Medium Voltage Substations Research Articles

Evaluation Method for Voltage Regulation Range of Medium-Voltage Substations Based on OLTC Pre-Dispatch

A new energy industry represented by photovoltaic and wind power has been developing rapidly in recent years, and its randomness and volatility will impact the stable operation of the power system. At present, it is proposed to enrich the regulation of the power grid by tapping the regulation potential of load-side resources. This paper evaluates the overall voltage regulation capability of substations under the premise of considering the impact on network voltage security and providing a theoretical basis for the participation of load-side resources of distribution networks in the regulation of the power grid. This paper proposes a Zbus linear power flow model based on Fixed-Point Power Iteration (FFPI) to enhance power flow analysis efficiency and resolve voltage sensitivity expression. Establishing the linear relationship between the voltages of PQ nodes, the voltage of the reference node, and the load power, this paper clarifies the impact of reactive power compensation devices and OLTC (on-load tap changer) tap changes on the voltages of various nodes along the feeder. It provides theoretical support for evaluating the voltage regulation range for substations. The day-ahead focus is on minimizing network losses by pre-optimizing OLTC tap positions, calculating the substation voltage regulation boundaries within the day, and simultaneously optimizing the total reactive power compensation across the entire network. By analyzing the calculated examples, it was found that a pre-scheduled OLTC (on-load tap changer) can effectively reduce network losses in the distribution grid. Compared with traditional methods, the voltage regulation range assessment method proposed in this paper can optimize the adjustment of reactive power compensation devices while ensuring the voltage safety of all nodes in the network.

Systematic testing, simulation, and mitigation of IEMI risks in medium-voltage substations

This paper introduces a comprehensive suite of testing, simulation, and mitigation strategies aimed at evaluating and countering intentional electromagnetic interference (IEMI) risks in medium-voltage (MV) substations. Diverging from conventional IEMI testing methods, the proposed testing approach assesses the entire substation control system, offering a more precise understanding of its IEMI vulnerabilities. Additionally, a novel simulation method coupling the transmitting antenna model and the full-wave substation model is presented for IEMI estimation, which simplifies the simulation process while maintaining good accuracy. Moreover, to further fortify substations against IEMI risks, a quantitative analysis is established to determine the necessary distance between the substation building and the fencing boundary. This analysis enables the integration of protective measures during the design and construction phase of the substation, substantially mitigating IEMI risks. Through a case study using a typical MV substation, the efficacy and capability of the proposed methods are demonstrated.

Boosting short term electric load forecasting of high & medium voltage substations with visibility graphs and graph neural networks

Modern power grids are faced with a series of challenges, such as the ever-increasing demand for renewable energy sources, extensive urbanization, climate and energy crisis, which set new standards and requirements in terms of their stability, sustainability and security, paving the way to transition to smart grids. Energy management, planning and control systems that include state-of-the-art technologies such as fifth-generation technology standard for cellular networks, Artificial Intelligence, Machine Learning and Internet of Things are considered to be the driving force of this transition, with short-term load forecasting constituting a crucial component in any such system. In this work, a novel graph neural networks model is proposed, which is boosted by the properties of visibility graphs for day-ahead mixed load forecasting. Specifically, the electric load time-series are transformed into an undirected graph by employing the visibility graph approach and then, trains a graph neural network with inputs the obtained graph along with the corresponding adjacency matrix. The efficiency of the so-called visibility graph neural networks is assessed by conducting a plethora of experiments using real data from a high voltage/medium voltage substation. Extensive results that presented confirm the dominance of the proposed method over widely used machine learning methods.

Transient overvoltage analysis in the medium voltage substations based on full-wave modeling of two-layer grounding system

In this paper, a comprehensive investigation of substation grounding soil structure effects on switching/lightning transients is presented. The full-wave computational solution Method of Moments (MoM) is adopted to solve Maxwell’s equations. The significant advantage of this technique is its ability to deal effectively with substation grounding systems (SGSs) at high frequency. This evaluation is carried out considering two soil structures: (1) a uniform soil and (2) soil with a layered structure. The impacts of both soil structures on the peak transient overvoltage values are compared. To begin with, the harmonic impedance matrix (HIM) of the layered multi-terminal SGS is computed. Then, a vector fitting approach is employed to incorporate the accurate SGS behavior by relying on the obtained HIM into time domain simulations. Finally, the transient overvoltages and maximum ground potential rise (GPR) are computed. The chief contribution of this paper is the transient assessment of the two-layer multi-terminal soil structure of the large SGS taking into account the frequency dependence model of the electrical parameters of soil, which is not generally investigated and instead, treated simplistically. According to the results of the study, the lack of an exact grounding system models may lead to underestimations/overestimations of the GPR and the overvoltage values. The results demonstrate the need for the grounding modeling of SGS considering layered soil structure to be incorporated into power system transient analysis in a wide range of frequencies.

