Medium Voltage Distribution Feeders Research Articles

Improving the distribution system capability by incorporating ZnO nanoparticles into high-density polyethylene cable materials

This paper introduces a novel insulated cable designed to enhance the distribution system’s capabilities. Accordingly, high-density polyethylene loaded with varying concentrations of zinc oxide (ZnO) nanoparticles (NPs) ranging from 0.0 to 5 wt% was prepared using the melt-blending technique. Zinc oxide (NPs) is synthesized by using sol–gel technique and their microstructure was examined by X-ray diffraction. The new insulated cable, HDPE nanocomposite loaded with 1 wt% of ZnO, demonstrates a 43% reduction in the relative dielectric constant and a 16.5% improvement in breakdown strength compared to pure HDPE. The observed changes in both the dielectric constant and breakdown strength offer several advantages in electrical applications. These benefits include a decrease in feeder current at the same loading level, mitigation of inrush transients during load switching, and a reduction in earth fault current values, particularly in unearthed distribution networks with ungrounded cables. A comparative study is conducted between the conventional insulating cable based on the original material (HDPE) and the new insulated cable incorporating ZnO nanomaterial at a ratio of 1.0 wt% of the total cable mass per unit length. This comparison utilizes data from two actual medium-voltage distribution feeders. Both actual feeders are simulated using the EMTP/ATP package. The obtained results prove the efficacy of the developed material cable (polymer doped with ZnO NPs) compared to the base material. The peak and duration of inrush current can be cut to 77.3% and 67% of their original values, respectively. The earth fault current can be reduced to 56.5% in ungrounded networks, while substation current under the normal operation can be cut to 84.3% with the same load currents.

Medium-voltage distribution feeders in closed-loop arrangement – neutral point grounding

This paper deals with medium-voltage networks where the closed-loop arrangement of feeders is used to improve the reliability of power supply. The paper focuses on the neutral point grounding in the medium-voltage loops. They are established by closing feeders, supplied form different transformers, in closed-loop arrangement. It is shown in the case when the neutral points of transformers supplying the feeders are grounded, the fault current at the fault location can be doubled, without to influence the neutral point current, which could cause safety problems.

Evaluation of Medium Voltage Distribution Network with/without Distributed Generation using ATP Software

This research has as main objective to analyze the contributions of a distributed generation unit when connected to a medium voltage distribution feeder (13.8 kV). The behaviour this electrical system is evaluated following the occurrence of some disturbances. Before this, all the modelling of the electrical system was performed using ATP - Alternative Transients Program. Three types of disturbances were simulated: phase-to ground short-circuit, islanding of part of the electrical system and load increase on the feeder. To easy the comparisons, all studies were carried out with and without the presence of the distributed generator taking into account the following variables: busbar voltage profile, output power provided by the substation and by the distributed generator when present.

Medium-voltage distribution feeders in open-loop and closed-loop arrangement

This paper deals with a medium-voltage distribution network. The feeders in the open-loop arrangement are changed to the closed-loop arrangement with the aim to improve reliability of the power supply. The paper focuses on the analysis of transient and steady-state operation in the closed-loop that is established by connecting feeders supplied from two different transformers located in the same transformer substation. The transformers are equipped with the tap changers that can change the amplitude of the 20 kV voltages in steps whilst the phase cannot be changed. The possibilities to control the active and reactive power at both ends of the medium-voltage loop are discussed for the case when only the voltage amplitude can be changed and for the case when the voltage amplitude and phase angle can be changed. A simple algorithm for closed-loop active and reactive control is applied. The results of simulations and field testing performed in a 20 kV network are presented.

