terminals ( U to V, V to W, and W to U). Since all three phases usually have unvaried windings, the ohm reading must be quite similar.

  • Winding Insulation:

Run the insulation resistance test by applying 500V DC current to test the resistance of the insulation between the winding and motor frame (earth). Check the resistance from phase to phase and phase to earth. 

The minimum insulation resistance is 500 megaohms.

3. Load test:

Load tests are important to indicate the power factor, torque, efficiency, and power output of the motor. It can be done with two types of tests;

  • No-Load:

Run the motor without any load and measure voltage and current. Now, check if the recorded voltage and current are in the specified range and balanced or not.

If no load voltage is within a few percent of the rated voltage and the current is under 2% of the full rating, your motor is in good condition.

  • With Load:

Check the voltage and current at full load and measure the current and voltage values. The current should be less than 10% of the load rating, the power factor should be at least 0.8, and while voltage should be within a few percent of the full rating. 

4. Temperature and Vibration inspection:

Check the motor temperature with a thermometer to evaluate if the motor is ventilated, lubricated, and not exceeding the ambient temperature. Now measure the vibrations to identify any mechanical stress, bearing issues, or misalignment. 

These check-ups ensure the motor’s lifespan and functionality.

Related reading: What Is A 3-Phase Motor – Everything You Should Know

How to test a three phase electric motor-Conclusion:

To detect any faults, it is important to test a three-phase electric motor. It can save your electric motor from motor failure or burnout. Xinnuo Motor is a leading electric motor manufacturer that designs high-quality and long-lasting 3-phase electric motors.

For additional information, feel free to contact us. 

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