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Instantaneous Torque as a Predictive Maintenance Tool for Variable Frequency Drives and Line Operate

Instantaneous Torque as a Predictive Maintenance Tool for Variable Frequency Drives and Line Operated Motors

Megger Baker Instruments

Technological advances in on-line testing of motors, diagnostics and motor monitoring have increased substantially over the past few years. Voltage and current signature analyses have improved the quality of predictive maintenance (PdM) compared to what RMS current and voltage measurements or power-factor readings have been able to achieve.

Author(s): Megger Baker Instruments

Technological advances in on-line testing of motors, diagnostics and motor monitoring have increased substantially over the past few years. Voltage and current signature analyses have improved the quality of predictive maintenance (PdM) compared to what RMS current and voltage measurements or power-factor readings have been able to achieve. Signature analysis has emerged from the laboratory stage to become the foundation for modern instrumentation in mainstream industrial maintenance programs. The most advanced method of current signature analysis is torque signal analysis due to the fact it offers multiple advantages. One is the instantaneous torque signature, gained from current and voltage signatures. It is inherently demodulated, and delivers a very clear signal independent of the line frequency (either 60Hz, or variable in VFD applications). In addition to demodulation, it delivers the clearest mechanical information available on the motor system, since torque production is the primary if not sole reason for the motor’s existence. Both motor and load failures can result in costly outages or reduced production for weeks at a time in a plant environment. The cost of such failures can easily run into millions of dollars. This paper presents three case studies where modern instrumentation averted downtime or reduced output and failure. One case study is based on findings of a coal-fired power plant, the second case study presents findings of a Lignite powered plant, and the third case study involves troubleshooting a VFD application in a sawmill.