Reliability enhancement and power loss reduction in medium voltage distribution feeders using modified jellyfish optimization

The reliability of electrical systems is a critical operational characteristic for distribution companies. On the other hand, they pay great attention on reducing losses in primary and secondary distribution lines. In this article, a modified Jellyfish Search (MJFS) algorithm is presented for handling Optimal Network reconfiguration (ONR) in Medium Voltage Distribution Feeders (MVDFs). An ONR formulation is proposed for reliability enhancement and power loss reduction in a multi-objective model where three reliability measures are incorporated which are total energy not supplied (TENS), system average interruption unavailability index (SAIUI) and system average interruption frequency index (SAIFI). The proposed MJFS expands on the JFS searching benefits by introducing a quasi-oppositional-based learning and social neighborhood strategies. Also, a proposed bus-line feeding matrix (BLFM) is incorporated to develop the MJFS. Through the BLFM, each distribution line is simulated as an outage and the regarding distribution nodes which are not supplied is estimated. The simulation results are performed on a large-scale IEEE MVFD of 137-bus which derive significant improvements of the proposed MJFS over the standard JFS algorithm. Considering the proposed multi-objective model, the proposed MJFS achieves great reduction in power losses, TENS, SAIUI and SAIFI with 44.42, 30.57, 30.78 and 23.92 %, respectively compared to the initial case. Also, versus the standard JFS, grey wolf optimizer, tuna swarm optimization, equilibrium optimizer and tunicate swarm optimization, the proposed MJFS acquires great reduction in the standard deviation with improvement of 2.5, 92.51, 10.67, 91.53 and 96.51%, respectively.

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.

Non-Linear Clustering of Distribution Feeders

Distribution network planners are facing a strong shift in the way they plan and analyze the network. With their intermittent nature, the introduction of distributed energy resources (DER) calls for yearly or at least seasonal analysis, which is in contrast to the current practice of analyzing only the highest demand point of the year. It requires not only a large number of simulations but long-term simulations as well. These simulations require significant computational and human resources that not all utilities have available. This article proposes a nonlinear clustering methodology to find a handful of representative medium voltage (MV) distribution feeders for DER penetration studies. It is shown that the proposed methodology is capable of uncovering nonlinear relations between features, resulting in more consistent clusters. Obtained results are compared to the most common linear clustering algorithms.

Formulation of reference network models for the Hungarian medium voltage distribution level

In the next two decades, a rapidly increasing photovoltaic penetration connected to the distribution electricity network is expected both nationally and internationally, which influences grid operation. Simultaneously, an essential development of network infrastructure is also expected. In order to determine development directions and opportunities, power system simulation is essential, which is based on the generation of representative feeders. In this paper, by clustering (using k-means clustering) medium voltage distribution feeders, valid Hungarian representative networks are formulated and described. The number of descriptive variables was reduced by, principal component analysis. The feeders are described with the first three principal components (95% coverage of the information). The optimal number of clusters was determined using four different validity criteria, and set to 6. The contributions of the paper are that the examined feeders are characterized by both electrical (physical) and mathematical parameters, in a new combination, from which the number of switches is a novel element in the literature. The applied principal component analysis works with more components (3) and greater coverage (95%) than the methods available in the examined literature. Based on topographic verification of the representative networks, the clusters are well characterized by the parameters of the feeders.

Optimal Preventive Maintenance Planning for Electric Power Distribution Systems Using Failure Rates and Game Theory

Current electric utilities must achieve reliability enhancement of considerable distribution feeders with an economical budget. Thus, optimal preventive maintenance planning is required to balance the benefits and costs of maintenance programs. In this research, the proposed method determines the time-varying failure rate of each feeder to evaluate the likelihood of future interruptions. Meanwhile, the consequences of feeder interruptions are estimated using interruption energy rates, customer-minutes of interruption, and total kVA of service areas. Then, the risk is assessed and later treated as an opportunity for mitigating the customer interruption costs by planned preventive maintenance tasks. Subsequently, cooperative game theory is exploited in the proposed method to locate a decent balance between the benefits of reliability enhancement and the costs required for preventive maintenance programs. The effectiveness of the proposed method is illustrated through case studies of large power distribution networks of 12 service regions, including 3558 medium-voltage distribution feeders. The preventive maintenance plans resulting from the proposed method present the best compromise of benefits and costs compared with the conventional approach that requires a pre-specified maintenance budget.

