David Sattler
L&S Electric
The goal of vacuum pressure impregnation is complete saturation of a winding with insulating resin. As resin penetrates the insulating materials, it causes them to darken. When VPI resin is drained from the winding, all end-turn insulation should be darkened to a uniform shade. Connection insulation should also show uniform darkening. If some insulation is a lighter shade, the coil or jumper is not fully saturated. The winding is not properly protected, and if the problem is not addressed, it is likely to cause premature failure of the unit. This could result in costly warranty work, or at a minimum, will be a failure to provide your customers with the quality they expect and deserve.
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