Rotor cage fault diagnosis in three-phase induction motors based on a current and virtual flux approach Dulce F. Pires a , V. Fernão Pires a,b, * , J.F. Martins c , A.J. Pires a,b,c a Escola Sup. Tecnologia Setúbal/Inst. Politécnico Setúbal, Setúbal, Portugal b LabSEI – Laboratório de Sistemas Eléctricos Industriais, Setúbal, Portugal c CTS, Faculdade de Ciências e Tecnologia/UNL, Lisboa, Portugal article info Article history: Received 24 July 2007 Received in revised form 15 May 2008 Accepted 16 December 2008 Keywords: Induction motor Diagnosis Fault detection Stator currents Virtual flux Rotor cage fault abstract This paper focuses on the detection of a rotor cage fault in a three-phase PWM feed induction motor. In inverter-fed machines there are some difficulties for the detection of a rotor cage fault. These difficulties are due to the fault signature that will be contained in the currents or voltages applied to the machine. In this way, a new approach based on the current and a virtual flux is proposed. The use of the virtual flux allows the improving of the signal to noise ratio. This approach also allows the identification of a rotor cage fault independently of the type of control used in the ac drive. The theoretical principle of this method is discussed. Simulation and experimental results are presented in order to show the effective- ness of the proposed approach. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction The diagnosis of the induction machines is receiving consider- able attention from the industry. The main reason of this attention is the reduction of the maintenance and down time expenses, and the significantly improvement of safe operations. So, during the last years there has been made a substantial amount of research in new condition monitoring techniques. The main features expected from fault diagnosis systems are, among others, low cost and volume, noise immunity, and simple algorithms for digital signal processing equipment. Many methods have been presented in order to monitor the condition of induction machines. Studies related to the detection of faults have normally been oriented toward the measurement and analysis of currents, power, magnetic flux, vibration, tempera- ture, etc. Intensive research has been made in order to detect electrical and mechanical faults based on the analysis of the stator current. In motor current signature analysis (MCSA) the analysis of the one-phase current spectrum or of the three-phase current space vector spectrum provides direct information on the presence of abnormal conditions [2]. Kliman et al. [1] describes an experimen- tal noninvasive method for the detection of broken bars based on the stator current analysis. The method is prepared to process other input signals such as vibration. Çalis and Çakır [4] analyzes the time for zero crossing stator current and decides accordingly to the respective frequency spectrum. In [5] the analysis of the space vector modulus spectrum is considered. Trzynadlowski et al. [8] and Legowski et al. [9] uses the instantaneous power spec- trum to discern the presence of mechanical abnormalities. Drif and Cardoso [10] uses the same methodology to perform an airgap eccentricity fault diagnosis. Also to detect airgap eccentricity [12] introduces vibration monitoring. Dister and Schiferl [13] uses the temperature signal in order to correct the current deviations. This methodology also uses motor model equations. The use of the flux signal is considered in [11]. Milimonfared et al. [3] detects broken rotor bars by injection of stator voltage with the machine discon- nected from the supply. Çolak et al. [6] performs an on-line fault diagnosis for motor protection. Digital signal processing technology is being applied to motor drive control enabling the integration of control and protection [7]. For closed-loop inverter-fed machines there are some difficul- ties in the detection and/or the severity classification. In open-loop inverter-fed machines, the drive appears as a controlled ac voltage source to the motor. On the other hand, in principle, closed-loop drives have a high-bandwidth current regulator. So, to the motor a closed-loop drive appears as a controlled ac current source [14,15]. Therefore, the fault signature will be contained in the volt- ages applied to the machine. However, in several closed-loop in- verter-fed machines, the drives appear both as a controlled a 0196-8904/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.enconman.2008.12.020 * Corresponding author. Address: Escola Sup. Tecnologia Setúbal/Inst. Politécnico Setúbal, Setúbal, Portugal. Tel.: +351 265790000; fax: +351 265721869. E-mail address: vpires@est.ips.pt (V.F. Pires). Energy Conversion and Management 50 (2009) 1026–1032 Contents lists available at ScienceDirect Energy Conversion and Management journal homepage: www.elsevier.com/locate/enconman