Medium Voltage Distribution Lines Research Articles

Improving the efficiency of medium voltage (MV) distribution lines using risk matrix for optimized maintenance

Medium Voltage overhead lines within North-West power utility companies in South Africa are confronted by higher volumes of deficiencies leading to frequent power failures. An essential quality of service factor considered in power distribution is the electricity supply to customers free of interruptions. Due to the higher number of electrical power line faults associated with the power system life span, achieving the desired level of reliability becomes an enormous task. The paper shares the findings of a study on performance improvement of MV distribution overhead lines using a risk matrix for deficiency analysis and clearing of such defects. A pilot study was conducted, and the risk matrix strategy developed in the study improved the reliability and key performance indicators by trimming down the overhead power line deficiencies. Defect clearing lowered outage frequency, durations, and power losses. The System Average Interruption Duration Index (SAIDI) was enhanced by lowering the outage duration by 108.64 h annually. The System Average Interruption Frequency Index (SAIFI) improved by reducing the outage frequency by 45.45 sustained occurrences annually and Reticulation Supply Loss Index (RSLI) by 8.31 MVA monthly.

Full-wave electromagnetic analysis of lightning strikes to wind farm connected to medium-voltage distribution lines

This paper studies the voltages developed on a wind turbine (WT) and a medium-voltage distribution line (MVDL) connected to a wind farm subjected to lightning strikes and located on frequency-dependent (FD) soils. The ground potential rise (GPR), voltages at the blade tip and on phase conductors of the MVDL are calculated using the full-wave electromagnetic software XGSLab® employing the rigorous Partial Element Equivalent Circuit (PEEC) method. The wind farm comprises four wind turbines with interconnected grounding systems using cables buried in resistivity soils of 1,000 and 5,000 Ω m. The voltages are computed for the first positive impulse (FPI) of 100-kA 10/350μs and for the subsequent negative impulse (SNI) of 50-kA, 1/200μs. Results have shown that voltage peaks increase notably as the soil resistivity increases. When the WTs are assumed, oscillations in the GPR waveforms for the SNI occur due to the multiple reflections between the blade and the turbine’s base. However, the voltages for the FPI present smooth time-domain responses. Furthermore, the overvoltages developed at the MVDL are significantly dependent on the soil resistivity and lightning current waveform.

Influence of a shield wire flashover on the indirect lightning performance assessment of distribution lines

This paper presents a new aspect of shield wire (SW) modeling for assessing the indirect lightning performance of overhead medium-voltage distribution lines: a flashover (FO) between an SW and the reinforcing bars of a distribution pole or a crossarm (SWFO). In general, an SW is periodically grounded approximately every four to ten poles and not grounded at the other poles. However, owing to lightning-induced overvoltages, the voltage difference between the SW and the distribution pole may even exceed 100 kV, and the SWFO can occur. In this paper, we evaluate the effect of the SWFO on the number of FO occurrences of phase-conductor insulators by the Monte Carlo method using a 2D finite-difference time-domain-based indirect lightning surge analysis program. The effect of the SWFO is more significant in lines with high soil resistivity (a soil resistivity of 1000 Ωm was assumed) regardless of the installation of surge arresters: the total number of FO occurrences markedly differs by up to 50% between cases in which the SWFO is considered and not considered. The analysis presented in this paper will assist the formulation of lightning protection measures particularly, in regions with high-resistivity soils.

Effect of PLTS Power Factor Settings on Power Losses and Voltage Conditions in 20 kV Medium Voltage Networks

As technology develops, the rapid increase in PV capacity will affect the grid. This makes it important to determine the PV limit that can be injected into the grid defined as the PV Hosting Capacity (PVHC). In this paper, the author evaluates and analyses the impact of PV connections on medium voltage distribution lines (20kv) using ETAP 19.01 simulation. A medium voltage Grid with a capacity of 30MVA, has an industrial load varies from 650 kVA to 25 kVA with the total load capacity of 2225 KVA. The loads are supplied from two sources, grid and PV system. The simulation results state that the best of grid performance which provide the best losses and voltage condition when connecting 100% capacity of PV to the existing grid network is by setting the inverter power factor to 0.9. This setting will provide lowest power losses of 0,7 kW and improve the voltage value.

