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In this paper, the effects of inverter harmonics on motor current fault signatures are studied in detail. It is theoretically and experimentally shown that the fault signatures caused by the inverter harmonics are similar and comparable to those generated by the fundamental harmonic on the line current. Theoretically-derived extended relations including bearing fault, eccentricity, and broken rotor bar relations are found to match experimental results. Furthermore, it is observed and reported that the asymmetries on the rotor caused by broken rotor bars increase the amplitude of even harmonics. To confirm these claims, bearing, eccentricity, and broken rotor bar faults are tested and the line current spectrum of each faulty motor is compared with the healthy one. The proposed additional fault data are expected to contribute positively to the inverter-fed motor fault decision-making algorithms. Index Terms--Bearing faults, condition monitoring, current signature analysis, fault diagnosis, inverter harmonics, spectral analysis.

This paper investigates the use of fuzzy logic for fault detection and diagnosis in a pulsewidth modulation voltage source inverter (PWM-VSI) induction motor drive. The proposed fuzzy technique requires the measurement of the output inverter currents to detect intermittent loss of firing pulses in the inverter power switches. For diagnosis purposes, a localization domain made with seven patterns is built with the stator Concordia current vector. One is dedicated to the healthy domain and the six others to each inverter power switch. The fuzzy bases of the proposed technique are extracted from the current analysis of the fault modes in the PWM-VSI. Experimental results on a 1.5-kW induction motor drive are presented to demonstrate the effectiveness of the proposed fuzzy approach. Index Terms--Concordia transform, diagnosis, fault detection, fuzzy logic, induction motor, voltage source inverter (VSI).

The dynamic behavior of a synchronous distributed generator connected to a distribution system during fault conditions is studied. A fault on an actual system was found to have a sag that was extended after the fault was cleared. It is shown that the combination of the generator and the load on the system contributes to the extended sag. The detailed simulation studies demonstrate that the primary factors are the reactive power drawn by the load during the fault and recovery along with the reaction of the generator. The prediction of such behavior requires proper modeling of the generator, the generator's controls, and the system and dynamic load. Operators of such generators need to be aware of this type of system and load response when synchronous DG is connected to a distribution network. Index Terms--Distributed generation (DG), distribution systems, excitation controls, fault analysis, power quality (PQ), voltage regulator, voltage sags.

This paper describes an advanced coordination method for an optimized protection time grading based on a new nonstandard tripping characteristic for overcurrent protection relays. The intention is the highest possible reduction of tripping times for a selective fault clearing in distribution networks protected by overcurrent relays without communication links. The new nonstandard tripping characteristic will be described from its basic idea to its constraints of the optimization problem. The optimization is solved by the method of Lagrange generalized with the Karush-Kuhn-Tucker conditions and is aimed at selective fault tripping with shorter tripping times as standard characteristics and conventional coordination methods. Overcurrent relay coordination becomes a mathematical optimization task. A comparison with the standard characteristics and conventional coordination methods shows a notable advancement regarding their average and maximum tripping times which can be achieved using this new method. Index Terms--Optimization method, overcurrent protection, protection coordination, selectivity, tripping characteristic, tripping time.

Carry-select adders are one of the faster types of adders. This paper proposes a scheme that encodes the sum bits using two-rail codes; the encoded sum bits are then checked by self-checking checkers. The multiplexers used in the adder are also totally self-checking. The scheme is illustrated with the implementation of a 2-bit carry select adder that can detect all single stuck-at faults on-line; the detection of double faults is not guaranteed. Adders of arbitrary size can be constructed by cascading the appropriate number of such 2-bit adders. A range of adders from 4 to 128 bits is designed using this approach employing a 0.5-[micro]m CMOS technology. The transistor overhead in implementing these self-checking adders varies from 19.51% to 20.94%, and the area overhead varies from 16.07% to 20.67% compared to adders without built-in self-checking capability. Index Terms--On-line fault detection, self-checking checker, transient faults, two-rail code.

