Showing papers by "Matti Lehtonen published in 2007"

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

Abstract: 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

Challenges in implementation of human-automation interaction models

Abstract: This paper presents the practical experience gained in the process of implementing the human-centered automation design methodology to an electric power utility management automation function, along with the analytical discussions on the implementation challenges This report of implementation challenges and the discussions made on the methods devised to conquer those challenges lead to an alternative approach to the original approach to the well-known human-centered automation design model in the literature

Adaptive autonomy: Smart cooperative cybernetic systems for more humane automation solutions

Abstract: Smart cooperation of human and computer agents should be harmonized by adapting the automation level of the cybernetic systems to the changing environmental and peripheral situations This paper presents an adaptive autonomy methodology that is based on an extension of a well-known human-automation interaction model, as well as the expert judgment technique and the performance shaping factors concept The method is implemented to a power distribution automation system, and the results are discussed through a scenario-based approach Then, the performance of the proposed methodology and the effectiveness of adaptive autonomy are shown by the wide span of the changes in the resulting automation levels The trends of the automation levels are investigated versus the criticality of the situations and the automation stages The application-oriented matters are also discussed to stress on the context-based nature of the human-centered automation models

DWT-Based Extraction of Residual Currents throughout Unearthed MV Networks for Detecting High Impedance Faults due to leaning Trees

Abstract: SUMMARY Modelling of a high-impedance arcing fault due to a leaning tree in medium voltage (MV) networks was experimentally verifiedand the network transients due to this fault were also investigated.Eventhough the tree had a very high resistance value, the initial transients were periodically caused by the arc reignitions after each zero-crossing. In this paper, these features are extracted from residual currents using discrete wavelet transform (DWT) to localise this fault event. The DWT performance at different measuring nodes throughout an unearthed 20kV network can be gathered at the base station using wireless sensors concept. So, the DWT is evaluated for a wide area of the network and the fault detection is confirmed by numerous DWTextractors. Due to the periodicity of arc reignitions, the initial transients are localised not only at fault starting instant but also during the fault period that will enhance the detection security. The term of locating the faulty section is determined based on ratios of the residual current amplitudes. The fault cases are simulated by ATP/EMTP and the arc model is implemented using the universal arc representation. Copyright # 2007 John Wiley & Sons, Ltd.

Covered-Conductor Overhead Distribution Line Modeling and Experimental Verification for Determining its Line Characteristics

Abstract: In this paper, theoretical model of the covered-conductor (CC) overhead distribution line is presented and the frequency-dependent distributed transmission line (TL) parameters, wave propagation characteristics, and characteristic impedance are calculated. The derived wave propagation characteristics are compared with those obtained from the time domain reflectometry (TDR) measurements to validate the theoretical model of the CC line. The TDR measuring system is also simulated in EMTP/ATP as real time verification. An accurate determination of the TL characteristics for practical CC lines can be used as a design aid for the modeling of partial discharge (PD) measuring system in EMTP/ATP; thus deciding the optimal locations of the sensors in getting reliable PD detection results due to falling trees on the lines.

Modeling of rogowski coil for on-line PD monitoring in coveredconductor overhead distribution networks

Abstract: In this paper, EMTP/ATP simulation environment is used to model the Rogowski coil for partial discharge (PD) monitoring due to leaning trees on the covered-conductor (CC) overhead distribution lines. The simulations are performed to obtain the Rogowski coil response at different lengths of the CC line and the results are compared with those obtained from the laboratory measurements. The results confirm that ATP simulations can effectively be carried out to model the transient behavior of the Rogowski coil for on-line PD detection.

High Frequency Current Transformer Modeling for Traveling Waves Detection

Abstract: Current traveling waves are utilized to localize faults on transmission lines using conventional current transformers. This paper investigates high frequency characterization of the current transformer. The current transformer parameters at high frequencies are experimentally determined. They are obtained using frequency response measurements where the current transformer transfer function is calculated from measured impulse signals. Therefore its performance under transient conditions can be studied using different programs such as EMTP and MATLAB. The current transformer modeling and its experimental verifications show that there are good replicas of high frequency traveling waves over a suitable range for fault locators. The test results insure the CT applicability to traveling wave fault location.