がいしの塩汚損が配電線直撃雷によるスパークオーバ発生率に与える影響

To improve the lightning-outage-rate calculation method of medium-voltage distribution lines, it is important to accurately assess sparkover rates of insulators. In salt polluted areas, lightning outage rates may increase due to the deterioration of insulation performance of insulators. Although the sparkover characteristics of salt-polluted insulators against the standard lightning impulse voltage have been reported in previous works, the sparkover characteristics against short-wave-tail lightning impulse voltages, which occur across insulators on distribution lines by direct lightning strikes, still remain not clarified.

LEMP and ground conductivity impact on the direct lightning performance of a medium-voltage line

• Assessment of the LEMP influence on direct lightning overvoltages of medium-voltage distribution lines of the type equipped with a shield wire and surge arresters. • Comparison between the results obtained by a 3D-FDTD method and the LIOV-EMTP code. • The LEMP contribution on the overvoltages across insulators increases with increasing values of the soil conductivity. • The appropriate modeling of the LEMP effects is important for the lightning performance assessment of the type of lines considered in this paper. In medium-voltage distribution lines equipped with a multi-grounded shield wire and with surge arresters installed along the line at relatively short intervals, lightning outages associated with indirect lightning are less frequent than those associated with direct ones. The protection for this type of distribution lines is therefore dependent on the response to direct strikes. This paper presents and analyses the response to direct lightning overvoltages of lines of such a type located over a lossy soil considering the influence of the lightning electromagnetic pulse (LEMP), which is typically disregarded in the calculation of overvoltages due to direct strikes. The calculation results, performed by means of a three-dimensional finite-difference time domain (3D-FDTD) method and of the LIOV-EMTP code, indicate that the voltage across the insulator is enhanced by LEMP effects. In addition, it is shown that the enhancement due to the LEMP increases with the increase of the soil conductivity value. The modeling of the LEMP effects is therefore important for the accurate assessment of the lightning performance of medium-voltage distribution lines of the type considered in this paper, even when direct strikes are considered.

Saving raptors in Mongolia: country-scale retrofitting of insulation to reduce avian electrocution at power lines

The delivery of electricity to widely dispersed communities across the open steppe grasslands of Mongolia depends on medium-voltage (10–35 kV) distribution lines, often carrying power over substantial distances. Previously utilizing wooden supports, upgraded and new distribution lines are now designed to be cheaper, using steel-reinforced concrete poles with galvanized steel crossarms that can carry an electrical charge to the ground. Consequently, any bird that perches on these poles and simultaneously touches a conducting cable can be electrocuted, which is a significant risk for medium to large-sized birds at 10 kV and 15 kV lines utilizing pin-insulators. Surveys and monitoring of these dangerous power lines revealed that raptor electrocution rates were high, especially in areas with abundant prey, and widespread across steppe habitats. With around 3,500 km of hazardous lines in the Mongolian steppe zone, it was estimated around 18,000 raptors, including 4,000 Saker Falcons, were electrocuted each year. Experimental trials indicated that retrofitting insulation could significantly reduce electrocution risk. However, off-the-shelf mitigation equipment was either not suitable or too expensive to be deployed at scale in Mongolia. Consequently, we designed and manufactured our own equipment to meet our six criteria of being (i) effective, (ii) durable, (iii) failsafe with (iv) no impact on power supply, (v) simple to install and (vi) low cost. This equipment comprises acrylonitrile styrene acrylate (ASA) insulation covers that fit over the crossarms and a concrete pole tops of standard line poles, suitable for retrofitting existing lines and being incorporated into new lines. Over to 34,425 poles at 67 power lines covering a linear distance of 3,450 km, at an equipment cost of less than USD $40 per pole. Comparison of carcass counts indicated a significant reduction in electrocution events. To our knowledge, this is the largest single powerline retrofitting project globally, demonstrating that effective mitigation can be deployed at scale, saving tens of thousands of raptors from electrocution for a relatively low cost. We hope to use this project as an exemplar to focus attention and attract funding to address the issue of raptor electrocution at a global scale.

