MV Networks Research Articles

A fault detection method in asymmetric networks based on the zero-sequence current

Abstract There is always zero-sequence current in the MV network because of its asymmetric parameters of transmission lines. Therefore, studying the distribution characteristics of natural unbalanced current through the feeder of an asymmetric distribution network is conducive to the feeder selection. In this paper, the expression of the current of each feeder is derived and its composition and distribution characteristics are analyzed. Based on this, the steady-state model of the feeder is constructed. To eliminate the effects of natural unbalanced current, it is proposed to subtract the current before and after a fault occurrence, and subsequently identify the faulted line according to phase-angle characteristics of the resulting zero-sequence current increment. Finally, a MATLAB/Simulink simulation system is constructed and employed for verification purposes.

Statistical characterization of reliability indices in medium voltage networks using a Monte Carlo-based method

Distribution companies are compelled to provide high-quality services to their customers in compliance with existing regulations. Key performance indicators such as system average interruption duration index and system average interruption frequency index are commonly employed to assess the quality of service provided by these utilities. In certain countries, distribution system operators may face penalties or receive bonuses based on their performance within specified thresholds in their reliability indices. This paper introduces a novel, integrated algorithm, based on Monte Carlo simulations, for conducting a risk assessment in real MV networks using local data from the distribution system operator. The proposed technique is tested in a real MV network, and the obtained results are analyzed both at feeder level and for the entire network. The feeder-level results might be used to identify the sections of the network with the worst quality of power supply, based on the estimated KPIs. The overall results of the study offer valuable insights into the likelihood of specific KPI values using probability density function. The Weibull distribution and log-logistic distribution are found to be those with the best-fitting probability density functions for the two indices evaluated in this work. Furthermore, a penalty-based rate approach is presented as an application of the proposed method to assess the economic risk of the MV network. The findings reveal that the test system is expected to incur penalties amounting to 7.55 million dollars per year.

Analytical target cascading based real-time distributed voltage control for MV and LV active distribution networks

This paper proposes a new real-time distributed voltage control (RTDVC) scheme for medium and low voltage (MV&LV) distribution networks (DNs) based on the analytical target cascading (ATC) method. In this scheme, photovoltaic (PV) units at the LV level, on-load tap changer (OLTC) and distributed generation (DG) clusters at the MV level are optimally coordinated to regulate the bus voltages in MV&LV DNs to be close to the nominal value while minimizing the number of operations of OLTC and smoothing the reactive power outputs of DGs. Based on the ATC method, the large-scale strongly coupled voltage control problem of MV&LV DNs is decomposed into several subproblems while guaranteeing the optimality of the primal voltage optimization problem. The decomposed subproblems are iteratively solved in parallel in the MV and LV controllers, which achieves optimal voltage control in a distributed manner and effectively reduces the computation burden. An MV&LV test system with two 20 kV feeders and 39 0.4 kV LV grids was simulated to demonstrate the control performance of the proposed distributed voltage control scheme.

Voltage and Current Sensor for State Estimation in Distribution Network with Generation

The penetration of Distributed Generation into the distribution networks has been increasing during the last decades. However, the increase of generation brings additional technical challenges for the Distribution Network Operators. Thus, the integration of Distributed Generation along with the improvement of the quality of service is driving Distribution Network Operators to actively control their networks. In order to achieve an effective control of the distribution network it is necessary to estimate the voltage on the network. This paper presents a method to accurately estimate voltage on the MV Network from limited measures of voltage and current. A method to determine the best location to place those voltage and current sensors is also explained

Active Earthing system for MV networks

This paper describes and a new technology, the active earthing system, based on a multi-frequency power converter, which combines a new power electronic device with a protection and control system. This system allows network enhanced operation and maintenance, overcoming some of the limitations of the traditional earthing systems, giving rise to relevant improvement in supply continuity. The key questions and results of the validation along with lab testing data and field details are shown in this paper. The experiences of the first real application in a MV distribution substation being conducted in Gernika– Spain will be presented in ICREPQ’13 conference.

POWER FREQUENCY OVERVOLTAGES GENERATED BY SOLAR PLANT INVERTERS

A new kind of overvoltage, not covered by present standards, has been detected in solar plants when switching the inverters off. This power frequency overvoltage can be transmitted to the MV network, giving rise to damages to some pieces of low voltage electronic equipment. This phenomenon has been investigated in the field, testing several inverters in different solar plants, where the overvoltages, as well as the damages in revenue meters, have been reproduced and recorded. It has been proved that some inverter configurations are more prone to create severe overvoltages than other. In addition, some solutions have been tested and a laboratory test to reproduce the phenomenon is proposed

The Italian MV network dip performance characterization by contour charts as defined by UIE/CIGRE’/CIRED WG-C4.110

Reporting and analysis procedures play an important role in power quality monitoring systems especially for long term surveys. As far as voltage dips are concerned, the network voltage dip performance can be effectively described in many different ways depending on the aims of the data presentations at both site and system level. The paper deals with network dip performance different representation methods focussing in particular on the way of presentation proposed by the working group UIE/CIGRE’/CIRED C4.110. This method has been applied to the Italian 2009 voltage dips statistic as acquired by the Italian power quality monitoring system named QuEEN. Contour charts have been drawn for both different percentage of the monitoring sites and voltage dips types.

