Low-Cost Diagnosis of Rotor Asymmetries of Induction Machines at Very Low Slip With the Goertzel Algorithm Applied to the Rectified Current

Abstract

Induction machines are essential components of many industrial installations and, therefore, their faults must be detected early. Fault detection using current spectrum analysis is attracting an increasing interest as a condition-based monitoring technique. However, its use to detect rotor asymmetries in high-power induction machines, which operate at very low slip, is particularly challenging, due to the closeness of the characteristic fault harmonics to the fundamental component, separated only a few mHz. Their reliable detection in harsh industrial environments requires a very high spectral resolution, that is, long acquisition times and a huge number of current samples, what hinders its implementation on embedded, online devices with limited computing resources. To address this problem, this paper presents a novel combination of diagnostic techniques, the use of the rectified current as diagnostic signal, and the Goertzel algorithm as signal processing tool. This unique combination allows for an optimized implementation ot the Goertzel algorithm, which provides a high spectral resolution in the full load range of the machine, with a low computational cost and a negligible memory footprint. This proposal is validated experimentally with the fault diagnosis of a high-power mediumvoltage industrial motor.

Detection of Broken Rotor Bars in a Cage Induction Machine Using DC Injection Braking

“…Finally, the general model of SCIM based on the MCMC approach is defined using ( 4)- (17). The model is derived by including the following basic approximations: the iron losses are neglected, ferromagnetic materials are considered linear, and inter-bar currents are neglected.…”

“…The reliability of the MCSA is significantly influenced by the operating conditions of the machine. This is particularly the case in near-zero slip conditions [14], where the spectral leakage of the current fundamental component submerges with the slip-dependent sideband components associated with BRBs, making them difficult to detect [12], [15]- [17]. In addition, the magnitudes of the components of interest are quite small under these operating conditions [15], [16], thus affecting fault identification accuracy.…”

“…The spectral leakage problem becomes even more prominent in inverter-fed machines, especially at low switching frequencies, which is typical for high-power drives [18]. Another issue associated with the MCSA technique is related to the spectral resolution, which has to be sufficiently high to properly identify BRB fault components in the current spectrum [17], [19]. Finally, the mechanical power transmission mechanism of the drive and mechanical loads (such as pumps, fans, or compressors), as well as pulsating loads, can provoke components around the fundamental current which can be misinterpreted as BRB fault indicators [15], [20], [21], thus compromising the reliability of the method.…”

“…Another alternative for the suppression of the main supply component, before its spectral decomposition, was proposed in [18] and [25], where the authors used a notch filter for current envelope extraction. Other studies have suggested spectral analysis of the square machine current signal [26], as well as the spectral decomposition of rectified machine current signals [17], [27].…”

Broken Rotor Bar Detection in Induction Motors through Contrast Estimation

“…In [25], a method for broken bar detection is proposed based on convolutional neural networks and the time-frequency representation of the motor current signals during the IM startup transient through the short-time Fourier transform. Many of the above-mentioned techniques offer high efficiency for BRB identification; however, their computational complexity prevents them from being utilized on online applications [26]. Furthermore, most of these techniques are used during the IM startup transient, since under this regime, the BRBs are easier to detect, despite an IM usually operating under a steady-state condition.…”