State Estimation of Medium Voltage Distribution Line with Distributed Generations: Selected Utilization of Smart Meter Measurements

AbstractWith regard to a medium‐voltage distribution system with low voltage electrical loads (hereafter written as ELs) and distributed generations (hereafter written as DGs), this study proposes a new calculation method for estimating electrical states such as line‐to‐line voltage vectors and line current vectors at connection points. The proposed method uses the following selected electrical data as input data: (i) active powers and reactive powers measured with the smart meters (hereafter written as SMs) on low voltage ELs and DGs and (ii) a line‐to‐line voltage and a current measured with a load break switch on the medium voltage distribution line, but does not use voltages and currents measured with the SMs on low voltage ELs and DGs. The selection of the used data attains reduction in the enormous number of data collected from SMs and also contributes to needless information on vast number of low voltage distribution lines such as their line impedances. Simulation results obtained, using the proposed method, show that the accurate electrical state of a medium voltage distribution line is derived through a small correction number for various generation powers of a DG. The knowledge acquired through this study is actually applied to the centralized voltage control system installed in an electric power company. © 2022 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Optimal Configuration of Hybrid AC/DC Distribution Network Considering the Temporal Power Flow Complementarity on Lines

To mitigate the voltage violation and overloading caused by the integration of Distributed Generation (DG) and Electric Vehicle Charging (EVC) loads, a feasible solution is to convert some AC medium voltage distribution lines to DC ones and formulate an AC/DC hybrid distribution network, based on which flexible power shifting between lines can be achieved. However, the complementarity of power flows amongst AC/DC lines is hardly described and embedded in existing configuration optimization methods in which only the average loading or the variations of loading for a certain period is considered. Solution space will be geometrically increased if operation scenarios are fully simulated for configuration caused by the strong uncertainties of DGs and EVC loads. This paper proposes an analytic quantifiable method to describe the power complementarity between AC/DC lines. The Gaussian mixture model is used to depict the temporal correlation and uncertainties. The complementarity is calculated by the conditional probability of multi-dimensional joint probability density function of AC/DC hybrid lines. Accordingly, an optimal configuration method of hybrid AC/DC distribution network is proposed considering the complementarity of power flows on AC/DC lines, in which the size and location of Voltage Source Converters (VSCs) are optimized. Simulations studies are performed to verify the proposed method.

Influence of Medium Voltage Distribution Line Configuration on Phase to Phase Sparkover Rate due to Direct Lightning Strike

In recent years, to reduce maintenance and management cost of distribution facilities, overhead ground wires are sometimes removed in a certain area. In such distribution lines, wire breaking at mid-span due to direct lightning is of concern. Although phase to phase sparkover is considered to be one of the factors of wire breaking at mid-span, its quantitative study has not yet been carried out. In this paper, at first, we experimentally examined detailed sparkover characteristics between phase conductors against short tail lightning impulse voltage, which is assumed to be phase to phase voltage. Next, based on experimental results, we estimate the phase to phase sparkover rate by means of lightning outage calculation program developed by CRIEPI. Estimated results suggest the phase to phase sparkover rate depends on the configuration of distribution lines, such as span length, arrangement of conductors, and so forth.

直撃雷に対する高圧配電線雷事故率の総合評価

In Japan, with the progress of lightning protection measures, lightning outages associated with indirect lightning are less frequent, and direct lightning is the main cause of lightning outages. To achieve an effective lightning protection design for medium voltage distribution lines considering cost performance, it is necessary to evaluate the lightning outage rate for each equipment configuration. As for this purpose, we have developed the lightning outage calculation program for medium voltage distribution lines due to direct lightning. The developed program can estimate not only the flashover rate of insulators and the absorption energy exceeding probability of surge arresters, which have been studied in previous studies, but also the flashover rate between the phase conductors and the energy absorption history of the surge arresters which have not been studied enough. In this paper, we show the outline of the developed program and some examples of calculation results.

