Medium Voltage Networks Research Articles

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.

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.

Efficient Strategies for Scalable Electrical Distribution Network Planning Considering Geopositioning

This article presents a heuristic model to find the optimal route or layout of a subway electrical distribution network, obtaining full coverage of users in different scenarios and respecting technical criteria such as maximum distance to avoid voltage drop and capacity. In this way, the location of the transformer substations is achieved through an analysis of candidate sites. The medium voltage network will connect each transformer to a minimum spanning tree (MST), reducing the cost of materials associated with constructing the electrical grid. This work considers the latitude and longitude of each house and electrical count. Georeferenced scenario information is taken from the OpenStreetMap platform to provide an authentic context for distance and location calculations in the deployment of the power grid. The heuristic model offers to decrease time in solving the electrical network layout. As input variables, different powers of the "multi-transformer" transformers are considered to minimize the number of transformers and solve the power supply, reducing the transformers’ oversizing and minimizing the transformers’ idle capacity. The experimentation showed that none exceeded the limit allowed in an urban area of 3.5%.

Target location service system in microgrid operation based on internet of things

Abstract With the gradual reduction of conventional energy sources, the problem of environmental pollution is becoming more and more serious. Environmentally friendly, efficient and flexible power generation models are widely favored, and microgrids emerge as the times require. Microgrid is a medium and low voltage network including power distribution, storage devices, loads and other equipment. It can operate in grid-connected mode or as a stand-alone system in an island environment, continuing to supply power to users even when the large grid is disrupted. Compared with traditional power grids, microgrids have small capacity and changeable operation modes, making it difficult to locate distribution areas and short-circuit currents. At the same time, it is difficult to trace the faults during operation. So far, microgrids have had a lot of technical issues in operation that need to be resolved quickly. In recent years, IoT technology has developed rapidly. The Internet of Things is a comprehensive network that integrates location services, monitoring services, information identification and monitoring services through information exchange and communication technologies, such as video recognition technology, positioning technology, and wireless sensor technology. In order to monitor the operation mode of the microgrid in real time, find the source of the fault and locate the operation target, based on the Internet of Things technology, this paper installs wireless sensors in the line segment to monitor the line and other applications. This paper uses wireless sensor networks to record positioning variables, processes and data analysis to achieve the accuracy of microgrid operation target positioning. In addition, in order to improve the positioning accuracy of wireless sensor monitoring network and solve the problem of energy limitation, DV-Hop algorithm EB-IDMF algorithm and R-A algorithm are also introduced. Finally, the feasibility of the system is verified through experiments and tests. With the blessing of the positioning algorithm, the positioning accuracy is improved by 4.9%, which has great practical value for the target positioning of microgrid operation.

A New Method to Distinguish between Nearby and Direct Lightning Strikes for Long Operational Medium Voltage Lines

Lightning strikes near Medium Voltage (MV) electricity distribution lines cause voltage transients to be induced onto the conductors of the power lines. The resultant Lightning Induced Overvoltage (LIOV) on the phase conductors may be estimated using computer models or measurements. Models and measurements are mostly limited to short floating lines to simplify calculations and to ensure accurate results that can be easily compared between different models. Existing measurement methods cannot be used to distinguish between nearby lightning and direct lightning strikes to an operational MV network by using only one instrument on a line that is more than 100 km long. The instrument needs to be less than a hundred meters from where the LIOV amplitude on the line is the highest. The new method described in this paper allows one to distinguish between nearby and direct lightning strikes to the line; by comparing the polarity of the current transient recorded at the substation to the lightning return-stroke polarity obtained from a lightning detection network. The new method also allows one to determine whether the LIOV of a particular lightning transient exceeded the Basic Insulation Level (BIL) of the line, by observing the power frequency fault current. The new method was applied to an operational 714 km network operating at 22 kV, and the results were compared with predictions in IEEE Std 1410-2010. Significantly fewer line faults due to nearby lightning were observed than predicted; the reason for this is explained.