A fault diagnostic and reconfiguration method for a cascaded H-bridge multilevel inverter drive (MLID) using artificial-intelligence-based techniques is proposed in this paper. Output phase voltages of the MLID are used as diagnostic signals to detect faults and their locations. It is difficult to diagnose an MLID system using a mathematical model because MLID systems consist of many switching devices and their system complexity has a nonlinear factor. Therefore, a neural network (NN) classification is applied to the fault diagnosis of an MLID system. Multilayer perceptron networks are used to identify the type and location of occurring faults. The principal component analysis is utilized in the feature extraction process to reduce the NN input size. A lower dimensional input space will also usually reduce the time necessary to train an NN, and the reduced noise can improve the mapping performance. The genetic algorithm is also applied to select the valuable principal components. The proposed network is evaluated with simulation test set and experimental test set. The overall classification performance of the proposed network is more than 95%. A reconfiguration technique is also proposed. The proposed fault diagnostic system requires about six cycles to clear an open-circuit or short-circuit fault. The experimental results show that the proposed system performs satisfactorily to detect the fault type, fault location, and reconfiguration. Index Terms--Fault diagnosis, multilevel inverter, neural network (NN), reconfiguration.

We consider a class of positive real infinite dimensional systems which are subjected to incipient actuator faults. The actuator fault is modeled as a time varying transition from an initial (linear or even nonlinear) map into another unknown nonlinear map at the onset of the fault occurrence. An infinite dimensional adaptive detection observer is utilized to generate a residual signal in order to detect the fault occurrence and to assist in the fault accommodation. This is done via an automated control reconfiguration which utilizes information on the new actuator map and adjusts the controller via a right inverse of the new actuator map. A robust modification is utilized in order to avoid false alarms caused by unmodeled dynamics. An example is included to illustrate the applicability of the proposed detection scheme. Index Terms--Actuator faults, distributed parameter systems, fault accommodation, nonlinear actuator dynamics.

This paper deals with the dynamic behavior of a 21-level (line-to-line) back-to-back (BTB) system based on series connection of 16 converter cells under a single-line-to-ground (SLG) fault condition. The BTB system is an ac-dc-ac power conversion system intended for achieving asynchronous power-flow control between transmission networks. When the SLG fault happens, an imbalance in the supply voltage brings an amount of negative-sequence current to the BTB system. The negative-sequence current should be mitigated because it would result in an increased supply current and a dc-capacitor voltage fluctuation. This paper intends for reducing both the negative-sequence current and the dc-voltage fluctuation to acceptable levels. A laboratory system rated at 200 V and 20 kW confirms the validity of the reduction scheme. In addition, this paper addresses the issue of magnetic saturation in the 16 three-phase converter--transformers. Index Terms--Back-to-back (BTB) system, multilevel converter, negative-sequence current, power-flow control, single-line-to-ground (SLG) fault.

This paper presents a robust approach to real-time detection of faults in the load-frequency control loop of interconnected power systems. The detection of faults takes place under different operating conditions, in the presence of modeling uncertainties, unknown changes in the load demand, and other external disturbances, such as plant and sensor noise. Although the approach is applicable to N-area systems, a two-area interconnected power system example is considered for simplicity. Index Terms--Load-frequency control, power systems, robust fault detection.

This paper proposes a protection scheme which utilizes modern voltage-source converters as fast-acting current-limiting circuit breakers. This paper investigates the main challenges of detecting and localizing a fault, and interrupting it as quickly as possible in a multiterminal dc system. A system protection scheme consisting of smart relays associated with converters has been developed. The protection relays monitor local quantities to detect and isolate disturbances/faults. It is shown that overcurrent-based schemes can be adopted for these relays to meet the fast response requirements. The effectiveness of the proposed protection scheme is illustrated through simulations. Index Terms--DC distribution, power-electronic converters, protection.

This paper introduces a new differential protection scheme based on zero-sequence voltages with 100% coverage for generator stator ground faults. Analysis shows that the A-fundamental zero-sequence voltages and the A-third-harmonic voltages at the generator neutral and the terminals will change simultaneously, and they present some similar characteristics. According to that, the new scheme that exploits the fault information of both the zero-sequence fundamental voltage and the third-harmonic voltage is described. As it combines the information of the zero-sequence fundamental voltage and the third-harmonic voltage, the scheme can detect the ground fault with high sensitivity in 100% coverage winding. Simulation and field test results show that the proposed scheme can obtain higher sensitivity than the traditional schemes. Index Terms--Fault contribution component, stator ground protection, third-harmonic voltage, zero-sequence fundamental voltage.

