Short-circuit Fault Conditions Research Articles

Algoritmo robusto para el diagnóstico de fallas eléctricas en el motor de inducción trifásico basado en herramientas espectrales y ondeletas.

This work present a group of tools based on the fast Fourier transform (FFT) and Haar, Daubechies and Coiflet discrete wavelet transform (DWT), using the Park's instantaneous space phasor module (ISP) of the three phase induction machine stator currents for electric stator and rotor fault diagnosis. A simulation and experimental validation for inter-turn stator short-circuit electric fault and end-ring broken rotor fault diagnosis was performed. The main objective of the work is to perform a non invasive electric fault diagnosis to avoid economical losses in the industrial process using the advantages of spectral and wavelet tools.

A novel fault tolerant permanent magnet synchronous motor with improved optimal torque control for aerospace application

Improving fault tolerant performance of permanent magnet synchronous motor has always been the central issue of the electrically supplied actuator for aerospace application. In this paper, a novel fault tolerant permanent magnet synchronous motor is proposed, which is characterized by two stators and two rotors on the same shaft with a circumferential displacement of mechanical angle of 4.5°. It helps to reduce the cogging torque. Each segment of the stator and the rotor can be considered as an 8-pole/10-slot five-phase permanent magnet synchronous motor with concentrated, single-layer and alternate teeth wound winding, which enhance the fault isolation capacity of the motor. Furthermore, the motor has high phase inductance to restrain the short-circuit current. In addition, an improved optimal torque control strategy is proposed to make the motor work well under the open-circuit fault and short-circuit fault conditions. Simulation and experiment results show that the proposed fault tolerant motor system has excellent fault tolerant capacity, which is able to operate continuously under the third open-circuit fault and second short-circuit fault condition without system performance degradation, which was not available earlier.

Analysis of rotor and stator winding inter-turn faults in WRIM using simulated MEC model and experimental results

In this paper, a 3-phase wound rotor induction machine (WRIM) has been simulated under the winding inter-turn short circuit fault conditions in the stator and rotor sides using the complete magnetic equivalent circuit model (MEC). Local saturation of the stator and rotor teeth, skewing of rotor slots, effect of stator and rotor tooth and space harmonics in the stator and rotor windings are considered in the developed model. The differences between rotor and stator winding inter-turn fault conditions in WRIMs such as amplitude of currents through inter-turn shorted link, dependency of fault current amplitude on the number of short circuit turns and load level, and phase angle difference between current through inter-turn shorted link and phase current in stator and rotor have been analyzed and compared with simulated results. Experimental results on a 1.1kW, 380V, 50Hz, 2pole WRIM are employed to validate the accuracy of the developed MEC model in faulty conditions.

Investigation of wound rotor induction machine vibration signal under stator electrical fault conditions

This paper investigates wound rotor induction machine torque and vibration signals spectra for operation with and without a stator short-circuit or open-circuit winding fault. Analytical expressions that enable the healthy and faulty machine pulsating electromagnetic torque frequencies to be related to shaft speed are derived and validated for operating conditions of interest. A coupled-circuit machine model is used to investigate the healthy and faulty electromagnetic torque signal. Shaft torque and stator frame vibration are measured on a laboratory test rig comprising a 30 kW wound rotor induction machine. It is shown that the existence of a stator winding inherent electrical unbalance or that arising from fault gives rise to a range of pulsating torque frequencies that are transmitted to the machine frame and can be detected in the measured vibration signal. The magnitudes of the resulting vibration components are demonstrated to be largely determined by the unbalance severity and the mechanical system response. The presented experimental results clearly validate the analytical and simulation analysis for the operating range of the investigated industrial machine design.

Fault Diagnosis of Induction Motors Based on RBF Neural Network

In order to improve the diagnosis accuracy of stator short circuit faults of three-phase induction motors, in this paper, a method using three-layered RBF neural network is proposed to diagnose the short circuit faults on the basis of analysis of structure and algorithm of RBF neural network. Then the approach to establish RBF neural network and the influence of different expanding coefficients upon the diagnosis accuracy are illustrated. The simulation results show that RBF neural network can successfully diagnose and classify six typical short circuit faults of induction motors. This method has a faster speed, higher accuracy and it needs fewer samples. In conclusion, RBF neural network is practical, efficient and intelligent in fault diagnosis of induction motors.

