Induction motor current signature for centrifugal pump load

Sensorless monitoring technology based on motor current signature analysis is a nonintrusive and economical technique to monitor motor-driven equipment. Sensorless monitoring technology can be applied to a centrifugal pump system. This technology is also based on the motor current signature of centrifugal pump load; however, systematic research regarding motor current signature in overall normal operation points which is the applied basic for sensorless monitoring technology has been rarely performed. As such, we partially examined the motor current signature of a centrifugal pump load by experimental observation, theoretical analysis, and numerical simulation. Results show that stator current is a sinusoidal alternating current that strictly follows sine law associated with the cycle of the fundamental frequency of supply power. The trend of the root mean square and peak–peak of current is the same as flow–shaft power characteristics; hence, this trend could be used as indicator of the pump operational point monitor. The frequency characteristics of a centrifugal pump, such as blade passing frequency, rotation frequency, and broadband noise, could be reflected as sidebands around the fundamental frequency. The stator current spectrum is composed of fundamental frequency component, harmonics component, and noise. The fundamental frequency component is directly related to the pump load in which changes associated with the law of fundamental frequency component are relatively similar to flow–shaft power characteristics. Harmonics component and noise are caused by load fluctuation in which the amount of energy of these two components exhibits a lower value at the preferred operation point. By contrast, the amount of energy likely increases when pump operation is at an unstable operation point. These results further indicate that motor current signature analysis is a feasible and cost-effective method to monitor centrifugal pump operation status. Therefore, motor current signature analysis can be applied to monitor-related flow phenomena.

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