Broken rotor bar detection in induction machines with transient operating speeds

Previous work on condition monitoring of induction machines has focused on steady-state speed operation. Here, a new concept is introduced based on an analysis of transient machine currents. The technique centers around the extraction and removal of the fundamental component of the current and analyzing the residual current using wavelets. Test results of induction machines operating both as a motor and a generator shows the ability of the algorithm to detect broken rotor bars.     

A method for magnetizing curve identification in rotor fluxoriented induction machines

Operation of an indirect rotor flux oriented induction machine in the field weakening region is usually realized by varying the rotor flux reference in inverse proportion to the speed of rotation. In order to provide the correct stator d-axis current reference at all speeds, it is necessary to incorporate the inverse magnetizing curve of the machine in the controller. The paper proposes an experimental method for identifying the inverse magnetizing curve, specifically developed for the type of vector controlled drives described. The method utilizes the same indirect vector controller and PWM inverter that are used in subsequent normal operation of the drive. It requires that the machine can run under no-load conditions and that the fundamental component of the stator voltage can be measured. The simplicity and accuracy of the method make it well suited for use during commissioning of the drive. The method is verified by extensive experimentation     

Determination of the absolute rotor temperature of squirrel cage induction machines using measurable variables

This paper presents a new method for observing the rotor temperature of high-power squirrel cage induction machines using measurable variables. The method is based on the fact that the rotor resistance depends on the actual rotor temperature. The main problem is to separate the changes in the rotor resistance due to temperature and skin effect. By comparing the input impedance with a known circle diagram measured during commissioning, it is possible to calculate changes in the rotor temperature. Further analyses also make it possible to obtain the absolute rotor temperature at any time. Results of procedure testing are demonstrated through computer simulations and evaluations of data recorded on a 75-kW test machine.     

Multiple signature processing-based fault detection schemes for broken rotor bar in induction motors

The existence of broken rotor bars in induction motors can be detected by monitoring any abnormality of the spectrum amplitudes at certain frequencies in the motor current spectrum. It has been shown that these broken rotor bar-specific frequencies are settled around the fundamental stator current frequency and are termed lower and upper sideband components. Broken rotor bar fault detection schemes should depend on multiple signatures in order to overcome or reduce the effect of any misinterpretation of the signatures that are obscured by factors such as measurement noises and different load conditions. Multiple discriminant analysis (MDA) provides an appropriate environment to develop such fault detection schemes because of its multi-input processing capabilities. The focus of this paper is to provide a new fault detection methodology for broken rotor bar fault detection and diagnostics in terms of its multiple signature processing feature and the motor operation partitioning concept to improve the overall detection performance. This paper describes two fault detection schemes within this methodology, and demonstrates that multiple signature processing is more efficient than single signature processing. The first scheme, which will be named the "monolith scheme," is based on a single large-scale MDA unit representing the complete operating load torque region of the motor, while the second scheme, which will be named the "partition scheme," consists of many small-scale MDA units, each unit representing a particular load torque operating region.     

What stator current processing-based technique to use for induction motor rotor faults diagnosis?

In recent years, marked improvement has been achieved in the design and manufacture of stator winding. However, motors driven by solid-state inverters undergo severe voltage stresses due to rapid switch-on and switch-off of semiconductor switches. Also, induction motors are required to operate in highly corrosive and dusty environments. Requirements such as these have spurred the development of vastly improved insulation material and treatment processes. But cage rotor design has undergone little change. As a result, rotor failures now account for a larger percentage of total induction motor failures. Broken cage bars and bearing deterioration are now the main cause of rotor failures. Moreover, with advances in digital technology over the last years, adequate data processing capability is now available on cost-effective hardware platforms, to monitor motors for a variety of abnormalities on a real time basis in addition to the normal motor protection functions. Such multifunction monitors are now starting to displace the multiplicity of electromechanical devices commonly applied for many years. For such reasons, this paper is devoted to a comparison of signal processing-based techniques for the detection of broken bars and bearing deterioration in induction motors. Features of these techniques which are relevant to fault detection are presented. These features are then analyzed and compared to deduce the most appropriate technique for induction motor rotor fault detection.     

