•The significant active power injection provided by high-capacity distributed generation (DG) units associated with the high R/X ratio of MV feeders may cause overvoltage at the point of common ...coupling.•High-capacity DG units can adversely affect step voltage regulator (SVR) control operations in reverse active power flow scenarios.•Reverse power tap changer runaway events are a threat to voltage security of active and reconfigurable distribution feeders containing SVRs.•The application of SVRs in long rural feeders with high-capacity DG units is crucial for maintaining voltage levels at all buses within predetermined operating ranges in the context of decentralized network operation.•The proposed optimal DG rescheduling approach prevents voltage issues and ensures reconfiguration options for the network whilst still benefiting the independent power producer.
This paper investigates and discusses voltage issues currently faced by engineers from a Brazilian utility in the high-capacity dispatchable distributed generation (DG) interconnection planning study on a real reconfigurable distribution network with cascaded step voltage regulators (SVRs). Based on this investigation, this paper proposes an optimal rescheduling approach applied to high-capacity dispatchable DG considering two additional technical constraints to the optimization problem for mitigating voltage issues, such as over/undervoltage violations and SVR runaway, while still allowing network reconfiguration schemes and benefiting the independent power producer (IPP). With this approach, the active power supplied by the IPP's DG is adjusted throughout the day with respect to the feeder load forecast, avoiding reverse power flow situations on SVRs and ensuring suitable control operation on reconfigurable distribution networks. The problem is formulated as a constrained optimization and solved through the primal-dual interior point technique. Simulation results on a real Brazilian reconfigurable distribution network demonstrate that the proposed method is effective to mitigate the identified voltage issues without affecting network reconfiguration operations and the weekly average active power injected by the DG.
Step voltage regulator (SVR) has been utilized in power distribution systems for decades as the voltage regulation device. Due to the increasing integration of distributed energy resources (DERs), ...the conventional SVR is severely challenged by the modern power distribution pattern with high renewable energy penetration. The induced arc from the conventional SVR tap change and more frequent tap changes due to voltage instability from the renewable energy impose constraints on the conventional SVR's lifetime. Meanwhile, the conventional SVR device cannot regulate the voltage accurately since the SVR regulates the voltage step by step. This paper proposed a hybrid voltage regulator with high efficiency and low contact wearing, which can achieve arcless tap change and stepless voltage regulation by using a fractionally rated back-to-back power converter. Accurate load voltage regulation is guaranteed while the tap changer mechanism remains in the system, which helps to promote the upgrade to the existing power distribution systems. The power converter capacity in the proposed topology is only 0.31% of the distribution transformer rating to achieve a stepless voltage regulation range of ±10%, significantly reducing the system cost compared with the full power electronics solutions and projects high total system efficiency. The proposed hybrid voltage regulator was simulated and experimentally validated. The experimental results demonstrate arcless tap change operation and stepless voltage regulation. Collaborative operation between the conventional mechanical tap change and the power converter operation is also demonstrated to acquire large voltage regulation with fast-acting voltage control.
High‐entropy layered oxide materials containing various metals that exhibit smooth voltage curves and excellent electrochemical performances have attracted attention in the development of positive ...electrode materials for sodium‐ion batteries. However, a smooth voltage curve can be obtained by suppression of the Na+‐vacancy ordering, and therefore, transition metal slabs do not need to be more multi‐element than necessary. Here, the Na+‐vacancy ordering is found to be disturbed by dual substitution of TiIV for MnIV and ZnII for NiII in P2‐Na2/3Ni1/3Mn2/3O2. Dual‐substituted Na2/3Ni1/4Mn1/2Ti1/6Zn1/12O2 demonstrates almost non‐step voltage curves with a reversible capacity of 114 mAh g−1 and less structural changes with a high crystalline structure maintained during charging and discharging. Synchrotron X‐ray, neutron, and electron diffraction measurements reveal that dual‐substitution with TiIV and ZnII uniquely promotes in‐plane NiII–MnIV ordering, which is quite different from the disordered mixing in conventional multiple metal substitution.
Dual‐substitution by Ti and Zn for Mn and Ni, respectively, in P2 type Na2/3Ni1/3Mn2/3O2 maintains in‐plane Ni–Mn ordering but disrupts Na+‐vacancy ordering, resulting in long‐cycling‐life non‐aqueous Na cells with smooth charge–discharge voltage curves and little structural change from the P2‐type layered structure.
Penetration of equipment such as photovoltaic power generations (PV), heat pump water heaters (HP), and electric vehicles (EV) introduces voltage unbalance issues in distribution systems. Controlling ...PV and energy storage system (ESS) outputs or coordinated EV charging are investigated for voltage unbalance compensation. However, some issues exist, such as dependency on installed capacity and fairness among consumers. Therefore, the ideal way to mitigate unbalanced voltages is to use grid-side equipment mainly. This paper proposes a voltage unbalance compensation based on optimal tap operation scheduling of three-phase individual controlled step voltage regulators (3ϕSVR) and load ratio control transformer (LRT). In the formulation of the optimization problem, multiple voltage unbalance metrics are comprehensively included. In addition, voltage deviations, network losses, and coordinated tap operations, which are typical issues in distribution systems, are considered. In order to investigate the mutual influence among voltage unbalance and other typical issues, various optimization problems are formulated, and then they are compared by numerical simulations. The results show that the proper operation of 3ϕSVRs and LRT effectively mitigates voltage unbalance. Furthermore, the results also show that voltage unbalances and other typical issues can be improved simultaneously with appropriate formulations.
