This will confirm that the iron core is still usable and was not damaged during the burn cycle. The iron core will have another core test performed, post-burn. After the burned coils are stripped from the iron core, the core is washed clean of any debris and put through a bake cycle between 250°-285☏ for several hours to remove any residual water and prevent any further flash rust. This will determine if the iron core was able to succumb to the high-temperature burn. A pre-core test before a burn cycle is a must. The type of connection, groups, wire size & turns per coil are especially important.Īdditionally, data must be taken for the iron core slots. After the burnout process is completed, supplemental data can be determined. Varnish flare-ups have the potential to damage the iron core, so it is important that the oven is equipped with water sprayers to alleviate any excess fire that may occur during the process. The typical temperature for this process is 650☏.
These ovens are designed to burn the existing varnish out of the coils in order to soften them up for extracting. To do this, all AC motor VPI stator windings will need to go through a process where the unit is placed in a high-temperature burn-out oven. 1 – Determine the Winding Dataīefore motor rewinding can begin, we must determine the winding data. Other manufacturers will place enough ground wall insulation to cover the temperature range the motor was designed for and have ample amount of slot width to do so. The manufacturer may design the horsepower, torque, and KVA code to its limits when designing how much ground wall protection the coils can absorb with a limited amount of slot width.
When stator windings do fail, there are many items to address to get the stator back to its original manufactured state or better. Mechanical failures could also cause the rotor to fail unexpectedly, calling for a rewind.
The timing of a needed motor rewinding will vary according to the application and environment. By Mike Switzer, Product Line Manager - Motorsĭuring the life span of every 3 phase electric AC motor, the stator windings will need to be rewound.
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