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Showing papers by "Matti Lehtonen published in 2008"


Journal ArticleDOI
TL;DR: These features are extracted using the discrete wavelet transform (DWT) to localize this fault event and the detection security is enhanced because the DWT responded to a periodicity of the initial transients.
Abstract: 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.

93 citations


Journal ArticleDOI
TL;DR: In this paper, the initial transients due to arc reignitions associated with high impedance faults caused by leaning trees are extracted using discrete wavelet transform (DWT), in which the fault occurrence is localized.
Abstract: SUMMARY In this paper, the initial transients due to arc reignitions associated with high impedance faults caused by leaning trees are extracted using discrete wavelet transform (DWT). In this way, the fault occurrence is localized. The feature extraction is carried out for the phase quantities corresponding to a band frequency 12.5–6.25 kHz. The detection security is enhanced because the DWT corresponds to the periodicity of these transients. The selectivity term of the faulty feeder is based on a novel technique, in which the power polarity is examined. This power is mathematically processed by multiplying the DWT detail coefficients of the phase voltage and current for each feeder. Its polarity identifies the faulty feeder. In order to reduce the computational burden of the technique, the extraction of the fault features from the residual components is examined. The same methodology of computing the power is considered by taking into account the residual voltage and current detail coefficients where the proposed algorithm performs best. Test cases provide evidence of the efficacy of the proposed technique. Copyright # 2007 John Wiley & Sons, Ltd.

29 citations


01 Jan 2008
TL;DR: In this paper, an online single-phase partial discharge (PD) measuring system using Rogowski coil is simulated in EMTP/ATP for the monitoring of falling trees on covered- conductor (CC) overhead distribution lines.
Abstract: An on-line single-phase partial discharge (PD) measuring system using Rogowski coil is simulated in EMTP/ATP for the monitoring of falling trees on covered- conductor (CC) overhead distribution lines. The simulation results are compared with those obtained from the labora- tory measurements. The effect of Rogowski coil terminat- ing impedance is analysed for the performance of PD measuring system. The proposed model can be used to estimate the length of the practical CC lines at which PDs due to falling trees can be detected; thus, deciding the number and positioning of the sensors over a particular length of the CC lines.

24 citations


Proceedings ArticleDOI
17 Oct 2008
TL;DR: In this paper, a transient fault detection technique in unearthed medium voltage systems is presented, based on the amplitude of the impedance, the feeder is confirmed to be faulted or not.
Abstract: This paper presents a transient fault detection technique in unearthed medium voltage systems. The system is simulated by ATP/EMTP program. A suitable fault detection window is introduced. The window width is the most sensitive part in the transient period. It is varying according to fault characteristics. The average impedance of the earth mode is calculated from voltage and current earth modes in the window. Based on the amplitude of the impedance, the feeder is confirmed to be faulted or not. The setting of detection is proposed from the simulation results that cover different fault inception angles and fault resistances.

17 citations


Journal ArticleDOI
TL;DR: In this paper, the authors present the analysis methods used in that study, the elimination techniques to remove the strategic or deviating responses from the survey data and correlation studies to depict how the harm depends on the size of the respondent.
Abstract: Electricity supply reliability and interruption costs are nowadays of great interest. Large blackouts around the world have aroused also customers' interest in the reliability of distribution networks. In addition to this, reliability worth values are widely used in the regulation of distribution companies, and they can offer an excellent tool for focusing the network investments on the most critical areas in the network. In Finland, Helsinki University of Technology and Tampere University of Technology as well as several Finnish distribution network companies worked on a common project concerning the updating of reliability worth values in 2004-2005. This paper presents the analysis methods used in that study, the elimination techniques to remove the strategic or deviating responses from the survey data and correlation studies to depict how the harm depends on the size of the respondent.

16 citations


Proceedings ArticleDOI
17 Mar 2008
TL;DR: In this article, the authors used the Discrete Wavelet Transform (DWT) detail coefficients of residual voltages to detect the presence of leaning trees in Nordic distribution networks, but the fault cases are not associated with arcs and the transients are only generated at the starting fault instant without repetition.
Abstract: The faults due to leaning trees are common in Nordic Distribution networks. In [1], the detection of this fault type has been discussed and the faulty section has been estimated using a novel selectivity technique. This detection was based on an absolute sum of Discrete Wavelet Transform (DWT) detail coefficients of the residual voltages. The detection selectivity function depended on the transient directionality of the residual voltage and currents which are extracted using DWT. In this presented paper, this technique is evaluated using 17 staged earth fault cases at a sampling frequency 10 kHz. These faults are accomplished in a 20 kV network using known fault resistances and natural trees. However, theses fault cases are not associated with arcs and the transients are only generated at the starting fault instant without repetition because the arc reignition impact on the network does not exist. Therefore, the transient features are localized using DWT at the fault instant only. The test cases can provide evidence of the detection efficacy.