Fault Diagnosis of Power Converter for Switched Reluctance Motor based on Discrete Degree Analysis of Wavelet Packet Energy

Power converter plays a very important role in switched reluctance motor (SRM) systems, and it is also the easiest one to experience failures. Power converter faults will cause the motor to run in non equilibrium states, and a long time fault operation will lead to motor and other modules damaged, and make the system completely lose working stability. This paper uses an asymmetric bridge converter as the research object with three-phase SRM, employs the wavelet packet decomposition for the phase currents. It analyzes and studies the short circuit fault condition of IGBT, uses an energy discrete degree of the wavelet packet nodes as the fault characteristic, and conducts the corresponding experimental and simulation analysis to verify the effectiveness and practicality of the proposed method.

Analysis of internal winding short circuit faults in power transformers using transient finite element method coupling with external circuit equations

SUMMARYInterturn short circuit faults are the leading cause of power transformer failures. If not quickly detected, these faults usually develop into more serious faults, which would result in irreversible damage to the transformer, unexpected outages, and consequential costs. The aim of this research is to obtain a better understanding of the physical behavior of the power transformers in the presence of interturn faults as well as to discover the best indicators for detection of interturn short circuit faults. To this end, a time stepping finite element model of power transformer has been developed to analyze the transient behavior of a real power transformer when the transformer is working under winding short circuit fault conditions. The transient model, coupled with external circuit equations, allows us to simulate the dynamic behavior of the transformer with the real power supply and external loads connections. The FEM computations show the ability of the electromagnetic flux inside the transformer, transformer terminal currents, and circulating current in the shorted turns as useful monitoring parameters for transformer fault detection. Copyright © 2013 John Wiley & Sons, Ltd.

Modeling of Different Winding Configurations for Fault-Tolerant Permanent Magnet Machines to Restrain Interturn Short-Circuit Current

This paper describes an analytical model to evaluate the short-circuit (SC) current resulting from an interturn fault by computing the self and mutual inductances under SC fault condition. Two different concentrated winding configurations, i.e., horizontally and vertically placed conductors in the slot of a fault-tolerant permanent magnet synchronous machine are considered. By computing the associated slot-leakage and air-gap fluxes, the self inductance of both healthy and faulty windings as well as the mutual inductance between them, the SC current can be determined for any position and number of shorted turns. The proposed model is verified with finite-element analysis and validated experimentally. It will be shown that the magnitude of an interturn SC current depends on both the number of shorted turns and their position in the slot. The measured SC inductance shows that a new proposed concentrated vertical winding configuration can inherently limit the SC current and reduce its dependence on the position within the slot.

Relaxed Fault Conditions for Stator Short-Circuit Fault Isolation in Induction Motors

In this paper, a geometric analysis has been carried out for stator fault isolation in three-phase induction motors (IM). Specifically, stator short-circuit faults in IM are considered in this study. For the geometric analysis, the study departs from the IM model in the stator reference frame (dq-frame). Nonetheless, a single fault in the abc-frame is reflected as concurrent faults in the dq-frame, where the number of concurrent faults and disturbances (load torque) is equal to the number of state variables. Hence, isolating stator short-circuit faults cannot be achieved even by considering the full state available. Thus, relaxed fault conditions are given to isolate stator short-circuit faults in the abc-frame for IM. Two different perspectives are presented to achieve these objectives. Finally, observer-based fault diagnosis schemes are suggested for both conditions, and simulation results are shown to validate the ideas illustrated in this study.