This paper presents an effective algorithm to protect unfused 22.9-kV shunt capacitor banks in grounded-wye connection by improving an existing voltage difference method-based algorithm. It has often been reported that it is difficult to detect ground faults with arc near the input points within the bank using existing algorithms that use only the magnitude of the differential voltage. In this paper, it is shown that ground faults with arc near the input point can be detected by fast Fourier transform (FFT) analysis of the differential voltage and that the proposed algorithm is not impacted by harmonics generated by nonlinear loads which have quantitative influence on the capacitor banks. Consequently, the proposed method using harmonics analysis can be applied as an extended version of the existing detection method. The proposed method is applied to a simplified 22.9-kV real-life Korea Electric Power Corporation system and it is verified that the proposed algorithm can clearly detect faults that are not easily detected by the existing method. Index Terms--Ground-wye connection, harmonics, protection algorithm, unfused shunt capacitor bank, voltage difference method (VDM).

Distance protection of flexible ac transmission lines, including the thyristor-controlled series compensator (TCSC), static synchronous compensator, and static var compensator has been a very challenging task. This paper presents a new approach for the protection of TCSC line using a support vector machine (SVM). The proposed method uses postfault current samples for half cycle (ten samples) from the inception of the fault and firing angle as inputs to the SVM. Three SVMs are trained to provide fault classification, ground detection, and section identification, respectively, for the line using TCSC. The SVMs are trained with polynomial kernel and Gaussian kernel with different parameter values to get the most optimized classifier. The proposed method converges very fast with fewer numbers of training samples compared to neural-network and neuro-fuzzy systems which indicates fastness and accuracy of the proposed method for protection of the transmission line with TCSC. Index Terms--Distance protection, flexible ac transmission system (FACTS) support vector machine (SVM), thyristor-controlled series compensator (TCSC).

A synchronous machine internal faults model based on the actual winding arrangement is described in this paper. Based on the winding function approach, the machine inductances are calculated directly from the machine winding distribution, thereby the space harmonics produced by the machine windings are readily taken into account. Moreover, the calculation of the machine inductances is made easier by the use of the machine electrical parameters instead of the geometrical ones. Simulation results for internal faults on a laboratory generator are compared with experimental results to verify the accuracy of the proposed model. Index Terms--Internal faults, space harmonics, synchronous machines, winding function.

Power systems on naval vessels and airplanes are good examples of self-contained power systems. State of the art LEM modules and voltage sensors provide real time current and voltage data. This paper shows how that information can be used to construct dynamic equivalent impedance representations of the system discretized into key trunk lines. Error analysis indicates that the algorithm performing this representation can be updated in one fifth of a cycle if the signal to noise data ratio is 5% or less. The magnitude of the equivalent impedance is sufficient to determine when fault control on either end of the trunk line is required. These same equivalent impedances can be used to determine the best switch configuration to maximize load power while minimizing transmission loss subject to line load capability. The accuracy of the equivalent impedance approach is assessed for transients with active and passive loads. Index Terms--Fault detection, phase analysis, reconfiguration, transient.

This paper presents a new numerical spectral domain algorithm devoted to blocking unsuccessful automatic reclosing onto permanent faults and fault distance calculation. Arc voltage amplitude and fault distance are calculated from the fundamental and third harmonics of the terminal voltages and currents phasors. The electric arc is modeled with its voltage waveshape defined numerically on the basis of a number of arc voltage records obtained in the high-voltage laboratory. From the calculated arc voltage amplitude, it can be concluded whether the fault is a transient arcing fault or a permanent arcless fault. If the fault is permanent, automatic reclosure should be blocked. The algorithm can be applied for adaptive autoreclosure, distance protection, and fault location. The results of algorithm testing through computer simulation and real field record are given. Index Terms--Arc resistance, electric power systems, fault location, numerical algorithms, protection, spectral analysis, transmission lines.