A new clustering method for the optimization of distribution networks layout considering energy efficiency and continuity of service

The electrification of final consumptions and the spreading of distributed generation have fostered the search for new and more advanced electrical grid planning techniques, considering many of the aspects affecting electrical grids operation, such as their electrical and economic performance, as well as system reliability. Distribution network clustering is defined to be the division of the utility service territory into several high voltage–medium voltage substation service areas, and it represents one of the most important steps for grids planning. In this context, the purpose of this paper is to propose an innovative clustering algorithm based on Mixed Integer Linear Programming (MILP) formulation, able to take into account some fundamental aspects of the distribution networks planning process, such as the electrical losses along lines, the existing distribution network layout, and the reliability of the system. The approach, tested on the medium voltage network of the medium-sized city of Meran in the North of Italy, has proved to effectively manage the computational burden needed to model and optimize the structure of a complex distribution grid, as those that usually cover large urban areas.

High Reporting Rate Smart Metering Data for Enhanced Grid Monitoring and Services for Energy Communities

Capturing the dynamic behavior of the power distribution grids, especially under high penetration of renewables, is of high interest for grid operators. The distribution power grids are not fully observable due to lack of sufficient metering infrastructure, especially downstream of medium-voltage substations. Therefore, fusion of data recorded at significantly different reporting rates is proposed to increase the situational awareness of the system with non-negligible effect on the accuracy of the monitoring tool. Higher reporting rates are possible for next generation smart meters (SM), but they raise higher concerns about data privacy, already an issue for SM rollout. This article proposes a framework for knowledge extraction from high reporting-rate SM data. The process takes place at SM level and with low computation and communication costs and preserving user privacy, with the scope to increase the accuracy of the monitoring tools for distribution power grids. The methodology makes use of statistical metrics able to capture system dynamics relevant for network diagnosis. The proposed approach is validated on a three-phase low-voltage power flow model applied to a realistic testbed microgrid and real field measurements synchronized at 1 s.

Experiences and Analyses of Reconstruction and Commissioning of Medium Voltage Substation

Abstract The paper will present experiences in the reconstruction of the transformer station, which supplies the industrial factory. The previous version of the medium voltage (MV) substation with oil-filled transformers, and the new MV substation with dry and more energy efficient transformers, will be presented. An analysis of the operation and maintenance methods of oil transformers will be given. As oil transformers have many disadvantages, the reason, choice and cost-effectiveness of replacement with new dry transformers will be presented. Tests and measurements of insulation resistance of the winding and transformer protection during commissioning will also be presented. PT100 probes, which are connected to the thermostat, are installed in each low voltage winding of the dry transformer. Testing of this thermal protection of the transformer will be presented as well. Since transformers supply industrial consumers, mostly nonlinear ones, it is important to analyse the losses and life span of transformers. Nonlinear consumers lead to early aging of winding insulation, premature failures and reduction of transformer life. The newly designed and installed MV substation with Ring-main unit is ABB type SafePlus, and its installation and operating instructions will also be presented. The MV is equipped with a protection terminal, so settings and measurements of this terminal in transformer cells will be done. After the commissioning of the transformer station, the most important are diagnostics and periodic tests. Methods of periodic testing of MV substations will be presented in this paper.

Soft Sensing Image Analysis and Processing Method of Substation Equipment Defects

Under the background of incentive regulation of distribution companies, reference network model can be used as a valuable tool to evaluate its effective cost. These models must plan large-scale distribution areas with different voltage levels. This paper describes a green space planning algorithm for optimizing the location, size and power supply area of RNM medium and low voltage substations. In this paper, from two aspects of “environment-friendly” substation and the importance of implementing “resource-saving” substation in China, the “environment-friendly” and “environment-friendly” are studied. The results show that feature 1 is 0.363, feature 2 is 0.835, feature 3 is 0.824.

XLPE Kabloların Orta Gerilim Dağıtım Sistemlerinde Kapasitif Etkisinin İncelenmesi

Cross-linked polyethylene insulation (XLPE) type underground power cables used in medium and low voltage distribution systems bring out a reactive effect with capacitive character due to the constructional properties of XLPE cables. If this effect is not eliminated, it causes negative influences on losses, cost, and capacity. Therefore, this study focuses on the capacitive effects of XLPE type underground cables and the appropriate compensation systems to overcome the issue on a medium voltage distribution system with 5500 m-length. The measurements taken from a medium voltage substation have been compared to corresponding simulation results. As a result, a very successful match between simulation and measurements has been achieved. Furthermore, a series of suggestions for establishing appropriate compensation has been presented, which is expected to serve the more efficient transmission and distribution of energy. Since the need for more energy and the amount of utilization are increasing, it is compulsory to carry out the works to decrease the loss rate of the transmission and distribution of energy.

