Medium Voltage Networks Research Articles

Optimization of Division and Reconfiguration Locations of the Medium-Voltage Power Grid Based on Forecasting the Level of Load and Generation from Renewable Energy Sources

The article addresses challenges in optimizing the operation of medium voltage networks, emphasizing optimizing network division points and selecting the best network configuration for minimizing power and energy losses. It critically reviews recent research on the issue of network configuration optimization. The optimization of the medium voltage power grid reconfiguration process was carried out using known optimization tools. The novelty lies in the inclusion of a probabilistic approach in the decision-making process in forecasting loads and generation from renewable energy sources (RES). Optimization studies utilizing heuristic optimization methods were completed, and an algorithm was developed for forecasting load and power generated from RES based on historical data and current weather data obtained from weather API. The solution proposed in the article allows multiple applications, including optimizing network division points’ locations (which decreases financial costs of modernizing network infrastructure) as well as improving the reconfiguration process, resulting in lower power losses while maintaining voltage requirements.

Optimal planning of photovoltaic and distribution static compensators in medium-voltage networks via the GNDO approach

This research employs the generalized normal distribution optimizer (GNDO) to address the simultaneous integration of solar photovoltaic (PV) sources and distribution static compensators (D-STATCOMs) in medium-voltage distribution networks. Through a discrete-continuous codification process, the GNDO method determines the optimal locations (nodes) and capacities (sizes) of PV systems and D-STATCOMs. A power flow approach based on the successive approximations method is used to solve the power flow equations and assess the solution's technical characteristics, including voltage profiles and power injections. Using a master-slave optimization strategy, the GNDO and the power flow method are used to address the studied problem. Numerical results in the 33- and 69-bus grids demonstrate the effectiveness of the proposed approach, showing superior performance compared to the vortex search algorithm (VSA) and the sine-cosine algorithm (SCA). The results indicate reductions of approximately 35.5554% and 35.6839% when using the GNDO in both test feeders. Additionally, the GNDO reduces the computational efforts required to find solutions in both test feeders, in comparison with the VSA and the SCA. All numerical validations were performed using MATLAB 2024a.

Unlocking responsive flexibility within local energy communities in the presence of grid-scale batteries

The transition towards a decentralized, decarbonized, and distributed energy infrastructure necessitates techno-economic initiatives to empower local energy communities (LECs) to achieve self-reliance and evolve into self-sustained electricity networks. It is crucial to underscore the significance of network resilience, especially in the context of local power generation, battery storage, and the radial topology of low-voltage (LV) networks. While contemporary LV networks have made significant attempts to integrate distributed energy resources (DERs), the notable deficiency lies in their lack of network redundancy, posing a substantial challenge in the occurrence of high-impact, low-probability (HILP) events. Therefore, to enhance LV network resilience and leverage its capability to withstand unexpected disruptions, the network operator needs to unlock the potential contributions of end-users within the active distribution networks (ADNs). In this paper, a comprehensive model is developed based on multi-temporal optimal power flow (MTOPF) for unbalanced LV networks addressing the technical issues in islanded microgrid operational planning. The contributions of the grid-scale batteries in forming islanded microgrids and the flexibility that can be provided by the end-users in the LEC have been considered in this paper. To demonstrate the performance of the proposed model, the simulation studies have been carried out on a part of medium and low voltage networks, consisting of network reconfiguration and load transferring capability to reduce the service interruptions during HILP events. The energy-not-served (ENS) is chosen as one of the key performance indicators (KPIs) in this study. With the unlocking flexibility potentials and contribution of the DERs, including grid-scale energy storage (GES) units and Photovoltaic (PV) panels, the ENS has been reduced from 700.8 kWh to 447.5 kWh by activating the local resources, proper switching action, and contribution of the flexible loads, for one of the severe HILP events, i.e., the main grid outage. In this case, the full load curtailment index is reduced from 180 to 106 client hours.

