Handling Fault Diagnosis Problem of Linear-Analogue Circuits with Voltage Phasor Measurement
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This paper proposes a novel method to estimate the influence of hard-fault in linear-analogue circuit system based on the measurement of voltage phasor with assistant branch introduced. Furthermore, a new fault diagnosis strategy based on the voltage phasor modeling is established, and the tolerance influence on the corresponding voltage measurement is also discussed. The actual analogue circuit test shows us that the proposed method is effective and reliable to locate the accurate fault signature in voltage measurement for the fault diagnosis. As a matter of fact, it includes both the amplitude and phase information in a complex value form when the linear-analogue circuit is under the AC test. Besides, it can be also applied to ambiguous groups and the sensitive test-frequencies determination in the process of fault diagnosis,while the effectiveness of multifrequencies test has also been testified through test-frequencies sweeping investigation and the maximum error evaluation of fault component value in the second circuit example.When two-phase earthing fault occurs in different sections of a feeder in a distribution system, part of section switches may have two phase fault current flowing through and part of section switches may have one phase fault current flowing through. So, fault current characteristic of this kind of fault is different from that of interphase short circuit fault. Then the traditional matrix algorithm will not be able to solve the fault location problem of this kind of fault. In order to solve the fault location problem, a single-phase matrix algorithm is put forward. This kind of fault has two fault phases and each fault phase has one single-phase fault information matrix. By multiplying each single-phase fault information matrix with the network describing matrix of the fault feeder, the single-phase fault judgment matrix of corresponding fault phase is generated. Both fault positions can be found by corresponding single-phase fault judgment matrixes.
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While the high resistance fault occurs near the teed node,the current fault location methods used for teed lines can't identify the fault section correctly,thus fail to locate the fault.To overcome the defect,a new fault location algorithm based on the phase characteristics of fault location function is proposed.The fault location function is established on the basis of the concept that selects a reference point to match the fault.It is concluded that,the phase characteristics of the function in the fault branch is different from that in the healthy branches,and the phase of the function will have a step jump when the reference point changes from the left to the right of the fault in the fault branch.So the position in the fault branch where the fault location function has a step jump is the fault position.The method can locate the fault without identifying the fault section first,thus remedies the defect of traditional fault location methods in which dead zone of fault location exists.The accuracy of the proposed method is hardly affected by fault location,transition resistance,fault types and load current,and has less amount of calculation than the current fault location methods.The results of simulation by PSCAD /EMTDC show that the proposed algorithm is correct and can locate the faults accurately.
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This study introduces a novel approach to power system fault diagnosis by synchronised phasor measurements. Conventionally, faults are diagnosed through the status of protective relays and circuit breakers which are activated following a fault. However, the hidden failures of the protection system has itself often been among the main suspects of partial or widespread blackouts. This study proposes an alternative fault diagnosis approach independent of the function of the protection system. An analytical method is introduced for power system fault diagnosis using dispersed synchronised measurements and bus impedance matrix ( Z bus ). Fault inception is first detected by local phasor measurement units (PMUs). Fault diagnosis is then carried out in a hierarchical manner so that first the faulted zone of the system is diagnosed, next the faulted line in the faulted zone is diagnosed and finally the fault point along the diagnosed line is located by gradient descent. The proposed method is applied to the WSCC 9‐bus, where fault incidents on all of the transmission lines are examined. Moreover, the proposed method is successfully applied to the IEEE 118‐bus test system consisting of 28 PMUs, which demonstrates successful fault diagnosis and location for a large‐scale power system despite the limited coverage of PMUs.
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An optimal input design problem in frequency domain is discussed for quick detection of the system fault without affecting the original system in normal mode. The input is designed to enlarge the distance measured by the Kullback discrimination information measure between the system models corresponding to the normal and the fault modes in single fault mode case. The idea is then extended to multiple fault modes case (fault diagnosis problem). In this case, the auxiliary input is designed to maximize the minimum distance among the distances between the normal and several fault modes in order to detect the true fault mode. Numerical simulation results indicate the applicability of the proposed auxiliary input in fault detection and fault diagnosis.
