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ABSTRACT: 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 345kV 100km 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.
Electrical Engineering 04/2012; 89(4):311-317. · 0.40 Impact Factor
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ABSTRACT: This paper proposes a phasor estimation algorithm based on the least square curve fitting technique for the distorted secondary current due to CT saturation. In this paper, the mathematical form of the secondary current during CT saturation is represented as the scaled primary current with the magnetizing current. The information of the scaled primary current is estimated from the data of saturated section. Therefore the proposed method can estimate the phasor of a fundamental frequency component during the saturated period, and accordingly can decrease the unnecessary time delay of the protection relays. The performance of the algorithm is validated under various fault and CT conditions using a C400 CT model. A series performance evaluations show that the proposed phasor estimation algorithm can estimate the phasor of the fundamental frequency component with high accuracy, regardless of fault conditions and CT characteristics.
PowerTech, 2011 IEEE Trondheim; 07/2011
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ABSTRACT: Conventional phasor estimation methods can causes error if the envelope of the signal is changed according to time. In this paper, a modified dynamic phasor estimation method was proposed to overcome the disadvantages of conventional phasor estimation methods. To evaluate the performance of the proposed method, a fault location algorithm which uses the proposed phasor estimation method was tested over varying fault distances and fault resistances. The fault location result using the proposed phasor estimation shows a very small error compared to fault location methods using conventional phasor estimation.
Modern Electric Power Systems (MEPS), 2010 Proceedings of the International Symposium; 10/2010
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ABSTRACT: New approach to high impedance fault detection, which allows for detecting it basing on yet some random arcing at the beginning of the fault, is presented in this paper. The proposed solution was developed within novel protection methodology - 3D power protection scheme (3DPPS). The identification of the fault is based on monitoring of symmetry deviations of three phase voltage or current signals. Fundamental signal components carry the biggest amount of information on the actual state of the protected system and are processed in order to extract out the necessary information proving an occurrence of a high impedance fault that must be cleared for safety purposes.
Modern Electric Power Systems (MEPS), 2010 Proceedings of the International Symposium; 10/2010
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ABSTRACT: A hybrid algorithm for phasor estimation is proposed that is immune to DC offset and current transformer (CT) saturation problems. The algorithm utilizes partial sum (PS)-based and multistage least-squares (MLS)-based methods before and after CT saturation is detected, respectively. The MLS-based method is initiated when the third difference of the secondary current detects the start point of the first saturation period. The determination of each saturation period is based on the sum of the secondary current from the start point of the first saturation period. A least-squares (LS) technique estimates the DC offset parameters from the single-cycle difference of the secondary current in the unsaturated periods. Removal of DC offset from the secondary current yields the sinusoidal waveform portion. Finally, the LS technique is used once again to estimate the phasor from the sinusoidal waveform portion. The performance of the algorithm was evaluated for a-g faults on a 345-kV 100-km overhead transmission line. The electromagnetic transient program was used to generate fault current signals for different fault angles and remanent fluxes. The performance evaluation shows that the proposed algorithm accurately estimates the phasor of a current signal regardless of DC offset and CT saturation. The paper concludes by describing the hardware implementation of the algorithm on a prototype unit based on a digital signal processor.
IEEE Transactions on Power Delivery 11/2009; · 1.35 Impact Factor
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ABSTRACT: In this paper, we propose a distance relaying algorithm using a discrete Fourier transform (DFT)-based modified phasor estimation method to eliminate the adverse influence of exponentially decaying DC offsets. Most distance relays are based on estimating phasors of the voltage and current signals. A DFT is generally used to calculate the phasor of the fundamental frequency component in digital protective relays. However, the output of the DFT contains an error due to exponentially decaying DC offsets. For this reason, distance relays have a tendency to over-reach or under-reach in the presence of DC offset components in a fault current. Therefore, the decaying DC components should be taken into consideration when calculating the phasor of the fundamental frequency component of a relaying signal. The error due to DC offsets in a DFT is calculated and eliminated using the outputs of an even-sample-set DFT and an odd-sample-set DFT, so that the phasor of the fundamental component can be accurately estimated. The performance of the proposed algorithm is evaluated for a-phase to ground faults on a 345 kV, 50 km, simple overhead transmission line. The Electromagnetic Transient Program (EMTP) is used to generate fault signals. The evaluation results indicate that adopting the proposed algorithm in distance relays can effectively suppress the adverse influence of DC offsets.
