Mechanical Systems and Signal Processing Mechanical Systems and Signal Processing 20 (2006) 1572–1589 A validated model for the prediction of rotor bar failure in squirrel-cage motors using instantaneous angular speed Ahmed Y. Ben Sasi à , Fengshou Gu, Yuhua Li, Andrew D. Ball Monitoring and Diagnostics Research Group, School of Mechanical, Aerospace and Civil Engineering, The University of Manchester, Oxford Road, M13 9PL UK Received 14 September 2004; received in revised form 12 September 2005; accepted 15 September 2005 Available online 25 October 2005 Abstract Instantaneous angular speed (IAS)-based condition monitoring is an area in which significant progress has been achieved over the recent years. This condition monitoring technique is less known compared to the existing conventional methods. This paper presents model-predicted simulation and experimental results of broken rotor bar faults in a three- phase induction motor using IAS variations. The simulation was performed under normal, and a broken rotor bar fault. The present paper evaluates through simulating and measuring the IAS of an induction motor at broken rotor bar faults in both time and frequency domains. Experimental results show a good agreement with the model-predicted simulation results. Three vital key features were extracted from the angular speed variations. One feature is the modulating contour of pole pass frequency periods in time domain. The other two features are in frequency domain. The primary feature is the presence of the pole pass frequency component at the low-frequency region of the IAS spectrum. The secondary feature which are the multiple of pole pass frequency sideband components around the rotor speed frequency component. Experimental results confirm the validity of the simulation results for the proposed method. The IAS has demonstrated more sensitivity than current signature analysis in detecting the fault. This research also shows the power of angular speed features as a useful tool to detect broken rotor bar deteriorations using any economical transducer such as low-resolution rotary shaft encoders; which may well be already installed for process control purposes. r 2005 Elsevier Ltd. All rights reserved. Keywords: Instantaneous angular speed (IAS); Condition monitoring; Induction motor; Broken rotor bar fault; Pole pass frequency; Modulation 1. Introduction Three-phase induction motors are by far the most common type of industrial drive, and although they are relatively reliable, they do inevitably breakdown, and hence need to be condition monitored. Condition monitoring of these machines is notoriously difficult because of the complex combination of mechanical and magnetic effects that occurs within them. Motors driven by solid-state inverters normally experience severe ARTICLE IN PRESS www.elsevier.com/locate/jnlabr/ymssp 0888-3270/$ - see front matter r 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.ymssp.2005.09.010 à Corresponding author. Tel.: +44 161 2754315; fax: +44 161 2754541. E-mail address: ahmed_bensasi@yahoo.co.uk (A.Y.B. Sasi). URL: http://www.maintenance.org.uk.