Lumped-parameter thermal model for induction machines

A novel lumped-parameter thermal model for induction machines that can be included in real-time applications is presented. The model considers just stator, rotor, and environment representative temperatures so that parameter estimation can be carried out. Thermal parameters are experimentally obtained and a sensorless vector control application with a 1-kW induction motor is included showing the effectiveness of the proposed solution.     

A two-factor saturation model for synchronous machines withmultiple rotor circuits

It is generally felt that no major accuracy breakthrough in predicting the steady-state and transient performance of synchronous machines could be achieved without taking proper account of the iron saturation effects as well as eddy-current losses. Although the two issues were often treated separately in the past, this paper attempts to unite them by developing a general model covering both the main-path magnetic saturation and frequency effects in the dynamic equations. Mathematical analysis in the d-q space pinpoints cross-saturation coupling which, a priori, does not seem to be symmetrical for salient-pole machines. Yet the model is theoretically sound, since it fulfils at least the physical constraints using energy balance principles. Some test points from a 555-MVA turbine-generator are used for an initial assessment the model's capability to predict the field current and internal angle for various loading conditions     

Reduced order models for induction motors with two rotor circuits

Induction motor behavior is commonly simulated by a fifth order differential equation model which includes two stator state variables, two rotor state variables, and shaft speed. Normally two more variables must be added to account for the effects of a second rotor circuit representing deep bars, a starting cage, or rotor distributed parameters. This paper presents a technique for including the effects of a second rotor circuit without adding more state variables to the fifth order model. Transient, as well as steady state effects are included. The model may be useful in cases where switching introduces transient torques and losses that are invisible to the fifth order model, and it is not desirable to expand the model to include two more state variables. A laboratory test is included     

Algorithm for the study of voltage sags on induction machines

This paper proposes an algorithm for the approximate calculation of the effects caused by a voltage sag in the induction machine supply system. The algorithm computes the current and torque peaks, and the mechanical speed loss for an extensive range of voltage sags. It has a high calculation speed because it makes two simplifications. The first supposes that speed varies insignificantly during the first cycles after the voltage drop and recovery points to solve analytically the electrical transients in these cycles. The second neglects the electrical transient during the sag duration for a quick evaluation of the speed loss. Machine sensitivity to voltage sags is graphically shown. The curves can be applied to protective relay coordination     

Determination of interbar current effects in the detection ofbroken rotor bars in squirrel cage induction motors

In present monitoring techniques for the detection of broken rotor bars in squirrel cage induction motors, the assumption is made that a broken bar conducts no current. This causes a magnetic imbalance, which can then be detected to indicate a broken bar. In certain motors, however, large currents are still able to flow in the broken bar by means of interbar currents. This paper deals with the effects these currents have on broken bar monitoring. The work shows theoretically and experimentally that interbar currents reduce any magnetic imbalance brought about by the broken bar     

Analysis of generically configured PSC induction machines

A multiple reference frame based model of a generically configured permanent split capacitor (PSC) induction machine is set forth. The model provides for the possibilities of asymmetrical winding arbitrary tapping of the main winding, and shifting of the auxiliary winding from the quadrature position. The model is valid for both steady-state and transient analysis, and features state variables which are constant in the steady-state. This feature makes the model readily linearizable for derivation of transfer functions. In addition, a procedure for estimation of the machine parameters based on standstill measurements is set forth. Finally, both the model and the parameter measurement scheme are verified experimentally     

Tracking control technique for induction motors

A novel application is presented of the tracking control technique to induction motor drive systems. By this technique, the position or the speed of the rotor can follow a preselected track (a time history of rotor position or velocity). An algorithm for the design of the tracking controller is developed. The induction motor model and the controller are modified to allow the inclusion of the nonlinear modes in the system without excessive computations. A simple and realistic criterion for selecting the proper reference tracks during starting, speed control and braking is proposed. The controller developed, is tested on a full-size nonlinear analog simulator. All test results show the effectiveness of the scheme in position-tracking applications such as robotics and manipulators     

A new and best approach for early detection of rotor and stator faults in induction motors coupled to variable loads

