Medium Voltage Distribution Network Research Articles

ANALYSIS OF THE IMPACT OF DIFFERENT DISTRIBUTED GENERATOR TECHNOLOGIES ON HARMONIC VOLTAGES

While distributed generators (DGs) can reduce carbon dioxide emissions, they can also cause disturbances and lead to power quality (PQ) issues, with harmonic voltages being an important parameter to consider. In this paper, the impact of 14 connected photovoltaics (PVs) and a small hydropower plant (sHPP) on harmonic voltage distortions in a real medium voltage (MV) and low voltage (LV) distribution network in Bosnia and Herzegovina was analyzed. Simulation tools carried out by DigSILENT PowerFactory offer a wide range of advantages that give system operators the ability to have insight into PQ behavior in the presence of intermittent renewable energy sources (RES). Due to the inverter-based electricity generation, PV power plants inject harmonics into the LV network. The impact is relatively small and does not violate the limits from the European PQ standard EN 50160 due to the relatively small power of the modelled existing PVs. However, integrating additional PVs could lead to a violation of limits. Therefore, where a large power of PV power plants is installed, if it is possible to integrate sHPP, they will contribute to the reduction of generated harmonics without the need to reduce the power of PV. The contribution of this paper is that it compares the impact of different power generation technologies on harmonic voltages using data from a real network rather than a test network.

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

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

Joint Planning Method of Virtual Power Plant for Distributed Generation and Grid in AC-DC Medium and Low Voltage Distribution Network

The high proportion of virtual power plants (VPPs) used for distributed generation may cause problems such as power fluctuations and voltage distribution. In contrast, AC/DC hybrid power grid has strong transmission capacity due to its power information transmission. However, Its power grid structure and the location and capacity of VPP have an impact on the consumption capacity of the system, and the relationship between them are closely coupled. In addition, Under different operation modes, power grids of different voltage levels also have great differences. Therefore, the cooperative planning of medium and low voltage AC and DC distribution networks can improve the transmission capacity of the power grid Further improve the ability of distribution network to consume distributed power, A method is proposed in this paper about siting and capacity determination and AC-DC distribution grid frame transformation planning for medium and low voltage systems. The upper-layer model mainly focuses on AC-DC transformation scheduling in the power grid, distributed node location in the access grid and transmission line transmission capacity, while the lower-layer model effectively communicates with the low-voltage system through information flow and changes the operation of the power grid to a certain extent.The results show that the distributed generation system can reduce the operation cost and improve the overall operation efficiency of the power grid.

A new methodology for optimization of overcurrent protection relays in active distribution networks regarding thermal stress curves

In this paper, a novel method for optimizing and coordinating directional overcurrent relays in active distribution networks considering thermal equivalent short-circuit current is proposed. A modified genetic algorithm is used as a tool in order to simultaneously minimize the operating times of the primary relays and maximize the time delay between the operation of backup relays and their respective protected elements’ thermal stress curves. In other words, the objective function to be minimized is defined as the sum of the operating times of all primary relays and the reciprocal sum of the thermal violation check. The latter part is necessary because a protection engineer needs to be sure that the operation of a backup relay is as far as possible from the thermal stress curve of the protected element. Needless to say, for every solution, the algorithm ensures the proper coordination between primary and backup relay pairs throughout the network. The simulation is carried out for a closed loop medium voltage distribution network and the results are presented to demonstrate the effectiveness of the proposed approach. The main benefit of this optimization process is that it indicates whether the existing protection system can operate safely below the thermal stress curves of the protected elements’ or whether additional measures are required.