Decision making under uncertainty for deploying battery storage as a non-wire alternative in distribution networks

The growing demand for electricity in emerging markets and developing economies (EMDE) is causing loading and congestion problems on distribution networks, particularly in urban locations, that adversely impact sustainable development and economic growth. Electric utilities in these economies face unique constraints regarding raising capital required to upgrade their congested networks. Battery storage has emerged as a non-wire alternative (NWA) to feeder upgrades. This article presents a flexible valuation framework for battery storage use in distribution networks and its application in the context of EMDE distribution network planning. We evaluate the value of storage as an NWA using a multi-stage decision making process that combines system optimization with Markov-decision processes (MDP) to identify the least-cost network upgrade strategy under demand growth uncertainty. This approach was applied to distribution feeders in Delhi, India, and results highlight the cost-effectiveness of battery storage to manage load growth while deferring network investments. Across the low, medium and high battery storage capital cost projections for 2030, we estimate that 18 to 29 GWh of battery storage capacity could be deployed to defer 11,752 to 15,914 km of medium voltage distribution feeder lines that are loaded at 60% or more of their ampere capacity in 2030, resulting in 12 to 16% capital cost savings. Interestingly, lowering storage capital costs does not always lead to increased storage deployment, due to network capacity constraints limiting opportunities for off-peak storage charging.

Pengembangan Nominal Aturan Fuzzy pada Metode Fuzzy Mamdani untuk Menyeimbangkan Beban Tiga Phasa pada Saluran Distribusi Tegangan Menengah

The use of electrical equipment on the customer side with low voltage absorbs unbalanced power. The load unbalances in each phase will result in an unbalanced current, resulting in a phase voltage shift in the secondary coil of the 20 kV/380 V medium voltage transformer. Shifting the voltage in the distribution transformer phase, then causes the flow of current in the transformer neutral wire causing losses. This paper proposes a fuzzy logic method with the Mamdani fuzzy inference system (FIS) to balance three-phase load currents at seven feeders of 20 kV medium voltage distribution at PLN Rayon Taman Jawa-Timur. The feeders are Ngelom, Tawang Sari, Geluran, Bringin, Masangan Kulon, Palm Residence, and Pasar Sepanjang. There are three input variables used, namely the load current in phase R, phase S, and phase T respectively. There are three output variables in one FIS block, namely changes in load current in phase R, phase S, and phase T respectively. With the number of fuzzy rules as many as 509 rules, the proposed method is able to produce the lowest load current unbalance value of 1.6% at Palm Residence Feeders. The development of a nominal (number) of fuzzy rules in the Fuzzy Logic Method with FIS Mamdani is able to reduce the value of unbalance load current at the 20 kV medium voltage distribution feeder better than the method proposed by previous researchers.

Evaluation of ancillary services in distribution grid using large‐scale battery energy storage systems

Battery energy storage systems (BESSs) are being presented as a prominent solution to the various imminent issues associated with the integration of variable renewable energy sources in the distribution system. Performance of grid-connected BESS depends on the type of application (power and energy), grid operating parameters and level of interconnection point, which shows the necessity of benefit assessment of BESS technology and its applications in terms of economic and grid operations before investment at a larger scale. In this study, real-time analysis and evaluation of two different battery technologies connected in a medium voltage (MV) distribution system are carried out. The main objective of this paper is focused on the impact analysis of large-scale BESS on MV distribution feeder. A real case of installation of lithium-ion and advanced lead-acid battery systems into the Indian distribution system has been considered for this study. Different operational strategies of BESS such as frequency regulation and energy time-shift have been performed with real-time data. The effectiveness in usage of BESS with these functionalities has been verified in terms of peak shaving, improvement in voltage profile and reduction in power losses in the feeder.