On-line PD measuring system modeling and experimental verification for covered-conductor overhead distribution lines

Abstract: In this paper, EMTP/ATP simulation environment is used to model on-line single-phase partial discharge (PD) measuring system using Rogowski coil for the monitoring of falling trees on the covered-conductor (CC) overhead distribution lines. The CC is modeled as a distributed parameters line and Rogowski coil is modeled based on its equivalent circuit as a saturable current transformer having linear magnetizing characteristics. The simulation results are compared with those obtained from the laboratory measurements. The model can be used to estimate the length of the CC line 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 overhead distribution line.

Comparing Wave Propagation Characteristics of MV XLPE Cable and Covered-Conductor Overhead Line using Time Domain Reflectometry Technique

Abstract: In this paper, the wave propagation characteristics of single-phase medium voltage (MV) cross-linked polyethylene (XLPE) cable are determined using time domain reflectometry (TDR) measurement technique. TDR delivers the complex propagation constant (attenuation and phase constants) of lossy cable transmission line as a function of frequency. The frequency-dependent propagation velocity is also determined from the TDR measurements through the parameters extraction procedure. The TDR measurement results for MV XLPE cable and covered-conductor (CC) overhead line are compared and it is proved that CC line has lower attenuation and higher propagation velocity than power cable. The measurement results can be used to localize the discontinuities in XLPE power cables and for PD detection to monitor falling trees on the MV CC overhead lines.

DWT-Based Investigation of phase currents for Detecting High Impedance Faults Due to Leaning Trees in Unearthed MV Networks

Abstract: In this paper, features of earth faults due to leaning trees are extracted from the network phase currents using the discrete wavelet transform (DWT). Due to the associated arc reignitions, the initial transients in the electrical network give behavioral traits. The detection security is also enhanced because the DWT is responded to a periodicity of the initial transients. The absolute sum of the DWT detail d3 coefficient corresponding to the frequency band 12.5-6.25 kHz is computed over one power cycle for each phase current of each feeder where the sampling frequency is 100 kHz. It is found that the faulty phase has the highest absolute sum when it is compared with the other healthy phases. Similarly, the absolute sum of the faulty feeder is the highest when the comparison is carried out with respect to other feeders. Therefore, two logic functions are suggested to determine the faulty phase and the faulty feeder. The fault due to a leaning tree occurring at different locations in an unearthed 20 kV network is simulated by ATP/EMTP and the arc model is implemented using the universal arc representation.

Experimental Investigations on Multi-end Fault Location System based on Current Traveling Waves

Abstract: Traveling waves recorders (TWR) are used to accurately find the location of different faults in transmission networks. These recorders are installed at few substation buses where current traveling waves can be extracted. The recorded signals' time delay of the initial wave is receded at each TWR. In this paper, the minimum travel time of the traveling wave has been calculated considering Dijkstra algorithm to select the nearest TWR to the faulted line. The wavelet transform is used to find the highest spectral energy of the frequency band of the traveling wave signals. Thus, the Wavelet Transform enhances the traveling wave fault location. The current transformers (CT) are modeled and experimentally verified to represent the traveling wave interaction with the CT. The secondary wiring from the CT secondary winding to TWR has also some effect on the measured traveling wave signal which motivates practical issues associated with measuring the arrival times. Correction factors are derived to monitor high frequency current traveling wave signals. Validation of fault location is examined by ATP/EMTP simulations for typical 400 kV power system faults.

Feature Extraction of High Impedance Arcing Faults in Compensated MV Networks. Part I: DWT-Based Analysis of Phase Quantities

Abstract: In this paper, the initial transients in the electrical network due to arc reignitions associated with high impedance faults caused by leaning trees are extracted from phase voltages and currents. The discrete wavelet transform (DWT) is used for the fault feature extraction corresponding to band frequency 12.5- 6.25 kHz and therefore localizing this fault occurrence. The detection security is enhanced because the DWT is responded to a periodicity of the initial transients. A novel technique for the selectivity term of the faulty feeder is introduced. It is based on the power polarity, in which, this power is computed by multiplying the DWT detail coefficient of the current and voltage for each feeder. The fault due to a leaning tree occurring at different locations in an unearthed 20 kV network is simulated by ATP/EMTP and the arc model is implemented using the universal arc representation.

