High Potential Testing Motor Windings with Very Low Frequency-EASA Document

EASA Document
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<strong>Good Practice Guide to Maintain Motor Efficiency Summary</strong><br /><br />The "Good Practice Guide to Maintain Motor Efficiency" is a comprehensive manual published by EASA and AEMT in 2021. It provides detailed methodologies for repairing and rewinding motors to ensure or enhance their efficiency, quality, and reliability. The guide builds on findings from the 2019 and 2003 studies on motor efficiency.<br /><br /><strong>Key Points:</strong><br /><br />1. <strong>Energy Losses in Induction Motors</strong>:<br />   - Core (iron) losses.<br />   - Stator I2R losses.<br />   - Rotor losses.<br />   - Friction and windage losses.<br />   - Stray load losses.<br />   <br />   Efforts should be concentrated on minimizing increases in these losses during the repair process.<br /><br />2. <strong>Motor Repair Processes</strong>:<br />   - <strong>Preliminary Inspection</strong>: Critical for recording motor nameplate data, the condition of the motor, and customer input regarding operational environment and motor history.<br />   - <strong>Dismantling the Motor</strong>: Involves careful documentation and orientation of parts to ensure precise reassembly. Rotor removal should be performed with care to avoid air gap surface damage.<br />   - <strong>Removing the Old Winding</strong>: Using controlled temperature burnout ovens to avoid overheating and damaging core laminations. Proper core cleaning methods include high-pressure washing, mild abrasive blasting, and careful scraping.<br />   - <strong>Rewinding the Motor</strong>: Emphasizing duplicating the original design or improving it by increasing copper cross-sectional area without increasing the mean length of turn (MLT). Duplication or modification must consider factors like coil extensions and proper impregnation with varnish to ensure efficient heat dissipation.<br /><br />3. <strong>Mechanical Repairs Impacting Efficiency</strong>:<br />   - <strong>Core Repair</strong>: Avoid extensive grinding or improper restacking.<br />   - <strong>Shaft Repair</strong>: Maintain correct dimension and material properties.<br />   - <strong>Housing Repair</strong>: Ensure proper fit and alignment to avoid concentricity issues.<br />   - <strong>Bearings and Seals</strong>: Correct installation and lubrication are crucial to preventing efficiency losses due to friction.<br />   - <strong>Fans and Covers</strong>: Should be correctly placed and of appropriate size to maintain cooling efficiency.<br /><br />4. <strong>Reassembling the Motor</strong>:<br />   - Ensure bearings and fans are correctly installed.<br />   - Avoid over-greasing bearings to prevent initial friction losses.<br />   - Maintain alignment and cooling duct integrity.<br /><br />5. <strong>Confirming Repair Integrity</strong>:<br />   - Measure core and stator losses before and after repair.<br />   - Use accurate logging tools for resistance tests.<br />   - Ensure rotor and bearing modifications have not induced additional losses.<br /><br />The guide also emphasizes the importance of maintaining clear and accurate documentation throughout the repair process to ensure consistent, efficient, and reliable motor performance. It serves as a crucial resource for technicians aiming to follow industry best practices in motor maintenance and repair.
Keywords
motor efficiency
EASA
AEMT
motor repair
rewinding motors
induction motors
energy losses
mechanical repairs
repair integrity
documentation