Medium Voltage Distribution Network Research Articles

A reliability-centered methodology for identifying renovation actions for improving resilience against heat waves in power distribution grids

In performance-based regulation paradigms, national authorities offer incentives to distribution system operators to develop plans for increasing the network resilience against natural hazards, such as heat waves, hurricanes, rain bombs, flooding. In this paper, we propose an approach, compliant with the Italian performance-based regulation framework, to prioritize renovation actions on sections of electrical power distribution networks for improving resilience against heat waves. The approach is made up of three steps, each addressed through a novel methodology: (i) define the hazard of interest, i.e., heat waves; (ii) estimate the reliability of the network branches; (iii) prioritize the renovation interventions on the network to improve its resilience. The methodology has been applied to the medium voltage distribution network of Milano, Italy, yielding the identification of prioritized intervention actions to submit to the authority for incentives.

Control and Monitoring Systems in Medium Voltage Distribution Networks in Poland – Current Status and Directions of Development

Control and Monitoring Systems in Medium Voltage Distribution Networks in Poland – Current Status and Directions of Development

A review of voltage and reactive power control algorithms in medium voltage distribution networks

Current power network was built in mind that there will be mostly one-way power transmission, but as there is increasing penetration of distributed generation (DG), power network evolves and changes. Thereof old control strategies and algorithms used in power distribution do not fully utilize ever evolving power network in ensuring minimum active power loses, best distribution power generation for optimal voltage and frequency control.The main objective of this paper is review and comparison of heuristic algorithms in medium-voltage (MV) distribution networks with high distributed generation (DG) penetration. The specific goal is integrating reviewed algorithms in distributer power network control to minimise power loss, control active and reactive power flow between transmission and distribution power networks and utilization of current power network structure with growing number distributed generation penetration and thus minimizing required cost for its upgrade. Due to complexity of different power network structures and control methods used in managing it, algorithms are reviewed used in ensuring fast and reliable calculations by guaranteeing as minimum active power loss as possible and by improving power system performance over existing centralised as well as decentralised control methods. For both control methods distributed generators requires to be endowed with communication capabilities, as it is effective in driving the voltages within the admissible intervals and, additionally, it exploits the cooperation among the distributed generators and controllers to reach power network objectives of minimal power loss, voltage stability as mentioned before.

Dynamic Impact Analysis of Integrating a 6 MW Solar Photovoltaic Power Plant into Medium Voltage Distribution Network

In this paper, the impact of integrating a 6MW solar PV plant installed in Zaouiet Kounta (Wilaya Adrar), in southwest Algeria into a medium voltage network during transient conditions is analyzed. This network is fed by two sources, either a grid source or a conventional power plant if a grid source is not available. Three different transient circumstances are considered in this analysis. The impact on voltage and frequency at the network’s main busbar as well as generator rotor angle is investigated. The analysis is carried out on the network by using ETAP software. The analysis results showed that the integration of this PV plant has an adverse effect on network performance during transient conditions when a Conventional power plant is used to feed network. Moreover, it has a slight effect on main busbar voltage when a grid source is used to feed network.

Research and Application of a Clear Diamond-Shaped Distribution Network Structure

Aiming at the problems of low power supply reliability, poor transfer capacity between stations, and low line utilization in the current distribution network, this paper proposes a diamond-shaped distribution network structure with a clear structure. First, we investigated the typical wiring patterns of medium-voltage distribution networks in Tokyo, Japan, Paris, France, and China’s developed cities, and summarized experience and shortcomings. Secondly, combining the typical wiring patterns of distribution networks in China and abroad, construct a diamond-shaped distribution network structure, and study its adaptability, safety and flexibility, power supply reliability, and economy. Finally, take the transformation of the wiring mode of a regional distribution network in a certain city as an example, compare the use of the diamond-shaped distribution network structure in this article with the use of cable double-ring network wiring, cable “double petal” wiring, and Shanghai diamond-type wiring distribution network grid reconstruction The effect verifies the superiority of the diamond-shaped distribution network structure in this paper.