State-of-the-art review on energy management and control of networked microgrids

As the United Nations plans to “ensure access to affordable, reliable, sustainable and modern energy for all,” great attention is paid to deploying sustainable networked microgrids to fulfill the future energy demand. Several neighboring low-voltage microgrids in a fixed or dynamic electric boundary will form a Multi-Microgrid. The unprecedented deployment of microgrids, brilliant communication, and infrastructure enable the concept of multi-microgrids to be an operational exemplar in future distribution networks, and it paves the way to deliver critical loads against all odds. This paper provides a state-of-the-art review of the evolution of networked microgrids with deep insight into the most critical research areas, opportunities, and challenges in energy management and control. Their operation and control in coordination with medium voltage distribution networks in time-varying loads and intermittent characteristics of renewable-based distributed generation sources are challenging for both distribution network and microgrid operators. Further, the complexities involved in the multiple control layers in the multi-microgrid network need appropriate strategies for optimal sharing and trading among neighboring microgrids. Numerous solutions based on advanced distribution control, reinforcement learning, adaptive deep neural networks, and game theory were reported in the literature. A systematic review of various energy management strategies, optimization scheduling frameworks, and multi-microgrid voltage and frequency control strategies are presented. Then, a detailed survey on hierarchical, decentralized, and distributed control architectures is reported. Finally, a comprehensive overview of research objectives and more than 30 solution methodologies with respect to both energy management and control is illustrated.

Research on Power Outage Sensing Technology of Medium and Low Voltage Distribution Network Based on Deep Learning of Multi-source Data Fusion

Aiming at the application of multi-source data fusion in intelligent operations of medium and low voltage distribution network system, a deep learning algorithm based on multi-source data fusion is proposed in this paper. Firstly, combining the stop/restart signals of a large number of users’ digital devices with the existing measurement information of the grid, two indicators of heartbeat and handshake signals have been constructed. Secondly, the convolutional neural network is combined with the improved D-S evidence theory, and an improved depth learning algorithm is proposed. Finally, taking a community as an example, the proposed algorithm is applied in practice and analyzed by simulation. The test results show that the model has good convergence and robustness. It is more intuitive and comprehensive in power failure evaluation. It has a wide power failure perception range and high accuracy and improves the quality of power supply service.

Study on fault waveform library of PT high voltage side fuse in hydropower station

In the arc-suppression coil grounding system of a medium voltage distribution network, high voltage side voltage transformer insurance fusing faults frequently occur, including fusing during startup and grid connection, fusing during operation, fusing during the shutdown, etc., which will directly affect the accuracy of measurement, metering, protection, and other secondary equipment. In this paper, we used the calculation of electromagnetic transient EMTP-ATP software, theoretical analysis of the typical hydropower station wiring and parameters of the medium voltage system, set up the improved model of neutral point grounding system, simulation of single-phase earth fault line and disappeared in the transient process, calculation of PT transient current, to verify that the way to study the mechanism of frequent fusing of fuse in the PT. Typical fault waveform databases are established under different bad working conditions (ferromagnetic resonance, low-frequency nonlinear oscillation, lightning wave invasion, etc.).

The online monitoring method of single-phase grounding fault in medium voltage distribution network based on multi-measuring point information

To reduce the error of single-phase ground fault and improve the security and stability of distribution network operation, an online monitoring method for single-phase ground fault in a medium voltage distribution network based on multi-measuring point information is proposed. Based on the analysis of single-phase grounding transient characteristics, the fault location is determined from the information of multiple measuring points according to the characteristics analysis results to realize the fault subsection location, identify the fault line section, and improve the location accuracy. Based on the fault location results, fault monitoring is realized through the “four-in-one” intelligent distribution terminal. The experimental results show that the accuracy of the monitoring results of this method is kept above 95%, and the monitoring error value of grounding fault is kept at about 1%, so the monitoring results have high reliability.

