Predicting motor failure

Aug. 11, 2008
Power signatures reveal potential problems with performance and reliability.

Electrical motor reliability and efficiency are directly influenced by the quality of the power supply. Power-quality disturbances such as transients, unbalance and harmonics can harm the windings and decrease motor performance. Voltage sags and interruptions can bring an industrial process to a halt. Voltage surges might induce equipment failure. The financial costs will be significant, particularly when downtime, production losses and premature equipment replacement or repairs are involved.

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While surge protectors, voltage regulators and ride-through systems limit the effect of short-term power disturbances on your equipment, ongoing motor analysis and power-quality monitoring increase the chance of detecting degradation before damage is done. Trending, benchmarking and being alerted when conditions deteriorate improve your ability to perform predictive maintenance and prevent unscheduled downtime.

Motor analysis revival: Monitoring motors in their operational state has long been a strategy for efficiency and performance management. Factoring in the influence of electrical supply and distribution extends the benefits of analysis. For instance, the rotor signature is used to determine a motor’s load and efficiency, but power quality affects its accuracy. “Systems that take the signature of a motor rotor and use it as an analysis tool are most useful when they calculate efficiency while the equipment is online,” says Dennis Bowns, executive director of Green Motors Practices Group. “Other alternatives require shutting the equipment down to perform a resistance test, and then bringing it back online.

“Less fanfare has been made of this technology recently, perhaps because the market is saturated or the low-hanging fruit has been picked. Issues such as inconsistent voltage supply and reverse harmonics will likely drive renewed attention to this and other motor efficiency and power-quality solutions as energy costs continue to rise.”

In-service analyzers: Baker Instrument offers online motor monitors that test for power conditions. The EXP3000/3000R’s portable, battery-operated Motor Control Center allows remote monitoring of voltage level, voltage balance, harmonic and total distortion, overcurrent, torque ripple, motor efficiency and other power-quality conditions. The newest feature, CM3000 continuous-monitoring software, allows users to choose which of more than 40 data points to monitor in real time. The continuous feed of data assists in detecting and analyzing intermittent power problems, allowing for better predictive maintenance.

The online motor current analysis capabilities of Emerson’s CSI MotorView technology support the diagnosis of electrical problems that might be missed by vibration monitoring. Motor signature data are transferred to the MotorView module of AMS Suite: Machinery Health Manager, from which automated analysis, trending and comparison with results from other diagnostic technologies is possible and corrective actions can be applied.

All-Test Pro On-line II performs electrical signature analysis and power-quality analysis from a handheld data collector. It reveals insights into the electrical and mechanical condition of an AC or DC motor and its driven load, as well as incoming power quality.

Start-up controls: Soft-starting technologies manage the power supply at startup to reduce motor wear. Baldor’s microprocessor-controlled Digital Soft-Start control regulates voltage, reduces inrush current to prevent overload, and uses power factor optimization to eliminate motor over-fluxing.

The Allen-Bradley SMC-3 offers soft-starting technology with extended current ratings. Electronic overload protection with adjustable trip class, motor and system diagnostics, configurable auxiliary contacts, and multiple start and stop modes are among the features of this controller. In a networked environment, it can perform signal conditioning, event detection and alarming.

Cost factors: Some devices exceed the cost of a small motor, particularly when you factor in installation. Hard-wiring or adapting the plant to Ethernet might be involved. A cost/benefit analysis will determine whether the device is cost-effective.

See if your electricity supplier will offset the cost of upgrading motor systems and controls. Idaho Power’s Custom Efficiency for Complex Projects program allows industrial customers with eligible efficiency projects to receive compensation — as much as 70% of the cost — to modify an existing process or install a more efficient one.

Making rewound motors more resistant to overload and voltage imbalances reduces energy costs and the risk of further equipment failure. The Australasian Chapter of the Electrical Apparatus Service Association (EASA) is developing a new Code of Rewinding Practice that will increase the efficiency and reliability of rewound motors, and strengthen the financial argument for choosing rewinding over replacement.

E-mail Contributing Editor Sheila Kennedy, managing director of Additive Communications, at [email protected].

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