Determining the Source of Dips Using Data of One Monitor in the MV Network

This work discusses about a method that could be used to determine the source of voltage dips based on voltage and power measurements from a single monitor in the MV distribution network. The method uses information of active powers of each feeder connected to the primary substation measured before, during and after the dip events. The ratios of during-dip and post-dip powers to the pre-dip power are used to distinguish the origin and cause of the disturbance. As a power quality problem related to the highest financial losses for industrial customers, knowing the origin and cause of voltage dips is very important in order to identify the weakest part(s) of the network and to take corrective measures that improve the power quality levels and reduce the potential impact of dips to customers.

Voltage Dip Measurements along MV lines vs Primary Substations Measurements

The Italian MV networks voltage quality monitoring system has been collecting power quality data since 6 years by 600 instruments, 400 of which installed on HV/MV substations MV bus-bars and statistical representative of the network, the other 200 installed at some nodes of the MV lines [1]. The paper is focused on the analysis of voltage dips monitored at some of the 200 measuring points considered more significant. The aims were to confirm, on a wider scale, the representativeness of the statistics gathered on the HV/MV stations MV bus-bars with respect to that expected along the MV lines and to investigate the events way of propagation along different voltage levels. The analysis has been performed by both statistical methods on real data and DIgSILENT1 simulations. The possibility to get the MV network voltage dip performance along the lines by measurements at HV/MV stations level has been widely confirmed. Measurements at MV lines have also confirmed the percentages of probable HV origin voltage dips, evaluated at national and macro area levels. The voltage dips duration distributions have shown a good accordance with the typical tripping times of the HV and MV protection system.

Self-Extinguishing Faults in MV Cable Networks - Feasibility Study of Fault Prediction

The Dutch grid operator Alliander started an ongoing substation refurbishment in 2006 with SASensor, a measurement, protection and control system, including fault localization of persistent faults. Around 20 percent of the recorded measurements comprise the phenomena of 1-phase selfextinguishing faults. In order to assess the usability of these events to predict faults, the phenomena and their behaviour in time are described in MV networks with isolated neutral and lowimpedance earthing. Furthermore the feasibility of fault localization using the information included in those events is discussed.

Wind energy integration into 380 kV system-impact on power quality of MV and LV networks

The amount of electrical energy produced by wind mills is constantly increasing. Nowadays detailed analyses considering the impact of wind energy integration on the transmission system are required. The goal of this study is to examine the power quality behavior of the network in case of integration of different amounts of wind energy at different locations of the 380 kV transmission system. In order to analyse the impact of wind energy integration on the network's power quality, a 380 kV transmission system with MV, and LV subsystems is modeled, integrated wind farms are used and power quality analyses are performed

APLICAÇÃO DE PROCEDIMENTOS PARA SERVIÇOS DE ENGENHARIA EM ESCALADAS EM ÁRVORES A PARTIR DA NR-35

This paper addresses the importance of safety when working at heights, focusing on tree climbing and related activities. The primary need for adequate training for workers who deal with unstable and potentially dangerous activities is highlighted. The presence of equipment such as chainsaws, mowers,foragers and cranes increases the risks associated with these tasks, requiring special attention and safety measures. The implementation of Regulatory Standard NR-35 proved to be a crucial milestone in establishing specific and mandatory guidelines for safety when working at heights. However, authors emphasize that the regulation may not cover all the nuances of different activities at height, requiring a flexible and specialized approach in applying the standard. Therefore, the objective of this work is to present instrumental procedures for working at height to prun trees in the energy distribution sector so that this does not harm and cause surges of both an electrical nature and worker safety. Emphasizing the standard in RDR – Rural distribution network with a right-of-way that can correspond to 3.0 meters for BT networks and 6.0 meters for MV networks in which the NR-35 standard would apply. The results were based on the use of standards and laws that govern the country and presents an instrumental procedure that found the use of 30kN anchor cables and all other protective equipment for services of this nature.