Research and analysis method comparison in finnish reliability worth study

Abstract: 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 [1]. This paper presents the research, analysis and strategic response elimination methods used in this study. There are several methods to calculate and normalize the reliability worth parameters, and the results may differ significantly depending on which method is applied. The principles of the calculating methods are also presented.

Evaluation of Energy Meters’ Accuracy Based on a Power Quality Test Platform

Abstract: Is it advisable to replace ferraris based meters with electronic meters? The permanence of the electromechanical meters currently in use is often justified on the grounds of their long working life and low price. However, it is well known that they are highly sensitive to external conditions and that many factors can lead to miscalibration. This work attempts to clarify some key points in order to answer the previous question. It reviews the operating principles of energy meters. The behavior of watt-hour meters under nonsinusoidal conditions is also studied. The disturbances considered were harmonics, unbalance and main frequency variations.

Vision of the future power system distribution network 2030

Abstract: This paper presents the results of the Finnish national "Technology Vision of the Future Distribution Network" project. The aim of the project was to create a technology vision of future distribution networks. Because the life span of networks is very long, a long term vision is very important for guiding network investments and technology development.

Simulation of combined shield wire and MOV protection on distribution lines in severe lightning areas

Abstract: This paper presents the protective effects of shield wire coupled with Metal Oxide Varistor (MOV) arresters in a distribution network located in a severe lightning area. The presented test case is the IEEE 34-node radial distribution 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.

Performance of surge arrester to multiple lightning strokes on nearby distribution transformer

Abstract: Overhead distribution lines are prone to lightning overvoltages due to their configurations and characteristics. Metal Oxide Varistor (MOVs) arresters for many years have proven to be more advantageous than others arresters in lightning surge protection; therefore it is worthwhile to continually assess the behavior and performance of these arresters to different kind of overvoltages caused by lightning strokes for power system applications. This paper presents the performance of MOV arresters to multiple lightning strokes nearby a substation transformer. All simulations were performed with Alternative Transients Program/ Electromagnetic Transients Program (ATP/EMTP Program). Key-words: Lightning strokes, surge arrester, ATPDraw, Transient Overvoltages.

Signal Processing Applications to Current Traveling Wave Fault Locators for EHV Transmission Networks

Abstract: Traveling waves recorders (TWRs) are used to accurately find the location of different faults in power transmission networks. These recorders are installed at few high voltage buses where current traveling waves (CTWs) can be extracted. The CTW signals' time delay of the initial wave is recoded at each TWR. In this paper, the minimum travel time of the CTW has been calculated considering Dijkstra algorithm to select the nearest TWRs to the fault point. Wavelet transform is used to find the highest energy of the details frequency band of the CTW signals. Optimum details level is extracted based on its energy content. The mean delay is calculated from the first packet of details' power profile for each TWR to be used in a double-end fault location algorithm. Time delay at the maximum power delay profile shows good results compared to the mean time delay.

Feature Extraction of High Impedance Arcing Faults in Compensated MV Networks. Part II: DWT-Based Analysis of Residual Components

Abstract: Electrical faults due to leaning trees have been studied in [1]-[2] and it was found that the initial transients due to the associated arc reignitions are behavioral traits. These transients have been localized using the discrete wavelet transform (DWT). In this paper, these features are extracted from residual voltages using DWT. Therefore, the fault localization is carried out. The term for locating the faulty feeder is based on the polarity of a specific frequency band-power computed by multiplying the DWT detail coefficient of the residual voltage and current for each feeder. The performance of the proposed technique is getting better when the residual waveforms are utilized. Test cases provide evidence of the efficacy of the proposed technique.