12 citations



Proceedings ArticleDOI
01 Sep 2008
TL;DR: In this article, an experimental study and electro-geometric modeling on the shielding effect of trees on direct strokes to medium voltage distribution lines is presented. And the results of the comparison will serve as good recommendations for the enhancement of lightning protection in power distribution circuits.
Abstract: Lightning overvoltages are responsible for the majority of faults and outages that occur in Medium Voltage (MV) distribution networks. The overhead lines can be protected from the above phenomena with adequate installation of surge arresters and shield wires. Insulation enhancement can also play a significant role in minimizing outage rates of the lines, though it will not be so effective. However, high and grounded structures such as trees or buildings will naturally protect the lines from direct lightning strokes, if adequate clearance between the lines and the structures is considered. This paper presents the experimental study and electro-geometric modeling on the shielding effect of trees on direct strokes to medium voltage distribution lines. The shielding effect of a nearby tree on an MV distribution conductor is compared with that of a concrete building which has been previously investigated in the literature. It is expected that the results of the comparison will serve as good recommendations for the enhancement of lightning protection in power distribution circuits.

11 citations


Proceedings ArticleDOI
01 Oct 2008
TL;DR: In this article, the authors proposed a step-by-step evaluation procedure to quantitatively assess the impacts of an advanced centralized FA scheme, designated as the ldquoLow Interruption Systemrdquo(LIS), on reliability worth indices of a typically distribution reliability test system.
Abstract: Feeder Automation (FA) has been recognized by researchers and utilities as one of the attractive remedial measures to enhance service reliability in the electric power distribution systems. Until now, several kinds of FA schemes have been developed for automating of distribution feeders. They can be categorized into three main approaches: semiautomatic, distributed and centralized schemes. The challenge for the utilities, especially in todaypsilas competitive electricity market, is to identify and evaluate potential FA schemes and determine that appropriate for implementation. In this context, reliability cost/worth assessment plays an important role. This paper aims to propose a step by step evaluation procedure to quantitatively assess the impacts of an advanced centralized FA scheme, designated as the ldquoLow Interruption Systemrdquo(LIS), on reliability worth indices of a typically distribution reliability test system.

10 citations


Proceedings Article
01 Jan 2008
TL;DR: In this article, the authors investigated the problem of fault location based on transient current signals measured at few transmission line ends in a large transmission net-work and proposed a practical solution to the existing fault location system and proposals for optimal location of recording units are suggested.
Abstract: This paper investigates the problem of fault location based on transient current signals measured at few transmission line ends in a large transmission net- work. Current traveling waves (CTW) are utilized to locate faults on transmission system since current trans- formers (CTs) can reproduce the current transient with sufficient accuracy in their secondary circuits. The num- ber of traveling wave recorders (TWR) is usually less than the number of buses; hence there is a need for an economi- cal method to find the fault from these recording units. The signals are analyzed using digital wavelet transform (DWT) and the optimum mother wavelet and optimum details level were selected according to their energy con- tent using MATLAB Wavelet toolbox. The shortest path between the best-selected TWRs is calculated. The fault can then be calculated using the double-end method. Trav- eling wave speeds were calculated at each DWT details level. Results show that traveling waves have different speeds at different frequency bands. Several test cases were investigated from ATP/EMTP simulation and measurements from the Finnish 400 kV Transmission System. Results show a practical solution to the existing fault location system and proposals for optimal location of recording units are suggested.

10 citations


Proceedings ArticleDOI
12 May 2008
TL;DR: In this paper, the effect of shield wires on lightning overvoltage reduction and the energy relief of MOV (Metal Oxide Varistor) arresters from direct strokes to distribution lines is discussed.
Abstract: This paper deals with the effect of shield wires on lightning overvoltage reduction and the energy relief of MOV (Metal Oxide Varistor) arresters from direct strokes to distribution lines. The subject of discussion is the enhancement of lightning protection in Finnish distribution networks where lightning is most severe. The true index of lightning severity in these areas is based on the ground flash densities and return stroke data collected from the Finnish meteorological institute. The presented test case is the IEEE 34‐node test feeder injected with multiple lightning strokes and simulated with the Alternative Transients Program/Electromagnetic Transients program (ATP/EMTP). The response of the distribution line to lightning strokes was modeled with three different cases: no protection, protection with surge arresters and protection with a combination of shield wire and arresters. Simulations were made to compare the resulting overvoltages on the line for all the analyzed cases.