PowerTech, 2009 IEEE Bucharest; 08/2009
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ABSTRACT: This paper proposes a Fourier transform-based modified phasor estimation method to eliminate the adverse influence of the exponentially decaying dc offsets when discrete Fourier transform (DFT) is used to calculate the phasor of the fundamental frequency component in a relaying signal. By subtracting the result of odd-sample-set DFT from the result of even-sample-set DFT, the information of dc offsets can be obtained. Two dc offsets in a secondary relaying signal are treated as one dc offset which is piecewise approximated in one cycle data window. The effect of the dc offsets can be eliminated by the approximated dc offset. The performance of the proposed algorithm is evaluated by using computer-simulated signals and Electromagnetic Transients Program-generated signals. The algorithm is also tested on a hardware board with TMS320C32 microprocessor. The evaluation results indicate that the proposed algorithm can estimate the accurate phasor of the fundamental frequency component regardless of not only the primary decaying dc offset but also the secondary decaying dc offset caused by CT circuit itself including its burden.
IEEE Transactions on Power Delivery 08/2009; · 1.35 Impact Factor
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ABSTRACT: Summary form only given: This paper proposes a fault location algorithm for ultra-high-voltage untransposed parallel transmission lines that uses only the voltages and currents at the local end. The proposed algorithm uses the voltage equation for the faulted phase of the faulted line. The equation contains the fault distance, fault resistance, and fault current. To obtain the fault current, Kirchhoffpsilas voltage law is applied on the loops of three phases consisting of the faulted line and the adjacent parallel line. The fault current can be represented in terms of the fault distance. Inserting the fault current into the voltage equation results in an equation that contains only two parameters, i.e., the fault distance and fault resistance. The fault distance is estimated by solving the equation. Test results indicated that the algorithm accurately estimates the fault distance regardless of the fault resistance and mutual coupling effects.
Power and Energy Society General Meeting - Conversion and Delivery of Electrical Energy in the 21st Century, 2008 IEEE; 08/2008
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ABSTRACT: This paper proposes a new modified Fourier algorithm to eliminate the adverse influence of a decaying dc offset when Discrete Fourier transform (DFT) is used to estimate the phasor of the fundamental frequency component. The proposed algorithm decomposes the DFT process into even sample set DFT and odd sample set DFT. The effect of the dc offset is eliminated by using the recursive relationship between the outputs of even sample set DFT and odd sample set DFT. The performance of the algorithm is evaluated by using computer- simulated signals and EMTP-generated signals. The evaluation results indicate that the proposed algorithm can estimate the accurate phasor of the fundamental frequency component regardless of not only the primary decaying dc offset but also the secondary decaying dc offset caused by CT circuit itself including its burden.
Transmission and Distribution Conference and Exposition, 2008. T&D. IEEE/PES; 05/2008
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ABSTRACT: In this paper, a fault location algorithm using travelling waves and a cross correlation method is proposed for HVDC cable lines. The arriving instants of the first fault-induced transient backward travelling wave and its subsequent reflected wave can be detected by using a cross correlation method. The fault distance is estimated by using the time difference between the two instants of incident waves and the velocity of the travelling wave. Because the fault-induced backward wave is much similar to a square wave when a fault occurs in the HVDC cable lines, a kind of step function is used as the reference function for the cross correlation in this paper. The proposed algorithm was verified with varying fault distances and fault resistances in submarine HVDC cables connected to the current source converter (CSC) type HVDC system and the voltage source converter (VSC) type HVDC system respectively.
