Low-voltage Distribution Lines Research Articles

Lightning-induced voltages on low-voltage distribution lines

Special attention has been drawn to transients in low-voltage systems in recent years. As the surge withstand capabilities of low-voltage networks are much lower than those of medium-voltage lines, they are more susceptible to lightning-caused disturbances. One of the primary sources of overvoltages is related to indirect lightning strokes. Such overvoltages are highly dependent on the soil characteristics and generally tend to increase with the soil resistivity. Considering realistic conditions, this paper discusses the effects of different parameters on the phase-to-ground and phase-to-neutral lightning-induced voltages on the low-voltage side of a typical distribution transformer. In the case of high-resistivity soils or high ground resistance values, phase-to-ground voltages induced by indirect strokes can reach several tens of kilovolts. Phase-to-neutral voltages higher than 5 kV may be common if surge protective devices are not applied.

Monitoring Energy Flows for Efficient Electricity Control in Low-Voltage Smart Grids

Modern low-voltage distribution lines, especially those linked with renewable energy sources, face technical hurdles like unaccounted and illegal electricity use, increased power losses, voltage control issues, and overheating. Tackling these challenges effectively requires continuously monitoring power flows and identifying problematic network spots. This study introduces a method involving ongoing energy flow monitoring from distribution transformers and other sources to end-users through auxiliary facilities. The algorithm seamlessly integrates with consumers’ existing smart power meters and supporting infrastructure, eliminating the need for extra equipment or data. Deployed in several distribution networks totaling about 40 GWh/year over two years, this diagnostic system showed promising results. It notably cut total power consumption by around 6% by detecting and mitigating illegal energy waste and addressing technical issues. Additionally, it reduced technical personnel involvement in operational tasks by approximately twentyfold, significantly enhancing network profitability overall.

Assessment of fault potential and touch voltage in the low-voltage distribution line system of the residential community

Considering the increasing risk of electric shock in old residential communities, this paper investigated fault potential and consequential human-body touch voltage in the low-voltage (LV) distribution network under typical line-fault conditions by numerical simulation with a circuit approach. Three protective grounding configurations of the LV distribution system were of concern, and the electric shock scenarios considering practical situations were introduced for assessment. It has been observed that the phase-to-ground fault potential of equipment increases when the fault location is closer to the faulty equipment itself and decreases when it moves further toward the circuit end. The equipment in a building is likely exposed to the dangerous phase-to-ground fault potential under the line fault. As for line-to-neutral short circuit and neutral-line-open fault, the fault potential distribution mainly depends on the specific grounding configurations. Bonding of non-exposed steelwork in the buried building foundation to the nearby grounded grid may not be recommended in the literature, but it could effectively mitigate the touch voltage in and around the building of concern in this paper. Note that this measure, together with the local equipotential bonding method inside a flat, can provide enhanced protection against electric shock even if the protective device fails to operate or is unavailable. Among three grounding configurations, the one with multiple grounding points of the neutral wires up to the entrance of a building leads to the least dangerous touch voltage cases.

Lightning Surge Overvoltage Protection for Low-Voltage Equipment Placed Outdoors in TT System

When a TT system is used for earthing a low-voltage distribution line, the conductive enclosure of the equipment is grounded separately from the system ground for the power line. In such a case, lightning protection depends on the installation of surge protective devices (SPD) on the equipment side. However, in newer systems, a protective earth (PE) line is wired from the power substation for stable operation and connected to the PE line in the outdoor equipment. In this case, the SPD of the distribution board can suppress the overvoltage on the equipment side. In this article, the overvoltage generated between the power and grounded PE lines of the equipment using a vinyl-insulated vinyl-sheathed flat-type cable for a low-voltage distribution line was examined using transient circuit analysis. Then, we demonstrated countermeasures to achieve electric shock and lightning overvoltage protection.

The Current Generation Mechanism in the Earth Lines of a Building in TT System Struck Directly by Lightning

Surge protective devices (SPDs) are installed between the neutral and earth lines at the power substation in a TT system to protect the equipment in a building struck directly by lightning. In this case, when operating the SPD, the wiring system of the low-voltage distribution line is a TN system. Using this system, our previous study clarified that the overvoltage generated in the distribution board on each floor was caused by the loop impedance of earth wiring connected to the distribution board. In this article, we elucidated the electromagnetic generation mechanism of the current flowing in the protective earth line that formed the wiring loop.

A Study of Lightning Performance to Multi-grounded System of KEPCO MV and LV Distribution Network

This paper presents the indirect lightning performance evaluation of Korea Electric Power Company (KEPCO) medium voltage (MV) and low voltage (LV) lines. The main topic of this paper is to analyze an effect of the grounding systems on the indirect lightning performance of MV and LV distribution lines. To this end, we define the models of the MV and LV distribution systems for the analysis of distribution line surge overvoltage due to lightning. With reference to the data typically adopted by KEPCO, the research describes and motivates the use of the most suitable models of distribution lines, transformers, and surge arresters (SAs) to be implemented in EMTP like simulation environments. The sensitivity of the lightning performance of the distribution lines to different configuration of MV and LV grounding systems, distance between SAs, as well as presence of overhead ground wires is also analyzed. Regarding overvoltage, both the temporary overvoltage and the surge overvoltage are considered. The presence of SAs at the MV terminals of distribution transformers is also considered.

