Medium Voltage Power Distribution Network Research Articles

Coordinated restoration optimization of power-gas integrated energy system with mobile emergency sources

In an integrated energy system (IES) composed of multiple subsystems, energy coupling causes an energy supply blockage or shutdown in one subsystem, thereby affecting the energy flow distribution optimization of other subsystems. The energy supply should be globally optimized during the IES energy supply restoration process to produce the highest restoration net income. Mobile emergency sources can be quickly and flexibly connected to supply energy after an energy outage to ensure a reliable supply to the system, which adds complexity to the decision. This study focuses on a power- gas IES with mobile emergency sources and analyzes the coupling relationship between the gas distribution system and the power distribution system in terms of sources, networks, and loads, and the influence of mobile emergency source transportation. The influence of the transient process caused by the restoration operation of the gas distribution system on the power distribution system is also discussed. An optimization model for power-gas IES restoration was established with the objective of maximizing the net income. The coordinated restoration optimization decision-making process was also built to realize the decoupling iteration of the power-gas IES, including system status recognition, mobile emergency source dispatching optimization, gas-to-power gas flow optimization, and parallel intra-partition restoration scheme optimization for both the power and gas distribution systems. A simulation test power-gas IES consisting of an 81-node medium-voltage power distribution network, an 89-node medium-pressure gas distribution network, and four mobile emergency sources was constructed. The simulation analysis verified the efficiency of the proposed coordinated restoration optimization method.

Inductive coupling-based narrowband PLC systems for overhead MV power distribution networks: New insights

This paper advances the investigation of the adequacy of inductive coupling-based narrowband power line communication (PLC) systems in overhead medium voltage power distribution networks (MV-PDNs). Relying on raw data obtained from a measurement campaign which was carried out in urban and rural feeders in the south region of Brazil, it shows that overhead MV-PDNs may be a challenging data communication media when considering inductive coupling devices since the level of insertion losses associated with the coupling process is relevant. Also, the presence of significant loads between the source and destination nodes can severely degrade loops of currents, which are necessary to perform data communication in an inductive coupling-base PLC system, resulting in an erasure data communication media. For the reliable links (i.e., without erasure), the performance analysis shows that PLC channel impulse responses and additive noises can be respectively modeled as time-invariant systems with a quasi-flat channel frequency magnitude and white Gaussian random processes in urban and rural areas. Last but not least, an attenuation model and achievable data rates are discussed for the reliable links.

Mapping of Electrical Distribution Networks at Jampit Distribution Substations Using ArcGIS

In the Ijen sub-district, care must be taken to avoid overlapping uses of PTPN XII-owned plantations, resident fields, and the medium-voltage power distribution network. To lessen the interference factor in the distribution of electricity, the proper power distribution path must be chosen. The contact between trees and lightning is one of the variables that disturbs the distribution pathway. It is well known that the Jampit distribution substation in the Ijen district is situated in a region with plantations and private fields, making it susceptible to lightning and contact with trees. The position of distribution substations, medium-voltage overhead lines, and the location of energy users are among the issues examined in this study. In order to create a map of the electricity distribution network at Jampit distribution substations that pass through agricultural land and plantation areas, ArcGIS is used to help process spatial data including regional administration data, type of conductor, power capacity, distribution substation poles and electricity users.

Optimal Routing and Design of Radial Medium Voltage Power Distribution Networks Considering Cables Short Circuit Withstand-Capacity

Cables short circuit withstand-capacity plays a crucial role in medium voltage distribution system design. For a given short circuit level at substation, fault current at any point in a radial distribution system depends on the location with respect to the substation, distributed generation as well as size and length of upstream cable sections. This paper addresses optimal routing, cable sizing, distributed generation allocation and sizing of radial medium voltage power distribution network considering cables short circuit withstand capacity. Both synchronous-based and inverter-based distributed generators are considered. Complete formulation of cables short circuit constraints (SCCs) is introduced in mixed-integer linear programming (MILP) form. A Benders-decomposition-based approach is used to solve the problem by considering short circuit at each system bus in a separate slave feasibility problem. Combinatorial cuts are proposed to exclude infeasible solutions in each iteration by investigating upstream routes, cable sizes and distributed generation. The proposed optimization framework and solution algorithm are applied on 54 bus, 84 bus and 138 bus systems. The results revealed potential saving in investment, maintenance and losses costs compared to upgrading method. Also the proposed solution algorithm showed great saving in the number of added constraints to the original problem.

