S. M. A. Cruz

Stator winding fault diagnosis in three-phase synchronous and asynchronous motors, by the extended Park's vector approach

This paper describes the use of the extended Parks vector approach (EPVA) for diagnosing the occurrence of stator winding faults in operating three-phase synchronous and asynchronous motors. The major theoretical principles related with the EPVA are presented and it is shown how stator winding faults can be effectively diagnosed by the use of this noninvasive approach. Experimental results, obtained in the laboratory, corroborate that these faults can be detected, in the EPVA signature, by the identification of a spectral component at twice the fundamental supply frequency. On-site tests, conducted in a power generation plant and in a cement mill, demonstrate the effectiveness of the EPVA in the detection of stator circuit faults in large industrial motors, rated up to 5 MW.

Inter-turn stator winding fault diagnosis in three-phase induction motors, by Park's Vector approach

The subject of on-line detection and location of inter-turn short circuits in the stator windings of three-phase induction motors is discussed, and a noninvasive approach, based on the computer-aided monitoring of the stator current Parks vector, is introduced. Experimental results, obtained by using a special fault producing test rig, demonstrate the effectiveness of the proposed technique, for detecting inter-turn stator winding faults in operating three-phase induction machines. On-site tests conducted in a power generation plant, using the diagnostic instrumentation system developed, are also reported.

Rotor Cage Fault Diagnosis in Three-Phase Induction Motors by Extended Park's Vector Approach

This paper introduces a new approach, based on the spectral analysis of the motor current Parks Vector modulus, for detecting the occurrence of rotor cage faults in operating three-phase induction machines. The major theoretical principles of the Extended Parks Vector Approach are described. Both simulation and laboratory test results demonstrate how the presence of rotor cage faults can be effectively detected by the application of this new approach. These results are also correlated with the ones obtained by the conventional motor current spectral analysis and by the classic Parks Vector Approach.This paper introduces a new approach, based on the spectral analysis of the motor current Parks Vector modulus, for detecting the occurrence of rotor cage faults in operating three-phase induction machines. The major theoretical principles of the Extended Parks Vector Approach are described. Both simulation and laboratory test results demonstrate how the presence of rotor cage faults can be effectively detected by the application of this new approach. These results are also correlated with the ones obtained by the conventional motor current spectral analysis and by the classic Parks Vector Approach.

Rotor cage fault diagnosis in three-phase induction motors, by Park's vector approach

The subject of on-line detection of rotor cage faults in three-phase induction motors is discussed, and a noninvasive approach, based on computer-aided monitoring of the stator current Parks vector, is introduced, Both simulation and laboratory test results demonstrate the effectiveness of the proposed technique, for detecting broken rotor bars or end-rings in operating three-phase induction machines. On-site tests conducted in a power plant, using the diagnostic instrumentation system developed, are also reported.

Multiple reference frames theory: a new method for the diagnosis of stator faults in three-phase induction motors

This paper proposes the use of the multiple reference frames theory for the diagnosis of stator faults in three-phase induction motors. The development of a simplified mathematical motor model allowed the establishment of the equivalent circuits of the motor, in d-q-0 axes, in the presence of stator interturn short circuits. The use of the stationary reference frame, clockwise and counterclockwise synchronous reference frames, allows the extraction and manipulation of the information contained in the motor supply currents in a way that the effects introduced by the fault are easily isolated and measured. A severity factor is defined and the simulation and experimental results presented demonstrate its independence in relation to the working conditions of the motor, such as the load level and unbalances in the voltage supply system. Although the technique is here introduced for the diagnosis of stator faults, it is possible to extend its use for the diagnosis of other asymmetries such as broken rotor bars and air-gap eccentricity.

A New Model-Based Technique for the Diagnosis of Rotor Faults in RFOC Induction Motor Drives

This paper proposes a new model-based diagnostic technique, which is the so-called virtual current technique (VCT), for the diagnosis of rotor faults in direct rotor field oriented controlled (DRFOC) induction motor drives. By measuring the oscillations at twice the slip frequency found in the rotor flux of the machine, and by conjugating this information with the knowledge of some motor parameters, as well as the parameters of the flux and current controllers, it is possible to generate a virtual magnetizing current which, after normalization, allows the detection and quantification of the extension of the fault. The proposed method allows one to overcome the major difficulties usually found in the diagnosis of rotor faults in closed-loop drives by providing information about the condition of the machine in a way that is independent of the working conditions of the drive such as the load level, reference speed, and bandwidth of the control loops. Although the VCT was primarily developed for traction drives used in railway applications, it can be incorporated in any DRFOC drive at almost no additional cost. Several simulation results, obtained with different types of DRFOC drives, as well as experimental results obtained in the laboratory, demonstrate the effectiveness of this new diagnostic approach.