Proceedings ArticleDOI
25 Mar 2008
TL;DR: In this paper, a Rogowski coil is used as a sensor for the detection of PDs produced due to falling trees on the covered-conductor (CC) overhead distribution lines.
Abstract: Partial discharge (PD) measurements are universally accepted as an effective and reliable tool for on-line condition monitoring of high voltage (HV) equipment. A relatively new application is the monitoring of falling/leaning trees on the covered-conductor (CC) overhead distribution lines. Rogowski coil is used as a sensor for the detection of PDs produced due to falling trees on the CC overhead lines. This sensor is non-intrusive and superior to the conventional PD detector methods. In the next stage, this wired sensor will be converted into a wireless one. This paper gives the brief introduction to the concept and methodology of PD detection and sensor characteristics for localization of falling trees on the CC lines.

Proceedings ArticleDOI
17 Oct 2008
TL;DR: In this article, the authors presented the results of theoretical studies about the number of short interruptions caused by lightning in various environmental circumstances and compared the results to the fault statistics collected from Kainuun Energia.
Abstract: Lightning strokes represent a considerable cause of short interruptions in overhead line medium voltage networks The overvoltages caused by lightning can not be avoided but their influence can be limited by appropriate overvoltage protection This paper presents the results of theoretical studies about the number of short interruptions caused by lightning in various environmental circumstances The results will be compared to the fault statistics collected from Kainuun Energia In the calculations, the environmental conditions, ground flash densities and various overvoltage protection types of power distribution transformers are taken into account At the end, further research is discussed

01 Jan 2008
TL;DR: This paper gives the brief introduction to the concept and methodology of PD detection and sensor characteristics for localization of falling trees on the CC lines.
Abstract: Partial discharge (PD) measurements are universally accepted as an effective and reliable tool for on-line condition monitoring of high voltage (HV) equipment. A relatively new application is the monitoring of falling/leaning trees on the covered-conductor (CC) overhead distribution lines. Rogowski coil is used as a sensor for the detection of PDs produced due to falling trees on the CC overhead lines. This sensor is non-intrusive and superior to the conventional PD detector methods. In the next stage, this wired sensor will be converted into a wireless one. This paper gives the brief introduction to the concept and methodology of PD detection and sensor characteristics for localization of falling trees on the CC lines.

Proceedings ArticleDOI
12 Mar 2008
TL;DR: In this article, a selectivity technique to estimate the faulty feeder in MV networks was introduced, which depended on the directionality of discrete wavelet transform (DWT) detail coefficients of a residual current of each feeder with respect to the DWT detail coefficient of the residual voltage.
Abstract: A novel selectivity technique to estimate the faulty feeder in MV networks was introduced in [1]. This technique depended on the directionality of discrete wavelet transform (DWT) detail coefficient of a residual current of each feeder with respect to the DWT detail coefficient of the residual voltage. The algorithm efficacy has been examined with high impedance arcing fault due to leaning trees. In this paper, the algorithm performance is tested with resistance earth faults over a wide range of the fault resistance values (1 mOmega to 100 kOmega) as well as concerning practical fault cases such as arcing faults. The fault cases occurring at different locations in an unearthed 20 kV network are simulated by ATP/EMTP. Test cases confirm the efficacy of the proposed technique.

Proceedings ArticleDOI
17 Oct 2008
TL;DR: In this article, the authors present results of a study where spark gaps were replaced with externally gapped metal-oxide surge arresters near the primary substation in case of lightning.
Abstract: In Finland during summer time, lightning may cause a considerably high number of short interruptions and voltage sags. In case of lightning, the overvoltage protection of power distribution transformers has an important role. In case of special concern of voltage sags, the means to limit the short circuit faults causing voltage sags should be focused to the neighbourhood of the primary (110/20 kV) substation. To contribute this matter, this paper presents results of a study where spark gaps were replaced with externally gapped metal-oxide surge arresters near the primary substation. As well the theoretical studies as measurement results encourage to carry on with such investments.