Convolutional Neural Network and Long-Short Term Memory based for Identification and Classification of Power System Events

In this present era, power system delivery has to be reliable and sustainable. The growth of demands increasing the complexity of the power system operations. An interrupted power supply must not occur for any reason. Hence, the improvement of the controller and protection devices is mandatory. One of the unnecessary interruptions in the power system is a false trip due to the incorrect setting of the protection devices. Therefore, a method to classify the symptom of the power system based on the voltage, current, and frequency measurements is required. However, since there are a ton of maneuver options and fault types, the number of data becomes complex, enormous, and irregular. This is where deep learning takes place. This paper proposed the use of Convolutional Neural Networks (CNN) combined with Long-Short Term Memory (LSTM) to recognize the categorize the type of events in a medium voltage power distribution network. As CNN's models are great at decreasing frequency variation, LSTM is great for temporal modeling, we take benefit of CNN's and LSTM's complementarity in this study by integrating it into a unified architecture. The simulation results indicate that CNN and LSTM can recognize the symptoms in power system operation with accuracy up to 79 % with a total epoch 350.

Smart Meter Based Two-Layer Distribution System State Estimation in Unbalanced MV/LV Networks

This article presents a smart meter based two-layer state estimation technique, design to enable integrated monitoring of medium-voltage (MV) and low-voltage (LV) power distribution networks. The main contributions of this work include the development of a novel topology reduction technique for LV networks in order to carry out state estimation with a reduced number of smart meter based measurements, and a linear LV state estimation technique, which reduces convergence problems in LV networks. In addition, a detailed framework for integrated MV/LV network state estimation in realistic, unbalanced three-phase networks is proposed and demonstrated using the IEEE 13 bus and IEEE 906 LV networks. The results suggest that the proposed two-layer state estimation technique is robust and provides improved distribution system state estimation accuracy compared to traditional approaches.

Orthogonal Chirp-Division Multiplexing for Power Line Sensing via Time-Domain Reflectometry

In this study, a time-domain reflectometry (TDR) system based on a baseband version of the orthogonal chirp-division multiplexing (OCDM) scheme, which is relies on a modified discrete Fresnel transform (DFnT), is proposed for power line sensing. After a detailed description of the system model, a multiple access scheme that exploits the contolution theorem of the modified DFnT for enabling distributed reflectometric and transferometric sensing of the monitored power line. Considering typical European underground low-voltage and US overhead medium-voltage (MV) power distribution networks, range resolution and maximum unambiguous range for the measurements are assessed for the proposed scheme. Next, a comparison with multiple access schemes based on the Hermitian symmetric orthogonal frequency-division multiplexing (HS-OFDM) discussed in a previous work is performed considering a Brazilian MV overhead scenario, being the number of measurements obtained over time, as well as signal-to-interference-plus-noise ratio (SINR) used as performance metrics. The attained results show that the proposed multiple access scheme results in the same range resolution as the others. Also, the highest number of measurements over time is obtained by the proposed scheme, which produces orthogonality among signals transmitted by different power line modems (PLMs) neither and time nor frequency domains, but rather in the Fresnel domain. Meanwhile, although its yielded SINR values are fair among the PLMs consisting the distributed sensing system, the proposed scheme is slightly outperformed by the HS-OFDM based on code-division multiple access and by the HS-OFDM based on frequency-division multiple access at some PLMs.

High Frequency Solid State Transformer Design Considerations for Power Systems Applications

The conventional power frequency (50 or 60 Hz) transformers are economical, highly reliable and quite efficient but they suffer with certain drawbacks like sensitive to harmonics, voltage drop under load, no protection from system disruptions and overloads, poor performance under dc offset load unbalances and no scope to improve power factor. These transformers with copper wound wires on iron cores are unable to respond to control signals as power generations become distributed and intermittent. So, the need of electronic based regulated power supply with software based remote intelligence has become essential. Also, to easily connect the new energy sources to the grid and to improve the power quality by harmonic filtering, voltage sag correction and highly dynamic control of the power flow, a new type of transformer based on power electronics, known as SST has been introduced. The SST realizes voltage transformation, galvanic isolation, power quality improvements such as instantaneous voltage regulation, voltage sag compensation and power factor correction. It is a collection of high-powered semiconductor components, high frequency power transformer and control circuitry which is used to provide a high level of flexible control to power distribution networks. The SST is a high frequency switched Power Electronic Devices (PEDs) based transformer with high controllability that enables flexible connectivity between existing medium voltage power distribution network, low voltage AC residential system and envisioned DC residential system. In this paper a systematic constructional detail of a SST with a power rating of 2 kVA, operating frequency of 20 kHz and voltage rating of 600/60 V as a scaled-down prototype used for power converter topologies is presented. The design is simple and it avoids the difficulty of choosing massive amounts of empirical parameters.