Fault tolerance is a critical attribute in automotive electrical and propulsion systems. In this paper, a control scheme is presented that allows an induction motor drive system to operate in the event of multiple sensor failures. Automatic diagnosis of sensor fault and recovery is performed and used to reconfigure the drive system controls to achieve the best performance in lieu of component degradation. This approach couples a new digital delta-hysteresis regulation scheme with a model reference adaptive system scheme in order to provide fault tolerance for both phase-current and rotor position (speed) sensors. Simulation and experimental results are provided to show the effectiveness of the proposed scheme. Index Terms--Current regulation, induction drives, model reference adaptive system (MRAS) speed identification, sensor fault diagnosis, sensor fault tolerance.

The great development in computing power has allowed the implementation of artificial neural networks (ANNs) in the most diverse fields of technology. This paper shows how diverse ANN structures can be applied to the processes of fault classification and fault location in overhead two-terminal transmission lines, with single and double circuit. The existence of a large group of valid ANN structures guarantees the applicability of ANNs in the fault classification and location processes. The selection of the best ANN structures for each process has been carried out by means of a software tool called SARENEUR. Index Terms--Artificial neural networks (ANNs), fault classification, fault location, learning vector quantization, multilayer perceptron.

The aim of this paper is to introduce a novel real-time digital signal processing technique for power quality disturbance detection. The proposed technique is inspired on the Divide and Conquer Principle and on the Innovation Concept. Essentially, the Divide and Conquer Principle is applied in splitting the monitored disturbance event into stationary and nonstationary components, allowing localized individual signal analysis. Thereafter, the Innovation Concept is introduced for revealing new information not previously observed in the energy of the nonstationary signals and so detecting a new event. In addition, this paper demonstrates a straightforward and feasible way to evaluate the Total Harmonic Distortion (THD) or a distortion measure for voltage signals. Simulation results indicate that the proposed technique is able to accurately detect a variety of voltage disturbances. Index Terms--Adaptive signal processing, amplitude estimation, discrete Fourier transforms, frequency estimation, phase estimation, power quality, signal detection, signal processing.

The effect of rotor faults, such as broken bars and end-rings, over the signals of a position estimation strategy for induction motor drives is analyzed using a multiple coupled circuit model. The objective of this analysis is to establish the possibility of using the estimation strategy signals for fault diagnosis in variable-speed electric drives. This strategy is based on the effect produced by inductance variation on the zero-sequence voltage, when exciting the motor with a predefined inverter switching pattern. Experimental results illustrate the feasibility of the proposal. Index Terms--Induction motor (IM) drives, position estimation, rotor fault detection.

This paper presents an artificial neural network (ANN) and support vector machine (SVM) approach for locating faults in radial distribution systems. Different from the traditional Fault Section Estimation methods, the proposed approach uses measurements available at the substation, circuit breaker and relay statuses. The data is analyzed using the principal component analysis (PCA) technique and the faults are classified according to the reactances of their path using a combination of support vector classifiers (SVCs) and feedforward neural networks (FFNNs). A practical 52 bus distribution system with loads is considered for studies, and the results presented show that the proposed approach of fault location gives accurate results in terms of the estimated fault location. Practical situations in distribution systems, such as protective devices placed only at the substation, all types of faults, and a wide range of varying short circuit levels, are considered for studies. The results demonstrate the feasibility of applying the proposed method in practical distribution system fault diagnosis. Index Terms--Artificial neural network, distribution systems, fault location, support vector machines.

In complex emergency situations, failed protection relays and circuit breakers (CBs) have to be identified in order to begin the restoration process of a power system. This paper proposes a novel neural-network approach to identify multiple failures of protection relays and/or CBs. The approach uses information received from protection systems in the form of alarms and is able to deal with incomplete and distorted data. All possible emergencies are simulated and analyzed separately for each section of a power system. Taking into consideration supervisory control and data-acquisition system malfunctions, the corrupted patterns are used to train neural networks. The preliminary classification of emergencies into two different classes is applied to improve the system's performance. The evaluation of results shows that the overall error rate does not exceed 5%. The developed system was tested on a real power system. Index Terms--Alarm systems, fault diagnosis, identification, neural networks, pattern recognition.

