Medium Voltage Networks Research Articles

Valenze strategiche delle Comunità Energetiche

The concept of Energy Community is currently beginning to be appreciated by non-experts. Until about a decade ago, electricity generation was exclusively centralized and mostly run by fossil fuels. the power produced would then reach people’s homes through high, medium, and low voltage networks. Today, with small-scale plants, energy generation has become increasingly local and clustered near the consumption places, particularly thanks to the spread of photovoltaic systems, which are versatile in their application and have very few limitations in geographical distribution. Recently, other renewable sources small-scale plants have been developed for local and domestic use, greatly reducing losses related to transportation and distribution. In this context, one of the main objectives of the Energy Communities is to maximize and, therefore, stimulate both prompt and proximity self-consumption with appropriate incentives like State and European funding.

Sensitivity assessment of a novel earth fault location method with optimally placed distributed measurements for MV networks

AbstractThis paper extends the study of a zero‐sequence impedance‐based fault location method (FLM) designed for medium voltage (MV) distribution feeders whose principle has been presented in a previous work Bach et al. This method is able to locate any type of earth fault with any type of neutral grounding inside a convex set of nodes forming the solution area. The total length of the lines inside this area is statistically computable a priori and depends only on the number and location of additional voltage measurements deployed on some remote end secondary substations. To be efficiently applied to the most challenging rural feeders presenting a lot of ramifications, simulations have shown a need for synchronized measurements, such as the ones obtained using phasor measurement units. Besides, this paper addresses the coupling potential of this method with more traditional ones such as Takagi‐based FLMs to enhance the performances of both, solving the multiple estimation problem while potentially locating the fault within one node. Finally, an extensive sensitivity analysis has been carried out, showing a good robustness with respect to impedance estimation errors or fault impedance values while showing the need for synchronization, especially on some remote measurement locations.

Development of an algorithm for identifying single-phase ground fault conditions in cable and overhead lines in the networks with isolated neutral

The paper addresses the issue of identification of the type of single-phase ground fault in medium voltage networks operating mainly with an isolated neutral. By analyzing the published research, the most promising methods for detection of a single-phase ground fault were selected. Further, using the selected parameters, algorithms were designed to determine the parameters, process them, and use them to identify the type of a single-phase ground fault. The algorithm developed by the authors was formalized for the application on the basis of microprocessor-based protection systems using digital signal processors. The operation process was modeled using real oscillograms of single-phase ground fault. The use of high-frequency zero-sequence current and voltage components, as well as the root-mean-square value of the zero-sequence voltage, made it possible to design an algorithm that identifies any of the possible single-phase ground fault types (bolted, arc, or contact resistance ones). The first part of the article gives an overview of the state-of-the-art of research in the field of detection and identification of single-phase-to-earth faults. In the second part, the parameters of emergency operating conditions are analyzed and the key parameters are determined based on them. The third part contains a description of the single-phase fault identification algorithm developed by the authors and the output oscillograms. The fourth part makes conclusions on the applicability of the algorithm.

Analysis and optimisation of battery storage systems for mitigation of the effect of PV and EV on the maltese islands electrical network

This paper shall look at storage technologies for the application to the Maltese islands as a means to carry out peak shaving of the power demand and reduction of reverse power flow into the Medium Voltage (MV) Network. Moreover storage, whether large scale or distributed, if strategically located, shall contribute to reduced stress on the electrical network infrastructure thus allowing it to provide service to new customers without having to upgrade the cables or existing transformer. Distributed storage can also reduce dramatically distribution losses and improve the overall efficiency. The paper briefly discusses the various means of energy storage, their capabilities, limitations, advantages and cost comparisons. The paper shall consider in detail a case study for storage application in second largest island of the Maltese Islands. Real life load patterns were obtained for the electricity demand and PV energy production on this island. Two scenarios will be studied, the current situation and the deployment of EVs on the island. For each scenario the Summer, Winter and Mid-Season instances shall be investigated.