Transition towards solar Photovoltaic Self-Consumption policies with Batteries: From the perspective of distribution networks

The transition towards low-carbon energy systems requires increasing the contribution of residential Photovoltaic (PV) in the energy consumption needs (i.e., PV self-consumption). For this purpose, the adoption of PV self-consumption policies as alternatives to the current net-metering policy may support harnessing batteries to improve PV self-consumption. However, the technical impacts of PV policies on distribution networks have to be adequately assessed and mitigated. To do so, a two-stage planning framework is proposed. The first stage is an optimization approach that determines the best sizes of PV and batteries based on the adopted PV policy. The second stage assesses the impacts of the resulting sizes on distribution networks using Monte-Carlo simulations to cope with uncertainties in demand and generation. The framework is applied on real medium and low voltage distribution networks from the south of Jordan. For the net-metering, the results show that the uptake of residential PV penetration above 40% will result in voltage issues. It is also found that the adoption of batteries for the benefits of customers (i.e., reduce electricity bills) will not mitigate the PV impacts for PV penetration above 60%. Further, the results demonstrate the important role of distribution network operators to manage the uptake of batteries for the benefits of customers and distribution networks. Network operators can support customers to adopt larger sizes of batteries to achieve the desired PV self-consumption in return of controlling the batteries to solve network issues. This facilitates the uptake of 100% PV penetration and improves PV self-consumption to 50%.

Optimization of the Configuration and Operating States of Hybrid AC/DC Low Voltage Microgrid Using a Clonal Selection Algorithm with a Modified Hypermutation Operator

The issue of optimization of the configuration and operating states in low voltage microgrids is important both from the point of view of the proper operation of the microgrid and its impact on the medium voltage distribution network to which such microgrid is connected. Suboptimal microgrid configuration may cause problems in networks managed by distribution system operators, as well as for electricity consumers and owners of microsources and energy storage systems connected to the microgrid. Structures particularly sensitive to incorrect determination of the operating states of individual devices are hybrid microgrids that combine an alternating current and direct current networks with the use of a bidirectional power electronic converter. An analysis of available literature shows that evolutionary and swarm optimization algorithms are the most frequently chosen for the optimization of power systems. The research presented in this article concerns the assessment of the possibilities of using artificial immune systems, operating on the basis of the CLONALG algorithm, as tools enabling the effective optimization of low voltage hybrid microgrids. In his research, the author developed a model of a hybrid low voltage microgrid, formulated three optimization tasks, and implemented an algorithm for solving the formulated tasks based on an artificial immune system using the CLONALG algorithm. The conducted research consisted of performing a 24 h simulation of microgrid operation for each of the formulated optimization tasks (divided into 10 min independent optimization periods). A novelty in the conducted research was the modification of the hypermutation operator, which is the key mechanism for the functioning of the CLONALG algorithm. In order to verify the changes introduced in the CLONALG algorithm and to assess the effectiveness of the artificial immune system in solving optimization tasks, optimization was also carried out with the use of an evolutionary algorithm, commonly used in solving such tasks. Based on the analysis of the obtained results of optimization calculations, it can be concluded that the artificial immune system proposed in this article, operating on the basis of the CLONALG algorithm with a modified hypermutation operator, in most of the analyzed cases obtained better results than the evolutionary algorithm. In several cases, both algorithms obtained identical results, which also proves that the CLONALG algorithm can be considered as an effective tool for optimizing modern power structures, such as low voltage microgrids, including hybrid AC/DC microgrids.

Fault Location for Underground Cables in Ungrounded MV Distribution Networks Based on ZSC Signal Injection

A distributed zero-sequence-current (ZSC) carrier signal injection via current transformer (CT) is proposed for underground cable single-phase-to-ground fault location in neutral isolated medium voltage (MV) distribution networks. High-frequency ZSC carrier signal is directly injected to a high-voltage underground cable of an energized distribution network via CT. The injected carrier signal travels along the cable to the receiving center in the substation, and is processed for quick fault line selection and fault location. No external power supplies or signal generators are needed due to the self-contained nature of the injector. The device can be constructed as a sleeve to be mounted around the underground power cable. This permits economical retrofitting to existing installations of power line communication (PLC) devices. In this paper, the operational principle and the application considerations for such an injection device and fault location tricks are explained, followed by the theory behind the proposed technique. Finally, MATLAB based numerical simulations are performed and a low-voltage prototype is tested to verify the validity of the proposed approach.

