phase burnt on 3 phase motor
phase burnt on 3 phase motor
(OP)
Hey there,
i'm new to this forum but having found it through google it really seems that the people here know there stuff.
i'm a maint. tech and we had a problem with a motor. the 's' phase burnt out and caused the vfd to trip.this is the second time to happen in the space of a year.the first time we just changed the motor and all seemed fine till problem occured again.
this time we cut back the cable and re-connected just to get it running while we investigate further the cause.
has anyone heard anything similar to this? if so let me know it would be appreciated.
i'm new to this forum but having found it through google it really seems that the people here know there stuff.
i'm a maint. tech and we had a problem with a motor. the 's' phase burnt out and caused the vfd to trip.this is the second time to happen in the space of a year.the first time we just changed the motor and all seemed fine till problem occured again.
this time we cut back the cable and re-connected just to get it running while we investigate further the cause.
has anyone heard anything similar to this? if so let me know it would be appreciated.





RE: phase burnt on 3 phase motor
You mentioned that, the first time, the motor winding 'Phase S' burnt out.
Then the second time, you mentioned that the problem was repeated, and to cure the problem you cut back the cable a little, and re-connected.
If the S Phase winding was burnt out a second time, I cannot see how cutting the cable back, and re-connecting, could solve the problem, unless the motor was changed as well? Did you cut back the cable in case the connection was at fault?
Was it the same phase winding that burnt?
Can you see my problem in understanding?
RE: phase burnt on 3 phase motor
* Algebra - The weapon of math destruction *
RE: phase burnt on 3 phase motor
Mostly, i encounter burning off was due to poor crimping of terminal lugs and loose tapping. This has a mean-time-failure that would led to long time interval of such failure. As heat build up at the tapping point, it later spreads up to the extent of considerable lenght, less than 5 inches, leading to burn out or even on worse case such single phasing.
If this not happen at the terminal point, as above, maybe you'll post some details.
RE: phase burnt on 3 phase motor
regards
tommy
RE: phase burnt on 3 phase motor
Use a non-contact thermometer to measure the temperature of the terminations while the motor runs on load. High temps indicate improper terminations.
* Algebra - The weapon of math destruction *
RE: phase burnt on 3 phase motor
RE: phase burnt on 3 phase motor
If so, I would say that you had a bad termination the first time, which damaged the motor connection and the cable. Once a cable has been overheated to the point of melting, the damage extends far up from the termination point as fbcybil mentioned. The conductor material changes it's properties and can become more resistive, which accelerates future failure, especially in VFD output circuits because of the additional heating from harmonics. You changed just the motor, which left the cable vulnerable to the second failure. Hopefully you cut that cable back far enough to avoid this again. You may also want to look at putting a filter or even just a reactor on the VFD output to lower the thermal stress on those cables (and the motor).
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RE: phase burnt on 3 phase motor
thanks again.
tommy