Research on insulation design of 10 kV medium-voltage cascaded energy storage system

Abstract The insulation design of a medium-voltage cascaded energy storage system is very important due to its direct access to the AC medium-voltage network. This paper focuses on improving the reliability and safety of the system operation, and realizes the insulation design of a 10 kV medium-voltage cascaded energy storage system through the selection of insulation materials and structural innovation. In the structure, high insulation sheet molding plastic was used to suspend the battery. The ultra-low conductivity coolant was used to enhance the insulation performance between battery modules. The stability and practicability of the insulation structure are demonstrated by effective test methods. The research shows that the medium voltage insulation design meets the insulation requirements of the 10 kV voltage class, and has high industrial practical value for the project of medium voltage cascaded energy storage system.

Optimal Operation of an Industrial Microgrid within a Renewable Energy Community: A Case Study of a Greentech Company

The integration of renewable energy sources in the European power system is one of the main goals set by the European Union. In order to ease this integration, in recent years, Renewable Energy Communities (RECs) have been introduced that aim to increase the exploitation of renewable energy at the local level. This paper presents an Energy Management System (EMS) for an industrial microgrid owned and operated by a greentech company located in the north of Italy. The company is a member of an REC. The microgrid is made of interconnected busbars, integrating photovoltaic power plants, a fleet of electric vehicles, including company cars and delivery trucks supporting Vehicle-to-Grid (V2G), dedicated charging stations, and a centralized battery energy storage system. The industrial site includes two warehouses, an office building, and a connection to the external medium-voltage network. The EMS is designed to optimize the operation of the microgrid and minimize the operating costs related to the sale and purchase of energy from the external network. Furthermore, as the company is a member of an REC, the EMS must try to follow a desired power exchange profile with the grid, suggested by the REC manager, with the purpose of maximizing the energy that is shared within the community and incentivized. The results demonstrate that, when minimizing only costs, local self-consumption is favored, leading to a Self-Sufficiency Rate (SSR) of 65.37%. On the other hand, when only the adherence to the REC manager’s desired power exchange profile is considered in the objective function, the SSR decreases to 56.43%, net operating costs increase, and the energy shared within the REC is maximized.

Analyzing impact of network constraints on feasible operation region of the radial distribution networks

Recently, there has been lot of research on finding the feasible operating region (FOR) of the active distribution network (ADN) to provide ancillary services to the transmission grid. The current focus of research is on finding methods that can accurately determine the shape of the FOR and have fast computation time. However, there is little focus on analyzing how network constraints impact the shape of the FOR. This paper attempts to address this issue and provides a mathematical derivation of how network constraints, such as cable loading and voltage limits, would influence FOR. The approach is based on a linear distflow mathematical analysis. The relations derived in the analysis are verified with numerical simulation on radial low-voltage (LV) and medium-voltage (MV) networks. The results show that cable loading constraints cut the FOR in a circular way and voltage constraints cut the FOR with a straight line of slope −ϵ, which is the ratio Rn/Xn of the path from root node to the node under analysis of the radial distribution network.

Statistical characterization of reliability indices in medium voltage networks using a Monte Carlo-based method

Distribution companies are compelled to provide high-quality services to their customers in compliance with existing regulations. Key performance indicators such as system average interruption duration index and system average interruption frequency index are commonly employed to assess the quality of service provided by these utilities. In certain countries, distribution system operators may face penalties or receive bonuses based on their performance within specified thresholds in their reliability indices. This paper introduces a novel, integrated algorithm, based on Monte Carlo simulations, for conducting a risk assessment in real MV networks using local data from the distribution system operator. The proposed technique is tested in a real MV network, and the obtained results are analyzed both at feeder level and for the entire network. The feeder-level results might be used to identify the sections of the network with the worst quality of power supply, based on the estimated KPIs. The overall results of the study offer valuable insights into the likelihood of specific KPI values using probability density function. The Weibull distribution and log-logistic distribution are found to be those with the best-fitting probability density functions for the two indices evaluated in this work. Furthermore, a penalty-based rate approach is presented as an application of the proposed method to assess the economic risk of the MV network. The findings reveal that the test system is expected to incur penalties amounting to 7.55 million dollars per year.

