Motor windings are essentially conductive coils of wiring that generate the magnetic fields and the resulting torque necessary for electric motors to function. Ensuring they are properly maintained is therefore crucial for optimal motor performance and avoiding winding issues that may require an unscheduled electric motor overhauling or rewind. In this guide, we shall go over the different kinds of windings and walk you through essential tests to identify potential failures.
4 Main Types of Windings in Electric Motors
1. Stator Winding
The stator winding serves different roles whether it’s in a DC or AC motor. In the former, it generates a constant magnetic field, while in the latter, it produces a rotating magnetic field. In some cases, it also functions as both the field and armature winding in AC motors.
2. Rotor Winding
Located on the rotating part of an electric motor, rotor windings act as the armature windings in DC motors. In AC induction motors, however, the rotor does not have a direct power source; instead, it induces current through interaction with the stator’s magnetic field.
3. Armature Winding
The armature winding is responsible for generating electromagnetic torque, which drives the motor’s rotation. Depending on the type of motor involved, this winding can be found on different components. It is on the rotor in DC motors, but it is one and the same with stator winding in AC motors.
4. Field Winding
This winding also helps create the magnetic field required for motor operation and is typically found on the stator or the stationary component of the motor. In DC motors, the field winding is separate from the armature, whereas in AC motors, it is integrated into the stator winding.
An Overview on Testing Motor Windings
Regular testing of motor windings helps diagnose issues such as shorts, open circuits, and insulation failures. A multimeter set is the primary tool for these tests.
1. Checking for a Short to Ground
This issue occurs when a winding makes contact with the motor housing or frame and causes current leakage. This can lead to electrical hazards, reduced efficiency, or tripped circuit breakers.
To perform the test, do the following:
- Disconnect the motor’s power source.
- Put the multimeter probes on the motor frame and a winding terminal.
- If the reading shows infinite resistance, the windings are intact. A zero-resistance reading, in contrast, means there is a short to ground.
2. Checking for Shorts Between Windings
Shorts within the windings happen when insulation failure causes winding wires to touch, creating low-resistance paths. This leads to overheating and performance issues.
Follow these steps:
- Evaluate the resistance between the T1, T2, and T3 winding terminals.
- Check the readings. If all pairs show a balanced resistance, then there is no short. If one pair shows a much lower resistance, a short circuit is likely.
3. Checking for an Open Circuit
Open circuits indicate a break in the windings that is preventing the flow of current. This may stem from overheating, broken wires, or damaged terminals.
To conduct the test, simply do the resistance test between the winding terminals again. This time, however, a low resistance value indicates a functioning winding, while an infinite resistance reading suggests an open circuit.
Testing Considerations
- While terminal labels such as T1-T3 are the standard used in 3-phase motors, they may vary for different makes and models. Always refer to the motor’s manual for precise information.
- For a more detailed assessment, an insulation resistance tester and other similar tools can help evaluate the insulation integrity of the windings.
Conclusion
Understanding motor winding failures and testing techniques is crucial for preventing costly downtime and ensuring efficiency. Common problems such as overheating, insulation breakdown, and wear from vibration can often be mitigated with routine inspections and tests. Investing in proper diagnostic tools and regularly scheduled maintenance can extend the lifespan of your motor and reduce unexpected failures.