Random clustering analysis in deterministic DG-based distribution planning

New feeders’ allocation, new lines connecting the substations to new feeders and other feeders to tie-line routes, should be defined for minimizing the costs of new facilities’ installation with some limitations as voltage loss, capacity of current, geographical restrictions of installation, and balance between loads, while feeders have been recently distributed in a system of distribution. However, finding the optimum plan for feeder distribution among different applicants, is difficult for planners. To confirm decision of planners of feeder distribution plan in this paper, the author proposes a technique to obtain the minimum cost distribution facilities by all the applicants’ searching that fulfill such distribution limitations as voltage loss, also geographical constraints of installation and power loss and etc. In this paper, optimal deterministic planning of distribution networks with (DG) will be discussed and all calculations will be done in medium voltage (MV) level. Weight clustering in distribution networks planning is a major topic that can be discussed by different methods like fuzzy algorithm. Weight clustering in reliability concepts of deterministic DG-based distribution planning such as failure rate calculations can be discussed, but its meaning in robust optimization (RO) will be very complex and profound. In this paper, the study of random clustering in both single and multi-cluster states has been investigated and concluded. The results of this research can be used in the field of robust optimization of distribution networks at the MV networks. The sample candidate of random clustering studies has been selected the Greenfield residential area. According flowcharts I and II in part of the appendix, detailed analytical results based on robust optimization of 32 candidate substations of case study has been extracted in two state consist of both single and multi-cluster states.

Analysis of the Influence of Load on the Value of Zero-Voltage Asymmetry in Medium-Voltage Networks Operating with Renewable Energy Sources

The phenomenon of voltage asymmetry is common in electricity networks and is the cause of many unfavourable phenomena occurring, such as an increase in power and energy losses, as well as the abnormal operation of certain loads. Voltage asymmetry can be caused by several different factors, which include the design of the transmission line (e.g., routing of conductors in relation to each other and the earth), the parameters of consumer circuits (e.g., unequal loading of individual phases), or the design of network equipment (e.g., generators or transformers). An asymmetrical condition also occurs during system disturbances such as single-phase short circuits or lightning. One of the many factors impinging on voltage asymmetry in the electrical network is also the effect of load, but in the case of medium voltage power networks, this effect is neglected in the literature. This paper presents and evaluates the influence of the power consumed by consumers on the values of zero-voltage asymmetry factor indices in medium voltage compensated power networks with the neutral point earthed by an inductance (Petersen coil) operating with wind and photovoltaic power plants.

Wide area monitoring, protection, automation, and control systems for medium voltage networks

Distribution medium voltage networks have a branched structure, many power centers, longcable and overhead lines. This complicates the process of their automation, since significant capital costs for new equipment are required. New solutions based on modern technologies can help speed up this process and make it more efficient. The authors propose the use of synchronized phasor measurement technology for automating medium voltage networks. This paper considers approaches that describe the possibilities of implementing the WAMPAC principles in such networks, provides several examples where these principles apply.

Application of WAMPAC principles in distribution networks

The paper examines the dissemination of principles for constructing WAMPAC systems in medium voltage networks. The authors provide the prerequisites for the use of WAMPAC in distribution networks and show the advantages of such systems over traditional ones. The first part of the paper considers directions for the development of monitoring, protection and automation systems in the distribution network. The second part is devoted to the localization of ground faults based on phasor measurement technology. The paper also presents the results of mathematical modeling and data on the experience of applying WAMPAC principles in 10 kV cable networks.

Comparison of Algorithms for the AI-Based Fault Diagnostic of Cable Joints in MV Networks

Electrical utilities and system operators (SOs) are constantly looking for solutions to problems in the management and control of the power network. For this purpose, SOs are exploring new research fields, which might bring contributions to the power system environment. A clear example is the field of computer science, within which artificial intelligence (AI) has been developed and is being applied to many fields. In power systems, AI could support the fault prediction of cable joints. Despite the availability of many legacy methods described in the literature, fault prediction is still critical, and it needs new solutions. For this purpose, in this paper, the authors made a further step in the evaluation of machine learning methods (ML) for cable joint health assessment. Six ML algorithms have been compared and assessed on a consolidated test scenario. It simulates a distributed measurement system which collects measurements from medium-voltage (MV) cable joints. Typical metrics have been applied to compare the performance of the algorithms. The analysis is then completed considering the actual in-field conditions and the SOs’ requirements. The results demonstrate: (i) the pros and cons of each algorithm; (ii) the best-performing algorithm; (iii) the possible benefits from the implementation of ML algorithms.

A Distributed Algorithm for Controlling Continuous and Discrete Variables in a Radial Distribution Grid

The increased integration of distributed energy resources (DERs) in the distribution network with intermittent generation profiles will likely make voltage regulation a difficult task. However, DERs bring both challenges and opportunities, as they can provide renewable forms of local energy and act as voltage regulating components. The DERs are usually interfaced with power electronic devices, in which both their active and reactive power outputs can be regulated and treated as continuous control variables. In contrast, other voltage regulatory devices such as On-Load Tap-Changing (OLTC) transformers are often controlled by making discrete tap changes. Thus, appropriate control strategies are required to control and coordinate the DERs with other voltage regulatory devices. In this work, a distributed control strategy based on the Alternating Direction Method of Multipliers (ADMM) is developed, which controls both the continuous and the discrete variables in a distribution grid. The proposed control strategy is compared to a centralized and a local control architecture, where optimal parameters have been computed for the local controllers. Finally, a simulation study is made for the three different control architectures using a modified CIGRE medium voltage network. The results showed significant improvements in the daily voltage profiles while also reducing the power losses by over 30% when using an optimal control strategy.

