Medium Voltage Research Articles

22.9 kV 배전계통의 피뢰기 접지저항에 따른 섬락률 분석

This paper presents an analysis of lightning induced over-voltage effect on medium voltage (22.9 kV-y) and low voltage (380/220 V) network regarding to different values of grounding resistance of lightning arrestor in terms of flashover rate. The study is focused on an indirect lightning effect considering a BIL of distribution line. Monte Carlo method is adopted to generate the total number of lightning events. The attractive radius model is used to determine direct or indirect lightning among the total lightning events and hence to evaluate the flashover rate. The shield effect is also analyzed for a case of urban area where buildings surround distribution lines.

Analysis of Maintenance Optimization on Medium Voltage Overhead Lines (SUTM) in Reducing Energy Not Supplied (ENS) at PT. PLN (Persero) ULP Tarakan

The background of this research is an analysis of equipment disturbances that occur in distributing electrical energy. The disturbance is a blackout. Power outages cause a decrease in the continuity of service to customers and result in a lot of loss of electrical energy that is not distributed to customers. The research objectives are to find out the optimization technique of distribution network maintenance, how to reduce the value of energy not supplied (ENS), find out the losses due to ENS, and find out the total electrical energy distributed after preventive maintenance is carried out. This research uses a preventive maintenance method, which is maintenance that can prevent unexpected damage to distribution system networks and equipment. This research optimized preventive maintenance actions by reducing disturbances after preventive maintenance from 7 disturbances in February to 2 disturbances in March. Before preventive maintenance, the loss due to ENS amounted to Rp. 36,192,017.626, and the total electrical energy not distributed was 25,025.76 kWh. After preventive maintenance, there was a significant decrease in the total loss due to ENS of Rp. 953,516,447, and the amount of electrical energy not distributed was 659.28 kWh. This research can increase maintenance efficiency due to electrical energy losses by 97.36% at the time interval when this research data is managed when data collection is carried out in the field.

Имитационное моделирование воздушных линий электропередачи напряжением 610 кВ для исследования алгоритмов определения места возникновения однофазных замыканий на землю

As part of evolution of single phase to earth faults protection methods and tools in 6–10 kV networks the development of simulation study methods of these networks and their components becomes relevant. A significant direction in this area is upgrading of sensors installed directly on the wires and electrical transmission towers. These sensors are installed in the conditions of an electromagnetic field acting on them and dynamically changes both in time and space, especially during emergency modes including single phase to earth faults. Application of modern software offers a challenge for complex simulation study of electromagnetic fields distribution at the location of the measuring transducers in continuously variable electromagnetic environment. The above-noted statement determines the relevance of the research goal, which is the development of a simulation study method of 6–10 kV overhead power lines, the model of which is designed to study existing and create new single phase to earth fault location algorithms and devices. To solve the tasks set the methods of simulation study of overhead transmission lines and corresponding medium voltage networks in PSCAD and COMSOL Multiphysics software have been used. The general concept of design of a 6–10 kV network and an overhead transmission line simulation model is formulated. The geometrical parameters of the section of the model of an overhead power transmission line to simulate electromagnetic transients are selected, considering the frequency dependence of the line parameters (inductance and active resistance). The proposed model of the overhead transmission line is verified, and recommendations for its application are given. The developed “inductive” component of the proposed overhead transmission line model allows to provide high accuracy of calculation of transient components of currents and voltages during single phase to earth faults. It makes possible to use this model for the development and research of single phase to earth fault location algorithms. The developed approach to simulation study of an overhead transmission line is the field of interest for further research, as it makes it possible to calculate the components of the electric field which are observed during single phase to earth faults.

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.

Segmentation of a conventional medium voltage network into solar PV powered microgrid

This paper aims to convert a feeder of a bulk supply point (BSP) into a microgrid with rooftop solar PV plants sited in senior high schools along that MV grid in Ghana. The study used a solar PV Python optimization and forward–backwards algorithms to arrive at its results. The results show that rooftop PV plants sited in the study area can produce electricity to meet the feeder’s peak demand (8.2 MW) and have an extra 11.3 MW fed back to the grid. Cases 1, 2, 3 and 4 saw increases of 1.16%, 1.74%, 2.26% and 2.32%, respectively, higher than the nominal voltage of 34.5 kV. The base case total loss was 1.1 MW, and case 1 was 0.3 MW.

