Fault Current Signals Research Articles

Reducing the Error in Phasor Estimates From Phasorlets in Fault Voltage and Current Signals

An assessment and reduction of the phasor-error infiltration in estimates from phasorlets are proposed in this paper through a generalized least-square formulation of the problem. It introduces a computationally simple and quick estimator that exploits the structure of the sinusoidal model and provides the finest stable phasor estimate, which is very useful for fault voltage signals. It also proposes an extended signal model, by including a dc component into the signal model, in order to allocate the phasor error, when an aperiodic component is present in the input signal. The numerical simulations illustrate the improvement in speed and accuracy of the estimates, which are obtained in decicycles, as well as its still wavering nature, which is considered as the persisting limitation of this technique

Distance relaying for transmission line using support vector machine and radial basis function neural network

The proposed technique consists of preprocessing the fault current signal samples using discrete wavelet transform to yield the change in energy (ce) and standard deviation (sd) at the appropriate level of decomposition of fault current and voltage signal for faulty phase identification and fault location determination. After feature extraction (ce and sd) from fault current signal, support vector machine (SVM) is used for decision of fault or no-fault on any phase or multiple phases of the transmission line. The ground detection is done by a proposed indicator ‘index’ with a threshold value. Once the faulty phases are identified, the fault location from the relaying point can be accurately estimated using RBFNN (radial basis function neural network) with recursive least square algorithm. For fault location both current and voltage signals are preprocessed through wavelet transform to yield change in energy (ce) and standard deviation (sd) which are used to train and test the RBFNN to provide fault location from the relaying point accurately. The combined SVM and RBFNN based technique is tested for faults with wide range of operating conditions and provides accurate results for fault classification and location determination, respectively.

Accurate phasor measurement for transmission line protection in the presence of shunt capacitor banks

This paper proposes a phasor measurement algorithm for transmission systems compensated with shunt capacitor banks. Since the shunt capacitor banks tend to lower the resonant frequencies, the dominant component, which has the lowest resonant frequency, is insufficiently attenuated by a low-pass filter and has an adverse influence on the phasor measurement of the fundamental component in a fault current signal. This paper theoretically investigates the dominant frequency in the presence of shunt capacitor banks and presents a phasor measurement algorithm immune to the dominant component and DC-offset. The performance of the algorithm is evaluated for a-phase to ground (a–g) faults on a 154-kV transmission system compensated with shunt capacitor banks. The evaluation results indicate that the algorithm can measure the phasor reliably and satisfactorily, although the fault current signal is distorted with the dominant component and DC-offset. The paper concludes by describing the hardware implementation of the algorithm on a prototype unit based on a digital signal processor.

A Method for Estimating an Instantaneous Phasor Based on a Modified Notch Filter

A method for estimating the instantaneous phasor of a fault current signal is proposed for high-speed distance protection that is immune to a DC-offset. The method uses a modified notch filter in order to eliminate the power frequency component from the fault current signal. Since the output of the modified notch filter is the delayed DC-offset, delay compensation results in the same waveform as the original DC-offset. Subtracting the obtained DC-offset from the fault current signal yields a sinusoidal waveform, which becomes the real part of the instantaneous phasor. The imaginary part of the instantaneous phasor is based on the first difference of the fault current signal. Since a DC-offset also appears in the first difference, the DC-offset is removed trom the first difference using the results of the delay compensation. The performance of the proposed method was evaluated for a-phase to ground faults on a 345kV 100km overhead transmission line. The Electromagnetic Transient Program was utilized to generate fault current signals for different fault locations and fault inception angles. The performance evaluation showed that the proposed method can estimate the instantaneous phasor of a fault current signal with high speed and high accuracy.

A novel distance protection scheme using time-frequency analysis and pattern recognition approach

This paper presents a new approach for distance protection of transmission lines using time-frequency analysis. The proposed technique consists of preprocessing the fault current signal samples using hyperbolic S-transform to yield the change in energy and standard deviation at the appropriate window variation. From these two features, a decision of fault or no-fault on any phase or multiple phases of the transmission line can be made. The ground detection is done by a proposed indicator with a threshold value. The fault distance from the relaying point can be accurately estimated using cubic polynomial interpolation technique, Feed forward Neural Network and Adaptive Network Fuzzy Inference System (ANFIS).

Modified Notch Filter-based Instantaneous Phasor Estimation for High-speed Distance Protection

A novel method for estimating the instantaneous phasor of a fault current signal is proposed for high-speed distance protection immune to a DC-offset. The method uses a modified notch filter in order to eliminate the fundamental frequency component from the fault current signal. Since the output of the modified notch filter is the delayed DC-offset, delay compensation results in the same waveform as the original DC-offset. Subtracting the obtained DC-offset from the fault current signal yields a sinusoidal waveform, which becomes the real part of the instantaneous phasor. The imaginary part of the instantaneous phasor is based on the first difference of the fault current signal. Since a DC-offset also appears in the first difference, the DC-offset is removed from the first difference using the results of the delay compensation. The performance of the proposed method was evaluated for a–phase to ground faults on a 345 kV 100 km overhead transmission line. The Electromagnetic Transient Program was used to generate fault current signals for different fault locations and fault inception angles. The performance evaluation showed that the proposed method can estimate the instantaneous phasor of a fault current signal with high speed and high accuracy. The paper concludes by describing the hardware implementation of the proposed method on a prototype unit based on a digital signal processor.

