This AC unit has 2 single phase fans and 2 3 phase compressors to it. I have tested all the windings on the motors and monitored the current on all the units and all is fine. It trips one of the fuses every once in awhile. I did notice that the lugs on 2 of the phases of the breaker was loose. There was no visible overheating other than the breaker being warm. Could the 2 loose lug cause an impedience on those 2 phase which in turn causes the one good phase that had a tight connection to over compensate and blow the fuse at the unit.
3 phase ac unit
- Thread starter JdoubleU
- Start date
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kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
What is operating temperature of the fuse holder like. What is condition of any possible places where there could be loose connection or poor contact? If some connection heats up to point where single phasing occurs this could easily be your problem, but after cooling off it works fine again for a while. If this is happening the phase that is lost initially will not be the same phase containing the blown fuse. A single phasing problem is not limited to the load side of the circuit breaker it can be anywhere between the load and the source. The closer to the source the problem is however the more likely other loads will also be affected.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
With loose lugs you get a voltage drop across them, which in turn creates a voltage imbalance and subsequent current imbalance. When you have a current imbalance, the motor ends up with negative sequence currents flowing in the stator, which create negative torque in the rotor. So the motor ends up 'fighting' itself and if left that way, pulling more current for the amount of work done. Not much of a problem if the motor is over designed or running lightly loaded, but at full load it will drastically shorten the motor life AND can cause nuisance clearing of circuit thermal protection devices.
So yes, that could have caused it.
So yes, that could have caused it.
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