Research on distribution network optimal operation with a novel medium voltage photovoltaic power generation device with the soft open point function

Soft open point (SOP) realizes the normal and flexible interconnection between distribution network feeders, leading to the improvement of the flexibility and rapidity of the distribution network control. However, drawbacks such as high cost and low utilization rate limit its application. A novel medium voltage photovoltaic power generation device with the SOP function is proposed in this paper. There are two grid-connected interfaces, and both of them adopt the cascaded H-bridge topology. A common DC-link is used for both H-bridge inverters belonging to the two grid-connected interfaces respectively. The proposed device eliminates the step-up transformers, and can be connected directly to the medium voltage distribution network. Therefore, advantages such as simple structure, low cost, low power loss and fault-tolerant operation capability are able to be obtained. The stability and flexibility of the distribution network operation are improved. The topology and power flow mode of the proposed medium voltage photovoltaic power generation device with the SOP function are analyzed, and the distribution network multi-objective optimal operation model with the proposed device is established. The proposed medium voltage photovoltaic power generation device with the SOP function is connected to the modified IEEE 33-node distribution network, and the network optimal operation with the device in terms of the power flow optimization and voltage improvement is analyzed.

Penelitian Efek Penggunaan Grid Tie Inverter pada Sistem Hibrid dengan Solar Panel dan Diesel

The distribution system of electrical power begins from generation and is transmitted to the load, namely consumers. In this distribution, it must be effective, efficient, and reliable. The amount of electrical power reaching the load is not the same as the amount of power generated due to voltage drop or power losses. This research aims to determine the magnitude of power losses in the medium-voltage distribution network located in Pasar Aceh. The research method employed is the analysis and simulation calculation method using ETAP 12.6 software. The study analyzes power losses due to load imbalance in the JTR distribution substation of Pasar Aceh. Based on the analysis results, the load imbalance in the Pasar Aceh substation has led to power losses. The power losses in the Pasar Aceh substation, specifically at the Side Transformer of Pasar Aceh, are 0.77% with a load imbalance of 16.33%. For the second transformer in the BNI 46 area, the power losses are 0.98% with a load imbalance of 30.33%, and for the transformer in the BLKG KOTTY area, the power losses are 1.17% with a load imbalance of 50.33%. Therefore, the larger the percentage of load imbalance in an electrical distribution network, the greater the resulting power losses.

Intra-day optimal power flow considering flexible workload scheduling of IDCs

The online interactive workloads and offline batch computing services of Internet data centers (IDCs) have scheduling flexibility. Batch computing tasks with low latency sensitivity and priority can adjust the processing time and provide flexibility temporally. In contrast, interactive workloads with high latency sensitivity and priority can change the physical server for processing and provide flexibility spatially. Considering the change of power supply cost with time and space, the load flexibility of IDCs brought by Internet workload scheduling can be utilized to respond to the power system for more economical operation. To take full advantage of the flexibility of IDCs’ load demand, IDCs coordinated by an Internet service company (ISC) as a special controllable load with both temporal and spatial flexibility potential are considered. Instead of operating separately in normal optimal power flow (OPF) models, a two-stage interactive framework of the distribution system operator (DSO) and ISC is established. The operating state of the ISC is considered in OPF and is introduced as regularization terms into the objective function, thus fully exploiting its load flexibility. Some operation constraints are also added to guarantee the quality of service (QoS) of the ISC. The effectiveness of the model and the interactive framework are evaluated in a typical 33-bus medium-voltage distribution network. The results validate the further reduction of the power grid operation cost compared with the traditional OPF operation.

Optimal power flow based coordinated reactive and active power control to mitigate voltage violations in smart inverter enriched distribution network

ABSTRACT Voltage violations are the main problem faced in distribution networks (DN) with a higher penetration of inverter-based generations (IBG). Active and reactive power control from smart inverters (SI) can mitigate such violations. Optimal power flow (OPF)-based control provides more accurate operating set points for the coordinated operation of SIs. Therefore, this paper presents a three-phase OPF-based control on SI-enriched unbalanced distribution networks. To consider this, first three-phase model using the current injection model (CIM) is developed. Later, the optimal active and reactive power set points for SIs are obtained by solving a quasi-dynamic optimization problem. The uniqueness of the proposed method is that it regulates the voltage at the affected nodes by obtaining the optimal set points for the smart inverter. The OPF is implemented with a mathematical CIM in Pyomo and solved using the Knitro solver. The proposed method is compared with the sensitivity-based Volt-Var Control (VVC), Volt-Watt Control (VWC), and combined VVC and VWC methods. The effectiveness of the proposed method is verified in a European low-voltage and CIGRE medium-voltage distribution network with 100% penetration. The analysis shows that the OPF-based control optimizes with less network loss and can maintain voltage violations with less reactive power support.