Fault classification and location using HS-transform and radial basis function neural network

A new approach for protection of transmission lines has been presented in this paper. The proposed technique consists of preprocessing the fault current and voltage signal sample using hyperbolic S-transform (HS-transform) to yield the change in energy and standard deviation at the appropriate window variation. After extracting these two features, a decision of fault or no-fault on any phase or multiple phases of the transmission line is detected, classified, and its distance to the relaying point found out using radial basis function neural network (RBFNN) with recursive least square (RLS) algorithm. The ground detection is done by a proposed indicator ‘ index’. As HS-transform is very less sensitive to noise compared to wavelet transform, the proposed method provides very accurate and robust relaying scheme for distance protection.

A Novel Digital Directional Transformer Protection Technique Based on Wavelet Packet

This paper presents a novel digital technique for transformer protection. The technique is based on deriving a directional quantity proportional to the fault current signal and the prefault voltage signal. Standard fast wavelet transform (FWT) schemes may not be as effective for data that has chiefly oscillatory features. An effective solution to discrimination involves examining the signal in both the time and frequency domains simultaneously. The wavelet packet transform is an extension of the FWT that allows for finer characterization of signal content for both time and frequency together. A 11/132-kV transformer connected to a 132-kV power system was simulated using Alternative Transient Program/Electromagnetic Transient Program (ATP/EMTP). Results indicate that the proposed technique is stable, reliable, and fast during the discrimination between internal and external faults, magnetizing inrush currents, and internal faults, ratio-mismatch, and saturation of current transformers (CTs).

High-speed differential busbar protection using wavelet-packet transform

A novel wavelet-packet-transform- (WPT-) based differential busbar-protection technique is presented. The paper uses the wavelet-packet- transform (WPT) method to extract features from a fault-current signal. The WPT can decompose the fault signal into different frequency bands in the time domain. The differential signal is computed from the decomposed extracted signal. The WPT-based differential busbar-protection scheme solves several problems of current protective relays. The CT error and ratio-mismatch problems do not have any impact on the proposed WPT-based scheme. ATP simulations are used to test and validate the proposed technique for model-power-system faults.

An analytic method for measuring accurate fundamental frequency components

This paper proposes an analytic method for measuring the accurate fundamental frequency component of a fault current signal distorted with a DC-offset, a characteristic frequency component, and harmonics. The proposed algorithm is composed of four stages: sine filter, linear filter, Prony's method, and measurement. The sine filter and the linear filter eliminate harmonics and the fundamental frequency component, respectively. Then Prony's method is used to estimate the parameters of the DC-offset and the characteristic frequency component. Finally, the fundamental frequency component is measured by compensating the sine-filtered signal with the estimated parameters. The performance evaluation of the proposed method is presented for a-phase to ground faults on a 345 kV 200 km overhead transmission line. The electromagnetic transient program (EMTP) is used to generate fault current signals under different fault locations and fault inception angles. It is shown that the analytic method accurately measures the fundamental frequency component regardless of the characteristic frequency component as well as the DC-offset.

An Analytic Method for Measuring Accurate Fundamental Frequency Components

This paper proposes an analytic method for measuring the accurate fundamental frequency component of a fault current signal distorted with a dc-offset, a characteristic frequency component, and harmonics. The proposed algorithm is composed of four stages: sine filer, linear filter, Prony's method, and measurement. The sine filter and the linear filter eliminate harmonics and the fundamental frequency component, respectively. Then Prony's method is used to estimate the parameters of the dc-offset and the characteristic frequency component. Finally, the fundamental frequency component is measured by compensating the sine-filtered signal with the estimated parameters. The performance evaluation of the proposed method is presented for a-phase to ground faults on a 345 kV 200 km overhead transmission line. The EMTP is used to generate fault current signals under different fault locations and fault inception angles. It is shown that the analytic method accurately measures the fundamental frequency component regardless of the characteristic frequency component as well as the dc-offset.

Fault location using digital relay data

The most accurate and reliable fault location results are obtained using new algorithms that consider the fault data from both ends of the line together. Obviously, the data from the two ends must be brought together via data communications, either from one substation to the other or to a computer at a third site to which both substations can send the data. This might be a control center, relay engineer's office, or maintenance depot, which are ideal locations for really accurate fault location displays to be presented. Some two-ended location algorithms require time synchronization of the data from the two ends, which is not widely available. This article presents new calculations that do not require any such synchronization of the records to achieve excellent accuracy. Following an overview of the technical problems in computing fault location from fault voltage and current signals, a sampling of the newest and most accurate techniques that are easily implemented in existing digital devices for calculating location from one-ended or two ended line fault data records is given. >

Detecting arcing downed-wires using fault current flicker and half-cycle asymmetry

The downed-wires problem, known as high impedance faults, is described. A high voltage laboratory setup was devised to investigate the phenomenon. The laboratory model results agreed with field test results, and previous research efforts. The arcing fault model was justified. The setup was used as a source of fault current signal. A simple approach was taken to design an arcing fault detector. The algorithm utilizes the random behavior of the fault current. It compares the positive and negative current peaks in one cycle to those in the next cycle to measure the flicker in the current signal. The asymmetry of the current is calculated by comparing the positive peak to the negative peak, for each cycle: the moving window length is half a cycle. Both values are used as a signature of arcing. The result is filtered and compared with a suitable detection threshold. The algorithm was tested by traces of normal load, and no-load current disturbed by currents of faults on dry and wet soil, arc welders, computers, and fluorescent light loads, as well as short circuit currents. The algorithm performed well under the test conditions, except for the arc welder load. This load is also a source of insecurity for other algorithms. The detection criterion will be integrated with another detection method to improve the security during arcing load events. >

Travelling-Wave Techniques Applied to the Protection of Teed Circuits:- Multi-Phase/Multi-circuit Sytstem

In a preceding paper [1], the authors had described new techniques based on the h.f. travelling-wave information contained in the post fault voltage and current signals. In an attempt to present the underlying principles without undue complications, the study was limited to a lossless, frequency independent single phase line model.