High impedance fault detection in 11 kV overhead line with discrete wavelet transform and independent component analysis

This paper proposes an analysis of high-impedance fault detection algorithms for medium voltage distribution lines based on the discrete wavelet transform (DWT) technique and a more advanced technique named independent component analysis (ICA) independently. Three-phase distribution line model and two diodes high impedance fault model, which represents the unsymmetrical fault current of electric arc, simulated using MATLAB/Simulink. High impedance fault (HIF) detection algorithm initially analyzes the sampled current waveforms through DWT and the resultant third level high-frequency components “d3” coefficients are analyzed through one cycle moving window approach. The proposed algorithm successfully detects any HIF in the distribution current even if there is a slight or no difference in the amplitude of the HIF and the waveform of the phase current. On the other hand, the ICA more developed algorithm than DWT successfully separated the noise signals from the obtained current waveforms and HIF noise signals can be differentiated with non-HIF noise signals. Because of this reason ICA is chosen in this research. The detected HIF current can be from 50 ma and up.

On-line fault judgment of integrated capacitive coupler based on signal line port impedance

Medium voltage carrier communication is a communication mode which uses 10kV medium voltage distribution line as transmission channel, and has been widely used in the field of distribution automation and power consumption information collection. Integrated capacitive coupler is the guarantee of stable and reliable operation of medium voltage carrier communication system. However, limited by voltage level, there is no effective method to judge whether the coupler fails when the 10kV distribution line is not powered off. In this paper, an on-line fault diagnosis method of integrated capacitive coupler based on signal line port impedance is proposed, which is beneficial for the improved medium voltage carrier communication machine to collect the signal line port impedance, and can judge whether the integrated capacitive coupler is faulty online under the condition of 10kV distribution line without power interruption. The method is simple and reliable, saving manpower and material resources, and having certain practical engineering value.

Direct Lightning Performance of Distribution Lines With Shield Wire Considering LEMP Effect

In medium-voltage distribution lines, lightning outages associated with indirect strokes are less frequent when surge arresters are installed at close intervals. In this case, the lightning performance is mainly determined by the line response due to direct strikes, usually assessed disregarding the effect of the lightning electromagnetic pulse (LEMP). This paper examines the influence of such an electromagnetic effect on the voltages across the line insulators caused by direct lightnings. The presence of both surge arresters and a shield wire is considered. By means of adequate modeling and numerical calculations, we show that the flashover rate due to the direct strikes is increased by the LEMP. The obtained results indicate that in the statistical assessment of the direct lightning performance of lines equipped by surge arresters and shield wires, the LEMP effect is not negligible and its accurate evaluation is hence required.

Classification of arc fault between broken conductor and high‐impedance surface: an empirical mode decomposition and Stockwell transform‐based approach

The high-impedance arc fault (HIAF) is a result of the interaction between the current-carrying conductor and the high-impedance surface. This study presents a detailed and comparative time-frequency based analysis for the classification of different arcs, generated by the interaction of a broken conductor and different arcing surfaces. The real-time arcing voltage signals are considered as the basis of the whole time-frequency based analysis from a medium voltage distribution line. In this proposed approach, empirical mode decomposition (EMD) is used to study the real-time arc voltage signals of various surfaces. The intrinsic mode functions obtained by the application of the EMD technique is used as the input to various machine learning techniques, which later successfully classifies different HIAFs from their harmonic footprints. The Stockwell transform (ST) is additionally applied to the same test cases, and the classification of the arc is performed using similar learning algorithms to get a quantitative view of both outcomes of EMD and ST towards the selection of appropriate signal processing technique and machine learning algorithm for the same.

Narrowband PLC Channel Attenuation Due to a Multi-Grounded Neutral

This paper presents a theoretical study on the influence of a multi-grounded neutral on the transmission of narrowband power-line communication (PLC) signals through a two-wire medium-voltage distribution line. Three different methods are proposed to calculate the transfer function of the line in the 3-500 kHz range: (i) nodal admittance method; (ii) travelling wave method; (iii) electrically-short line approach. The validity, advantages and shortcomings of each method are presented and discussed. It is shown that improving the grounding impedance at the transmitter and receiver locations will contribute to reducing the channel attenuation. It is also shown that the number of intermediate grounding points along the neutral is more relevant for the attenuation of PLC signals than their impedance. In general, increasing such number will always reduce the attenuation in frequencies where the line is electrically short. A similar behavior is observed at the higher end of the 3-500 kHz range provided the grounding interval is less than 300 m, which is half wavelength of the 500 kHz frequency. If the separation between grounding points is greater than that, reducing the number of grounding points is likely to reduce the average channel attenuation, but at the cost of introducing multiple resonant frequencies.