Energy and Demand Forecasting Based on Logistic Growth Method for Electric Vehicle Fast Charging Station Planning with PV Solar System

Electric vehicle (EV) charging may impose a substantial power demand on existing low voltage (LV) and medium voltage (MV) networks, which are usually not prepared for high power demands in short time intervals. The influx of E-mobility may require an increase in grid reinforcements, but these can be reduced and optimized by a combination of new technologies, tools, and strategies, such as the deployment of solar PV generation integrated with aggregated energy storage systems. One of the challenges in the implementation of charging infrastructures in public stations is coupling the projected sizes of energy demand and power requirements in each location for each charger. This paper describes a method to estimate projected values for energy consumption and power demand in EV fast charging stations (CS). The proposed ideas were applied in a concept facility located in Campinas, Brazil, in a structure equipped with two 50 kW DC Fast Chargers, local 12.5 kW/13.2 kWp PV generation (to reduce energy impacts to the grid), and a 100 kW/200 kWh storage system, using electrochemical batteries (to minimize peak power requirements).

Повышение электробезопасности обслуживающего персонала в условиях неполных однофазных замыканий на землю

The results are given related to the analytical studies of the causes of accidents occurrence and abnormal operating modes of electric receivers in the medium-voltage networks. It is established that the main cause of damage is the single-phase earth fault mode. It is established that the main cause of damage is a single-phase ground fault. It is found that a long single-phase ground fault increases the likelihood of transition to a more severe phase-to-phase short circuit. It is accompanied by immediate shutdown and long downtime of the equipment, large economic losses, as well as the appearance of touch and step voltages that are dangerous for people. It is identified that the earth fault current in a network with an isolated neutral will decrease in proportion to the decrease in the coefficient of the share of the transient resistance in the total earth fault current. Analysis of the operability of protection against single-phase earth faults is carried out on the example of a section of 6 kV distribution network of the coal mining enterprise JSC Polosukhinskaya Mine. Experimental studies of the efficiency of the functioning of non-directional current protection against single-phase earth faults were carried out. In the event of an incomplete single-phase earth fault, a drop in the zero-sequence current in the protected line invariably leads to a critical decrease in the sensitivity coefficient. There is a violation of the selectivity of the protection action, as a result of which the probability of electrical injury to the maintenance personnel increases. Boundary conditions for stable operation of relay protection and automation systems in case of incomplete single-phase earth faults are established. Definition of these conditions allows developing new algorithms for the operation of non-directional current protection in order to improve the electrical safety of the operating personnel.

Reliability Analysis of MV Electric Distribution Networks Including Distributed Generation and ICT Infrastructure

In recent years, the increased distributed generation (DG) capacity in electric distribution systems has been observed. Therefore, it is necessary to research existing structures of distribution networks as well as to develop new (future) system structures. There are many works on the reliability of distribution systems with installed DG sources. This paper deals with a reliability analysis for both present and future medium voltage (MV) electric distribution system structures. The impact of DG technology used and energy source location on the power supply reliability has been analyzed. The reliability models of electrical power devices, conventional and renewable energy sources as well as information and communications technology (ICT) components have been proposed. Main contribution of this paper are the results of performed calculations, which have been analyzed for specific system structures (two typical present network structures and two future network structures), using detailed information on DG types, their locations and power capacities, as well as distribution system automation applied (automatic stand-by switching on—ASS and automatic power restoration—APR). The reliability of the smart grid consisting of the distribution network and the coupled communications network was simulated and assessed. The observations and conclusions based on calculation results have been made. More detailed modeling and consideration of system automation of distribution grids with DG units coupled with the communication systems allows the design and application of more reliable MV network structures.

Clarke Transform Based Fast Assessment of Switching Overvoltages in an MV Distribution Network

The paper investigates the use of the Clarke transform in time-domain simulations, namely the evaluation of transient overvoltages in medium voltage (MV) distribution networks. A simplified Clarke equivalent circuit can be set up using readily available symmetrical components data used in steady-state studies, such as line series impedances and the aggregate MV network capacitance. Attention was focused on an existing 20 kV radial distribution system, a large mixed cable/overhead network operated with ungrounded neutral. The worst-case scenario of a single-line-to-ground (1LG) fault occurring at the end of a long overhead line was simulated by means of equivalent lumped-parameter Clarke circuits which were implemented and solved by means of ATP-EMTP. An extensive transient simulation parametric study was carried out using Clarke circuits with different degrees of simplification, and results were compared with those yielded by a complete 3-phase ATP model, evidencing a very good agreement and a drastic reduction of computation times.

