Standard Core Loss Testing for Electric Motors

The core loss test is one of the most critical quality control steps during motor rewinding and repair. In accordance with ANSI/EASA AR100 2020 standards, this test measures the magnetic losses (iron losses) in a stator core to confirm that its lamination integrity remains within acceptable limits after coil removal, burn off, and cleaning. The test ensures that a repaired motor will operate efficiently without overheating due to excessive iron losses.

Purpose of the Core Loss Test

The primary objective of the core loss test is to detect inter lamination faults or hot spots in the stator core. Shorted laminations increase eddy current losses, resulting in additional heat generation that can lead to insulation degradation and reduced motor efficiency. The test ensures that the magnetic core remains sound before the motor is rewound and placed back into service.

Test Procedure (According to EASA AR100)

1. Preparation: Remove all windings and clean the stator bore thoroughly. Mount the stator securely and connect the test equipment per EASA recommendations.
2. Excitation Loop: Insert a single turn loop around the stator bore. Apply an alternating voltage until the desired flux density is achieved (typically matching original magnetizing conditions).
3. Instrumentation: Use a search coil and voltmeter to monitor flux, and a wattmeter to record total iron loss in watts. The flux should match baseline readings within ±2%.
4. Thermal Evaluation: Use an infrared camera or temperature probe to observe uniform heat distribution. No local area should exceed 10°C above the average temperature.
5. Comparison: Compare losses before and after the stripping or burn off process. According to EASA, the post burn loss should not exceed 120% of the pre burn value when flux levels are equal.

Acceptance Criteria

• Uniform temperature distribution across the stator surface (ΔT ≤ 10°C).
• Normalized core loss values consistent with the original baseline (After ≤ 120% of Before loss).
• No localized hot spots or irregular magnetic fields detected.

Corrective Actions

If abnormal heating or high losses are observed, the affected areas of the core must be repaired. Typical corrective methods include restacking laminations, removing damaged sections, or applying high temperature core varnish to restore inter lamination insulation. A follow up test is then conducted to verify that losses are within acceptable limits before rewinding.

Importance of EASA Compliance

Performing the core loss test according to EASA AR100 ensures that motor repairs meet international standards for electrical and mechanical reliability. It also provides documented verification that the magnetic performance of the stator core has not been compromised during repair, which is essential for long term efficiency, warranty validation, and customer confidence.