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In order to solve the problem of soft fault diagnosis in linear analog circuit, this paper proposes a new analytic model-based method. By using hard-fault voltage value, the impedance-voltage equation is constructed for calculating the circuit output voltage when soft-fault happens and therefore forming the fault characteristic vector for soft-fault diagnosis. The single-fault modeling and testability analysis of circuits are discussed in the condition that the impedance parameter is continuously changed. Taking the most common multiple soft fault-double faults as example, the soft-fault model derived from the impedance-voltage equation is presented. At last, a strategy to determine fault location and identify fault component values is formed. The soft-fault modeling and diagnosis are demonstrated through an example circuit which is driven by an alternating signal. The result shows that the proposed soft-fault modeling and diagnosis algorithm run effectively, and can obtain the accurate fault diagnosis results.
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Fault diagnosis of a circuit of vehicle system is analyzed in this paper. Complex field fault modeling is used for fault diagnosis of the conditioning circuit of vehicle system. And all single faults of components in the circuit are modeled in complex field. Soft fault and hard fault of single components are analyzed in detail. The problem of coincidence of fault characteristic equations is solved by changing the topological structure of circuit. And the problem of intersection is analyzed by increasing the frequency of excitation source. Fault detection process and fault dictionary are given. Then the fault detection process is tested by six assumed faults. No matter soft fault and hard fault of single components, the fault detection in this paper can locate source of fault accurately.
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Based on the harmonics within the power system, in this paper, a phasor domain single-ended transmission line fault location method is proposed. The method does not require communication channels from the remote terminal, and works without remote side voltages, currents, or source impedances. First, the apparent impedance at the fundamental frequency seen by the relay at the local terminal is presented. Second, with the apparent impedance at an example harmonic, additional information is introduced to the fault location problem, resulting in 4 real equations and 4 real unknowns. Finally, the unknowns are solved via Newton's method, including the fault location. Numerical experiments verify that the proposed single-ended fault location method presents higher fault location accuracy compared to the existing single-ended fault location method without remote side information in t he IEEE C37.114 standard, with different fault types and fault locations.
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When a fault occurs in power grid, accurate and timely fault location is of great significance in reducing fault losses. With the rapid development of synchronous phasor measurement technology, the high-precision big data brought by the synchronous phasor measurement brings many possibilities to the on-line fault diagnosis of the distribution network. This paper proposed an augmented state estimation fault location method based on on-line parameter identification. By using the initial and terminal voltage and current phasor measured by PMU, the relationship between voltage and current along the positive sequence network and negative sequence network is deduced. The line parameters and the fault information (the fault distance and the voltage phasor of the fault point) are augmented into the state quantity, and the state estimation is performed together with the original node state quantity to realize on-line parameter identification and accurate fault location. The radial distribution network model is built in PSCAD. The simulation results verify the correctness and high precision of the proposed algorithm.
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k-fault diagnosis theory is an important branch in the fault diagnosis of analog circuits.The existing k-fault diagnosis methods include branch-fault diagnosis,node analysis method,cut faulty diagnosis,the loop-fault,and mesh-fault diagnosis.Fault location and fault fault identification have been carried out by all methods perfectly.Also the methods have been developed in design for testability.But there is no united theory model.The summary of the methods and the mathematical model of k-fault diagnosis are introduced in this paper.The aim of the research work is to strengthen the systematization and integrality ofk-fault Diagnosis theory.And it provides the theory basis for the further research and practice.
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This work elaborates problem of determining the fault point in middle voltage distribution networks of 10(20) kV voltage level. Distribution network characteristics, protection and automation in distribution networks are described in order, an overview of fault types and thair representation by simmetrical components is given, and characteristics of fault resistance on the fault point are described. Further more, the function of fault locating in power systems regardless of the voltage level is described and some basic methods for fault locating in transmission networks are presented. Overview of specific factors that have impact on determining the fault point in distribution network are then presented. Next chapters describe important components of fault locating methods: fault indicators, calculation methods for determining the fault point and statistics about fault frequency. Other aspects, like fault diagnostics are also described. Some informations about practically applied technics for fault locating in world and domestic practice are given. Three algorithms for calculation of fault point, developed in last few years, are detailly described. A model for cost/benefit analyses of applying a fault locating method in distribution network is also presented, and an influence by greater appearance of distributed generation on a fault locating process is described.
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