Delta to single phase xformation?

[thaley68]

I have a troubleshooting problem. I have a machine with a 480v 3 phase motor for a hydaulic pump. There is a 120v control circiut, with the normal stop/start/pilot, two left/right piston joysticks, and an up down piston button. The machine has run for five years, with no problems. A few days ago it started to drop out the control circuit intermittently, and was getting worse. I replaced the 480v motor starter first, and then after still having the problem, I changed the control Xformer(480v/120v) The buiding has a center tapped delta service and the machine is fed off of the 600amp busway. After changing the xformer with one off my shelf (used) the machine ran fine. A little while later the xformer smoked! I previously tested the incoming voltages and found 498v+/- on each phase, and my secondary xformed voltage at 133 volts. could the higher voltages be the problem? I took an extention cord to a nearby 120v outlet and tied it into the control circuit and the machine ran fine. Should I replace the xformer with a new one? Is there anyway to change my voltage easily to get closer to 480/120v?

Thanks

Thaley

 

[augie47]

was the "new" ransformer the same kva as the one you removed ??

 

[wirenut1980]

498 volts phase to phase is getting pretty close to the high end of the acceptable range of voltage (504 volts is pretty much as high as you want to get), and 133 volts is definately outside of acceptable range, IMO. Given that, I don't think that could cause a transformer to smoke. It may explain the control circuit dropping out, but usually it is voltage sags that would take these out and not swells. Sorry not much help, here.:-?

 

[ptonsparky]

Are the cylinders controled via 120v solenoids?
Could one of them be faulted enough to drop the voltage on a small control transformer but not the 20 amp branch circuit?