Analysis of voltage limit‐induced barrier for connecting inverter‐based distributed generators to medium voltage networks: Australian case studies

AbstractInverter‐based distributed generators (IBDGs), mainly solar photovoltaic, connected in medium‐voltage (MV) networks cause challenges, such as voltage limit violations, for distribution network service providers (DNSPs), and require advanced network management strategies to mitigate these challenges. A theoretical analysis of the voltage limit‐induced barrier to IBDG connection and their export limits due to the change in network characteristics is imperative for developing new strategies. The authors formulated a relationship between the network equivalent impedance and the IBDG's connection point in the network and further explored the link between the network equivalent impedance and voltage magnitude due to the IBDG connection point. The authors also assessed the voltage limit‐induced barrier to IBDG connections in MV networks and proposed solutions to overcome issues with the dynamic export limit of IBDGs. Four representative Australian MV networks are analysed in DIgSILENT PowerFactory under different scenarios, such as variation in IBDG location and static and dynamic export limits. The authors found that an IBDG connected at the end of the network can achieve better performance in supporting the network voltage. An IBDG with a dynamic export limit can export three times more energy than the static export limit, which benefits both the DNSPs and IBDG owners.

Distribution Pattern of ELF Field Exposure Electricity Distribution Substation Portal Pole Type 20 kV Medium Voltage Network

The electricity distribution substation is one of the components of the electricity distribution system. Electrical distribution substations, especially portal pole-type electrical distribution substations, can emit ELF fields. However, people need to be aware of the health risks of ELF fields and continue to carry out various activities near electricity distribution substations. This research aims to create a distribution pattern for ELF Field and determine its safety level based on WHO thresholds. The research was conducted in the Jember Regency, particularly in Sumbersari District. This research uses a portal pole-type electricity distribution substations. The substation criteria studied were a portal pole distribution substation on a 20 kV transmission line with a transformer capacity of 160 kVA. The measurement points are 0 m below the transformer, 0.7 m, 1.4 m, 2.1 m, 2.8 m, 3.5 m, 4.1 m, and 4.9 m from the distribution substation building at a height of 1.5 m from the ground for three days at 21.00 WIB and 30 measurements were taken. The distances of these points to the transformer are 4.256 m, 4.313 m, 4.480 m, 4.745 m, 5.094 m, 5.510 m, 5.979 m and 6.490 m respectively. The type of research used is quantitative research with survey data collection techniques. The research design used was cross sectional study. Cross sectional study is a type of observational research design that collects data at one specific point in time from a sample which represents the population studied. ELF field measurements show a spherical distribution pattern with an average magnetic field intensity between 0.0358 µT and 2.91 µT and an average electric field intensity between 2.35 V/m and 16.42 V/m. The magnitude of the magnetic field and electric field measured gets smaller as the distance from the measurement point increases. According to WHO, these results are below the threshold for the general group. This research concludes that the portal pole-type distribution substation in the medium voltage network produces a safe ELF field with a spherical distribution pattern that is inversely proportional to the distance.

Evaluation of Distribution Transformer Placement Optimal Based on Load Balance

The distribution system is divided into primary and secondary distribution networks. The primary distribution network is the network from the main substation transformer (GI) to the distribution substation, while the secondary is the channel network from the distribution substation transformer to the consumer or load. The primary distribution network is better known as the medium voltage network (JTM 20kV) while the secondary distribution is the low voltage network (JTR 220/380V). The distribution network is the part of the electric power system that is closest to customers or loads compared to the transmission network. Currently, network electricity conditions throughout Indonesia are experiencing a decline of 5% which is due to various factors such as the medium-scale diameter of the conductors used, so at the farthest SR the value of overvoltage is 10%, the allowable voltage drop and must anticipate an increase in electrical load of 22.7 %, the placement of the transformer is not optimal and the distance the electrical energy travels from the transformer to the load is not paid enough attention so that the capacity of a transformer is not optimal and the voltage drop is also greater. Given these conditions, re-evaluation and planning is needed that takes into account planning criteria such as allowable voltage drops and continuity of electricity services so that optimization of the network used can emerge.