Impacts of Renewable Sources on Power Quality in Distribution Systems

This paper analyzes the influence of renewable sources (RS) on voltage quality in MV networks and summarizes problems considered of general interest relating to the power quality of dispersed generation. We are interested in voltage fluctuations, flicker, harmonic distortion, interharmonic distortion, and the effect of dispersed generation on ripple control signals. The influence of DG on voltage stabilization, line losses, and short circuit impedance are also investigated. A basic analysis of the possibility and effectiveness of using a parallel Active Filter (AF) to compensate for the constant-speed wind turbine (WT) flicker, reactive power, and terminal voltage variation is presented too.

A Surge Absorber for the Sri Lankan Distribution Substation to Mitigate Lightning Damage

Due to high grounding resistance and soil conditions surge arrester performance decreases. Even though in installation the standard earthing resistance is achieved with time the earthing resistance would be at a high value. When a high voltage arrives at the surge arrestor it discharges the excess voltage by providing low impedance shunt path to ground and providing protection for the transformer. Because of high impedance path the voltage would not divert to the ground and carry on its original path and damage the transformer. Therefore, for areas with high earthing resistances protection must be improved for distribution substations. Throughout this research method of reducing the peak and the rate of rise of surge was analyzed for providing extra protection for the transformer. The selected substation was AV047 it was selected because of lightning occurrence in the selected area, Replacement of the transformer due to damages cause by overvoltage surges and high earthing resistance of the installed substation. Usage of the surge absorber for additional protection was investigated throughout the research. By this method proposed by the research group it was able to provide the sufficient protection for the transformer during surge conditions and reduce the peak and the rate of rise of the surge. Losses of the surge absorber were also analyzed at different conditions. Further an algorithm was developed so that the surge absorber could be implemented to any MV and HV networks for protection of the transformer.

Regulatory Proposals for the Insertion of Distributed Energy Resources based on a Brazilian Utility Case and International Experiences

Utilities, policymakers, regulators, free market, and prosumers share a common interest in understanding whether benefits associated with such increased of DERs outweigh costs. To dimension and qualify B/C relationship, there are intrinsic variables relative to DERs' technical-economic arrangement and standard mechanisms used for its compensation: NEM, feed-in policies, etc. Other side, DERs must be adjusted on established regulatory framework, tariff schemes and utility revenue models. In this article, these three ambits are analyzed including a Brazilian southeastern region user's case study connected to MV network with DG measured data. Thus, some guidelines are pointed for the comprehensive implementation of DERs from the perspective of those involved.

Collaboration model between Distribution System Operator and flexible prosumers based on a unique dynamic price for electricity and flexibility

The paper presents an innovative coordination model between flexible final customers and an aggregator in providing flexibility service to the Distribution System Operator called Coordination Via Aggregator (CVA). The problem is formulated as a stochastic two-stage bilevel model in which the leader acts as both the aggregator and the supplier, and maximizes its profit by determining the price signal for flexible final customers composed of energy-based component and the incentive for service provision. Final users, modeled as followers in the lower level of the model, minimize their costs following the price signal from the upper level. The aggregator in this model is a non-zero-profit market entity, i.e., the price determined by the aggregator covers the balancing costs, the energy supply costs and at the same time incentivizes flexible customers to adequately change their consumption patterns. The CVA results are compared with the Direct Service Activation (DSA) approach in which final customers have a predefined two-tariff pricing option and receive a fixed amount of annual network charges discount for participating in the direct load control program. Based on the small-scaled and medium-scaled MV network results, customers with Renewable Energy Sources (RES) face lower electricity costs when providing flexibility service under the CVA approach compared to DSA (15% lower costs in small-scaled network). However, the results show that prosumers with high PV capacity (inject more energy in the grid than withdraw on an annual level) if not involved in providing flexibility, are more prone to signing up for a contract with the aggregator achieving lower electricity cost compared to two-tariff pricing option, however if they are providing flexibility services, direct load control results in 14% lower costs. In contrast, providing flexibility service under DSA with reduced network charges results in 9% lower cost in small-scaled and 16% in medium-scaled networks for final users without RES.

Evaluation effects and preliminary designing of sheath reactors for mitigation of overcurrent flowing through the earthed elements of underground cables following cross country faults on MV network

Evaluation effects and preliminary designing of sheath reactors for mitigation of overcurrent flowing through the earthed elements of underground cables following cross country faults on MV network

Optimized deployment of online partial discharge monitoring solutions for branched MV networks

Optimized deployment of online partial discharge monitoring solutions for branched MV networks

MV network maintenance planning decision support tool considering flexibility of DER

MV network maintenance planning decision support tool considering flexibility of DER

Challenges and considerations for the design and implementation of a centralized protection and control solution for MV networks

Challenges and considerations for the design and implementation of a centralized protection and control solution for MV networks