Optimization of recloser methods on medium voltage distribution networks

Reassessing methods within a business is important as it can prove certain concepts could indeed work, improve current methods and reinforces knowledge to the assessors. The utility’s (Eskom) recloser placement methodology mainly focuses on improving their performance figures and reaching their performance targets and does not focus on the financial aspect of their methods. The purpose of this paper is to present a method that will optimize the placement of reclosers on medium voltage distribution networks. Eskom can by focusing on the financial aspects of the recloser placements, benefit by improving performance as well as saving money at the same time, especially during fault conditions. A cost-benefit analyses methodology is applied where data is derived from a medium voltage distribution network in the Free State that serves more than 2000 customers. The number of reclosers and the placement of them will be determined by using matrix tables and formulas. Data was extracted from the utility record systems. The findings suggested that a recloser can pay itself back within one year using this method. In order to make an informed decision as to the placing of a recloser on a medium voltage distribution network, it is recommended to use the proposed method. The proposed method will assist in the decision as to the viability of placing a recloser on a specific pole location. Future studies may be done by combining recloser placement methods with other protection sensing equipment like fault path indicators and current-voltage monitoring systems to isolate and find faults.

Wavelet Analysis-Based Simulation Study Of Small-Current Ground Fault System Routing

Small-current grounding is commonly used in medium-voltage distribution networks in China, including ungrounded neutral points, grounding via arc extinguishing coil and resistance grounding. In this paper, the power system modeling simulation of the grounding system via arc extinguishing coil and the transient characteristics when single-phase grounding occurs are studied. The principles and methods for selecting the wavelet basis function in transient component line selection are given. Wavelet analysis of the line current is carried out. It is verified by simulation that the wavelet analysis method in the small current ground fault selection can compare the difference of different lines.

Conditional Multivariate Elliptical Copulas to Model Residential Load Profiles From Smart Meter Data

The development of thorough probability models for highly volatile load profiles based on smart meter data is crucial to obtain accurate results when developing grid planning and operational frameworks. This paper proposes a new top-down modeling approach for residential load profiles (RLPs) based on multivariate elliptical copulas that can capture the complex correlation between time steps. This model can be used to generate individual and aggregated daily RLPs to simulate the operation of medium and low voltage distribution networks in flexible time horizons. Additionally, the proposed model can simulate RLPs conditioned to an annual energy consumption and daily weather profiles such as solar irradiance and temperature. The simulated daily profiles accurately capture the seasonal, weekends, and weekdays power consumption trends. Five databases with actual smart meter measurements at different time resolutions have been used for the model's validation. Results show that the proposed model can successfully replicate statistical properties such as autocorrelation of the time series, and load consumption probability densities for different seasons. The proposed model outperforms other multivariate state-of-the-art methods, such as Gaussian Mixture Models, by one order of magnitude in two different distance metrics for probability distributions.

A hybrid charging management strategy for solving the under-voltage problem caused by large-scale EV fast charging

A hybrid charging management system (HCMS) is proposed to solve the nodal under-voltage problem in medium-voltage radial distribution networks caused by the concentrated high-power charging of electric vehicles (EVs), which contains a pre-centralized charging management platform (PCMP) and local charging management controllers (LCMCs) located at fast charging stations (FCSs). The proposed PCMP can formulate half-hourly charging power threshold plans for LCMCs based on a pre-centralized voltage regulation algorithm (PVRA) to prevent concerned nodes from under-voltage. Two sub-strategies, i.e., charging management sub-strategy (CMS) and cooperative control sub-strategy (CCS), are integrated in the LCMS, which can aggregate EVs charging at different FCSs to provide the voltage support service for the concerned node, so that the under-voltage problem of these concerned nodes can be alleviated. The load forecasting error, load uncertainty, and the need of the plug-and-play are considered as well. Finally, an IEEE 69-bus test system is used for simulation verification. Simulation results verify that the HCMS can be used to solve the nodal under-voltage problem caused by centralized high-power charging of EVs.