Pemeliharaan dan Perhitungan Umur Travo Jaringan Distribusi 20 KV

The distribution transformer is one of the main components in an electric power distribution system. Without a distribution transformer, consumers cannot use electrical energy directly considering that the operating voltage in the distribution system is 20 KV or what is called a medium voltage network. Disruptions that occur in distribution transformers will result in blackouts and obstruction of the distribution of electricity to consumers so that services for electricity needs will be disrupted. For this reason, routine and scheduled maintenance of distribution transformers is required which aims to prevent sudden equipment damage, as well as maintaining optimum equipment work according to its technical age, and safe for humans and the environment, as well as reliable in the electric power distribution system. One of the causes of disruption and damage to transformers include overvoltage due to lightning, overload and unbalanced loads, loss of contact at bushing terminals, broken insulators and failure of transformer oil insulation. These disturbances cause damage to distribution transformers and stop the flow of electricity. to consumers. In calculating the usage time of a transformer, we can predict the usage time of the transformer from calculating the voltage and current used every day, so if we know the usage time of a transformer, we can prevent damage to the distribution network by replacing the transformer before the transformer is damaged.

Controllable Meshing of Distribution Grids through a Multi-Leg Smart Charging Infrastructure (MLSCI)

The paper provides a novel approach for controllably meshing traditional medium-voltage networks by means of a fast-charging parking station with multiple points of delivery connected to different radial feeders. Regulating power flows at each point of delivery while the charging service is being provided, which means actively controlling power exchanges between radial distribution feeders can significantly increase the hosting capacity of the power system. Remarkable benefits are expected when the distribution networks to which the charging infrastructure is connected differ in terms of main characteristics, e.g., rated voltage level, end-user type and operating profiles, and the number and type of renewable plants. The paper focuses on technical targets, such as loss reduction and power quality in terms of admitted voltage deviation from the rated value. The power exchanges between distribution feeders are made possible by a controlled DC link, where bi-directional DC/DC converters are connected so as to charge or discharge vehicles according to the Vehicle-To-Grid approach. A multiplexer topology in which several vehicles can be alternatively connected to the same DC/DC converter is modeled. The proposed concept can contribute to network flexibility by controllably meshing distribution feeders and, jointly, by modulating charging processes according to assigned charging constraints.

Dynamic Management of Flexibility in Distribution Networks through Sensitivity Coefficients

Due to a rising share of renewable energy sources on the production side and electrification of transport and heating on the consumption side, the efficient management of flexibility in distribution networks is crucial for ensuring optimal operation and utilization of resources. Nowadays, the sensitivity-based approach is mainly used in medium-voltage (MV) networks for regulating voltage profiles with reactive power of distributed energy resources (DER). The main disadvantage of the simplified sensitivity-based method is its inaccuracy in case of a high deviation of the network voltage from the nominal values. Furthermore, it was also noted that despite the fact that the method is well described in the literature, there is a lack of systematic approach to its implementation in real-life applications. Thus, the main objective of this paper is to address this disadvantage and to propose an algorithm designed to calculate required consumer flexibility in near real-time to ensure distribution grid operation within operational criteria. In the first part of the paper, network state, including line loading and node voltages, is assessed to determine distribution network node capacity. By analyzing the sensitivity of network busbars to changes in consumption and production, our algorithm effectively identifies the most efficient nodes and facilitates strategic decision-making for resource allocation. We demonstrate the effectiveness of our approach through simulations of real-world distribution network data, highlighting its ability to enhance network flexibility and improve resource utilization. Leveraging sensitivity coefficients, the algorithm enables flexible consumption and production management across various scenarios, supporting the transition to a more dynamic and efficient power system.

