A weird thing happened when our transformer blew up

  • #1
A few nights ago, the pole on the side of the road that holds our transformer snapped, the transformer exploded and set the pole on fire. In my plant we were running on 2 out of 3 phases for a while until we completely lost power. Now here's the "weird" thing...

Just about every motor starter in our plant fried. When I say fried I mean the starter coils melted, and the contacts seemed like they were welded in the open position, meaning you could not push on the starter to close the contacts. We had one panel with easily about two dozen starters and all of them fried in this exact same way. It seemed like it happened to every coil that was energized at the time. We saw this plant-wide, from our wastewater pump panel to a washing machine, all the coils in the starters were melted in the exact same way. We had no blown fuses, no tripped circuit breakers, just melted starter coils galore. Now for my question...

What would cause this? I'm afraid I don't have any more details than that as I consider myself a novice in this area (I'm more of a controls person than a utilities person). But why would an event like the one I described only attack that ONE type of component? As I said there were no blown fuses or tripped breakers. No other types of electrical components were harmed at all. It only happened to the starter coils. If you need any more details I'll see if I can get them. Thanks!
  • #2
Just a thought: starter coils are not meant for continuous duty, so if the fault caused current to run through the coils to ground continuously, that could have overheated the coils and caused the failures.
  • #3
Fuses and breakers only activate if there's an over voltage or over current. If I had to guess, I would say the loss of one of the legs somehow caused a change in the reactive power or a frequency change which would fry any type of induction machine. Although I'm not exactly an expert at utilities either.
  • #4
Just a thought: starter coils are not meant for continuous duty, ...
Actually they are. Here's a http://www.sea.siemens.com/step/templates/lesson.mason?components:3:2:8" [Broken].

When single-phasing occurs on a 3-phase motor circuit, unbalanced currents flow through the motor. This condition might cause the current through the contactor coil to increase.
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  • #5
Its because one of your phases went out. The starter portion of your machines are not designed to run on two pahses. Once this happens your starter motor and switches are fried! For example even if a tree limb took out a phase down the road it would have the same effect. Three phase power is a balance of power. Some dishwashers run on 3 phase electrcity. If one phase goes out the machine will last five minutes and blow up . It will basically shakes apart. Because generally what ac power does is push and stop, push, stop. In a graphically way, the high end of the sine wave puches power in and the lower one pulls power out. This is only on one pahse. With all three phases working togather the balace is complety and the motors in this case run smooth. Three phase was dsigned for efficiency! A physical example is you have 3 men pushing a car up ap a hill. You can also have one large man push the same car up the hill by hiself. Whoes getting more tired? The bigger man!
Right? The starter motors were not made to run only one two phases is what I am saying.
  • #6
My guess
When relays/solenoids try to close at low voltage, they hang open and draw a high current. If the relay/solenoid remains open with a lower than rated voltage for a long period of time, they will overheat.
The relays/solenoids probably had line to neutral voltage applied instead of line to line and so burned up.

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