Motor Decisions Matter: Move from Panic to Planning

By Walker Larsen, Program Manager, Consortium for Energy Efficiency (CEE)

No one wants to get that 2:00 a.m. call that production has stopped because a critical piece of equipment has a burned-out motor or that the air conditioning has failed in a crowded conference room. Plant and building managers can avoid situations like these and save money by adopting predictive and preventive maintenance policies, procedures and technologies.

According to the “Operations and Maintenance Best Practices Guide” from the U.S. Department of Energy Office of Energy Efficiency and Renewable Energy, predictive maintenance costs half that of reactive maintenance. The Motor Decisions Matter campaign recommends that predictive and preventive maintenance programs focus on the following five factors to successfully reduce the rate of unexpected motor failure:

Heat: Undersizing, incorrect starting torque characteristics, high ambient temperature and poorly ventilated motors all cause motors to overheat. Correct motor selection and placement is especially important to prevent overheating.

Dirt: Debris in a plant or outdoor work area can damage a motor’s mechanical and electrical components and contribute to overheating. Many motor manufacturers make models designed to keep out dirt and other potentially harmful materials. Talk with your motor sales and service center to see if these motors or other modifications such as debris shields or bearing isolators are appropriate for your operations.

Moisture: Moisture is corrosive to the motor’s mechanical and electrical components, and is particularly harmful to motors that are used infrequently. Using forced ventilation or mechanical dehumidification may help reduce these effects in damp motor-running environments. Idle motors can be protected with internal space or winding heaters.

Vibration: Various failing or malfunctioning components of the motor or its load may be responsible for vibration. Vibration gradually destroys motor bearings. If the vibration is severe, mechanical components may develop cracks or fractures. Using today’s sophisticated vibration-analysis tools and software, both mechanical and electrical imbalances can be detected and rectified.

Voltage irregularities: Fluctuations beyond the motor’s specified capabilities—undervoltage, overvoltage, unbalanced voltage, voltage transients and harmonics caused by other equipment—may cause windings to overheat. In three-phase motors, this overheating may occur even with relatively small variations in voltage. Voltage should be checked frequently and corrected if necessary.

Predictive maintenance

There are several ways to predict motor failure, including the use of monitoring equipment to assess the impact of the factors mentioned above. For example, infrared thermal imaging can be used to identify overheating wiring and bearings; vibration sensors can identify vibration and bearing problems; and electrical analyzers can identify power-supply problems. With this equipment you can create a baseline for your motor population.

Regular monitoring of motor-operating characteristics can help you detect changes that may indicate a problem so appropriate maintenance can be scheduled. In addition, modern motor-driven equipment often comes equipped with onboard sensors that detect operating conditions and feed motor diagnostics into an energy-management information system (EMIS) or supervisory control and data-acquisition (SCADA) system that alerts you when operating conditions are out of tolerance. Both of these approaches are preemptive strikes against motor failure and equipment downtime

Establishing and following scheduled maintenance practices on your motor-driven systems can identify problems early, which helps avoid shortsighted, costly decisions. For these reasons, predictive and preventive maintenance are important considerations in your motor-management plan. See the Motor Decisions Matter campaign Website (motorsmatter.org) or contact the campaign sponsors for details on how to get started. MT

wlarsen@cee1.org