Maintenance of Pole Mounted Circuit Breaker as Medium Voltage Network Protection at PT. PLN (Persero) UP3 Sidoarjo

Maintenance of Pole Mounted Circuit Breaker as Medium Voltage Network Protection at PT. PLN (Persero) UP3 Sidoarjo

Pengaruh Panjang Jaringan Terhadap Drop Tegangan Pada Penyulang Duku dan Kurma PT. PLN (Persero) ULP Rumbia

Voltage drops in distribution systems can occur in medium voltage networks (JTM), distribution transformers, low voltage networks (JTR) and house lines. Voltage drops in the network cause suboptimal distribution and increase power losses. PT. PLN (Persero) ULP Rumbia has two feeders with pure radial network characteristics sourced from the Seputih Banyak Main Substation. The length of the Duku Feeder network has a voltage of 96.8 KMS with a load of 150 A while the length of the Kurma Feeder network is 207.21 kV with a load of 155 A. The network reconfiguration of the Dente Teladas Substation was carried out to shorten the network length. This research aims to calculate the voltage drop that occurs at the Duku and Kurma feeders before and after network configuration. This research uses the quantity method to compare the calculation results with the voltage drop standards set by PT. PLN (Persero). After reconfiguring the Duku and Kurma feeders, there was an increase in tip voltage which indicated improvement. From the calculation results before adding the network to the Duku feeder, the voltage at the receiving end was 19.5 kV with a voltage drop of 7.1%, and at the Kurma feeder the voltage at the end of the line was 17 kV with a voltage drop of 19%. This is clearly no longer in accordance with the local TMP, and requires further study to overcome this problem. The voltage on the two feeders goes through a step up process using a Medium Voltage OLTC (On Load Tap Changer) so that the voltage on each feeder becomes between 19.86 kV to 20.16 kV.

Application of Under-Impedance Criterion to Protect against Effects of Phase-to-Phase Short Circuits in Medium-Voltage Networks

Common overcurrent criteria used to detect phase-to-phase short circuits in medium-voltage (MV) networks in some cases do not bring the expected results. In particular, this applies to instantaneous overcurrent protections in lines with variable ranges and lines leading to local power plants (LPP), which generate a short-circuit current slightly greater than the rated current. When using overcurrent protections, there are some problems with ensuring the appropriate sensitivity and selectivity. This article proposes a protection based on impedance measurement against the effects of phase-to-phase short circuits in MV lines. The protection can be used at switchgears and also at protection points (PP) located deep in the network. The under-impedance criterion has a range independent of the value of the short-circuit current, and it can be alternative or complement to classic overcurrent protection. The introduction of these criteria allows the protection range to be independent of the type of short circuit and the short-circuit power on the busbar, and to determine this range more precisely. The under-impedance protection is particularly useful in conditions of a growing number of energy sources deep inside the networks and its automation. The main idea was to develop a uncomplicated characteristic that would ensure the possibility of setting the under-impedance protection by people who are not specialists in the field of distance protections. The characteristics have been optimally developed both in terms of the area of detected impedances and easy implementation, operation, and configuration.

Voltage/load Control Strategy for Smart Distribution Grids with a High Penetration of Renewable Energy Sources

The exponential increase of renewable energy sources (RESs) penetration in the power grid introduces the of voltage instability when RESs are integrated into medium and low voltage networks. This paper proposes a state-machine based voltage/load control strategy for different operating scenarios in a system comprised of a large RES power plant connected to a medium voltage bus at 11kV, and small RES systems scattered across low voltage networks at 415V. Three modes of operation are summarized, in which the appropriate action is taken according to the availability of RES power generation in the network and the loading condition of this network. Efficient power sharing is achieved via the utilization of a communication network deployed between the RES systems. The communication protocol of the network is represented in four messages adopted by the RES systems integrated into the grid. The effectiveness of the proposed voltage/load control strategy to surpass overvoltage cases caused by over-generation of RES power is illustrated through simulations. The proposed strategy can be adopted by either agreement between a utility and RES owners, or by making it the basis for a standard for RES installation.