Permanent Closed-Loop Operation as a Measure for Improving Power Supply Reliability in a Rural Medium Voltage Distribution Network

Power supply reliability is one of the critical elements of power quality. Its improvement in medium voltage distribution systems in urban areas is typically achieved by cabling. Unfortunately, this approach is often too expensive to be applied in rural areas. One of the possible alternative solutions that can be used in rural medium voltage distribution networks is permanent closed-loop operation. It requires the introduction of additional reclosers with properly parametrized protection relays enabling directional protection. This paper focuses on the case study performed in the 20 kV rural distribution network of Elektro Celje d.d.. Two feeders, where the reliability of the power supply was low, were analyzed. Results of techno-economical evaluation eliminated cabling as a viable solution. The permanent closed-loop operation was selected and implemented after proper placement and parameterization of relays with directional protection functions. The results of two years operation in permanent closedloop arrangement of feeders show substantial improvement in the reliability of power supply.

The Influence of the Characteristics of the Medium Voltage Network on the Single Line-to-Ground Fault Current in the Resistor Grounded Neutral Networks

One important problem in the operation of medium voltage networks is the detection of a single-line-to-ground fault in its incipient state, when the fault resistance values are very high. In a medium voltage (MV) distribution network with a neutral grounding resistor (NGR), one of the methods employed to discriminate a single line-to-ground fault is the use of an overcurrent relay with an operating characteristic adjusted according to the effective value of the current flowing through the limiting resistor. In case of a single line-to-ground fault with a high fault resistance value, the correct tripping settings of the protective relay require the precise computation of this current. In comparison to the assumptions made by the models from the literature—the three-phase voltage system of the medium voltage busbars is symmetrical and there are no active power losses in the network insulation—the model proposed in this paper considers the pre-fault zero-sequence voltage of the medium voltage busbars and the active power losses in the network insulation, which is necessary in certain fault conditions where the use of the former leads to unacceptable errors.

On damage rate of overhead power transmission lines in power supply systems

The purpose of the article is to analyze the damage rate of overhead power transmission lines (OPL) in medium-voltage electrical distribution networks of the Irkutsk region. The established International Indices that determine the level of reliability of the functioning of electric networks are considered, and information on the compliance of the condition of electric networks in Russia with these indices is analyzed. Analytical information on the damage rate of elements of these networks and their causes in Europe, America, and Russia is presented. The emphasis is placed on the fact that the most common damage is characteristic of overhead power lines, especially 6–10 kV lines. As an object of research, two branches of the Irkutsk electric grid company (IEC) were taken, one of which provides electricity to rural consumers, the other — mainly to consumers residing in the territory of the city Irkutsk. The characteristics of these electric networks, their territorial location and basic technical data are presented. To conduct analytical monitoring of the level of reliability of overhead power transmission lines, logs of disconnection of the Eastern and Southern electric networks of the IEC over a long-term period were used. On the basis of this information, tables of failures and their consequences in the studied electrical networks were compiled for monthly average data over the period under examination for various causes of damage. To plot time diagrams of the parameters under examination, computer programs were compiled in the Matlab system, the use of which made it possible to obtain visualization of changes in failures for various reasons for the electrical networks under consideration. The information on the time of power supply interruptions in these networks, as well as the amount of electricity underutilized by consumers during these interruptions and its cost are analyzed. It is shown that in the electric networks under consideration, most of the power failures are related to the territorial dispersion of these networks, and the low level of equipment controls and insufficient qualification of operating personnel, as evidenced by the significant number of failures for unknown reasons. Besides, a significant part of the failures is due to damage to the overhead line wires, switching equipment and the effect of wind load. Recommendations for improving the condition of power transmission lines and a number of measures aimed at improving the level of reliability of power supply are presented.

Monte Carlo analysis for solar PV impact assessment in MV distribution networks

The rapid penetration of solar photovoltaic (PV) systems in distribution networks has imposed various implications on network operations. Therefore, it is imperative to consider the stochastic nature of PV generation and load demand to address the operational challenges in future PV-rich distribution networks. This paper proposes a Monte Carlo based probabilistic framework for assessing the impact of PV penetration on medium voltage (MV) distribution networks. The uncertainties associated with PV installation capacity and its location, as well as the time-varying nature of PV generation and load demand were considered for the implementation of the probabilistic framework. A case study was performed for a typical MV distribution network in Malaysia, demonstrating the effectiveness of Monte Carlo analysis in evaluating the potential PV impacts in the future. A total of 1000 Monte Carlo simulations were conducted to accurately identify the influence of PV penetration on voltage profiles and network losses. Besides, several key metrics were used to quantify the technical performance of the distribution network. The results revealed that the worst repercussion of high solar PV penetration on typical Malaysian MV distribution networks is the violation of the upper voltage statutory limit, which is likely to occur beyond 70% penetration level.

