A critical process in the plant includes a mixing vat. The drive motor of that vat has blown its overloads multiple times in the past few weeks. The process engineer determined the rated torque of the motor exceeds what’s required, even accounting for the maximum viscosity of the mixture.
The plant engineer noted that motor failure in the plant seems high, but the mechanical supervisor dismissed this as extraneous information. The mechanics have gone over everything from the motor coupling to the vat impeller, and there’s no mechanical problem. Everything rotates freely, axial runout is practically zero, and there are no alignment issues.
The motor was replaced, but the new one has the same problem. How do you solve this?
Rule number one in any maintenance organization is never dismiss the plant engineer’s input. In this case, that information points to a systemic issue.
The motor is drawing too much current, but the cause isn’t load related. We can deduce from that (and the fact it’s not the motor unless two duds in a row were installed) the cause is supply-related. Look for these power quality issues:
- Low power factor.
- Voltage imbalance exceeds 2%.
- Excess 3rd and/or 5th harmonic.
- Waveform is severely distorted.
Each of these has its own solution, but all of them can exist simultaneously. Don’t stop looking just because you found one of them.