Optimal substation capacity planning method in high-density load areas considering renewable energy

With the increasing penetration of renewable energy, the adaptability of the existing substation planning model in terms of capacity and quantity of transformer needs to be further studied when preferring large-capacity substations. Considering the variations of renewable energy penetration rate and load, this paper proposes a method to optimize the total capacity of substations in distribution networks. This paper introduces the influence of renewable energy access on power supply reliability and introduces the idea of partitioning for economic analysis of reliability. An economic analysis model for simultaneously optimizing the capacity and quantity of substation transformer in the distribution network is constructed, taking into account the effects of reducing net load and enhancing the reliability of the distribution feeders resulting from renewable energy access to the medium and low voltage side of the substation. Various wiring means of the distribution network are retained and the impact of renewable energy access on the reliability of the network power supply is quantified. The optimization model is solved by the multivariate universe optimizer(MVO) algorithm with stronger optimality finding capability and short solving time. Finally, the case study results of a regional distribution network are employed to demonstrate and verify the validity and rationality of the method.

A High Voltage Gain Interleaved DC-DC Converter Integrated Fuel Cell for Power Quality Enhancement of Microgrid

Fuel cells have drawn a lot of interest in recent years as one of the most promising alternative green power sources in microgrid systems. The operating conditions and the integrated components greatly impact the quality of the fuel cell’s voltage. Energy management techniques are required in this regard to regulate the fuel cell’s power in a microgrid. The active/reactive power in the microgrid should be adjusted in line with US Energy Star’s regulations whereas the grid current needs to follow the standard set by IEEE 519 2014 to enhance the power quality of the electrical energy injected into the microgrid. Uncontrolled energy injection from the fuel cell can have serious impacts including superfluous energy demand, overloading, and power losses, especially in high power and medium voltage systems. Although fuel cells have many advantages, they cannot yet produce high voltages individually to compensate for the demand of a microgrid system. Due to these reasons, the fuel cell must be interfaced with a DC-DC converter. This research proposes a novel high voltage gain converter integrated 1.26 kW fuel cell for microgrid power management that can boost the fuel cell’s voltage up to 20 times. Due to this high voltage gain, the voltage and current ripple of the fuel cell is also reduced substantially. According to the analysis, the proposed converter demonstrated optimal performance when compared to the other converters due to its high voltage gain and extremely low voltage ripple. As a result, the harmonic profile of the microgrid current persists with a reduced THD of 3.22% and a very low voltage ripple of 4 V. To validate the converter’s performance, along with extensive simulation, a hardware prototype was also built. The voltage of the fuel cell is regulated using a simplified proportional integral controller. The operating principle of the converter integrated fuel cell along with its application in microgrid power management is demonstrated. A comparative analysis is also shown to verify how the proposed converter is improving the system’s performance when compared against other converters.

Hybrid space vector modulation for low‐order common‐mode voltage reduction in current‐source rectifier for transformerless medium voltage drives

AbstractFor transformerless current‐fed medium voltage drives, low‐order harmonics of common‐mode voltages (CMVs) are more concerned with than peak values. To mitigate low‐order harmonics, the average values of CMVs should be suppressed. A hybrid space vector modulation (SVM) is proposed in this study to further reduce CMV average values generated by a current‐source rectifier (CSR) compared to existing zero‐state vector selection modulation. The proposed SVM is a combination of zero‐state vector selection and active zero‐state modulations. The transition points between two modulations are defined based on various modulating index. Power losses and efficiency of the proposed hybrid SVM are analysed in detail. Simulation on a medium‐voltage CSR (1 MW/4160 V/139 A) and experiments on a scale‐down CSR (2.5 kW/208 V/6.94 A) are conducted under various working conditions, which validates the effectiveness of the proposed SVM to further mitigate 180 Hz and other low‐order harmonics in CMVs in contrast to that by conventional zero‐state vector selection modulation.

