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Motors, Drives

Diagnosing motor health: Start with the basics

Temperature, power quality, and torque all are strong indicators of a motor's health.

By Frank Healy January 30, 2019
Courtesy: Fluke Corporation

Electric motors carry a big load in industrial plans. They keep processes working efficiently and reliably. A failed or poorly performing motor can rack up significant costs in downtime, excessive energy consumption, and perhaps spoiled product. Maintaining healthy motors is critical to keeping processes running safely and profitably.

Plants and facilities can have hundreds or even thousands of motors of all sizes that require a detailed maintenance program to keep them up and running. Still, there are basic indicators in all motors that can identify potential points of failure to trigger further investigation and repairs before a failure occurs.

1. Temperature 

Challenge: An increase in temperature can indicate a variety of problems. Overheated bearings and couplings can indicate poor lubrication or misalignment of mechanical components. This puts undue stress on a motor and may lead to early failure. Hot spots in motor casings can indicate a short-circuit in the internal iron core or motor winding caused by aging insulation. Overheated cables and power connections can be a sign of unbalanced voltage, overloads, or degraded wires.

Action: Take a baseline temperature measurement of the bearings, motor casings, switches, and cables right after installation or when running normally. Use an infrared camera or visual infrared thermometer to scan for hot spots from a safer distance. At the next regular maintenance, check those same components and compare the new measurements to the baseline or to measurements of similar components to find temperature differences.

For example, a switch running 30 degrees hotter than the others may indicate the contacts are failing. A hot bearing may need lubrication or may be about to fail. Addressing these issues before they cause a failure can reduce stress on the motor and avoid more expensive repair or replacement costs down the road.

2. Power quality

Challenge: Poor power quality shows up in transients, harmonics, and unbalanced loads and can have a direct negative affect on motor performance. Transients can damage motor insulation and trip overvoltage circuits. Distorted voltage and current from harmonics and unbalanced loads can cause motors and transformers to run too hot, which leads to excessive wear. If not addressed soon enough those power quality issues can lead to failure.

Action: Using power quality and motor analysis tools, the three-phase input to the motor can be measured to analyze the electrical and mechanical performance of electric motors. A broad range of data can be captured to assess the overall power quality and root out the causes of motor inefficiency.

3. Torque

Challenge: Torque has a significant impact on the overall performance and efficiency of a motor. A motor’s torque is measured in pound-feet or Newton meters (Nm) and is the single most critical variable defining instantaneous mechanical performance. Running motors in a mechanical overload condition stresses motor bearings, insulation, and couplings, and ultimately decreases efficiency and can lead to premature failure.

When conducting a motor analysis, it’s important to measure a number of key factors, starting with motor temperature, power quality, and torque. Courtesy: Fluke Corporation

When conducting a motor analysis, it’s important to measure a number of key factors, starting with motor temperature, power quality, and torque. Courtesy: Fluke Corporation

Action: Mechanical torque has traditionally been measured with mechanical sensors. Modern motor analysis tools calculate torque using electrical parameters, such as instantaneous voltage and current, along with the rating plate data of the motor. Measuring torque can provide clear insight into the health of the motor, the load, and the process itself. By ensuring the motor torque level is running within specifications, the motor life can be extended, resulting in reliable operation over time.

All of these actions can work in tandem with a comprehensive maintenance program. By finding potential issues at an early stage this approach can determine whether additional inspections, such as vibration testing, shaft alignment analysis, or insulation testing, are needed.

Frank Healy
Author Bio: Frank Healy is a manager for Fluke power quality products. He has advised and consulted on many aspects of instrumentation for electrical engineering, including installation testing, earth/ground testing, and power, for more than 25 years.