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Over current condition

Over current condition

Over current condition

(OP)
I'm looking for trouble shooting help to isolate problem of imbalanced current condition. Source power is 220 through Step-up transformer 3ph 480v to VFD (ABB 550). I'm running a 30 hp motor. The imbalance persists with varying the RPMs. Current is 8 amps higher on one leg at 1500 RPM. Not sure if motor is the problem or VFD.

RE: Over current condition

Current imbalance where? Probably between transformer and VFD, but not stated. Current imbalances don't happen in a vacuum, what do your voltages look like?

RE: Over current condition

Current unbalance often follows a voltage unbalance. Or a blown diode in a VFD.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Over current condition

(OP)
The over current exists at switchbox pre Xformer and on output of VFD to motor. Voltages @ output of VFD are good. Again, VAC output from VFD between the 3 legs and each leg to gnd. Also, VAC to the DC +&- connections. Balanced and consistant. I'm leaning towards the motor, maybe a partial short in the winding?

RE: Over current condition

How did you measure the current between the VFD and the motor? Very difficult to get good measurements except from the VFD itself.  

RE: Over current condition

(OP)
The current was measured with a Clamp-On Ammeter. Also note: I do not have the advanced control panal. Machine has remote panal mounted control with limited functions. (monitors pump pressure and RPM)

RE: Over current condition

Don't measure VFD output current with anything not expressly designed for that purpose, you'll only see things to make you worry as it is anything but a clean sine wave. The best your typical clamp-on meter will do is current/no current and sort of a rough magnitude.  

RE: Over current condition

(OP)
Point taken, although this started with 70 amp fuse blowing in switch box. Second time with clamp on meter attached to A phase reading around 65 plus amps then noting delta between legs of 8 amps consistant through output of VFD. Appears questionable with A phase 8 amps higher? bump up fuses and leave it alone or????

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