Grid‐aware provision and activation of fast and slow power flexibilities from distributed resources in low and medium voltage grids

AbstractThe intermittencies of renewable generations give rise to situations, which require both slow‐ and fast‐ramping flexibility capability from a variety of resources connected at the medium voltage (MV) andlow voltage (LV) distribution grids. Moreover, this may increase the grid reinforcement costs. To defer this reinforcement, the grid needs to be operated optimally. This paper proposes—(a) such an optimal operational methodology forthe MV and LV grids; and (b) an aggregated flexibility estimation methodology separately for fast and slow services at the primary substation (transmission interface). The methodologies based on model‐based MV grids and sensitivity coefficients‐based LV grids are suitable for LV grids where an up‐to‐date, accurate model and topology are not always available. Besides, the costs and resources associated to create full LV grid model and visibility should be prevented. The approaches, here, use the synchronised and accurate measurements from grid monitoring devices located at the LV distribution grids. They have been validated on a real MV and LV networks of a Swiss distribution grid operator equipped with such devices. The results, in terms of reducing technical losses, reducing grid violation costs,and estimating flexibility capability show the efficacy of the proposed methodologies and therefore, can be easily deployed.

Estimation of Pressure and Temperature Rise Due to Internal Arc Generation in Switchgears

The switchgears are vital component in energy system which protects, regulates and isolates the electrical transmission line by making or breaking the high voltage circuit with the use of circuit breakers. During the operation of switchgear internal arc is a failure criterion which is a result of a short circuit current. To quench this arc, the internal arc chamber is used which encapsulates the energy generated and protects the further transmission system and appliances. The gas insulated switchgears used for medium voltage application are enclosed inside the metal chambers and thus design of these chambers becomes crucial as they handle high pressures and temperatures. This fact is also exacerbated by the condition that metal chambers are prone to sudden increase in pressure due to internal arc phenomenon. The type testing process used for validating the design of chamber against internal arc is time consuming, costly and thus shall be performed with no margin of error. The paper aims to establish the standardized approach to calculate the instantaneous pressure and temperature rise inside the gas tank of switchgear which are otherwise impossible to approximate given the short timeframe in which internal arc occurs by using the approaches discussed in the CIGRE committee reports.

Developing bird friendly transmission power lines in Kenya

Background: Kenya's rich wildlife is an important natural resource and is vital to the country's economy. However, rapid infrastructure development in key wildlife areas has threatened the survival of numerous species including raptors. Policy: The growing distribution of electricity grids in Kenya poses a significant risk to raptors and populations of other large birds. This research aimed to review the policy gaps in Kenya’s National Energy Policy (2018) examining the strategies for developing bird friendly transmission power lines in Kenya, with a goal to reduce the negative impact on raptor populations and improve their conservation. The findings indicate a high overlap between the ecological niche of raptors with medium and high voltage transmission power lines, with indication of high-risk hotspots for electrocution and collisions. Recommendations: This policy brief therefore proposes the adoption of bird friendly power lines in new transmission infrastructure projects and retrofitting existing power lines with bird friendly devices. This can be achieved through strengthening the legal and regulatory frameworks in the National Energy Policy. This will help prioritize avian conservation in power lines infrastructural development projects including the development of specific policies and guidelines for the placement, orientation, and marking of power lines to reduce the risk of electrocution and collisions of raptor species. Conclusions: Kenya committed to protecting migratory bird species and their habitats by signing the Convention on the Conservation of Migratory Species of Wild Animals in 1999. However, the National Energy Policy of 2018 lacks guidelines for bird-friendly power lines. Addressing this requires collaboration from the government, power companies, research institutions, conservation groups, and local communities. A concerted effort involving public education, targeted funding for research, and stakeholder collaboration can help Kenya meet its conservation obligations and safeguard vital habitats for migratory birds.

