Hal,
If I recall, this was a heater transformer wasn't it, not the plate
transformer? Before you send it back, let me know what the core is
(C-Core or EI) and the measurements of the core, width, height, and
depth. Also, what the secondary voltage and current rating is. I can
then calculate the primary wire size that should have been used. The
reason being, the magnet wire shouldn't have gotten hot enough to melt
through that quick, I wouldn't think. When one is connected out of
phase, one winding is bucking the other which is almost the same as an
short. Within no time, the breaker should have kicked and or a fuse
blowed if in the amp. This one wasn't but your breaker should have
caught it. Generally when one is out of phase, as soon as the power hits
it, it will create a loud hum, and within 1-2 seconds kick out the
breaker or fuse. The wire size should have been large enough to handle a
momentary overload such as this. By your description, the only thing
that could have happened is the winding got hot and opened, thus the
smoke. What I'm thinking could have happened is that they nicked a wire
when they were making the coil, or made a bad connection at one of the
leads. Then, when you powered it up, it just burnt in two, especially if
it were out of phase and putting a load on the winding. On re-winding
motors, the same wire size is generally used as in transformers. A
similar result would have been the current drawn from what's known as
"locked rotor current". This is when the shaft of the motor is froze and
the coils are energized. I've never seen a motor burn out that quick
either, with trying to start a locked rotor motor.
You mentioned some Linoleum catching on fire too. Your meaning some the
transformer was setting on? Or the fish paper that the transformer is
wrapped with? Those Dahl transformers are wrapped with regular blue fish
paper for insulation. The black color you see is a black dye they
purposely mix in the varnish. Theoretically, this is supposed to help
take heat away from the windings. This black color also makes it hard to
see anything burnt too!
When your winding transformers, each lead is attached after the coil is
completed before the last wrap of fish paper is put on the coil. The
worker will label each lead per the prints they are provided. On the
primary leads for 240 Vac service, the start and stop of each winding
determines the phase. If the worker got this mixed up, it was labeled it
out of phase. Either or, what happened would not of been the fault of
anything you did. I would say that transformer was probably never tested
before it left the factory.
Will Matney
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