Winding Resistance Test – Techno Control Corp

Introduction

The Winding Resistance Test is a crucial diagnostic test for electric motors, transformers, and generators. It helps detect faulty windings, poor connections, and internal damage before they lead to motor failure.

In this article, we will cover the importance, procedure, and benefits of the winding resistance test.

Why Is the Winding Resistance Test Important?

Over time, motor windings can develop loose connections, corroded terminals, or damaged coils due to mechanical stress and overheating. These issues can result in:

• Uneven current distribution
• Increased motor heating
• Reduced efficiency
• Risk of short circuits or motor failure

By performing a winding resistance test, industries can ensure motors operate at peak performance, avoiding costly breakdowns and downtime.

How to Perform a Winding Resistance Test?

Equipment Needed:

• Micro-ohmmeter or Digital Low Resistance Ohmmeter (DLRO)
• Temperature sensor (to compensate for temperature variations)
• Proper safety gear

Step-by-Step Procedure:

1. Prepare the Motor:

• Ensure the motor is disconnected from the power supply.
• Let the motor cool down to ambient temperature for accurate readings.

1. Connect the Test Leads:

• Connect the positive lead of the micro-ohmmeter to one end of the winding.
• Connect the negative lead to the other end.

1. Apply the Test Current:

• Use a low DC test current (typically 1A–10A).
• Higher currents may be used for large motors.

1. Measure the Resistance:

• The winding resistance is displayed in milliohms (mΩ) or ohms (Ω).
• Measure each phase separately (U-V, V-W, W-U).

1. Compare the Readings:

• The resistance values of all three windings should be equal or within ±5% tolerance.
• Imbalanced readings indicate a problem such as damaged windings or loose connections.

Industry Standards for Winding Resistance

• Small Motors (≤10 HP):5Ω to 10Ω
• Medium Motors (10–100 HP):1Ω to 1Ω
• Large Motors (≥100 HP): Milliohm (mΩ) range

Benefits of the Winding Resistance Test

✅ Detects Internal Faults Early – Identifies issues before they lead to complete motor failure.
✅ Ensures Balanced Operation – Helps maintain equal resistance in all phases, ensuring smooth performance.
✅ Prevents Overheating – Reduces heat buildup caused by uneven winding resistance.
✅ Improves Motor Efficiency – Ensures minimal energy losses and optimal power output.
✅ Reduces Maintenance Costs – Helps avoid costly repairs by detecting problems early.

Best Practices for Winding Resistance Testing

• Measure resistance at a stable temperature to avoid errors due to thermal variations.
• Compare resistance values with previous test results for trend analysis.
• Perform the test during scheduled maintenance to prevent sudden failures.
• If an imbalance is detected, check for loose connections, broken windings, or corroded terminals.

Conclusion

The Winding Resistance Test is a vital part of motor maintenance. It helps industries prevent failures, reduce energy losses, and extend motor lifespan.

Regular testing ensures motors operate efficiently, minimizing the risk of unexpected breakdowns. By integrating winding resistance testing into a preventive maintenance plan, companies can enhance motor reliability and performance.