Developments in Power System Protection, 2008. DPSP 2008. IET 9th International Conference on; 04/2008
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ABSTRACT: Application of two new ANN-based algorithms for arcing high impedance fault (HIF) detection in multigrounded medium-voltage (MV) distribution networks is presented in this paper. The paper provides an evaluation of two new structures of artificial neural networks (ANNs) that may be used for reliable HIF detection in multigrounded as well as isolated, compensated, and grounded via small resistance distribution grids. The results obtained by use of both neural nets are presented. The performance was tested using data obtained from staged HIFs in real MV network as well as from electromagnetic transients program-alternative transients program simulations. A small number of necessary neurons in developed ANNs, short measuring sliding data window, and easy interpretation of obtained output signals are the main advantages of the proposed approach. Satisfactory results of ANN performance were observed for all examined HIF cases in which the ground fault current was greater than 16 A. The selected ANNs of best performance show high reliability and immunity to transients resulting from switching operations in protected feeders and from capacitor bank switching.
IEEE Transactions on Power Delivery 02/2008; · 1.35 Impact Factor
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ABSTRACT: The application of the wavelet-based algorithm for arcing high-impedance fault detection medium-voltage (MV) distribution networks is presented in this paper. This paper describes continuation of research on HIF detection with particular reference to algorithm application in solidly grounded MV networks. The results obtained by use of the improved version of the algorithm are presented. The algorithm performance was tested using data obtained from staged HIGFET in a real MV network as well as from EMTP-ATP simulations. Satisfactory results of the algorithm performance were observed for all examined HIF cases in which the ground fault current was greater than 3 A root mean square. The improved algorithm also proved to be more immune to transients generated during switching operations in protected feeders and to capacitor bank switching.
IEEE Transactions on Power Delivery 11/2007; · 1.35 Impact Factor
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ABSTRACT: This paper proposes a fault location algorithm for cross-bonded cables. The algorithm uses nonlinear equations that describe
the voltage drops between both ends of core conductors and sheaths in terms of the phase voltages and currents of both the
local and remote ends. Arranging these equations about the sheath currents yields a sheath impedance matrix, which is singular
independently of the fault distance. Due to this singularity, the equations have no solution or an infinite number of solutions.
The proposed algorithm finds the condition for which a solution to the equations exists. Since the equation of the condition
is linear and explicit, the fault location can be found easily. Test results indicate that the algorithm accurately estimates
the fault distance regardless of fault impedance, fault type, and fault section.
Electrical Engineering 06/2007; 89(7):525-533. · 0.40 Impact Factor
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ABSTRACT: This paper proposes a single phase-to-ground fault location algorithm for ungrounded radial distribution systems. The algorithm
uses the voltage equation from the relay location to the fault location, which contains three unknown variables: zero-sequence
fault current, fault resistance, and fault distance. The zero-sequence fault current can be determined using the zero-sequence
relay current. Inserting the zero-sequence fault current into the voltage equation results in an equation that contains only
the fault resistance and fault distance. The fault resistance is removed by extracting the components orthogonal to the zero-sequence
fault current from the equation and finally the fault distance is estimated. Simulation results indicate that the algorithm
performs well regardless of fault resistance and fault distance.
Electrical Engineering 05/2007; 89(6):503-508. · 0.40 Impact Factor
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ABSTRACT: Reliable method to predict lymph node metastasis is not yet available. In the present study, therefore, we examined LI-cadherin expression in human gastric cancer and attempted to find its relationship with clinicopathologic data, especially with lymph node metastasis. We also analyzed the expression in preoperative biopsy specimen to uncover its possibility of prognostication for lymph node metastasis.
The paired preoperative endoscopic biopsy and postoperative resected specimens from 208 patients who had surgically been treated for gastric cancer were retrospectively analyzed immunohistochemically for expression of LI-cadherin.
There were 47 (22.6%) and 161 (77.4%) tumors which had positive and negative LI-cadherin expression, respectively. LI-cadherin expression was significantly correlated with tumor histology and lymph node metastasis: Furthermore, reduced expression of LI-cadherin was closely associated with tumor progression and lymph node metastasis in human gastric carcinoma. LI-cadherin expressions in both resected tumor and preoperative endoscopic tissues were found to be independent factors associated with lymph node metastasis.
There is a close association between reduced expression of LI-cadherin and lymph node metastasis in human gastric cancer. Immunohistochemical study of LI-cadherin is relatively simple compared to sentinel node navigation surgery, and it could be a practical prediction method for lymph node metastasis in patients with this malignancy.