An Active–Reactive Power Method for the Diagnosis of Rotor Faults in Three-Phase Induction Motors Operating Under Time-Varying Load Conditions

This paper presents a new method to diagnose rotor faults in operating three-phase induction motors under the presence of time-varying loads. The proposed diagnostic strategy relies on a combined analysis of the amplitude and phase spectra of the instantaneous active and reactive powers of the motor, and allows to discriminate the effects introduced by a rotor fault from the ones caused by an oscillating load torque, even when these phenomena occur simultaneously. A theoretical analysis carried out using a linearized model of the induction motor in a synchronous reference frame, complemented with several simulation and experimental results, confirms the validity of the proposed diagnostic approach.

Diagnosis of stator, rotor and airgap eccentricity faults in three-phase induction motors based on the multiple reference frames theory

This paper describes the use of multiple reference frames for the diagnosis of stator, rotor, and eccentricity faults in line-fed and direct torque controlled (DTC) inverter-fed induction motors. The use of this new technique, which was proposed by the authors for the diagnosis of inter-turn short circuits, is extended for the detection and classification of different types of faults. Each fault causes a different disturbance or introduces different components in the motor supply currents. Based on the multiple reference frames theory, by choosing a proper reference frame, it is possible to transform each one of these current components to a d-q frame. In these d-q reference frames, those current harmonics will appear as constants, thus being easily measured, extracted or manipulated. Because each fault causes a different disturbance, the multiple reference frames technique can easily discriminate between different faults. Simulation and experimental results demonstrate the effectiveness of the proposed technique for the diagnosis of stator, rotor, and airgap eccentricity faults in three-phase induction motors. Moreover, due to the operating philosophy of the multiple reference frames technique, its integration into the control system of a DTC induction motor drive is a straightforward task and is briefly addressed at the end of the paper.

Analysis and Diagnosis of Open-Circuit Faults in Matrix Converters

This paper presents a new diagnostic technique, known as the Modulated Error Voltages (MEV), for the diagnosis of open-circuits faults in the power switches of matrix converters. The proposed technique is based on the monitoring of nine modulated output error voltages, each one associated to a bidirectional switch of the converter. For each output phase, an error voltage is calculated and subsequently modulated by the gate signals of each one of the three bidirectional switches connected to that specific phase. Each modulated signal is subsequently averaged over a certain period of time. If at the end of this averaging period the obtained value is higher than a threshold limit, it will trigger the indication of an open-circuit fault in the power switch associated to the monitored signal. By using the MEV it is possible to concurrently detect and locate open-circuit faults, independently of the type of load of the matrix converter or its operating conditions, namely amplitude and frequency of the output voltages, both in steady-state and transient regimes. Moreover, the MEV allows to speed up the diagnostic process when compared to other diagnostic techniques, and can easily deal with the presence of multiple faults occurring simultaneously.

Diagnosis of stator inter-turn short circuits in DTC induction motor drives

This paper addresses the subject of stator fault diagnosis in DTC induction motor drives. The particularities of the behavior of a DTC drive, when in the presence of inter-turn short circuits, are exploited, thus allowing the proposal of two different approaches for the diagnosis of this type of fault. One of the proposed diagnostic techniques is the well known motor current spectrum analysis. It is demonstrated that in a DTC induction motor drive, with stator inter-turn short circuits, the action of the torque and flux controllers introduce a strong third harmonic in the motor supply currents, which can be used to detect this type of fault. The other diagnostic technique is based on the multiple reference frames theory, proposed by the authors for the diagnosis of stator faults in line-connected motors. Here, its use is exploited in the diagnosis of stator faults in DTC induction motor drives. Simulation and experimental results demonstrate the effectiveness of the two proposed techniques for the diagnosis of stator faults but emphasize the fact that the multiple reference frames technique is the preferred one when the residual asymmetries of the motor are not negligible.