Predictive Versus Preventive Maintenance: Future Control Technologies in Motor Diagnosis and System Wellness

OVER THE PAST FEW YEARS, INDUSTRIAL MANUFACTURING DISCIPLINES have evolved from a strategy of routine scheduled maintenance of electrical equipment to condition-based maintenance (CBM). In the CBM approach, equipment maintenance based on a routine schedule can be replaced with an approach based on system wellness diagnostics. This approach might rely on noninvasive monitoring of three-phase induction motors to report equipment condition and enable maintenance intervention before a failure occurs. Recent research conducted at Georgia Institute of Technology and the Eaton Innovation Center in Milwaukee, Wisconsin, has been conducted developing algorithms of motor current signature analysis (CSA) and power signature analysis (PSA), resulting in a reliable model to predict motor and driven load failure. Pump cavitation, rotational unbalance and mechanical alignment are some of the areas where a mathematical model has been developed using fast Fourier transform (FFT) analysis, enabling online diagnostics during operation. An extensive testing program to validate and refine the mathematical model was conducted both in the test lab and in field process applications. A "motor-wellness relay " is under development in a mechanical package designed to replace a conventional thermal-overload relay of a National Electric Manufacturing Association (NEMA) or Internacional Electrotechnical Commission (IEC) rated motor starter. With this approach, the online motor-wellness relay enables CBM via a control device that is already required for the control circuit. This article discusses the mathematical model and field tests to validate the model and introduce a motor-wellness relay chat could be used to perform online diagnostics. Alternative system communication architectures to support a wellness platform are also reviewed and discussed.