Pilot Tests of FasTR Method for Locating Transient Faults in Medium Voltage Underground Power Networks

This paper presents the results of pilot tests performed on a real medium voltage (MV) underground network in Switzerland with the aim of assessing the performance of a fault location system. The deployed fault location platform is based on a very sensitive and precise acquisition system which is capable of capturing perturbations or events on a dedicated portion of a given MV network. Thanks to a post processing algorithm based on the tenets of time reversal theory, FasTR method, an accurate localization of relevant events can be worked. Due to the fact that each acquisition system shares a clock reference based on a GPS antenna, the localization accuracy is within tens of meters. To the best of the Authors knowledge, this is the first time that the FasTR-based fault location technique is validated through live tests. The pilot network is a three branch system part of live radial MV distribution feeder consisting of a total of 2.6 km long underground three-phase cables. The branched lines are composed of coaxial cables of different types. The tests involve solid- and resistive-type single-phase-to-ground fault occurrences triggered along one of the laterals when the network is operational. The obtained results demonstrated the capacity of an on-deck portable system to make an on-line accurate detection of transient faults in a complex network.

Assessment on the Behavior of Harmonic Phase Angles

Existing methodologies and protocols for characterizing the harmonic components of voltage and current from digital measurements only consider the measurement of the amplitudes of these quantities. Thus, the phase angles of the harmonic components, required for some types of analysis in electrical systems, are simply ignored. In fact, there is no standardized methodology for measuring and temporal aggregation of phase angles of harmonic components. In this context, the present article aims to contribute to the subject by presenting the behavior of the phase angles of the harmonic components over time under different conditions. For this purpose, specific voltage and current waveform measurements were performed to analyze the phase angle behavior of the harmonic components over 24 hours, considering individual electrical loads, as well as residential and commercial installations, both connected to a low voltage power distribution system. Additionally, the behavior of the phase angles of the harmonic components measured at the output of a medium voltage distribution feeder will be presented. The results show a sporadic behavior for these quantities, reinforcing the need to develop a new methodology for temporal aggregation of phase angles of harmonic components.

Detecting the Fault Section in the Distribution Network with Distributed Generators Based on Optimal Placement of Smart Meters

Abstract One of the most important issues in employing distribution networks is detecting the fault location in medium-voltage distribution feeders. Due to the vastness of distribution networks and growing distributed generation (DG) sources in this network, detection is difficult with the common methods. The aim of this paper is to present a method based on voltage distributed meters in a medium-voltage distribution network (by smart meters installed along the feeder) in order to detect the fault location in the presence of DG sources. Due to vastness of distribution network and cost of installing smart meters, it is not economically possible to install meters in all the Buses of the network. That’s why in this article, combination of genetic and locating algorithms and fault-based on voltage drop has been used to suggest a method to optimize the meter locations. In order to evaluate the efficiency of the method suggested, first we determine the optimal number and location of the meters and then we apply the fault that has been simulated in different Buses of the sample network, using PSCAD/EMTDC software. After results analysis, the fault location is estimated by MATLAB. Simulation results show that the fault locating method by optimal number of meters has good efficiency and accuracy in detecting faults in different spots and in different resistance ranges.

Earth Fault Location Using Negative Sequence Currents

In this paper, a new method for locating single-phase earth faults on non-effectively earthed medium voltage distribution networks is proposed. The method requires only current measurements and is based on the analysis of the negative sequence components of the currents measured at secondary substations along medium voltage (MV) distribution feeders. The theory behind the proposed method is discussed in depth. The proposed method is examined by simulations, which are carried out for different types of networks. The results validate the effectiveness of the method in locating single-phase earth faults. In addition, some aspects of practical implementation are discussed. A brief comparative analysis is conducted between the behaviors of negative and zero sequence currents along a faulty feeder. The results reveal a considerably higher stability level of the negative sequence current over that of the zero sequence current.