Continuous Line Loss Calculation Method for Distribution Network Considering Collected Data of Different Densities

In order to find the causes of statistical line loss abnormalities and propose better loss reduction strategies, it is necessary to improve the accuracy of theoretical line loss calculations. Since Distributed Generation (DG) access to the distribution network causes variability of power flow in the distribution network within a short period, the error of the traditional line loss calculation method increases. For the line loss calculation of medium-voltage distribution networks containing DGs with high-density collection data, a continuous line loss calculation method for the distribution network was proposed, aiming at improving the accuracy compared with the traditional line loss calculation method. The proposed method makes full use of the high-density collection data on the dispatch side and DG side, distributing the supply power to each load node by power to calculate real-time power flow, thus obtaining a more credible line loss value. The effectiveness and accuracy of the proposed method were verified in the IEEE 17-node distribution system.

STUDI PEMECAHAN PENYULANG OMBILIN UNTUK PERBAIKAN DROP TEGANGAN DI PT PLN (PERSERO) RAYON PADANG PANJANG MENGGUNAKAN APLIKASI ETAP

Ombilin feeder is one of the longest feeders in PT. PLN (Persero) Rayon Padang Panjang. The total length of the medium voltage network is 117.116 Kms. With a large load, the length of the network and the cross-sectional area vary, causing a voltage drop in the feeder. According to SPLN 72:1987 the allowable voltage drop is 5%. Therefore, a solution is needed to reduce the voltage drop on the feeder to comply with PLN standards. One of them is by changing the load splitting. The loading pattern was changed by optimizing the cross-sectional area of the 240 mm2 AAAC wire which has a better KHA and a smaller impedance. To analyze and find out how much improvement the voltage drop is before and after the load splitting is done, a simulation is carried out using the ETAP 12.6 software. Based on the simulation results, the voltage drop before breaking the load in Baing is 6.67% with a voltage value of 19.413 KV and in Simawang data it is 6.71% with a terminal voltage value of 19.404 kV. After breaking the load, the voltage drop in Baing is 4.19% with a voltage value of 19.929 KV and in Data Simawang it is 4.23% with a terminal voltage value of 19.921 kV. Based on these results, the cause of the voltage drop is influenced by several things, namely the current flowing in the channel, the distance and cross-sectional area of the conductor used.Keywords: Load, Voltage Drop, ETAP.

Power system neutral point grounding

The method used for neutral point grounding is very important for power network operation. There are many ways of grounding, which are used in practice, and the decision on the method of neutral grounding depends on the situation in the network connected to the substation. When deciding on the method of neutral grounding it is necessary to thoroughly consider all the advantages and disadvantages of individual modes of neutral grounding, and then choose the best technical and economical solution. This paper analyzes the ways of neutral point grounding in medium voltage networks used in the current practice in Croatia which are isolated neutral point, low resistance earthing, partial compensation and resonant earthing. The use of shunt circuit-breaker is also described. Additionally, a survey of the relays used for the neutral point grounding system inside the substations was conducted and a brief analysis of the results is presented in the paper.

Integration of distributed generations by coordinating electric vehicle charging station in medium voltage network by Swarm intelligence

PurposeNotable energy losses and voltage deviation issues in low-voltage radial distribution systems are a major concern for power planners and utility companies because of the integration of electric vehicles (EVs). Electric vehicle charging stations (EVCSs) are the key components in the network where the EVs are equipped to energize their battery. The purpose of this paper is coordinating the EVCS and distributed generation (DG) so as to place them optimally using swarm-based elephant herding optimization techniques by considering energy losses, voltage sensitivity and branch current as key indices. The placement and sizing of the EVCS and DG were found in steps.Design/methodology/approachThe IEEE 33-bus test feeder and 52-bus Indian practical radial networks were used as the test system for the network characteristic analysis. To enhance the system performance, the radial network is divided into zones for the placement of charging stations and dispersed generation units. Balanced coordination is discussed with three defined situations for the EVCS and DG.FindingsThe proposed analysis shows that DG collaboration with EVCS with suitable size and location in the network improves the performance in terms of stability and losses.Research limitations/implicationsStability and loss indices are handled with equal weight factor to find the best solution.Social implicationsThe proposed method is coordinating EVCS and DG in the existing system; the EV integration in the low-voltage side can be incorporated suitably. So, it has societal impact.Originality/valueIn this study, the proposed method shows improved results in terms EVCS and DG integration in the system with minimum losses and voltage sensitivity. The results have been compared with another population-based particle swarm optimization method (PSO). There is an improvement of 18% in terms of total power losses and 9% better result in minimum node voltage as compared to the PSO technique. Also, there is an enhancement of 33% in the defined voltage stability index which shows the proficiency of the proposed analysis.