A Linear Equivalent Method of PV Array for Fault Analysis of Medium-Voltage Networks

A Linear Equivalent Method of PV Array for Fault Analysis of Medium-Voltage Networks

Prospective Submodule Topologies for MMC-BESS and Its Control Analysis with HBSM

Battery energy storage systems and multilevel converters are the most essential constituents of modern medium voltage networks. In this regard, the modular multilevel converter offers numerous advantages over other multilevel converters. The key feature of modular multilevel converter is its capability to integrate small battery packs in a split manner, given the opportunity to submodules to operate at considerably low voltages. In this paper, we focus on study of potential SMs for modular multilevel converter based battery energy storage system while, keeping in view the inconsistency of secondary batteries. Although, selecting a submodule for modular multilevel converter based battery energy storage system, the state of charge control complexity is a key concern, which increases as the voltage levels increase. This study suggests that the half-bridge, clamped single, and full-bridge submodules are the most suitable submodules for modular multilevel converter based battery energy storage system since, they provide simplest state of charge control due to integration of one battery pack along with other advantages among all 24 submodule topologies. Depending on submodules analysis, the modular multilevel converter based battery energy storage system based on half-bridge submodules is investigated by splitting it into AC and DC equivalent circuits to acquire the AC and DC side power controls along with an state of charge control. Subsequently, to validate different control modes, a downscaled laboratory prototype has been developed.

New Selective Directional Ground Fault Protection Method for Ungrounded Systems

Ground faults are the main cause of electrical failure in transmission and distribution systems. In ungrounded distribution networks, it is difficult to detect where a first ground fault has happened as only capacitive currents are available. Also, it is important to trip only the faulty line in order to ensure the system's reliability. Directional residual overcurrent relays are the standard solution for these systems, but their difficult commissioning and high costs make it not trivial. This paper introduces a new selective and directional protection method to determine the faulty line in ungrounded medium voltage networks with three or more feeders. The method evaluates the residual currents in the feeders coupled to the same busbars in combination with a reference current created by the sum of a combination of residual currents of all feeders. Both simulation and laboratory results validate this new method, which is easy to start up, as it does not need previous configurations for its implementation, and it presents an economical solution to this problem.

Improving the Efficiency of Earth Fault Detection by Fault Current Passage Indicators in Medium-Voltage Compensated Overhead Networks

The article presents a method for detecting earth faults in a compensated medium-voltage network, which can be used especially in fault current passage indicators, but also in standard protection devices. The method is based on the adaptation process of the zero-sequence current protection setting, with the adaptation factor depending on the current value of the zero-sequence voltage. In this article, a comparative analysis of the classical and adaptive zero-sequence current criterion is conducted, taking into account the errors of the measuring system. The results of simulations performed in the PSCad environment are also presented. For a representative set of example short circuits, it was shown that the effectiveness of the presented criterion can be more than 50% higher than that of the standard criteria, taking into account the range of detected transition resistances. A comparison of the proposed method with admittance criteria was also drawn, and it was shown that it is suitable for the detection of high-resistance earth faults.

Applications and practices of comprehensively improving the intelligence level of Guangzhou's medium and low voltage distribution network

At present, there are various domestic distribution automation models in China, and there is no literature to carefully analyze which automation mode is selected for the regional distribution network; There is no literature research on collaborative protection and automation to achieve fault isolation of the distribution network in closed-loop operation. Experience in implementing network security protection requirements in secondary services of distribution networks is scarce; The construction and application of optical fiber communication in urban distribution network is lack of practical solutions that can achieve a balance between efficiency and economy. This paper will consider factors such as technology, economy and sustainable development, selecting the centralized self-healing scheme for the medium voltage distribution network, and a solution is given for the closed-loop operation distribution network. Flexible application of various communication modes such as optical fiber and wireless provides a communication service that gives consideration to network reliability and economical of service for distribution network protection and control. A security system architecture is designed to meet the safety requirements of network, which is applied in the application of medium and low voltage network. Applications of wide-area measurement technology and programmed operation of distribution network will improve fault location accuracy and operation efficiency. According to the above technical practices, Guangzhou distribution network has successfully been through some extreme conditions, and its power supply reliability has been among top ten of China's urban distribution network for a long period.