High-resistance grounding and ungrounded power systems have many advantages, including continuous operation after a ground fault. However, locating ground faults is inherently difficult and is a major disadvantage with these systems. The problem stems from the lack of a good signal, such as a large fault current, that points to the fault. Classical search methods use injected locating signals, but they have shortcomings with intermittent faults, multiple 'same-phase' faults, and closed-loop/mesh power networks. New location methods attempt to overcome these previous problems by providing signals that can be used during system operation and with microprocessor-based detectors. This paper explores some of the key technical issues surrounding locating signals. Of concern are the signal flows through the power network including the uniqueness of the signal path. Other issues that are addressed are signal levels and power requirement, network impedances, and the impact of grounding capacitances and grounding resistances that divert the locating signal. Index Terms--Ground-fault location, high-resistance grounding, ungrounded system.

A transient model for an induction machine with stator winding turn faults is derived using reference frame transformation theory. A state-space representation of the dynamic equations, suitable for digital simulation is provided. Steady-state equivalent circuits are derived, from which the sequence components of the line currents can be estimated as a function of fault severity. Experimental results are provided to validate the derived model. Index Terms--Fault diagnostics, induction machine transient model, negative sequence, stator winding turn fault.

The internal fault of armature windings is one of the most severe faults for turbogenerators. It is necessary to know the transient currents of the machine when the internal faults occur so as to design suitable protection. Based on the multiloop method, a mathematical model of a turbogenerator with internal faults is developed. The air-gap permeance analysis is used to calculate the parameters and eddy current of the solid rotor. The method is verified by computer simulation and experimental results. The developed model accurately predicts transient currents and provides theoretically insightful information for protecting turbogenerators with internal armature faults. Index Terms--Internal faults, multiloop method, protection, turbogenerator.

Classical fault analysis methods for power systems are based on symmetrical components to represent various fault configurations. The complete electrical network is decomposed using a complex transformation matrix into decoupled zero, positive and negative sequence circuits. Faulted power system steady-state voltages and currents are computed using a nodal analysis solution method. This paper presents an extension of the above methodology using discretized RLC elements for the computation of the actual transient response of a network for various fault types. The decoupled networks are obtained using a real transformation matrix. Keywords: Short-circuit currents, transients, fault analysis

When a ground fault occurs at a substation, the part of the fault current that flows between the grounding system and the surrounding earth is known as grid current. This current determines the magnitude of the dangerous voltages within and around the station. It may vary from a few percent to almost 100% of the earth fault current. It is necessary to make an accurate estimate of grid current for an economical and safe design of ground electrode. The available analytical methods for determining the grid current require complete system data, which is voluminous and often unavailable. In this paper a simple and accurate analytical method for determining the grid current is presented. The method requires limited data. A computer program based on the proposed method has been developed and tested. Keywords: grounding, earth fault, substations, grid current, ground wires, step voltage, touch voltage, transferred potential

An accurate fault-location algorithm for two-parallel transmission line of direct ground neutral system is presented. The algorithm employs the faulted circuit and healthy circuit of two-parallel line as fault-location model, in which remote source impedance is not involved. It effectively eliminates the effect of load flow and fault resistance on the accuracy of fault location. It embodies an accurate location by measuring only one local end data and it is used in a procedure that provides the automatic determination of fault types and phases, rather than requires engineer to specify them. Simulation results have shown the effectiveness of the algorithm under the conditions of non-earth fault (phase-to-phase fault and three-phase fault with and without earth-connection). Key words: fault location, two-parallel transmission line, phase-to-phase fault, three-phase fault

This paper presents a new approach to the detection of high impedance fault (HIF). The proposed approach (or detector which implements this approach) has four distinct features. First, the detector input signal is the three-phase unbalanced current (or feeder 3[I.sub.0]), rather than the conventional three individual phase-currents. Secondly, the detector is designed by monitoring the energy variance for the second, fourth and sixth harmonics of 3[I.sub.0] individually, and by requiring the increment of randomness of all these harmonics to indicate an HIF. Thirdly, a self-tuning scheme based on the statistical confidence is applied to the automatic setting of threshold level for the energy variances monitored. Fourthly, effective counters are designed to detect both persistent and intermittent arcings. The detector has been tested on 51 staged faults and 8 unfaulted feeders. The test results show that the detector can have 100% fault detection rate so long as the arcing current at fault location is not less than 5A. As to the dependability tests, no false alarm (or tripping) has happened for all of the unfaulted feeders under test. These feeders either supply special (including arc furnace) load, or have leakage current (referring to the intermittent zero-sequence load due to the feeder location along coast), or are under the normal capacitor or load switchings. The test results and the investigation for the high sensitivity and dependability and for the limitation of proposed fault detection method are presented. Keywords: Distribution feeder, High impedance fault, Digital relaying, Arcing fault, Staged fault test, Dependability test, Three-phase unbalanced current.