Ferroresonance phenomena in power systems

It is a known fact that the world's dependence on electrical energy is increasing day by day. The fact that electrical energy has some advantages over other types of energy, the increasing world population and changing living conditions can be considered among the reasons for this increase. This increase in dependence on electrical energy can be met by expanding existing facilities and establishing new facilities. In these studies, the transmission of electrical energy from the place where it is produced to the place where it is consumed poses important problems as the system expands. Some work is required to eliminate these technical and economic problems and to ensure stable operation of the system. These are problems that were not considered beforehand as the system grew. One of these problems is the ferroresonance phenomenon that occurs at the fundamental frequency due to the nonlinear magnetization characteristics of transformers. Ferroresonance is a resonance phenomenon that occurs in an electrical circuit containing an iron-core self-coil as a nonlinear element. This resonance manifests itself with sudden oscillations in the output size of the system caused by a small change in the amplitude or frequency of a magnitude applied to the input of the system. High voltage transmission lines are double-circuit lines that share the same pole. In special cases such as maintenance or malfunction of such a transmission system, one of the lines can be disconnected from the system and continue energy transmission with the other line. In the high voltage transmission line, the system may oscillate due to the stored energy in the magnetic field of the transformer inductance on the disabled line and the electric field of the line capacity. This oscillation disappears after a certain period of time due to iron losses and other circuit losses. When these losses are covered by the other transmission line, permanent oscillations and over voltages may occur at the transformer terminals. All these events are the negative effects of ferroresonance on transmission systems. In the energy transmission system, ferroresonance phenomenon occurs. Over voltages may occur in case of idle power transformers in star point/isolated networks. In medium voltage networks, ferroresonance occurs due to the melting of a fuse, the opening and closing of voltage transformers with one pole, and the dissymmetry that occurs as a result of a connection process. These negative effects caused by ferroresonance in the energy transmission power system are discussed in detail within the subject of this study.

The use of PSS2A system stabilisers to damp electromechanical swings in medium voltage networks with distributed energy sources

The use of PSS2A system stabilisers to damp electromechanical swings in medium voltage networks with distributed energy sources

Parallel Operation for 11 kV Ring System with Normally Open Point at Distribution Networks in AADC

Currently, Al Ain Distribution Company (AADC) 11 kV distribution circuits are electrically split by Normal Open Points (NOP)s. NOPs can be closed for load restoration in case of planned or unplanned outages. Also, changing the NOP locations helps in load shifting to achieve network optimization between adjacently located 33/11 kV primary substations. This paper discusses a new operation mode in medium voltage distribution power network of AADC at Al Ain area in the United Arab Emirates by introducing closed loops of parallel 11 kV feeders from different busbars or substations. This operation mode is intended to end the continuous debate of optimal NOP locations in addition to expected reduction in the required time for load restoration in case of failures at distribution (11/0.4 kV) substations. A detailed case study is performed to explore the achieved benefits and enhancements on load balancing, voltage profile, and power factor in medium voltage networks. On the other hand, the impact on load flow, protection scheme, and loading violation are evaluated. Furthermore, the proposed model is in line with the regulations of the Department of Energy (DoE), regulatory body in Abu Dhabi Emirate, and should fully comply with Electricity Distribution Code (EDC) of Security of Supply Standards. Accordingly, while the current used operation mode is still valid, it is found that closed loops arrangement can be only allowed for rings from same 33/11 kV substations feeding from same source with considerable protection limitations. Moreover, it was concluded that closed loops from different 33/11 kV Substations will result in load flow problems.