Two mistaken ideas about how to dry wet windings have persisted for years. One is that heating the windings with a welding machine is good way to dry out an electric motor. The other is that windings should not be dried at oven temperatures above 180 F (82 C).
Welding machine method. Before using a welder or other dc power source for to dry out an electric motor, make sure you know what you’re getting into.
For starters most electric motors large enough to warrant consideration have three leads–one per phase. Internally, they are connected either wye (Y) or delta (∆). (Incidentally, the terms wye and delta come from the Greek letters they resemble.)
With the welder applying current from T1 to T3, only two phases of a wye-connected motor are heated. If the internal connection is delta, one phase is heated with four times the wattage of the other two phases. In both cases, the welder leads must be periodically moved to heat the entire winding evenly.
If you apply dc to any two leads of a delta winding, two phases will be in series, and the third will be in parallel with them. That means one phase will carry twice as much current as the series pair, so it will get much hotter. For the wye connection, only two phases carry current, leaving the third phase cold.
Whether the winding is connected wye or delta, someone must monitor the current and winding temperature, and periodically move the welder leads. Otherwise, parts of the winding may not dry completely, if at all. Welding machines also have a duty cycle that’s a lot shorter than the two or three days it might take to dry out one winding!
Welding machines are useful when both ends of each phase are brought out as six leads. An ohmmeter will confirm three separate circuits. In that case, the three phases can be connected in parallel or series, depending on the capacity of the welding machine, and dried simultaneously. Read More