Feature Extraction ofHighImpedance Arcing Faults inCompensated MV Networks. PartI:DWT-BasedAnalysis ofPhaseQuantities

Abstract: Inthis paper, theinitial transients intheelectrical network duetoarcreignitions associated withhighimpedance faults caused byleaning trees areextracted fromphasevoltages andcurrents. TheDiscrete Wavelet Transform (DWT)isusedfor thefault feature extraction corresponding tobandfrequency 12.5- 6.25kHzandtherefore localizing this fault occurrence. The detection security isenhanced because theDWT isresponded toa periodicity oftheinitial transients. A noveltechnique forthe selectivity termofthefaulty feeder isintroduced. Itisbased onthe powerpolarity, inwhich, this poweriscomputed bymultiplying theDWT detail coefficient ofthecurrent andvoltage foreach feeder. Thefault duetoa leaning treeoccurring atdifferent locations inan unearthed 20 kV network issimulated by ATPIEMTPandthearcmodelisimplemented using theuniversal arcrepresentation.

Current status of research on lightning-induced overvoltages

Abstract: The present understanding of lightning induced overvoltages (LIOs) is reviewed. Influences of lightning parameters (ground resistivity, lightning current peak amplitude and rise time, return-stroke velocity, geometry of lightning stroke, Basic impulse level etc.) in LIOs are examined with valuable judgments from current research literatures also; various models that have been used extensively to reduce the possible threat of induced overvoltages on power system lines are presented. The comparison between the theories and experimental results of these models are evaluated.

Diagnosis of MV Oil Filled Cable Terminations with X-Ray Imaging and Infrared (IR) Thermography

Abstract: A main purpose of doing a diagnostic in cable system including its accessories such as impregnated paper insulated oil filled cable termination is to predict failure before they occur Those cable and accessories, which are about to fail, can be replaced, thereby reducing the incidence of electrical system failure, thus reducing the electricity outages This paper presents the work carried out to find any possible method that can be used to detect a drying out of oil impregnated paper tape cable terminations Furthermore, the diagnosis has to be used without destroying the terminations Two diagnosis methods; infrared (IR) thermography and X-ray imaging are reviewed and the diagnosis result is presented By comparison of two-diagnosis method in this work, the X-ray imaging method is the best approach to observe and detect a drying out of paper tape oil impregnated cable terminations

DTW-based detection of high impedance fault due to leaning trees in compensated MV networks

Abstract: Features of faults due to leaning trees are extracted using discrete wavelet transform (DWT) and an absolute sum of the detail coefficient d3 over a period of power frequency cycle is used as a detector. DWT is processed on the residual voltage at different measuring nodes allocated in a wide area of the network and such correlation of DWT performance at different nodes can be carried out using distributed wireless sensors. Therefore, the fault detection is confirmed by numerous detectors. Other fault features that can enhance the detection security are that the initial transients are frequently repeated and therefore localized with each current zero crossing. The fault detection selectivity is carried out considering the multiplications of DWT detail coefficients of the residual current and voltage at each measuring nodes. A sum over two cycles is then computed to estimate the direction of the transient power and therefore to discriminate between the healthy and faulty sections. Test cases prove with evidence the efficacy of proposed technique.

Feature Extraction ofHighImpedance Arcing Faults inCompensated MV Networks. PartII:DWT-BasedAnalysis ofResidual Components

Abstract: Electrical faults duetoleaning trees havebeenstudied in(1)-(2) anditwasfoundthattheinitial transients duetothe associated arcreignitions arebehavioral traits. Thesetransients havebeenlocalized using thediscrete wavelet transform (DWT). Inthis paper, these features areextracted fromresidual voltages using DWT.Therefore, thefault localization iscarried out.The termforlocating thefaulty feeder isbasedonthepolarity ofa specific frequency band-power computed bymultiplying theDWT detail coefficient oftheresidual voltage andcurrent foreach feeder. Theperformance oftheproposed technique isgetting better whentheresidual waveforms areutilized. Test cases provide evidence oftheefficacy oftheproposed technique.