A Linear AC Power Flow Model for Unbalanced Multi-Phase Distribution Networks Based on Current Injection Equations

A realistic and practicable modeling of unbalanced distribution networks (DNs) is the missing link in most studies undertaken in these networks, e.g., optimal power flow (OPF), energy markets, etc. To address the issue, this letter proposes an unbalanced linear three-phase four-wire power flow (PF) model based on current injection equations at nodes. Also, the ZIP representation is considered for loads. The model can be easily generalized for unbalanced three-wire networks with minor changes and assumptions. Hence, the scope of the proposed method can be extended to cover both low-voltage and medium-voltage DNs. The performance of the proposed model is verified through simulations on two IEEE test feeders.

Automatic routing of medium voltage distribution network based on load complementary characteristics and power supply unit division

In view of the problems of large network scale and low equipment utilization efficiency caused by the lack of consideration of load complementary characteristics in the current distribution network planning, a new practical automatic routing method of medium voltage distribution network considering load complementary characteristics and power supply unit division is proposed. Firstly, based on the existing conclusions of load clustering and gridding planning, the concepts of feeder block and power supply unit of medium voltage distribution network are redefined, and the framework of medium voltage distribution network planning considering the power supply unit division is proposed. Secondly, the evaluation indexes of feeder block division and power supply unit division considering the load complementary characteristics are proposed, and a centerline swing distance weighted clustering algorithm is proposed, which is used to realize the feeder block division. Thirdly, considering the annual comprehensive cost of line planning and the outage loss cost based on reliability index, the medium voltage distribution network planning model is established based on the power supply unit division. The automatic routing method is proposed based on ant colony algorithm, which is used to realize the combinatorial solution of the trunk line and branch line. Finally, an example is given to verify the scientificity and practicability of the model and method proposed in this paper.

Mid-term operational planning of pre-installed voltage regulators in distribution networks

In this paper, a methodology is presented to maximize the effectiveness of pre-installed Voltage Regulators (VRs) in medium voltage distribution networks. While considering the daily tap operation limitation of VRs, this method contains mid-term operational planning of VRs' settings which is carried out to satisfy voltage constraints in distribution networks and reduce power losses throughout the network. The proposed approach optimizes the settings periodically, leading to Distribution System Operators (DSOs) ' financial benefit because energy losses are reduced by applying the proposed method. Using different combinations of ZIP load model coefficients in the optimization process, the importance and impacts of the load model in the optimization of VRs' settings are also investigated because the operation of a VR directly influences the consumption of voltage-dependent loads (depending on their type of voltage dependency). Due to the discrete nature of the problem, the Genetic Algorithm (GA) has been employed as a tool to attain the previously mentioned goals by optimizing the settings of VRs for forthcoming months. Numerical studies carried out for a 70-bus distribution network show that a reduction of energy loss is achieved by applying the article's proposed method.

Performance Evaluation of Solar PV Inverter Controls for Overvoltage Mitigation in MV Distribution Networks

The incorporation of real and reactive power control of solar photovoltaic (PV) inverters has received significant interest as an onsite countermeasure to the voltage rise problem. This paper presents a comprehensive analysis of the involvement of active power curtailment and reactive power absorption techniques of solar PV inverters for voltage regulation in medium voltage (MV) distribution networks. A case study has been conducted for a generic MV distribution network in Malaysia, demonstrating the effectiveness of fixed power factor control, Volt–Var, and Volt–Watt controls in mitigating overvoltage issues that have arisen due to the extensive integration of solar PV systems. The results revealed that the incorporation of real and reactive power controls of solar PV inverters aids in successfully mitigating overvoltage issues and support network operating conditions. Furthermore, the comparative analysis demonstrated the importance of employing the most appropriate control technique for improved network performance.