Numerical modelling of transformers interturn faults and characterising the faulty transformer behaviour under various faults and operating conditions

Interturn short circuit faults are the leading cause of power transformer failures. If not quickly detected, these faults usually develop into more serious faults that would result in irreversible damage to the transformer, unexpected outages and the consequential costs. This contribution is aimed at obtaining a better understanding of physical behaviour of power transformers in the presence of interturn faults as well as extracting several features that would be useful to specify the faults. To this end, a circuit-coupled time-stepping finite-element model (FEM) of power transformer has been developed to characterise the transient behaviour of a real power transformer when the transformer is working under winding short circuit fault conditions. An experimental set-up consisting of the same transformer used with the FEM transformer simulation was used to validate the FEM of the faulty transformer. The results of the experiments demonstrate the remarkable ability of the model to reproduce the real behaviour of the transformer with interturn winding faults. The study characterises the faulty transformer behaviour under varying conditions of load, supplying voltage, location of the fault, and fault severity and size. Useful characteristic signatures associated with interturn faults extracted from the transformer behaviour under varying fault and transformer operating conditions are expected to yield insights into developing reliable and sensitive fault detection and localisation methods in power transformers.

Detection of stator short circuit faults in three-phase induction motors using motor current zero crossing instants

Stator faults typically have a significant share amongst the common type of faults in industrial three-phase induction (asynchronous) motors. This paper presents a motor current signature analysis (MCSA)-based diagnostics of the stator winding short circuit fault. This type of fault happens due to the destruction of the turn insulation, and can be very detrimental causing motor shutdown. Instead of traditional MCSA using the motor stator current, in this paper, analysis using the zero crossing time (ZCT) signal of the stator current is presented. The theoretical aspects of the stator short circuit detection are presented. Following that, a diagnostic algorithm utilizing the ZCT signals is proposed. Experiments are performed with real motors, healthy and with shorted stator windings. Frequency analysis of the ZCT signals from the experimental data substantiates the theoretical arguments with significant accuracy.

Fault detection for stator inter-turn short circuit in doubly fed induction generators using adaptive observers

This paper presents an observer-based fault detection approach for inter-turn stator short circuit fault in doubly fed induction generators (DFIG). A state-space model is developed, which can represent both the healthy and faulty conditions. Based on this model, two different adaptive observers: asymptotic adaptive observer and exponential adaptive observer are constructed, which are both able to estimate the fraction of short circuited winding online. The case when the rotor speed is immeasurable is also considered in this paper. The proposed exponential adaptive observer is reformulated into a new observer, which is capable of estimating the fault level and the rotor speed simultaneously. The simulation results demonstrate that this approach has effectiveness on fault detection under both steady state operation and transient state operation. It has strong robustness against the speed and load variations. This advantage has significance on fault detection of wind turbine DFIGs, since the DFIGs are predominantly under varying speed operation.

Enhanced Optimal Torque Control of Fault-Tolerant PM Machine Under Flux-Weakening Operation

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper describes an enhanced optimal-torque-control strategy for fault-tolerant permanent-magnet (PM) machines under flux-weakening operations. By adjusting the degree of flux weakening according to estimated instantaneous-torque-control errors, the torque-control performance of the machine can be improved when operating above its base speed under either open- or short-circuit fault condition. Extensive simulations under both healthy and fault conditions have been undertaken in order to validate the effectiveness of the proposed control strategy. Experimental results have also been given based on the testing of a prototype five-phase fault-tolerant PM machine. </para>

Analytical Prediction of Short-Circuit Current in Fault-Tolerant Permanent Magnet Machines

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper describes an analytical technique that can be utilized to predict the short-circuit current in a fault-tolerant permanent-magnet machine under partial-turn short-circuit fault conditions. It has been shown that the current in partially short-circuited turns is dependent on their relative position in the slot where the phase winding is accommodated, and the slot-leakage flux associated with these turns has a significant influence on the short-circuit current when a remedial action has been applied. An analytical model that quantifies the variation of the slot-leakage flux as a function of the relative position of partially short-circuited turns has been developed. Both finite-element analysis and experimental results demonstrate the effectiveness of the proposed technique for predicting the short-circuit current. </para>

Conductive polymer switching mechanism for high power current-limiting applications