Time reversal applied to fault location in power networks: Pilot test results and analyses

This paper presents the results of a pilot test performed on a real medium voltage distribution network in Switzerland with the aim of assessing the performance of a fault location system relying on the Electromagnetic Time Reversal (EMTR) method. To the best of the Authors’ knowledge, this is the first time that the EMTR-based fault location technique is validated through live tests. The pilot network is a live radial medium voltage distribution feeder, which consists of 11.9-km long double-circuit lines operating at 18/60 kV and multiple 18-kV three-phase laterals. The branched lines are overhead lines, underground cables, or mixed configuration with lengths ranging from tens of meters to a few kilometers. The test involves solid- and resistive-type single-phase-to-ground fault occurrences triggered along one of the laterals when the network is operational. The fault location task is performed by a real-time industrial controller prototype that integrates the functions of fault detection, data acquisition, time-reversal processing and Electromagnetic Transients simulations. Concerning the methodological aspects, the EMTR Fault Current Signal Energy (FCSE) metric is used to determine the location of the fault. The obtained results show that the FCSE metric is capable of accurately identifying the faulty phase and the real fault location in all tested fault cases, with a location accuracy of less than 10 m.

OLTC-Induced False Data Injection Attack on Volt/VAR Optimization in Distribution Systems

This paper presents a new class of false data injection attacks (FDIAs) on volt/VAR optimization (VVO), which may result in abnormal voltage conditions along the radial medium voltage (MV) distribution feeder with an on-load tap changer (OLTC), capacitor banks (CBs), solar photovoltaic (PV) systems, and smart meters. In comparison with existing FDIAs against voltage control that do not consider the VVO process, we propose a new attack strategy with which the adversary can maliciously change the distribution feeder voltage profile by misleading the VVO function through stealthily injecting false data into smart meter measurements that are used for the VVO. The proposed attack strategy is formulated as a bilevel optimization problem using mixed integer linear programming (MILP). Injected false load data that raise or lower the tap position of the OLTC are calculated at the upper level while the VVO process is guaranteed to correctly operate with false data at the lower level. The bilevel optimization problem is finally reformulated to a single-level optimization problem based on Karush–Kuhn–Tucker conditions of the lower level optimization problem. A simulation study is carried out in an IEEE 33-bus distribution system with an OLTC, CBs, PV systems, and smart meters, and our results demonstrate the feasibility and capability of the proposed attack approach in terms of voltage level, attack effort, and PV penetration rate.

A Bi-Level EV Aggregator Coordination Scheme for Load Variance Minimization with Renewable Energy Penetration Adaptability

The provision of ancillary services by electric vehicles (EVs) such as load smoothing and renewable energy (RE) compensation in the form of an aggregated storage is more regulated in the smart grid context. As such, the presence of multiple EV aggregators in the distribution network requires adept supervision by the distribution system operator (DSO). In this paper, a coordination scheme of aggregators is proposed to smoothen the load profile of distribution networks by enacting EV discharging during peak load and off-peak charging, keeping in view the EV driving requirements. A bi-level on-line interaction procedure from the DSO to the aggregators and vice versa is devised to manage the aggregators based upon their energy capacity and requirements. The aggregators employ a water-filling algorithm in a two-step EV power allocation method. The proposed scheme operation is demonstrated on an medium voltage (MV) distribution feeder located in Seoul with its actual traffic density data. The results show the achievement of peak shaving and valley filling objectives under aggregator coordination and that the EVs are completely charged before departure. The effect of various EV penetration levels and adaptivity of the scheme to RE incorporation is also verified. Furthermore, a comparison with an existing peak shaving method shows the superior performance of the proposed scheme.

Optimisation algorithm for Earth fault location on MV distribution feeders

This study presents an earth fault location algorithm based on optimisation approach, which is developed for medium voltage (MV) distribution networks with resistance-earthed neutral. The objective function is written based on relation between voltage and current measurements at substation, line parameters, fault distance and fault resistance. The optimisation process is performed with MATLAB optimisation toolbox that gives values to the last two variables. To deal with the heterogeneity of MV feeders, fault location is carried out successively on every homogeneous section lines and the optimal points of the different sections will be compared with given final solution. The performance tests, which are performed on an MV CIGRE benchmark network, show encouraging results. In this study, impacts of load consumption uncertainty and of DG connection are also discussed.