IMPLEMENTATION OF 20 kV VOLTAGE NETWORK IN UKRAINE

Background Due to the war, the medium voltage networks are in an extremely difficult condition, they have a high degree of depreciation of electrical equipment and a low level of automation. The energy system of Ukraine has a problem of modernizing medium voltage networks and transfer them to a new class of rated voltage of 20 kV.
 Objective Overall overview of 20 kV networks and organization of their topology with renewable energy sources and " energy storages ". 
 Methods A network model in the MatLab software package was used to study "energy accumulators". The study of the efficiency of the "energy storages" was carried out in the variability of the power to the total load, as well as the time of connection to the network.
 Results The need to transfer voltages of 6 (10) kV to a higher level of 20 kV has been proven. Various methods of grounding the neutral of medium voltage networks are considered and the most effective modes of neutral grounding for 20 kV networks are determined: through an arc suppression coil or through a resistor. A comparative analysis of networks with and without energy storage was carried out. In 20 kV networks, without the use of energy storage, energy consumption from the network and power losses will increase. When using storage devices, they are permanently connected to the network and have their own power losses. Batteries connected to a 20 kV network lead to an oscillating process that has a damping character (within 2 seconds).
 Conclusions The transition from the voltage level of 6 (10) kV to 20 kV will significantly increase the efficiency of distribution networks and reduce electricity losses. The installation of energy storage in 20 kV distribution networks will allow the introduction of new intelligent systems to ensure the interests of safety, economy and energy efficiency and will create the prerequisites for the implementation of the Smart Grid concept.

A Comprehensive Review and Analytical Comparison of Non-Isolated DC-DC Converters for Fuel Cell Applications

The use of renewable energy sources such as solar photovoltaic, wind, and fuel cells is becoming increasingly prevalent due to a combination of environmental concerns and technological advancements, as well as decreasing production costs. Power electronics DC-DC converters play a key role in various applications, including hybrid energy systems, hybrid vehicles, aerospace, satellite systems, and portable electronic devices. These converters are used to convert power from renewable sources to meet the demands of the load, improving the dynamic and steady-state performance of green generation systems. This study presents a comparison of the most commonly used non-isolated DC-DC converters for fuel cell applications. The important factors considered in the comparison include voltage gain ratio, voltage switch stress, voltage ripple, efficiency, cost, and ease of implementation. Based on the comparison results, the converters have been grouped according to voltage level applications, with low voltage applications being best served by converters such as DBC, DuBC, TLBC, 2-IBC, 1st M-IBC, PSOL, SEPIC, and 1st M-SEPIC owing to their lower cost, smaller size, and reduced switch stress. Medium voltage applications are best suited to converters such as TBC, 1st M-TLBC, 2nd M-TLBC, 4-IBC, 1st M-IBC, 2nd M-IBC, 1st M-PSOL, 2nd M-PSOL, 1st M-SEPIC, and 2nd M-SEPIC, which offer higher efficiency. Finally, high voltage applications are best served by converters such as TBC, 1st M-TBC, 2nd M-IBC, 3rd M-IBC, 3rd M-PSOL, 4th M-PSOL, 2nd M-SEPIC, 3rd M-SEPIC, and 4th M-SEPIC.

Reconstruction ofthepower supply system based onanalternative energy source

The article presents a solution for the reconstruction of an oil refinery using gas piston power plants. The oil refinery is a structural subdivision of Kogalymneftegaz. The work of the plant is intended for the production of high-quality petroleum products for technological transport of the divisions of Lukoil — Western Siberia LLC in Kogalym, Langepas, Pokachi; in addition, the plant’s products are in demand at other enterprises of the Khanty-Mansiysk region. In the course of the study, the goal was to offer an alternative source of energy for the trouble-free operation of an oil refinery, to ensure the reliability of objects belonging to the first category. Based on the analysis of the existing power supply system of the plant, it was found that the power receivers of the ELOU-AVT-Bitumen plant are provided from two sources of power supply from the Tyumenenergo network, which does not guarantee uninterrupted and trouble-free operation of the plant. The power supply of the refinery is provided with a voltage of 6 kV from Substation No. 7 35/6 kV. Substation No. 7 is powered by 110/35/10 kV Substation Druzhnaya from the medium voltage side via two power feeders Druzhnaya-1 and Druzhnaya-3. In the study, the calculation of loads, short circuit currents was carried out, the necessary power equipment was selected, and a method was proposed for transferring the refinery to power supply from a stationary power plant operated on hydrocarbon gas utilized from the production process. The proposed solution allows: to eliminate the occurrence of emergencies at the refinery due to a power outage; reduce the cost of purchasing electricity and thereby reduce the cost of commercial petroleum products; increase the percentage of hydrocarbon gas utilization by reducing the amount of gas flared.