This paper presents a new, accurate and robust fault locating algorithm for series compensated lines. The algorithm is developed as a one-end fundamental frequency based technique and offsets both the series compensation effect and the reactance effect resulting from the remote end infeed. The method uses phase coordinates (abc) instead of symmetrical components (012). The basic algorithm is presented for a line compensated by one three-please bank of series capacitors. The presented fault locating method has been extensively tested using the EMTP model of a 400kV 300km transmission line. The enclosed results demonstrate very high accuracy and robustness of the algorithm. Keywords: fault location, fault analysis, numerical relaying, series compensated line.

For limitation and interruption of short circuit currents in medium voltage (MV) applications, fuses and circuit breakers are widely used today. Fuses exhibit excellent current limitation, but work only for a single shot. Circuit breakers are multi-operation devices, but allow several periods of the short circuit current to pass. based on new PTC materials (positive temperature coefficient of resistance), we propose a new current limiting device for MV applications, which offers the chance to combine the advantages of fuses with the advantages of circuit breakers: a fast current limitation with a repetitive operation. The active material consists of conducting particles in a polymeric matrix. Its challenging property is a change on resitivity by eight to ten orders of magnitude upon temperature increase. This allows the limitation of available short circuit currents in a stable insulating state for a long period of time. The device consists of a series connection of PTC resistors with varistor elements connected in parallel, which serve for a perfect voltage distribution. Using this principle, repetitive current limitation of prospective currents of 4 to 14 kA within about 1 ms could be demonstrated at circuit voltages up to 12 kV. Keywords: fault current limiter, PTC resistor, polymer composite, medium voltage system

This paper describes a series of development tests carried out when developing a GIS (Gas Insulated Substation) fault location system using pressure wave sensors for a GIS with a main bus in which each gas section per bay is connected by gas piping. This paper also refers to the basic construction of the software of the fault location system actually applied to a GIS with a rated voltage of less than 168kV. Keywords: GIS, Fault location system, Sensor, Pressure wave

A technique for the detection of shorted turns in the field-windings of operating synchronous turbine-generators is described. The measuring method used is the twin-signal sensing method, where pulses are injected into each terminal of the rotor. The reflected signals are subtracted to produce a signature signals that contains information about the rotor's state. The signature signals are sampled and accepted or rejected as valid based on an outlier detection criteria. Novelty detection is applied to the accepted signals. The current signature signal is compared to a range of signature signals taken when the rotor was known to be free of shorts. If the current signature signal strays too far from the known healthy signal, the signature signal is 'novel' and the possibility of a short is declared. The method was tested on a running test rotor with voltage excitation. A comparison of methods shows that an elliptical novelty grouping algorithm gives highly accurate results. Keywords: novelty-detection, shorted-turn-detection, on-line-fault-detection, twin-signal-sensing, outlier-detection, synchronous-machines, condition-based-maintenance.

The reliability of power electronics systems is of paramount importance in industrial, commercial, aerospace, and military applications. The knowledge about fault mode behavior of an induction motor drive system is extremely important from the standpoint of improved system design, protection, and fault-tolerant control. This paper addresses the application of motor current spectral analysis for the detection and localization of abnormal electrical and mechanical conditions that indicate, or may lead to, a failure of induction motors. Intensive research effort has been for some time focused on the motor current signature analysis. This technique utilizes the results of spectral analysis of the stator current. Reliable interpretation of the spectra is difficult since distortions of the current waveform caused by the abnormalities in the induction motor are usually minute. This paper takes the initial step to investigate the efficiency of current monitoring for diagnostic purposes. The effects of stator current spectrum are described and the related frequencies determined. In the present investigation, the frequency signature of some asymmetrical motor faults are well identified using advanced signal processing techniques, such as high-resolution spectral analysis. This technique leads to a better interpretation of the motor current spectra. In fact, experimental results clearly illustrate that stator current high-resolution spectral analysis is very sensitive to induction motor faults modifying main spectral components, such as voltage unbalance and single-phasing effects. Index Terms - Broken bars, damaged bearings, fault detection, induction motors, rotor eccentricity, shaft speed oscillation, single-phasing effects, spectral analysis, stator current, unbalanced voltage.