Power Demand Forecast for Optimization of the Distribution Costs

The aim of the paper is to investigate and develop of a method for reducing the own technological consumption in distribution networks involving the power demand forecast. In order to solve the mentioned main objective it is proposed an optimization model that is built on the main characteristics of a medium and low voltage power distribution network. In order to validate the developed solution a study, discussion, recommendations and conclusions are formulated based on real experimental data.

Effects of imbalance on single-phase to ground fault characteristics in low-resistance grounded systems

Single-phase to ground faults (SPGFs) are common in low-resistance grounded systems (LRGSs), a type of medium-voltage power distribution network (MVDN). Imbalance is one of the main characteristics of MVDNs. However, there has been little research on the effects of imbalance on SPGF characteristics in LRGSs, especially from the perspective of theoretical analysis. Hence, in this study, a controlled source-based simplified linear model suitable for calculating SPGFs in unbalanced LRGSs is proposed. Based on the model, the effects of unbalanced loads and asymmetrical lines on SPGF are discussed. The analysis results show that “zero-sequence (ZS) parameter intrusion” of loads is absent in LRGSs, and asymmetrical line parameters have a substantial effect on the phase angle between the ZS line current and the ZS bus voltage, which is related to the fault resistance, fault phase and line parameters. Finally, two phase-related detection methods are analyzed, and both methods produce erroneous detection results. Therefore, it is recommended that the effects of imbalance be considered when using detection methods based on the relationship between the voltage and current in LRGSs.

Review on design and control of solid state transformer based microgrids

Solid state transformer (SST) is a high frequency switched power electronic based transformer with high controllability that enables flexible connectivity between existing medium voltage power distribution network, low voltage AC residential system and envisioned DC residential system. The SST is not a direct replacement of a conventional low frequency transformer, but a multi-purpose device that offers improved functionalities. The demanded requirements of the future power systems such as integration of distributed generation, DC loads and storage have enabled the microgrid technology to evolve. This paper is focused on the SST as an intermediary tool for microgrids. An overview of existing and possible SST based microgrid designs and control architectures, their advantages, disadvantages and the identified selection criteria are presented. With a special focus on existing experimental setups, the paper is concluded highlighting the possible areas of research that would enhance the integration of the SSTs into microgrids in the future.

Approach for identification and classification of HIFs in medium voltage distribution networks

The modern power system operation is faced with numerous challenges related to the power quality improvements such as identification and classification of power distribution network (PDN) faults. The recent advances in the area of signal processing allow the development of new algorithms and methods which can be used for fault identification and classification in PDN. This study presents a comparison of two approaches for identification and classification of high-impedance faults (HIFs) in medium-voltage PDN. The first approach is based on the voltage phase difference algorithm, whereas the second approach is based on the combination of discrete wavelet transform and artificial neural networks algorithm. The proposed algorithms are tested on models of a real distribution network, which represents a typical PDN currently used in Bosnia and Herzegovina. It was demonstrated that the proposed methods are capable to accurately detect and classify HIF in PDN. This study makes a contribution to the existing body of knowledge by developing, testing and comparing two methods for HIF classification and identification, whose application represents an improvement when compared with the capability of the existing protection devices.

Single-Loop Optimization for Losses Minimization in Medium-Voltage Power Distribution System

One important goal during the reconfiguration of a medium-voltage power distribution network is to minimize the active-power losses of the system. Therefore, the objective function of an optimization problem would represent the total power losses of the distribution system, by considering only the active component of power losses while ignoring the reactive part. Constraints would be load flow, voltage drop, and the network configuration. In this paper, losses problem during the reconfiguration of a medium-voltage power distribution system have been minimized using a single-loop optimization method, whereas the load-flow analysis has been performed by utilizing the Newton-Raphson method. The optimization method was aimed to minimize the active-power losses of the system by formulating the problem as a matter of network reconfiguration. The solution scheme has been begun with a mesh distribution-network which had been obtained previously by assuming all the switches to be closed and then opened sequentially to eliminate loops. The optimization results showed that in a 21-bus distribution system there had been 10800 combinations, in which the lowest power losses occurred under the combination of NO 23, NO 21, NO 22, NO 24, NO 25, whereas the combination of NO 7, NO 10, NO 20, NO 15, NO 20, resulted in the power losses of 0.1676 per unit, being equal to 16.76 kVA at the base power of 100 kVA.

Support Vector Machine Based Method of Earthed Fault Location in Neutral Un-Effectual Grounded Power System

Abstract. Neutral un-effectual grounded system (NUGS) is widely used in Chinese medium voltage power distribution network. However, existing earthed fault location methods in NUGS are not satisfactory in practical application due to weak fault current and unstable arc. Based on analysis of spectrum characteristics of current signals in single-phase earthed fault feeder, this paper proposed an earthed fault location method based on support vector machine (SVM). Firstly, the zero sequence current signal was sampled, and its spectrum was gotten by discrete Fourier transform. Secondly, the three dimensional feature vector that constituted by fundament, harmonic, inter harmonic component, had been extracted as the input of SVM. Furthermore, the SVM was trained with the samples obtained by simulation under different fault distance, different fault resistance and different fault close angle. Finally, the earthed fault feeder is selected using the trained SVM. The simulation results indicate that the fault location by the presented method is more precise.

