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Sensorless speed estimation of mains-fed induction motors for condition monitoring using motor relays

Continuous online monitoring of electrical assets is critical for reducing the process downtime and the associated financial losses in industrial applications. Majority of large induction motors, which are critical to industrial applications, are mains-fed. Condition monitoring of these mains-fed motors is critical for reducing the failure rate of these motor systems. Motor relays, commonly used to protect these motors, are ideal candidate for implementing condition monitoring techniques. Accurate speed estimation is essential to ensure reliable online and continuous monitoring of industrial motors. However, due to limited data collection capabilities of the motor relays, limited speed estimation accuracy has been the bottleneck toward reliable condition monitoring using motor relays. In this paper, an accurate speed estimation technique is proposed for mains-fed induction motors. The technique only requires shorter memory of the motor current/voltage data in comparison to previous techniques, which makes it ideal to implement in motor relays. The technique is demonstrated through lab validation. The improvement of condition monitoring reliability with the help of the proposed speed estimation technique is also presented.