Interoperability of single-controllable clusters: Aggregate response of low-voltage microgrids

Microgrid clusters are complex systems that require the implementation of management strategies to control multiple elements and regulate the offering energy services. This paper proposes a management approach capable of aggregating the operation of clusters of multifunctional microgrids, aiming at improving the resiliency of distribution and transmission systems, as well as enhancing the microgrids’ power quality, under predictable and unpredictable events. Since the approach manages microgrids inserted into cluster to operate as single-controllable entities, a variety of ancillary services can be offered (e.g., energy time shifting, peak shaving, islanded operation, and many others). Consequently, operational goals can be pursued locally (i.e., at the point of common coupling of each microgrid) and systematically (i.e., at specific medium and high-voltage circuit branches). To demonstrate the applicability of the proposed energy management system, simulations were carried out using Matlab/Simulink, considering customized blocks in phasor domain, and taking the CIGRE’s European benchmark as reference model for the low-, medium- and high-voltage power systems. Different from previous studies, the simulations fully emulate the interoperability among microgrid central controllers, microgrid system operators and distribution system operator, demonstrating that a wide range of ancillary services can be put into action by means of the aggregate response of microgrids and based on price signals, without causing electrical overload. It is also demonstrated in the results that the active and reactive power flow in the high voltage grid is flexibly regulated, the power factor is increased up to 0.955 at different circuit branches, and the power quality is improved in the distribution level during absence of power generation at the medium voltage grid.

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.

Ageing and energy performance analysis of a utility-scale lithium-ion battery for power grid applications through a data-driven empirical modelling approach

Energy storage systems are becoming one of the most relevant technologies to effectively support renewable energy source (RES) deployment at large. The present work proposes a detailed ageing and energy analysis based on a data-driven empirical approach of a real utility-scale grid-connected lithium-ion battery energy storage system (LIBESS) for providing power grid services. The system under investigation is an operative utility-scale LIBESS integrated with a multi-MW PV plant and connected to the medium voltage network, located in Southern-Italy. The ageing and energy analysis has been performed using data measured by the supervisory control and data acquisition (SCADA) system directly connected with the LIBESS. This large amount of data is collected in a cloud database and then elaborated using proper software tools. This experimental campaign applied on a commercial LIBESS covers the impact of degradation mechanisms, such as cycle and calendar ageing, the battery and global system efficiency as well as the role of auxiliaries' power consumption under normal and power grid services operations. Thanks to the low complexity of the proposed data-driven model, it could be easily replicated in any other LIBESS facility, both operative in real-world framework and in laboratory context. The state-of-health (SOH) estimated by the degradation model implemented in this work after 3 years of operations and after 356 full-cycles equivalents is equal to 95.88 %, with an average capacity loss compared to the nominal capacity of about 1.37 % per year. Energy analysis revealed an average system global efficiency of 85 % for operations close to the nominal power that decreases to 65 % for operations at low power rates. While considering the grid network services operations, the power grid applications investigated are primary frequency regulation, secondary voltage regulation and PV unbalances reduction. Our results show that primary frequency regulation is the most efficient service in terms of ageing and energy performances. It has been evaluated a capacity loss of 0.03 kWh per each full-cycle equivalent performed during primary frequency regulation. Differently, secondary voltage regulation and PV unbalances reduction present a capacity loss of 0.1 kWh and of 0.05 kWh per each full-cycle equivalent, respectively. At the same time, the global efficiency of primary regulation (around 83 %) is remarkably higher compared to secondary voltage regulation (about 47 %) and to PV unbalances reduction (about 55 %). Results support the relevance to identify the most impacting key performance indicators for effective exploitation of LIBESS in power system and network services applications.

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.

Problems Related to Selected Methods and Techniques of as-Built Surveys of Low- and Medium-Voltage Electricity Connectors with a Practical Discussion

Abstract The aim of the paper was to analyse problems related to the inventory (as-built survey) of low and medium voltage power lines. Measurement methods and techniques were analysed as well as the influence of the network type (low and medium voltage) on the as-built survey procedure. For this purpose, information obtained from five as-built survey reports of medium and low voltage using different measurement methods was also used. Three of them were sample as-built survey of low voltage cable lines measured by tacheometric method, one as-built survey of medium and low voltage lines measured by GNSS method and one of low voltage cable made by indirect method using cable locator and measured by GNSS technology. The paper analyses the differences arising from the accuracy of the measurement, the difficulties encountered during the implementation, the time-consuming nature of the work performed, taking into account safety aspects for the persons performing the work.

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.