New Sensor for Medium- and High-Voltage Measurement

Measurements of medium and high voltages in a power grid are normally performed with large and bulky voltage transformers or capacitive dividers. Besides installation problems, these devices operate in a relatively narrow frequency band, which limits their usability in modern systems that are saturated with power electronic devices. A sensor that can be installed directly on a wire and can operate without a galvanic connection to the ground may be used as an alternative voltage measurement device. This type of voltage sensor can complement current sensors installed on a wire, forming a complete power acquisition system. This paper presents such a sensor. Our sensor is built using two dielectric elements with different permeability coefficients. A finite element method simulation is used to estimate the parameters of a constructed sensor. Besides simulations, a laboratory model of a sensor was built and tested in a medium-voltage substation. Our results provide a proof of concept for the presented sensor. Some errors in voltage reconstruction have been traced to an oversimplified data acquisition and transmission system, which has to be improved during the further development of the sensor.

Electrical Infrastructure Design Methodology of Dynamic and Static Charging for Heavy and Light Duty Electric Vehicles

Full electrification of the transport sector is a necessity to combat climate change and a pressing societal issue: climate agreements require a fuel shift of all the modes of transport, but while uptake of passenger electric vehicles is increasing, long haul trucks rely almost completely on fossil fuels. Providing highways with proper charging infrastructure for future electric mobility demand is a problem that is not fully investigated in literature: in fact, previous work has not addressed grid planning and infrastructure design for both passenger vehicles and trucks on highways. In this work, the authors develop a methodology to design the electrical infrastructure that supplies static and dynamic charging for both modes of transport. An algorithm is developed that selects substations for the partial electrification of a highway and, finally, the design of the electrical infrastructure to be implemented is produced and described, assessing conductors and substations sizing, in order to respect voltage regulations. The system topology of a real highway (E18 in Norway) and its traffic demand is analyzed, together with medium-voltage substations present in the area.

Application Method of Communication Technology in Integrated Automation System of Substation

Since its application in my country, the integrated automation system of substations has been rapidly developed and popularized. Its application range has covered medium and low voltage substations, even high voltage substations, and has achieved certain application effects. With the continuous development of my country’s power industry, higher and higher requirements have been placed on the automation level of the entire power system. As the heavy pressure link of the entire power system, the automation level of the substation system will directly affect the operation level of the entire power grid. This has also prompted the continuous upgrading of the integrated automation system of this substation. This article focuses on the development status of communication technology in the integrated automation system of substations, analyzes the characteristics and requirements of communication technology in substations, and discusses the application of communication technology in the integrated automation system of substations.

Minimization of Energy Losses in Mid-Delta Zone.(Dept.E)

This paper aims al minimizing energy losses in the Mid-Delta zone using load flow methods. The mathematical model is applied to the Mid-Delta zone. The 220 kV network is modeled in the load flow program for each season of the year while the losses in the high voltage substations. medium voltage network and medium voltage substations are calculated using a heuristic approach. This paper presents a practical approach that would asist, the decision making process in an electric utility to optimize the operation procedures to save investements required to install new equipment to meet the growth on electric demand if the losses are minimized.

On single pole instrument voltage transformer overheating

Abstract The paper deals with calculation of overheating of a voltage instrument transformer used in medium voltage substations. Calculation of the primary and secondary windings is compared with measured values. These values are evaluated according to IEC 618691:2007, IEC 61869-3:2011 and IEC 60085:2007. In evaluation we focused on the state 1.9 × nominal voltage and thermal limiting output state. The article also compares the results for various parameters of instrument transformers that are necessary for clarification of calculation.

Multi-objective optimization for the superconducting bias coil of a saturated iron core fault current limiter using the T-A formulation

The short-circuit levels have increased considerably in transmission and distribution systems in the last years. Fault current limiter (FCL) devices are a potential solution to this problem. Among several FCL topologies, this group has good experience in the use of superconducting fault current limiters (SFCL) to reduce the electrical current during short-circuits. The literature also presents studies of the saturated iron core superconducting fault current limiter (SIC-SFCL) topology employing mathematical modeling and prototypes design. Some of them have shown promising results, including the construction of pilot prototypes in medium and high voltage substations. The SIC-SFCL simulation studies presented optimal topologies that reduce the amount of ferromagnetic material used in the core and represent well the behavior of this limiter. The finite element method and the finite element analysis are suitable to model the SIC-SFCL. However, a more detailed study focusing on the optimization of the DC bias superconducting coil of the SIC-SFCL has not been presented in the literature yet. In this context, this work proposes a multi-objective optimization method using the Nelder–Mead algorithm to find an optimal geometry for the superconducting coil. In this optimization, the objectives functions are: to maximize the critical current density in the high-temperature superconductor (HTS), minimize the voltage drop in the copper winding, minimize the current through the DC biased superconducting winding, and minimize the price of the HTS superconducting winding. Before implementing the multi-objective optimization algorithm, we have tested a non-superconducting saturated iron core prototype and used the results to validate the simulation models. After that, we have replaced the DC copper winding with an HTS coil in the simulations and initiate the optimization process. Results show that constructing the DC bias superconducting coil using the minimum possible fill factor might not be the best choice.