Post-emergency reconfiguration of a distribution network as a method for restoring power supply to consumers

The work is aimed at solving the problem of using reconfiguration and additional reactive power sources to restore power to consumers of the medium-voltage distribution network in the case of emergency disconnections of connections by bus section circuit breakers. The reconfiguration problem for a 118-node test distribution network is solved using a high-speed algorithm involving the construction of a maximum spanning tree on a network graph as the basis for determining information about the composition of branches and chords of independent circuits necessary to restore power following disconnection. To ensure acceptable voltage levels following power restoration, additional reactive power sources determined using singular Jacobian matrix analysis methods are installed in the sensor nodes of the network. For the test circuit, the modes for single disconnections of individual sectional switches, including in dead-end sections, are analysed. By optimally reconfiguring the network in the normal mode, it is possible to reduce voltage deviations from 13% to 7%. For the modes caused by disconnections of individual bus section circuit breakers that lead to unacceptable voltage deviations, the set-down locations and reactive power of additional sources are selected. In the most severe of the considered disconnection scenarios, the installation of additional sources provided a reduction in voltage deviations from 18 to 8%. Thus, the methods proposed by the authors make it possible to restore the test network mode following emergency disconnections and ensure that the voltages in the network nodes are maintained within acceptable limits, both in normal and in post-emergency modes.

Fault Segment Location for MV Distribution System Based on the Characteristic Voltage of LV Side

The voltage and current measurement of the medium-voltage (MV) side are used for the traditional fault location method, which leads to a high installation cost of the measurement and complicated post-operational and maintenance work. A fault location method is proposed based on the distributed measurement at the low-voltage (LV) side. On the analysis of voltage distribution rules and the influence of the distribution transformer on voltage transmission, obvious differences are found in the variation of voltage (phase voltage and sequence voltage) at the LV side for different faults—specifically, the detection sensitivity of the voltage to different faults varies. Therefore, a fault location method for the MV distribution network based on characteristic voltage at the LV side is proposed. Firstly, the characteristic voltage is selected adaptively according to the fault type. The suspected fault path is then determined by the characteristic voltage amplitude of measuring points. Finally, the fault segment is located via the characteristic current of each segment. This method can be applied in combination with the widely used LV measurement equipment such as the power consumption information acquisition system and the intelligent fusion terminal to acquire LV side voltage without adding new measurement devices. The distribution difference of the characteristic voltage at the LV side is applied for accurate fault finding, which is an economical and practical new idea for the fault location of the distribution network. The correctness and effectiveness of the method were verified by the simulation of the IEEE 34 system built in PSCAD/EMTDC and a real distribution network.

Provision of reactive power services by energy communities in MV distribution networks

The paper presents a procedure for the optimal operation of a community of prosumers connected to a medium voltage distribution network equipped with generation and storage units that considers the penalization for low power factor operation, the exploitation of direct exchanges of both active and reactive power between the prosumers and the provision of reactive power services by the community to the local distribution system operator and the transmission system operator. The proposed procedure calculates the maximum and minimum reactive power deviations that each community participant can provide with respect to the reference profile. A deterministic day-ahead scheduling problem is considered assuming the forecast of load and photovoltaic production known without uncertainties. The formulation of the optimization problems and the solution computational requirements are suitable for the inclusion in a stochastic approach. The effectiveness of the approach is supported by numerical simulations of the daily scheduling for different test cases.