Annals of Surgical Oncology 02/2007; 14(1):94-9. · 4.17 Impact Factor
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ABSTRACT: A new simple and effective algorithm of arcing fault detection in distribution networks with the application of a wavelet transform technique is presented in this paper. The protection algorithm developed observes the phase displacement between wavelet coefficients calculated for zero-sequence voltage and current signals at a chosen high-level frequency. The final decision in regards to feeder switching off (or alarm issuing) is met either with a deterministic logic scheme or with the use of a neural net trained especially for that purpose. The developed wavelet-based high-impedance fault (HIF) detector has been tested with Electromagnetic Transients Program-Alternative Transients Program (ATP)-generated signals, exhibiting better performance than traditionally used algorithms and methods. The protection method proposed may be used for HIF detection independent of the network neutral-point grounding mode. The scheme proved to be robust against transients generated during normal events such as feeder energizing and de-energizing as well as capacitor bank switching
IEEE Transactions on Power Delivery 11/2006; · 1.35 Impact Factor
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ABSTRACT: Application of wavelet transform technique to high impedance arcing fault detection in distribution networks is presented. Phase displacement between discrete wavelet coefficients calculated for zero sequence voltage and current signals at natural network frequency is tracked. The developed wavelet based HIF detector has been tested with EMTP-ATP generated signals, proving better performance than traditionally used algorithms and methods. The protection method proposed is efficient, robust and may be used for HIF detection independently of the network neutral point grounding mode.
Power Tech, 2005 IEEE Russia; 07/2005
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ABSTRACT: The design, evaluation and implementation of a busbar current differential protection relay suitable for use with measurement type current transformers (CTs) is described in the paper. The relay operates in conjunction with a saturation detection algorithm, which effectively detects the start and end of each saturation period using a technique based on the third-difference function applied to the current signal. A blocking signal is activated immediately after the onset of saturation and is maintained active until the saturation period plus an additional delay of one cycle has expired. For internal faults that result in CT saturation, the relay issues a trip command before the blocking signal is activated. For external faults, that result in CT saturation, the blocking signal arrives first and the trip command remains inactive. Test results indicate that the relay successfully discriminates between internal and external faults, even when the remanent flux in a CT is high and the fault capabilities of the measurement CTs are severely limited. The paper concludes by describing how the relay was implemented on a prototype relay based on a digital signal processor. Compared to a conventional busbar differential protection scheme, the new relay achieves greater stability on external faults and enhanced sensitivity for internal faults.
IEEE Transactions on Power Delivery 05/2005; · 1.35 Impact Factor
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ABSTRACT: This paper focuses on a systematic and cumulative statistical approach for identifying symptom parameters of incipient faults in distribution feeders. The proposed method aims at providing a tool for evaluating and identifying the best and highly correlated parameters to the faults so that they could be used for incipient fault detection and feeder condition monitoring. The Laplace test statistic is adopted for trend analysis of the event log of candidate parameters and applied to actual feeder event data for online detection and monitoring purposes.
IEEE Transactions on Industry Applications 12/2004; · 1.66 Impact Factor
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ABSTRACT: Current-transformer (CT) saturation may cause the maloperation of a protection relay. This is particularly onerous when the remanent flux in the core of the CT adds to the flux change caused by the fault. The CT is forced into deep saturation and the waveshape of the secondary current is severely distorted. An algorithm for compensating the distortion in the secondary current caused by saturation and remanence in a CT is described in this paper. A second-difference function detects when the CT first starts to saturate. At this instant, the negative value of the second-difference function corresponds to the magnetizing current which, in conjunction with the magnetization curve, is used to estimate the core flux. This is then used as an initial value to calculate how the flux changes during the fault. The magnetizing current is estimated by inserting the estimated core flux into the magnetization curve and added to the secondary current; the result, the compensated secondary current, is equal to the secondary referred primary current. Various test results indicate that the proposed algorithm can accurately compensate a severely distorted secondary current and is not affected by remanence. The paper concludes by describing the hardware implementation of the algorithm on a prototype compensation unit based on a digital signal processor.
IEEE Transactions on Power Delivery 11/2004; · 1.35 Impact Factor