Various thermoplastic and thermo-set based polymers, blended with acetylene carbon blacks and graphite fillers to form electrically conductive polymers, were investigated to determine the switching mechanism under high power short-circuit fault conditions. Presently, a positive temperature coefficient (PTC) effect is the accepted switching mechanism for low power overcurrent devices. However, for high power, distribution level devices, this mechanism has been assumed to be the same under high fault conditions. This work proposes another possible switching mechanism responsible for a steep change in resistance under high power faults. The proposed mechanism of resistance change comes, not from the PTC change in the material, but rather from the vaporization of the conducting polymer contact areas at the polymer/electrode interface. A comparison between low power polypropylene based devices with a positive temperature coefficient (PTC) effect (thermal expansion of the polymer bulk) and high power devices was done to support this theory. A model was developed along with numerous short-circuit tests to support this theory. Modifications with e-beam irradiation were made to alter the PTC characteristics of thermoplastics but had little effect on high fault short-circuit switching. Also, numerous short-circuit testing on thermo-set based materials without any PTC transition still switched under high fault currents. These all supported the proposed theory that switching, under high fault currents, was from vaporization of the contact areas at the polymer surface rather than thermal expansion in the bulk of the conductive polymer as previously accepted.

Analytical Prediction of the Short-Circuit Current in Fault-Tolerant Permanent-Magnet Machines

This paper describes an analytical technique that can be utilized to predict the short-circuit current in a fault-tolerant permanent-magnet machine under partial-turn short-circuit fault conditions. It has been shown that the current in partially short-circuited turns is dependent on their relative position in the slot where the phase winding is accommodated, and the slot-leakage flux associated with these turns has a significant influence on the short-circuit current when a remedial action has been applied. An analytical model that quantifies the variation of the slot-leakage flux as a function of the relative position of partially short-circuited turns has been developed. Both finite-element analysis and experimental results demonstrate the effectiveness of the proposed technique for predicting the short-circuit current.

Testing of a 250-Kilowatt Fault-Tolerant Permanent Magnet Power Generation System for Large Civil Aeroengines

This paper describes the experimental testing of a 250-kW fault-tolerant permanent magnet power generation system (machine and converter) for the low-pressure shaft of a large civil engine. The relative merits of this system as a reliable electrical power source for safety critical applications are discussed, and its performances under both healthy and fault conditions are analyzed and experimentally tested. It has been shown that the power generation system has a high efficiency over a wide output power range under healthy conditions. However, a large torque ripple and potentially destabilizing shaft power swing will result under an open- or short-circuit fault condition. This problem can be eliminated by employing an optimal torque control strategy. The utility and effectiveness of the control technique have been experimentally validated.

FE-based physical phase variable model of PM synchronous machines under stator winding short circuit faults

An FE-based physical phase variable model is proposed for PM machines under stator short-circuit faults. The parameters of the proposed model, inductances and back EMFs are determined using the FE-circuit coupled computation of the machine under the same type of fault. The parameters obtained include information on the fault location and the number of turns involved, in addition to the space harmonics and the effects of stator saturation. The FE-based phase variable model that has been developed is verified through comparison with the FE model. The significance of the work is that it introduces a feasible procedure to build a physically accurate and computationally fast phase variable model for PM machines under stator short-circuit fault conditions. Such a model is useful for the study of fault diagnosis and prognosis.

Loop Selective Direction Measurement for Distance Protection

Distance relays achieve selective tripping by measurement of all short circuit fault conditions inside set reaches. The direction of the fault, forward or reverse is commonly determined with a dedicated measurement to ensure selectivity under all conditions. For the direction decision (measurement) a number of alternatives are available. This paper describes a loop selective direction measurement and illustrates by means of a typical fault why this is superior to a non loop selective direction measurement such as that based on negative sequence quantities.

A New 600 V Punch Through-Insulated Gate Bipolar Transistor with the Monolithic Fault Protection Circuit Using the Floating p-Well Voltage Detection

A new fault sensing scheme of the insulated gate bipolar transistor (IGBT) employing the floating p-well, which detects the over-voltage of the floating p-well under the short circuit fault condition, is proposed and implemented by fabricating the main IGBT and gate voltage pull-down circuit using the widely used planar IGBT process. The floating p-well structure also improves the avalanche energy of IGBT in addition to detecting the fault signal. The detection of fault and gate voltage pull-down operation is achieved by the proposed fault protection scheme employing the floating p-well voltage detection. The proposed fault protection circuit was measured under the hard switching fault (HSF) and fault under load (FUL) conditions. The normal switching behavior of the main IGBT with the proposed protection circuit was also investigated under inductive load switching conditions.