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Old 03-03-2018, 10:29 PM   #1
MTW
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Default Generac transformer control transformer troubleshoot

Had a good one the other day. So the boss sends me to change out a control transformer in a Generac industrial transfer switch for a pump station, 480 volt primary, 240 secondary. There are two transformers, one one normal power and the other for generator power. The original normal power transformer burned out in spectacular fashion. There is no primary or secondary OCPD for these, they are tapped right off the incoming 200 amp feeders, and the control circuit has no OCPD whatsoever either

I tell the boss "This burned out for a reason, you know. There is something wrong in the control circuit." "Change it out anyway, see what happens." So I do. I replace it and fire it back up, all is well.

I then put the transfer switch back in automatic mode, throw the main, and the generator starts as it should. Immediately a horrible noise starts coming from the transfer switch and I know what is happening. Within a few seconds the transformer dies with a very loud bang and cloud of smoke inside the pump house, however, it's not the one I just replaced but rather the emergency power transformer.

So my question is why did the normal power one not die when I put the normal power back on? Did it have something to do with keeping it in manual mode instead of automatic? Once I switched it back to auto mode and threw the main to test it, the carnage began. I'm guessing the problem is likely a bad transfer solenoid.
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Old 03-04-2018, 06:24 AM   #2
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I don't work on the industrial ones, but wondering if there was a bad limit switch within the transfer mechanism, or like you say shorted solenoid. Tough without a wiring diagram to see how its wired.
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Old 03-05-2018, 08:16 PM   #3
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The real question is whether the primary transformer would blow up again in automatic mode once it has online power.

Assuming it was in automatic mode during the first failure--the primary blew up while in automatic, the emergency blew up while in automatic, but the primary did not while in manual. Would need schematics to say if this is a valid theory, but it seems the only explanation is that the source of over-current must be somewhere in the automatic power delivery before the load... something that manual mode is bypassing.
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