Impacts of Reduced Motor Cooling on Reliability

It has been well documented that bearing failures are the leading cause for grease lubricated motor repairs, and grease service life deterioration is a leading cause of bearing failures. Grease service life deteriorates rapidly with elevated operating temperatures, so it may be ascertained that a design change significantly reducing motor cooling would result in elevated bearing temperature, marginal lubrication, premature bearing failures, and reduced motor reliability. In recent years, the ever increasing drive for higher motor efficiencies has resulted in motor designs with less cooling capacity. A recent refinery motor reliability study confirms this correlation and highlights the issue with inadequately cooled motors. Results of the study reveal why new IEEE Standard 841 high-efficiency motors are at greater risk of a drive end bearing failure than the older motors they are replacing. The current IEEE Standard 841 allowable bearing temperature rise is exceedingly high (50 °C/90 °F rise on two-pole motors). To optimize bearing service life and motor reliability, this allowable temperature rise should be reduced significantly.