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.

Information model of low-voltage distribution IoT monitoring terminal based on IEC 61850

Abstract Low-voltage distribution lines lack efficient monitoring. With the massive proliferation of distributed energy resource supply, it is necessary to establish an effective monitoring system for low-voltage distribution lines to ensure the electrical safety and continuity of power supply services. This paper proposes monitoring system for low-voltage distribution lines based on the Internet of things (IoT) technology. An IoT based monitoring system contains a large number of low-voltage monitoring terminals, different manufacturers, and different types of terminal equipment to solve the interconnection problem of information interaction. This paper first analyzes the terminal functional communication requirements based on IEC 61850 standards. Further, the information models required by the electrical volume collection and non-electric quantity collection functions are studied. The information modeling for different types of monitoring terminal equipment is presented and thus provide the configuration suggestions. The monitoring terminal based on the information model developed in this paper is applied in a university campus to realize the monitoring of low-voltage lines and distributed power supply.

Optimization of distribution network reconfiguration based on Markov chain Monte Carlo method

Peak load shaving and load balancing are of great significance to reduce distribution network loss and improve resource utilization. Given this background, an optimization strategy for distribution network reconfiguration based on Markov chain Monte Carlo method is proposed. In this strategy, a load characteristic curve clustering method considering DBI index is proposed to obtain the typical load curves of each public transformer and special transformer user under low voltage distribution line based on the historical load curves. Then, an optimization model for distribution network reconfiguration based on Markov chain Monte Carlo method is proposed to minimize the average peak–valley difference of the distribution line, and the line connection modification scheme is obtained. Finally, case studies on two 10 kV distribution lines in Zhejiang province are performed for verifying the effectiveness of the proposed model. The results show that the proposed method can improve the line load rate and realize the peak load shaving and valley load filling of line load, which provides a reference for distribution network reconfiguration.

Sizing Procedure of Reactive Electric Spring

Reactive electric spring (RES) is a technique aimed at stabilizing the user voltage in presence of grid voltage variations by means of a user-encapsulated circuit. In spite of the numerous papers on the matter, no expressions are still available to size the RES elements. This paper fills this lack, by drawing up a sizing procedure of them. The procedure starts with a targeted investigation of the RES operation and exploits the outcomes to provide expressions for the values of the passive elements as well as for the voltage-current ratings of the voltage source inverter (VSI). The sizing expressions are formulated in normalized form to emphasize their dependence on the parameters of the user non-critical load. Focus of the sizing procedure is on the two RES key-elements, namely the AC-side capacitor and VSI but the AC filter inductor and the DC-side capacitor are also sized. Two options for sizing the AC-side capacitor are also discussed. At last, the study case of a user supplied by a low-voltage distribution line is considered and the sizing expressions are utilized to calculate the RES data. Experimental results, obtained by an on-purpose arranged hardware-in-the-loop (HIL) rig, validate the sizing procedure.

Reduction Measures of the Overvoltage in the TN System of a Building Struck Directly by Lightning

To protect the equipment in a building struck directly by lightning, surge protective devices (SPDs) are installed between the neutral line and ground lines at the power utility substation of a TT system. In this case, when operating the SPD, the wiring system of the low-voltage distribution line will be a TN system. Although the overvoltage between these lines at the power utility substation can be limited during SPD operation, an overvoltage between these lines is induced at each floor distribution board connected thereafter. Here, we analyzed this overvoltage in the VSTL electromagnetic analysis software. The overvoltage was found to largely depend on the loop impedance of the wirings as the lightning current flowed from the structure to the protective ground line. The most effective solution was separating the ground lines from the power supply lines connected to the distribution boards of each floor with another electric pipe shaft.

저압배전선로 전압안정화를 위한 상태관측과 반복제어를 적용한 무효전력 보상기

In this paper, a new reactive power control algorithm using a stat observer and repetitive control for voltage adjustment to the low-voltage distribution line is proposed and verified by simulation and experiment. A reactive power compensator has a single -phase full bridge inverter structure and consists of DC voltage controller to maintain a constant DC voltage, and current controller for reactive power generation. A DC ripple compensation method use an output from the state observer and the output is used as the DC voltage controller feedback to regulate the DC voltage constant. In order to inject a stable reactive power, the fundamental component of current is controlled by a PI controller, and a repetitive controller is connected in parallel with the PI controller to compensate for lower-order harmonics. The repetitive controller, as implemented in the synchronous coordinate system, serves to eliminate low-order odd harmonic components. The proposed control technique is experimented with a ±5kVar single phase inverter system and verified the performance of the proposed algorithm by confirming that THD is reduced to 2% from 9%.