Generally, utilities regulate the voltage on the long power distribution line within a permissible range by using a step voltage regulator (SVR), which is located around the middle of the line and ...operates according to the condition of the line current. However, as large-scale distributed generations (DG’s) are interconnected into distribution lines, it is difficult to maintain the line voltage properly owing to bi-directional power flow or reverse power flow. Therefore, this paper proposes a novel SVR tap-changing algorithm to solve the problem, considering line load conditions and reverse power flow. Its validity is verified through the PSCAD/EMTDC software tool and simulations.
Recently, utility-scale photovoltaic (PV) plants in remote areas are drastically increasing due to abundant and low-priced land. These remote areas are usually connected to zone substations through ...long weak feeders with open-delta step voltage regulators (SVRs) installed in the middle to regulate downstream voltages. However, frequent PV and load power fluctuations can lead to undesirable voltage variations and hence excessive tap operation issues. Currently, it is not clear about the percentage of responsibility by load or PV fluctuations to excessive tap operations. In this article, a novel method based on line-to-line voltage sensitivity and time series evaluation is proposed to respectively quantify the interactions between PV/load fluctuations and tap operations. The accuracy of this method is firmly validated with the measured data from a real-life unbalanced distribution network with high PV penetration. Further, this proposed method is implemented to statistically quantify the causes of excessive tap operations with half-year field data under the support of the local utility and the PV plant owner. The investigation results can provide valuable insights for utilities to better manage the voltage profiles and tap maintenance for remote distribution networks with high PV penetration.
In recent years, with the rapid development of the coastal economy and the large-scale development of marine resources, power demand has risen sharply. So it is urgent to promote the construction of ...UHVDC projects. Coastal saline areas often contain more chloride and other salts than other inland areas due to the high humidity, salinity and light intensity of the marine climatic and environmental conditions, which lead to the different electrical performance of grounding electrodes under different layouts. Therefore, one of the key issues to realizing the rapid development of UHVDC in coastal countries is how to choose the best layout of the coastal DC grounding electrode. It is intended to simulate the coastal environment and establish a mixed stratified soil model using CDEGS to verify the validity of the model through experiments in this paper. Based on the mixed soil model, the changes in grounding resistance, surface potentials and step voltage of grounding electrode sites under zigzag shape, two-row and circular shapes layouts are studied. The results show that when the zigzag shape layout is selected, the ground potential amplitude of the grounding electrode is reduced by 45.77% and 42.7%, the step voltage amplitude is decreased by 39.85% and 32.22%, and the grounding resistance is decreased by 28.45% and 27.68%, compared with the two-row and circular layout. In addition, its utilization rate of electrodes is better than the other two layout shapes.
In this paper, we propose a comprehensive scheme to determine a suitable method and timing for upgrading the voltage control method. Voltage control methods are expected to be upgraded in accordance ...with the photovoltaic (PV) penetration in distribution systems. The suitable method and timing detailed in this paper are based on the limit of the PV penetration rate, which is constrained by the regulated voltage deviation. The upgrade process involves moving the on-load tap changer (OLTC) control method from the conventional scalar line drop compensator (LDC) method to the vector LDC method or centralized control method. Then, a static var compensator (SVC) or step voltage regulator (SVR) is installed. The locations of the SVR and SVC are determined to maximize the PV penetration rate. The suitable method and timing are demonstrated using a general distribution system. In addition to the numerical simulations, experiments are performed using an active network system with energy resources. The experimental results are consistent with the numerical simulation results, thus validating the proposed scheme. The maximum PV penetration rate obtained using the OLTC control method is 55%. Whereas, the installation of the SVR and SVC increased the rate to 95% and 100%, respectively.
Bridges are usually located at the junction of land and water, where the surrounding area is open terrain, making them to be easily damaged by lightning strikes. The quantitative analysis of ...lightning transient characteristics and the impulse effect on bridges can provide scientific data to support the lightning protection design for bridges. In this study, a single-tower cable-stayed bridge is taken as a representative case. The CDEGS (Current Distribution Electromagnetic Interference Grounding and Soil Structure Analysis) software is used to establish a three-dimensional simulation model of the bridge. With this model, the magnetic field, step voltage, and lightning current distribution on the tower top, stay cables, and bridge deck under the most severe direct lightning strike scenario typical for cable-stayed structures are simulated. The results are as follows: (1) when the stay cables are struck by lightning, the peak of the magnetic field intensity is highest at the location of electronic information e
PDF
