Hatem A. Darwish

Practical Considerations for Recursive DFT Implementation in Numerical Relays

In this paper, practical considerations for recursive discrete Fourier transform (DFT) implementation in numerical relays are presented. The DFT filter instabilities which would produce magnified errors are emphasized. The aspects ruling error magnification of the estimated magnitude and phase are highlighted. Novel solutions directed for the elimination of error magnification are proposed and intensively tested. Digital signal processing (DSP) board based test set-up is utilized for results corroboration. The paper results are valuable for the protection engineers particularly those concerned with the development and implementation of numerical relays

Universal arc representation using EMTP

A preliminary description of a new arc representation has been introduced in . In which, the Modified Mayr (P-/spl tau/ model) arc equations are solved in the transient analysis control system (TACS) field of the electromagnetic transient program (EMTP) and represented in the power network by TACS controlled voltage source. In this paper, substantial improvements of this representation are carried out. A performance comparison with the EMTP built-in Avdonin model is incorporated to validate the proposed representation effectiveness. SF6 breakers with experimentally defined arc parameters are used to perform this comparison. The thermal limiting curve is computed by the proposed and the built-in models and compared with the measured characteristic. Also, universality of representation is verified via carrying out different arc model examples of circuit breaker and transmission-line arcing faults. The study results validated the proposed representation regarding accuracy and universality.

Modeling and experimental verification of high impedance arcing fault in medium voltage networks

A high impedance arcing fault due to a leaning tree in medium voltage (MV) networks is modeled and experimentally verified. The fault is represented in two parts; an arc model and a high resistance. The arc is generated by a leaning tree towards the network conductor and the tree resistance limits the fault current. The arcing element is dynamically simulated using thermal equations. The arc model parameters and resistance values are determined using the experimental results. The fault behavior is simulated by the ATP/EMTP program, in which the arc model is realized using the universal arc representation. The experimental results have validated the system transient model. Discrete wavelet transform is used to extract the fault features and therefore localize the fault events. It is found that arc reignitions enhance fault detection when discrete wavelet transform is utilized

DWT-Based Detection and Transient Power Direction-Based Location of High-Impedance Faults Due to Leaning Trees in Unearthed MV Networks

Electrical faults due to leaning trees are common in Nordic countries. This fault type has been studied in and it was found that the initial transients in the electrical network due to the associated arc reignitions are behavioral traits. In this paper, these features are extracted using the discrete wavelet transform (DWT) to localize this fault event. Wireless sensors are considered for processing the DWTs on a residual voltage of different measuring nodes that are distributed in the network. Therefore, the fault detection is confirmed by numerous DWT processors over a wide area of the network. The detection security is also enhanced because the DWT responded to a periodicity of the initial transients. The term for locating the faulty section is based on the polarity of a specific frequency bandpower computed by multiplying the DWT detail coefficient of the residual current and voltage at each measuring node. The fault due to a leaning tree occurring at different locations in an unearthed 20-kV network is simulated by the alternate transients program/electromagnetic transients program and the arc model is implemented using the universal arc representation. Test cases provide evidence of the efficacy of the proposed technique.

Development and implementation of an ANN-based fault diagnosis scheme for generator winding protection

In this paper, the development and implementation of a new fault diagnosis scheme for generator winding protection using artificial neural networks (ANN) is introduced. The proposed scheme performs internal fault detection, fault type classifications and faulted phases identification. This scheme is characterized with higher sensitivity and stability boundaries as compared with the differential relay. Effect of the presence of nonsynchronous frequencies on the scheme performance is examined. Effect of different values of ground resistance on ground fault detection sensitivity is outlined. The scheme hardware is implemented based on a digital signal processing (DSP) board interfaced with a multi input/output (MIO) board. Test results of the proposed scheme corroborate the scheme stability and sensitivity.

ANN-based novel fault detector for generator windings protection

Summary form only given as follows. In this paper, an artificial neural network (ANN) based internal fault detector algorithm for generator protection is proposed. The detector uniquely responds to the winding earth and phase faults with remarkably high sensitivity. Discrimination of the fault type is provided via three trained ANNs having a six dimensional input vector. This input vector is obtained from the difference and average of the currents entering and leaving the generator windings. Training cases for the ANNs are generated via a simulation study of the generator internal faults using Electromagnetic Transient Program (EMTP). A genetic algorithm is employed to reduce training time. The proposed ANN algorithm is compared with a conventional differential algorithm. It is found to be superior regarding sensitivity and stability.

Performance of Power Differential Relay With Adaptive Setting for Line Protection

In this paper, proposed setting and response evaluations of power differential relay scheme for line protection are presented. Mathematical expressions describing the adaptive features of both active and reactive power settings are given. The union action of these two detectors is adopted to provide sensitive detection for high impedance internal faults and avoid maloperation for all power swings and external fault conditions. Response is computed for both active and reactive power detectors under different operation and fault conditions. The results corroborate the applicability and the immunity of the proposed relay scheme against the sampling misalignment and practical frequency drift. High sensitivity for high impedance internal faults is verified

Investigation of power differential concept for line protection

In this paper, investigation of a novel fault detection concept for line protection is presented. In this concept, the difference and average quantities for phase active and reactive power entering and leaving the line are compared. Performance of the developed detector is computed under sampling misalignment as compared with conventional current differential approach. This computation is carried out via simulating a tie line connecting two power system networks using the Electromagnetic Transient Program (EMTP). The detector sensitivity for internal fault and stability for external fault are examined for wide range of fault resistance and operating conditions. The test results show distinguished performance of the proposed power differential concept in detecting high impedance faults and remarkable stability during system severe power swings.

Modeling and Experimental Verification of a High Impedance Arcing Fault in MV Networks

In this paper, a high impedance arcing fault of the tree leaning type in medium voltage (MV) networks is modeled and experimentally verified. The fault is represented as two parts; an arc model and a high resistance. The arc is generated by the tree leaning towards the network conductor and the tree resistance limits the fault current. The arcing element is dynamically simulated using thermal equations. The arc model parameters and resistance values are determined using the experimental results. The fault behavior is simulated by the ATP/EMTP program, in which the arc model is realized using the universal arc representation. The experimental results have validated the system transient model. Discrete wavelet transform (DWT) is used to extract the fault features and therefore localize the fault events. It is found that arc restrikings enhance fault detection when DWT is utilized

Close Accord on DWT Performance and Real-Time Implementation for Protection Applications

In this paper, a simpler and faster algorithm of discrete wavelet transform (DWT) for a digital signal processing (DSP) implementation is proposed and intensively tested. Applicability of real-time implementation of this algorithm is verified. The computational frame in this algorithm is independent on the sampling rate, but it depends on the length of the mother wavelet filters. Therefore, signal with any sampling rate can be analyzed with the same computational effort. This implementation algorithm is exploited to investigate the DWT response experimentally. Impact of the mother wavelet, sampling frequency, fault inception angle and the signal transients on the resulted DWT levels is evaluated from the protection perspectives. Considering the DSP channel noise, these factors are strongly affect DWT response especially in high details spike, which the most of the protection applications depended on. Shortcomings of DWT application for protection relays are outlined and corrective recommendations are included.