Total output power variation of several small wind turbines

There is a concern that connection of several small wind turbines may cause severe voltage fluctuation and voltage flicker in low-voltage distribution lines due to their output power variations. In this study, output power variations of four 5-kW-class small wind turbine systems were measured with an interval of 0.1 s at a site in Wakkanai, Hokkaido, and their correlations and smoothing effect in the frequency range from [Formula: see text] to 5 Hz were analyzed and compared with those of five residential photovoltaic power systems. The results indicate that a smoothing effect occurs more in small wind turbines than in photovoltaic systems, because of lower correlation coefficients in lower frequency ([Formula: see text] Hz) components. Voltage flicker at the point of common coupling was also measured and it was confirmed that the impact of small wind turbines on voltage flicker is low enough at the site. In addition, the upper limits of the installation number and/or the system resistance are estimated theoretically using the measured flicker values.

On the Eddy Current Losses in Metallic Towers

The existence of magnetic field around high-voltage overhead transmission lines or low-voltage distribution lines is a known fact and well-studied in the literature. However, the interaction of this magnetic field either with transmission or distribution towers has not been investigated. Noteworthy it is to remember that this field is time-varying with a frequency of 50 Hz or 60 Hz depending on the country. In this paper, we studied for the first time the eddy currents in towers which are made of metals. As the geometrical structures of towers are extremely complex to model, we provide a simple approach based on principles of electromagnetism in order to verify the existence of power loss in the form of eddy currents. The frequency-domain finite difference method is adapted in the current study for simulating the proposed model. The importance of such a study is the addition of a new type of power loss to the power network due to the fact that some towers are made of relatively conductive materials.©2020. CBIORE-IJRED. All rights reserved

Fault Ride-Through Characteristics of Small Wind Turbines

There is significant potential for an increase in the use of kilowatt-class small wind turbines (SWTs) in Japan due to reduced limitations with respect to installation, despite their high cost. At this stage, the Japanese grid code has not been considered sufficiently with respect to grid-connected SWTs, and the addition of fault ride-through (FRT) requirements for SWTs has been requested. Moreover, the FRT of SWTs is challenging to achieve owing to the low inertia constants when compared with those of large-scale wind turbines, which result in significant acceleration of the rotor speed and an increase in the input voltage of the power conditioning system (PCS) during FRT operation. In this study, FRT field tests were conducted on SWT systems against a voltage dip with a duration of ~1 s, and it was confirmed that the SWT systems satisfied the FRT requirements for photovoltaic (PV) systems connected to low-voltage distribution lines in Japan. The behaviors of the rotational speed of the SWTs and the PCS input voltage in an FRT operation were then analyzed, and it was noted that the increase in the PCS input voltage with the overspeed of the turbine can reach the upper limit and make the PCS cease operation, which indicates failure of the FRT. The overvoltage, therefore, requires restriction using a method such as pitch control, furling, and electrical and/or mechanical brakes.

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.

Design of fault arc detection device based on STM32

The detection of the load current signal is one of the effective methods for judging whether an arc fault occurs in the low-voltage distribution line; according to the national standard GB/T 31143-2014 General Requirements for Arc Fault Protection Devices (AFDD), the analog series fault arc is built. The experimental platform studies the characteristics of the current waveform when the fault arc occurs. The db4 wavelet function is used as the wavelet basis function to decompose and reconstruct the current waveform after noise reduction, and extract the wavelet high-frequency component, calculate the periodic variance value of the wavelet high-frequency component, and detect the arc fault according to this value; The feasibility and effectiveness of the detection algorithm are verified. The arc fault detection algorithm is transplanted to the STM32 platform, and the fault arc detection device based on STM32 is designed. The device can realize the functions of current signal acquisition, data processing and series arc fault detection and recognition. Experiments with resistive loads, LED light, vacuum cleaners and microwave ovens have shown that the device can detect series arc faults with high reliability and will not cause false positives without generating fault arcs.

低圧連系用三相パワーコンディショナへの適用を想定した低圧配電線側からの高低圧混触地絡事故の直接検出手法

低圧連系用三相パワーコンディショナへの適用を想定した低圧配電線側からの高低圧混触地絡事故の直接検出手法

Propagation Characteristics of kHz Band PLC Signal on MV–LV Distribution System

SUMMARYThe kHz band power line communication (PLC) is one of the convincing mediums of the communication system for smart meter reading. Data transmission between medium‐voltage (MV) and low‐voltage (LV) points to pass the transformer by PLC is interested. In this paper, the PLC signal propagation characteristics between points of MV at substation and LV at customer are calculated and analyzed. The results show that direct communication between points on MV distribution line and most LV customers is impossible due to large propagation losses at MV–LV transformer and on LV distribution line.

地絡電流波形を用いた需要家構内低圧配電線路の事故原因判定法

地絡電流波形を用いた需要家構内低圧配電線路の事故原因判定法