Analysis of single-phase grounding fault and its protection in the medium and low voltage distribution system

The single-phase ground fault of the medium and low voltage distribution system occurs most frequently in the distribution network. The fault should be eliminated in a short time. The single-phase ground short circuit fault that occurs when the neutral point of the power supply is not directly grounded in the medium and low voltage distribution network should be simulated and analyzed. The study seeks to understand the trend of voltage and current as well as the changes of its amplitude and phase when the fault occurs, which are consistent with the theoretical calculation and analysis. According to the analysis of single-phase grounding fault based on the simulated data, the acquisition of zero sequence current, the protection configuration, and the method of setting the point are discussed.

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.

Enhancing Voltage Compliance in Distribution Network Under Cloud and Edge Computing Framework

While high penetration of DER significantly helps facilitate the decarbonization of the electric power grid, it also brings unexpected operational challenges, among which voltage compliance has been a significant concern. To address this issue, the efficient load profile forecast, the operational framework and related strategies are critical challenges that need to be addressed urgently. Hence, this paper presents the cloud-edge computing-based framework to effectively operate a coupled medium-voltage (MV) and low-voltage (LV) distribution network. The high computational efficiency in cloud computing and low data latency in edge computing are presented and explored to coordinate the day-ahead and intraday operations ranging different framework layers. Under the framework, a customer-level forecasting algorithm is employed to predict both day-ahead and real-time load profiles. Next, an optimization model based on unbalanced-three phase optimal power flow is proposed and solved by an efficient and accurate linearization-based approach that considers the controllability of on-line tap changers, distributed static var generator and the PV inverters. Simulations based on an extensive mocked MV-LV distribution network and show the proposed forecasting method is adopted in the real-time operations in terms of high accuracy, and demonstrate the efficiency of the proposed method in enhancing the voltage compliance in the network.

Impact of Photovoltaic Penetration on Medium Voltage Distribution Network

Nowadays, large-scale solar penetration into the grid and the intermittent nature of PV systems are affecting the operation of distribution networks. This paper aims to investigate the effect of PV penetration on a typical medium-voltage distribution network in Malaysia. The main objectives of this study are to investigate voltage stability, power loss, and short circuit under two conditions: peak load and no load. The network is evaluated using two methods: static and dynamic analysis, utilizing the Digsilent Power Factory software. The network comprises two 33/11 kV parallel transformers connected to the 11 kV busbar and consists of 13 feeders and 38 loads. PV penetration of 500 kW per node is added, and the maximum potential PV penetration that is acceptable to connect to the grid is evaluated. The findings indicate that during peak load conditions, some nodes experience violations, but by increasing the PV penetration, the lower violations move up to the acceptable range. The highest power loss is 191 kW, occurring during peak load conditions at 0% PV penetration level. On the other hand, dynamic simulations were carried out with specific load time characteristics, and the results were compared under different PV penetration levels. The dynamic simulation results show that during contingency conditions, there are violations in peak load, and the maximum PV penetration for this study was determined to be 2MW. It is observed that the nodes 27, 28, and 29 violate lower voltage limits even at 100% PV penetrations.

Wind Forecast at Medium Voltage Distribution Networks

Due to the intermittent and variable nature of wind, Wind Power Generation Forecast (WPGF) has become an essential task for power system operators who are looking for reliable wind penetration into the electric grid. Since there is a need to forecast wind power generation accurately, the main contribution of this paper is the development, implementation, and comparison of WPGF methods in a framework to be used by distribution system operators (DSOs). The methodology applied comprised five stages: pre-processing, feature selection, forecasting models, post-processing, and validation, using the historical wind power generation data (measured at secondary substations) of 20 wind farms connected to the medium voltage (MV) distribution network in Portugal. After comparing the accuracy of eight different models in terms of their relative root mean square error (RRMSE), extreme gradient boosting (XGBOOST) appeared as the best-suited forecasting method for wind power generation. The best average RRMSE achieved by the proposed XGBOOST model for 1-year training (January–December of 2020) and 6 months forecast (January–June of 2021) corresponds to 13.48%, outperforming the predictions of the Portuguese DSO by 20%.