Most motors in your plant are under automatic monitoring for vibration and temperature. In one area, the motors keep setting off their temperature alarms. Motor failure rates there are higher than in other areas of the plant.
The Plant Engineer told you voltage imbalance isn’t an issue, “…because it’s only 2.6% and you’re allowed 3%.” He’s looked into the cooling provided to the motors. As a test, the mechanical techs built a sheet metal hood for one motor and ducted forced air to it. That motor stopped setting off its temperature alarms.
He wants you to determine how many breakers are needed to supply cooling air to all the motors. What should you do?
The plant engineer is wrong about the voltage imbalance. The heat generated by voltage imbalance increases exponentially. So a small increase of imbalance means a big increase of excess heat. A 2% voltage imbalance can shorten motor life by 50%.
The cooling hoods are a solution appropriate for high ambient heat, not for high heat due to a correctable problem.
You must correct the cause of the imbalance. Ask the electric utility to verify it’s providing balanced voltages. As this problem is localized in the plant, the electric utility is only a possible contributing factor. It may add to errors in single-phase distribution fed by the feeder(s) supplying the area of the plant with this problem; check for those, too. Also look at power factor.
