Future control technologies in motor diagnostics and system wellness

Abstract

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. Research conducted at the University of Sussex in the United Kingdom and at Georgia Institute of Technology 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 NEMA or IEC rated motor starter. With this approach, the on-line motor wellness relay enables CBM via a control device that is already required for the control circuit. This paper discusses the mathematical model and field tests to validate the model and introduce a motor wellness relay that could be used to perform on-line diagnostics. Alternative system communication architectures to support a wellness platform are also reviewed and discussed.