Distributed Generation Effects on Large-Scale Distribution Networks

This paper examines the results of the distributed generation penetration in large-scale medium-voltage power distribution networks. The network examined as a study case consists of twenty one lines fed by three power substations. The injected power comes mainly from photovoltaic units. Specifically, the influences of distributed generation on the network branch currents, losses and voltage profile as well as on the short-circuit level at the medium voltage busbars of the infeeding substations are examined according to international and national standards. The arising problems are explored and technical solutions are proposed. This paper is a pilot application as general conclusions concerning the extended distributed generation penetration in real power distribution networks are set out.

Power Restoration in Medium Voltage Network Using Multiagent System

The article describes a novel approach to a power restoration in medium voltage power distribution network. It focuses primary at searching of a new network configuration enabling to minimalize the size of faulted area and to restore the power for the highest possible number of loads. It describes characteristic features of medium voltage power distribution network and discusses the implementation of the presented approach in existing networks. A software tool, developed by the authors, including physical simulation of model network and its autonomous control system is described. An example of fault situation in a virtual distribution network is presented. Afterwards, the solution of restoration problem by proposed multiagent system is simulated using the software tool described in the paper.

Mixed distributed generation technologies in a medium voltage network

This paper examines the results of the penetration of mixed distributed generation technologies in a medium-voltage power distribution network. Specifically, the connected distributed generation resources are mainly photovoltaic units, a wind farm, and a hydroelectric plant; these all operate with different power factors. Their influence on the network currents, losses, voltage profile, and the short-circuit level at the medium-voltage busbars of the infeeding substation are examined for differed load conditions according to international and national standards. The problems that arise are explored through parametric investigations concerning the operating characteristics of the connected units. Furthermore, the optimum allocation of the same or different types of distributed generation resources to the examined network is determined in order to obtain the maximum penetration without technical problems. Finally, general conclusions regarding the handling of the relevant practical problems are given.

Power Factor Optimization of Distributed Generations in Distribution Networks Based on Improved Particle Swarm Optimization Method

The gradually extensive penetration of small-scale distributed renewable generators in existing medium-voltage power distribution networks highlights many technical challenges which call for urgent solutions from power utilities. This paper attempts to optimize the power factor of distributed generators (DGs) integrated in distribution networks and presents a novel algorithmic solution. With the aim of minimizing power loss whilst maintaining the node voltage, the problem is formulated with a mathematical model elaborating the DGs and a set of constraints in distribution networks and addressed through adopting an extended particle swarm optimization (PSO) approach. The suggested algorithm is assessed through numerical simulation experiments with the IEEE 33-bus system and the outcome shows that the optimization algorithm can effectively reduce the power loss and promote the node voltages across the overall distribution network.

The Selection Algorithm for Connection Modes of Medium Voltage Power Distribution Network Based on FAHP-GRA

This paper used fuzzy analytic hierarchy process (FAHP) and gray relational analysis (GRA) to solve the selection for the connection modes of medium voltage (MV) power distribution network. Firstly, it established the comprehensive evaluation indicator system from technicality, economy, and adaptability. Secondly, FAHP can evaluate the indicator weights, and avoid the ambiguity and uncertainty of judgment matrix. Finally, it combined with GRA to complete the comprehensive decision-making. This method also solves the error of the fuzzy albino number caused by fuzzy comprehensive evaluation theory. In the end, a practical example verified the reasonable and practical of this method.

Optimum allocation of the maximum possible distributed generation penetration in a distribution network

In this paper a method is proposed to determine the optimum allocation of the maximum distributed generation penetration in medium voltage power distribution networks. The method is based on an already-known but suitably modified and optimized method. Technical constraints, such as thermal rating, transformer capacity, voltage profile and short-circuit level are considered. A real network with already installed distributed generation resources is examined as a case study. The type, locations and ratings of these resources are predetermined. The satisfaction of the aforementioned technical constraints is examined initially in the framework of the existing network situation. The problems observed are solved by applying the required modifications in the network structure. Next, the proposed method is used to determine the optimum allocation of the maximum distributed generation penetration either in the predetermined network buses or in other random buses, in order to overcome the technical problems, without changing the network structure. Finally, the results are suitably estimated and extended in order to allow for more general conclusions concerning real power distribution networks.