THE NEUTRAL CONDUCTOR VOLTAGE IN A MEDIUMVOLTAGE NETWORK DURING A GROUND FAULT

Of all the ground faults that can occur in medium-voltage networks from the standpoint of human and equipment safety, the most problematic is a ground fault in a medium-voltage/low-voltage substation. The grounding system of a lowvoltage network is directly connected to the grounding electrode of the substation. Therefore, each increase in the potential of the grounding electrode of the substation is transmitted directly via the neutral conductor into the customer’s installation. For these reasons, in this article a detailed investigation is presented of the problem of determining the neutral conductor voltage in a low-voltage network during a ground fault at the medium-voltage level in a supply substation that is an element of a medium-voltage network with an isolated neutral point (star point). A computer model is presented for the analysis of the neutral conductor voltage in actual distribution networks. Two characteristic distribution networks located on karstic terrain are analyzed. The results obtained are compared to the results of measurements.

Photovoltaic Energy Conversion System Integrated Into Unbalanced Distribution Electrical Networks Through Hardware in the Loop

In this article, a real-time, hardware in the loop (HIL) and experimental photovoltaic energy conversion system (PVECS) integrated into unbalanced distribution electrical networks is presented. Commonly, the three-phase voltages are not balanced, because the input–output of single-phase loads in low and medium voltage networks. In this context, the photovoltaic (PV) systems integration under the dq0-Frame control operation scheme, tend to generate current deformations. In contrast, a new control technique for PVECS interconnection is validated in a HIL scheme, even in the presence of unbalanced voltage. This new technique is considered simple and easy to implement, since it consists of a single PI control loop, guaranteeing reliable operation under unbalances voltage events. Thus, preserving favorable characteristics, such as: 1) always balanced currents; 2) low harmonic distortion; 3) unit power factor; and 4) Compliance with the rules of the network code. The PVECS effectiveness is assessed by complete mathematical model, the simulation results are evaluated using MATLAB-Simulink (MATLAB r2018, Mathworks, Natick, MA, USA), and the experimental results are validated with a small-scale prototype operating in a HIL environment and the real-time simulator Opal-RT Technologies (Montreal, QC, Canada); integrating a power capacity of 15 kW in distribution networks.

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.

Studi Pendekatan Formula Jogja Pada Jaringan Distribusi PT PLN UP3 Pondok Gede

<em><span lang="EN-US">PT. PLN (Persero) at the Customer Service Implementing Unit (Unit Pelaksana Pelayanan Pelanggan, UP3) Pondok Gede, in order to make the loss reduction program more effective, first find out whether the biggest contribution to shrinkage in Pondok Gede UP3 is technical or non-technical. By using the shrink formula method, Jogja has several mechanisms to perform the analysis. The results of the Jogja Formula Shrinkage are presented in the Dupont Chart which divides losses into two parts, namely non-technical losses and technical losses, while technical losses are divided into four parts, namely medium voltage network losses, distribution substation losses, low voltage network losses, and house connection losses. So that we can evaluate and analyze these losses and the program's efforts to reduce losses are on target. In the calculation of the cumulative loss of UP3 Pondok Gede globally in the first quarter of 2020, it is 58,403,338 kWh or 12.27%. After performing a calculation simulation using the Jogja Formula, it was obtained with a technical loss composition of a total of 34,813,582 kWh or 7.31% (this technical loss cannot be avoided or eliminated because it is a shrinkage caused by the components of the equipment used), and non-technical losses. engineering of 23,589,757 kWh or 4.95%.</span></em>

Simultaneous Planning of the Medium and Low Voltage Distribution Networks under Uncertainty: A Bi-Level Optimization Approach

Distribution network expansion planning (DNEP) is one of the important matters in the field of planning and operation of electrical power systems. Since many costs and losses have occurred in the distribution networks, it has increased attention towards this network. The electrical energy distribution network is divided into two parts: the medium voltage (MV) network and the low voltage (LV) network. The main problem in this field is that planning is done either only on the MV network or only on the LV network. While planning in each of these networks has a significant effect on the other networks, this important case has not been considered in most research studies. Therefore, this study has tried to do integrated planning in the form of a bi-level model in the presence of different types of distributed generations (DGs) and consider the uncertainties of renewable sources and load demand in both MV and LV networks so that the planning and operation costs are minimized. In the proposed bi-level model, the upper-level section aims to minimize the investment and the operation cost of the MV network, and the lower-level problem minimizes the investment and the operation cost of the LV network considering the DGs and pollution emission. The obtained results show the effectiveness of the proposed model.