Today, induction machines are playing, thanks to their robustness, an important role in world industries. Although they are quite reliable, they have become the target of various types of defects. Thus, for a long time, many research laboratories have been focusing their works on the theme of diagnosis in order to find the most efficient technique to predict a fault in an early stage and to avoid an unplanned stopping in the chain of production and costs ensuing. In this paper, an approach called Park’s vector product approach (PVPA) was proposed which was endowed with a dominant sensitivity in the case in which there would be rotor or stator faults. To show its high sensitivity, it was compared with the classical methods such as motor current signature analysis (MCSA) and techniques studied in recent publications such as motor square current signature analysis (MSCSA), Park’s vector square modulus (PVSM) and Park-Hilbert (P-H) (PVSM_P-H). The proposed technique was based on three main steps. First, the three-phase currents of the induction motor led to a Park’s vector. Secondly, the proposed PVPA was calculated to show the distinguishing spectral signatures of each default and specific frequencies. Finally, simulation and experimental results were presented to confirm the theoretical assumptions.     

Transient thermal characteristics of induction machine rotor cage

Thermal analysis of an induction machine cage rotor during stall conditions forms an important part of design calculations. The study of rotor circuit thermal behavior is also useful to identify causes of failure in large cage rotor induction machines. The authors present a three-dimensional finite-element-based electrical-thermal analysis of the bar and end-ring area of a large rotor to examine its thermal characteristics during a stall. Details of temperature variations at key locations in the bar and end ring are provided. The calculations are compared to experimental results, and the advantages and limitations of the solution technique for rotor analysis are discussed     

Analysis of concentrated winding induction machines for adjustablespeed drive applications-experimental results

An approach to an analysis of multiphase concentrated winding induction machines specifically designed for operation with static power converters has been presented and simulated by means of a digital computer simulation in previous papers. In order to substantiate the theoretical conclusions regarding the performance of multiphase induction motors, an experimental five phase induction motor and its corresponding power converter and control are designed and fabricated. In this paper some of the design criteria and the experimental results obtained from the tests are presented and discussed     

Experimental setup for the measurement of surge propagation in induction machines

This paper presents the experimental setup for the measurement of surges and their propagation within the turns of a coil in an induction machine. Recent advances in data capture techniques makes this work possible, which will lead to an improved understanding of the mechanisms involved.     

Estimating the parameters of induction machines at standstill

This paper presents a method to determine the continuous-time parameters of induction machines which are necessary to implement a field- oriented control strategy. This method does not require the use of any mechanical devices or speed measurement sensor and it is conceived to be used during the auto-commissioning of the drive-system. The estimation of the stator resistance is based on the dynamic model of the machine considering that the variables are DC quantities. The estimation of the stator transient inductance, the stator inductance, and the rotor time constant, are based on the dynamic model of the machine. The experimental results which are presented demonstrate the feasibility of the proposed method     

A simple model-based online rotor time constant estimator for an induction machine

A new model-based online rotor time constant estimator for an induction machine is developed. The estimation algorithm is based on induction machine models in two different reference frames. Novel mechanism is proposed to avoid the singularity problem. Encouraging simulation results are given to demonstrate the effectiveness of the simple yet accurate estimator.     

Three phase induction machines asymmetrical faults identificationusing bispectrum

Bispectrum analysis is introduced for three-phase induction machine faults identification and condition monitoring. Bispectrum analysis is capable of providing more information than power spectrum analysis. In the present investigation, machine vibration signals operating at different rotating speed and degree of unbalance are thoroughly analyzed. Very promising results were obtained and presented. The results and analysis indicate that bispectrum analysis can be successfully applied to machine asymmetric faults, machine rotation speed and stator winding fault analysis and identification     

Motional time-harmonic simulation of slotted single-phase induction machines

Considering motional effects in the steady-state finite-element simulation of single-phase induction machines inevitably requires a transient approach. The resulting computation time seriously hampers the application of finite elements within technical designs. In this paper, time-harmonic finite-element simulation, as commonly applied to the three-phase induction machine model, is also enabled for single-phase motors by decomposing the air-gap field in two revolving fields in the opposite direction. The advantages and drawbacks of the novel approach are illustrated by a benchmark model. Issues such as ferromagnetic saturation, external circuit coupling, adaptive mesh refinement, and torque computation are addressed. The method is used to simulate a capacitor start/run motor.