Object-oriented modeling of transformers and other Y-connected devices preserves neutral nodes and impedances, making them available as points to fault. This is in contrast to conventional modeling in which all neutral nodes are eliminated by modifying the parameters of the devices. Phase-domain expressions are developed for faults between an energized node and a neutral node, and between two neutral nodes. An example using a three-circuit transformer shows the effects of faulting various neutral points. The results show that fault currents may be either higher or lower than for standard phase-to-ground faults, depending on the interaction of source, transformer, and neutral device impedances. The modeling was verified by comparison with phase-to-ground faults on a conventional transformer model.

This paper presents a method for the calculation of faulted power systems using phase coordinates. The method is more efficient and easier to program than the classical symmetrical components based fault analysis methods. Furthermore, it allows the study of any complex fault conditions and the inclusion of multi-phase components such as high phase order transmission lines. Keywords: Fault Calculations, Power System Imbalance, Phase Coordinates, Transmission Line

This paper presents an adaptive protection scheme for Advanced Series Compensated (ASC) transmission lines. The scheme is based on Kalman and adaptive Kalman filters. The adaptive scheme utilizes the differences in the transient current signals for faults encountering and not encountering the ASC to determine the fault location with respect to the ASC and the faulted phases. Equations to determine the line impedance to the fault on these lines are developed. The adaptive scheme is tested for faults along and outside the protected line using EMTP simulated data. Keywords: Digital protection, Transmission line protection, FACTS, ASC, Series Compensation, Faults Transients.

The application of a Radial Basis Function (RBF) Neural Network (NN) for fault diagnosis in a HVDC system is presented in this paper. To provide a reliable pre-processed input to the RBF NN, a new pre-classifier is proposed. This pre-classifier consists of an adaptive filter (to track the proportional values of the fundamental and average components of the sensed system variables), and a signal conditioner which uses an expert Knowledge Base (KB) to aid the pre-classification of the signal. The proposed method of fault diagnosis is evaluated using simulations performed with the EMTP package. Keywords: Radial Basis Function, Neural Networks, HVDC System, Fault Diagnosis

A versatile distribution system simulator integrating load flow, fault current calculation and modeling of overcurrent relays and breaker operation is described. Appropriate sets of scenarios are generated for different levels of exercise and all actions taken by the students are logged, evaluated and awarded a grade. The simulator is then configured to link to a knowledge based system and the students can attempt to diagnose fault and restore supply using a knowledge base approach. Through a series of hands-on exercise, the students strengthen their understanding of generic diagnostic rules, restoration algorithms, knowledge acquisition and inference mechanism.

Failure events in substations often result in multiple outages of generators, lines and/or loads in power systems. The simulation of substation originated outages for practical substation configurations is difficult, due to the complex switching actions with disconnect switches and circuit breakers that can take place. A digital computer program has been developed at the Delft University of Technology, which simulates these complex switching actions following substation failures. The simulation algorithms, which deduce the contingencies before and after switching actions with their corresponding reliability indices, are described in detail in the paper. The paper reports on results obtained from analyzing six different busbar schemes with redundant components.

The combined effects of a high impedance ground fault condition and a fast power swing condition cause the apparent impedance 'seen' by distance protection schemes to vary over a wide range. Previous research work has shown that detection and location of high impedance faults during power swings is very difficult. A new principle for high impedance fault detection during fast power swings is presented which overcome these deficiencies. This method forms a part of a complete power swing relaying scheme and can be implemented on standard relaying hardware. Results are presented based on extensive simulation studies carried out on a typical 400 kV system, using the Electromagnetic Transient program (EMTP).