Power System Impedance Estimation Using a Fast Voltage and Current Changes Measurements

Equivalent power system impedance is an important electrical quantity from many points of view. Areas in which this parameter plays an important role include, in particular: Voltage stability analysis, power quality, or fault condition analysis. Power system impedance estimation in real operation conditions can be performed by one of the non-invasive methods described by different authors. This paper aims to investigate and compare seven different methods for power system impedance estimation based on voltage and current variations measurement. After a brief description of selected methods, these methods were applied for power system impedance estimation in the case of two simple simulation tests and then in the case of three real measured data. Voltage and current changes used for power system impedance estimation in real conditions were measured in high voltage (HV) and medium voltage (MV) substations feeding steel mill with the electric arc furnace (EAF) operation. As the results presented in this paper have shown, not all of the methods analyzed are suitable for determining the power system impedance based on the fast step changes of voltage and current that occur, for example, during an EAF operation. Indeed, some of the tested methods were originally designed to determine the power system impedance from changes in voltages and currents recorded at steady state.

Graph-Based Second-Order Cone Programming Model for Resilient Feeder Routing Using GIS Data

One important task in power distribution system expansion planning is feeder routing (FR), which is to determine the optimal route from a medium voltage substation to load points and the optimal size of the conductors to be installed. This paper proposes a novel graph-based model for the resilient feeder routing problem using geographical information system (GIS). We show that incorporating GIS data enhances the FR solution optimality. Moreover, by introducing a representing graph, radiality of the planned network is guaranteed. A second-order cone programming (SOCP) model is used to model power flows through feeders. Since the representing graph ensures radiality, the SOCP model is exact. The uncertainty of rooftop solar generations and demand forecasting errors are taken into account, and a stochastic programming-based solution algorithm is developed. The proposed model represents practical aspects such as economic objectives (installation cost, power losses, resiliency), technical constraints (voltage limits, radiality constraint, reliability), and geographical constraints. The efficiency of the algorithm is demonstrated using three case studies: a small test system, a realistic one, and a synthetic large test system.

Modularization of High Voltage Gas Insulated Substations

Many existing petrochemical facilities are replacing outmoded high voltage (HV) air insulated switchyards (AISs) with new gas insulated switchgear (GIS) substations. Modularization or prefabrication has strategic advantages over site-built substations. While medium voltage (MV) and low voltage (LV) substations have been modularized for many years, the HV GIS substation modularization has not caught up with the construction industry. The modularized HV GIS substations are significantly different compared to other electrical MV or LV substations. This article addresses the modern philosophy and approach to modularization and how the end-user can benefit, in terms of design flexibility, cost-effectiveness, reduced lead times, premium quality, and accelerated site execution in a new or an operating facility. It describes the technological developments, design concepts, quality assurance, and environmental impact in delivering complete solutions based on site conditions.

Design of an Underground, Hermetic, Pressurized, Isolated and Automated Medium Voltage Substation

This paper presents a new concept in underground medium voltage substations for an optimized operation performance and overall cost reduction. Due to its high-level embedded automation and communication systems, increased standards of reliability, availability and security are reached. Moreover, less expensive IP00 equipment can be used instead of higher IP-rated equipment, since the substation enclosure is hermetic and pressurized. Cost and time of construction works are reduced, as is the inconvenience to the population, especially when it comes to intense traffic areas. In addition, overall personnel labor is downsized, which reduces costs. In this context, the features and design guidelines of the proposed substation concept are presented, along with the methodology developed to address the thermal, structural and electric design issues.

Uticaj podzemnih kablova na merenje impedanse sistema uzemljenja primenom FSM koncepta

Ground impedance measurement in medium voltage substations, designed to operate in a predominantly cable network, is a complex research task. Namely, the inability to consider all the factors that can affect the measured value, in a situation where one deenergized cable line is used to form the Fall-of-Potential (FOP) measurement scheme, is directly reflected to an adequate assessment of safety risks. This paper proposes an alternative measurement method so called Frequency Shift Method (FSM), which inherently guarantees "better" measurement than any of the conventional methods. By providing insight into the behavior of the active and reactive ground impedance components, and at the same time taking into account the topological structure of the existing cable network, the application of the FSM concept in the FOP measurement scheme points out to alternative paths of test current distribution, and in that way pointing to the illogicality of the obtained measurement results. Experimental verification was conducted under real operating conditions, and can serve as a guide for solving similar problems in practice.