Detection and Experimental Validation of High Impedance Arc Fault in Distribution System Using Empirical Mode Decomposition

The effect of high impedance faults (HIFs) in a distribution system has an effect on the system stability and reliability. The high impedance arc fault (HIAF) even poses a significant threat to the living being as it involves arcing. The HIAF have the same V–I characteristics as HIF, but the enormous amount of heat generation is a significant concern to differentiate between them. Moreover, there are different types of arc which may occur depending on the arcing conditions and arcing surfaces. In this article, arc due to leaning-tree on a medium-voltage distribution line and the arc in between sphere-gaps are considered as the main event of analysis. An empirical mode decomposition (EMD)-based approach is used along with artificial neural network (ANN) for the analysis of real-time arc signals. The result obtained by the application of EMD and ANN on arc voltage signals successfully detects and classifies the arcing events by their predominant harmonic signatures. A comparison of EMD results with other techniques is presented. Arc in soil and wet-sand is also considered for the validation of the proposed algorithm for other arcing surfaces. Support vector machine and K th nearest neighbor machine learning techniques are also utilized for classification.

Optimal current calculation for a PMSG based wind energy system integrated into an unbalanced weak grid

Grid connection is an important consideration when it comes to integrating an energy source. A common problem with the existing wind energy conversion systems is that they are often located far from energy consumption centres. Owing to their remote location these systems are sometimes forced to connect with weak distribution networks which are usually designed for small linear loads. When the nature of these loads is changed, the voltage level at the point of common coupling may go above or below the nominal value which may result in power system instability. To improve the voltage variation, this study discusses an optimal current calculation technique based on Thevenin equivalent parameters of an electrical network. The functional capability of the technique is demonstrated with the help of a traditional converter topology utilised as a power conditioning system for a permanent magnet synchronous generator connected to a weak grid. The system in particular monitors a medium voltage distribution line, measures line load impedance and redistributes the currents in a way that provides maximised power transfer into a network with least incurred losses. A real-time controller with built-in data acquisition/field-programmable gate array modules is used for the execution of experimental investigations.

Generalized distance-based protection design for DG integrated MV radial distribution networks — Part II: Application to an actual distribution line

The first part of this two-paper series proposes generalized guidelines for the design of distance protection in medium-voltage radial distribution systems with distributed generation. In this second part, these guidelines are applied to a real medium-voltage radial overhead distribution line of the area of Xanthi, Greece. A considerable penetration level of distributed generation is also assumed for this application. Based on the proposed guidelines, the designed protection scheme addresses all the factors affecting distance relay operation in distribution system applications, also dealing with any particularities of the specific distribution system examined. The installed distance relays prove to operate dependably and selectively against various faults, considering different fault types, fault positions, fault resistance and penetration level of distributed generation. In fact, selectivity is preserved between the distance relays and the remaining protection means (fuses) in the line, as well as between successive distance relays. Economic feasibility of the designed distance protection scheme is evidently taken into account, as the minimum number of distance relays is ultimately installed.

Methods to ascertain the resistance of stranded conductors in the frequency range of 40 Hz–150 kHz

Although a few years have passed since the first electromagnetic compatibility problem occurred in the supraharmonic frequency range (2–150 kHz), a lot of questions are still to be answered before the completion of appropriate electromagnetic compatibility (EMC) standards. An exciting question is how supraharmonic disturbances spread and aggregate on the network. To get a better picture of this, the frequency dependent characteristics of the network elements must be examined. This paper deals with the resistance of three stranded conductors with different cross section areas typically used in the low voltage (LV) and medium voltage (MV) distribution lines. From the methodology point of view, the problem was approached by laboratory measurements, numerical simulations with Filament technique, which was realized in MATLAB. In addition the results are compared with a few other analytical calculation methods (e.g. series expansion of Bessel functions, skin factor method, Hankel method, K. Simonyi’s approximation) found in the literature. These were performed, assessed and compared. Besides that, a new method combining two analytical methods is proposed to approximate the internal impedance of conductors. It must be noted that our intention was to cover not only the supraharmonics area, but also the power harmonics range; therefore, investigations start from 40 Hz instead of 2 kHz.