kV Network Research Articles

Solar on-grid power plant and its connection to the electric network

The network solar power plant and its connection to the electric network are considered. This system of autonomous alternative power supply belongs to the network type. The main focus of the system is the supply of generated electric power to the consumer's network and the transfer of the surplus to the city network according to the “Green Tariff”. The expected electrical capacity of the solar power plant is 860 kW. The system is a multi-branched star consisting of the following elements: solar batteries; network inverters; systems for monitoring network solar power plant mode parameters; electricity meters; power lines. The necessary number of solar panels to cover the power of consumers has been determined. The distribution of energy generated by solar panels is uniform between phases. Solar panels are placed on special metal ground structures. Inverters are selected to connect the panels to the three-phase alternating current network. Three-phase inverters are installed at this electrical station. The inverter is equipped with additional protective devices to guarantee safe operation in any conditions. Fuses are installed in the inverters to protect the equipment from short circuit and overvoltage. Inverters are installed on metal structures that are placed under tables with solar panels. All direct current wiring is made of specialized solar single-core cable with double polyvinyl chloride non-flammable insulation. The cross-section of the cables is selected according to the permissible current loads and checked for voltage losses. Tiles are laid in metal trays and open on structures. The connection of the solar power plant to the 10 kV network is transferred using a complete transformer substation of the external installation.

ОГЛЯД ПРИНЦИПІВ СЕЛЕКТИВНОСТІ ЗАХИСТІВ В РОЗПОДІЛЬЧИХ МЕРЕЖАХ СПОЖИВАЧІВ НАПРУГОЮ 0,4 кВ

The analysis of existing principles of selectivity indicates the complexity and incompleteness of ensuring the coordination of the operation of protection devices in distribution networks of 0.4 kV consumers. Current selectivity is ensured only in the area of action of short-circuit currents. To ensure it, electromagnetic or electronic decouplers with a constant deceleration setting are required. This type of disconnectors is used to perform time selectivity and limit the thermal impact of short-circuit currents on the electrical installation and device. The use of devices with "pseudo-time" selectivity ensures the selectivity of the operation of automatic switches in the area of short-circuit currents. Selectivity "SELLIM" is provided with a speed of 0.01 s, but it is possible only in automatic circuit breakers "Schneider Electric". Logical selectivity requires a communication channel between switching devices and the presence of circuit breakers with appropriate communication ports. It is easiest to ensure selectivity by using switches from the same manufacturer using selectivity tables. But such a solution is not always found in practice. The method of energy selectivity allows, taking into account the ratio between ratings, to implement either partial selectivity or full selectivity up to the limit of the breaking capacity of automatic switches. To ensure energy selectivity between two or more current-limiting devices, it must be taken into account that depending on the location of the short circuit, a different number of circuit breakers will be involved in limiting the emergency current, and therefore, the value of the limited current will also be different. By using circuit breakers with a high level of current limitation and a tripping speed that is inversely related to the short-circuit current, full selectivity can be provided at several levels of the network. This makes it possible to simplify the analysis of selectivity, minimize electrodynamic and thermal effects and reduce the level of voltage drop due to the action of a short circuit. Improvement of electrical installation protection systems makes it possible to design power supply systems without excessive reserves of electrical equipment overload, which reduces their cost, dimensions and weight. On the other hand, in the event of malfunctions in the operation of electrical equipment, this limits emergency currents and prevents failure of the undamaged part of the electrical installation, which significantly reduces downtime. Key words: selectivity, relay protection devices, circuit breakers, electrical devices, 0.4 kV network.

Towards an interpretable data-driven switch placement model in electric power distribution systems: An explainable artificial intelligence-based approach

The fault management process is facilitated by equipping power distribution systems with automated devices, especially remote-controlled switches (RCSs). Although RCS plays a key role in improving the system's reliability, it imposes significant investment, installation, and maintenance costs. Hence, RCSs should be optimally located in distribution feeders for the highest profit. In previous works, reliability-oriented mathematical optimization models have been formulated to reach this goal. However, the number of test solutions exponentially grows with the problem size to find the globally optimal solution. This paper uses machine learning to propose a scalable and easy-to-implement model for optimal switch placement in real power distribution systems. At first, the features of candidate points for installing RCSs are introduced. Then, a learning model is applied to deeply explore the relationship between these features and optimal locations for installing RCSs. After training, the learning-based surrogate model directly determines the optimal RCS placement strategy in real power distribution systems by leveraging knowledge gained from past experiences. Simulation results demonstrate that the proposed surrogate model is approximately 29 times faster than the integer programming-based mathematical model, without a significant loss of accuracy, when implemented on a modified 11 kV network connected to Bus 4 of the Roy Billiton test system. This paper also employs explainable artificial intelligence (XAI) tools to select the most important features, where the Hamming loss is decreased by approximately 5%.

Implementation and laboratory verification of method utilizing phase and neutral quantities for detection and location of low‐current earth faults in resonant grounded networks

AbstractEarth faults is a challenging fault type to locate in resonant grounded networks due to their naturally low fault current, and the problem increases with an increased fault impedance. This paper describes the detailed implementation and laboratory testing of a method for detection, location and clearing of earth faults with very small fault currents. The method consists of two indicators used in the fault detection stage, where their simultaneous operation ensures selective fault detection and faulty feeder selection. One of these indicators also enables continuous fault indication throughout a sectionalizing process. The laboratory tests demonstrate that both indicators function as intended, and it is the current sensors which ultimately limit the attainable sensitivity. Faults up to 15 kΩ were detected successfully in the laboratory network based on phase current measurements, while the sectionalizing indicator showed much higher sensitivity and functioned as intended in a 50 kΩ fault. Measurements from one field test in a 22 kV network corroborate the laboratory results and demonstrate the expected earth fault indicator response.

Algorithm for phase distribution in power supply systems of single-phase electric receivers according to the criterion of minimization of the coefficient of load ununiformity of the phases used at the design stage

RELEVANCE. Unbalance of loads adversely affects both the work of consumers and the electrical network itself. This phenomenon leads to a decrease in the efficiency of the processes of transmission and distribution of electrical energy due to the appearance of additional losses. Balancing of loads in electrical networks of 0.4 kV is carried out both at the design stage of networks and during their operation. At the design stage, they try to evenly distribute the loads across the phases. The authors of the article solve the actual problem of distributing single-phase electrical consumers at the stage of designing a power supply system to analyze the total share of additional losses from unbalance in the structure of total losses in distribution networks of 0.4 kV.THE PURPOSE. To consider the problem of unbalance of loads in electrical 0.4 kV networks, causing additional losses of electricity. To analyze the existing methods of balancing when distributing the phases of the lines L1, L2, L3 of single-phase power receivers at the stage of designing electrical networks. Develop an algorithm for single-phase power consumer distribution, using arrays of instantaneous values of the current strength of individual electrical receivers as initial data. It stipulates calculating the best distribution of power consumers across the phases of lines L1, L2, L3 using the minimization of the load unbalance impact on the losses in power grid elements used for the electric power transfer.METHODS. To solve this problem, the authors employed the complete enumeration method implemented with a tertiary numerical system used to code power consumer distribution across the power supply grid phases. The coefficient accounting for the unbalance of load distribution across power grid phases is used as the target function.RESULTS. The developed algorithm can be applied as an external plug-in for the design software package to distribute the power consumers of one of the rooms in a BIM office building. The developed algorithm is compared to the existing widely-used approaches to single-phase power consumer distribution in power grids.CONCLUSION. The developed algorithm allowed producing brand-new engineering solutions while developing a design document for the power supply grid (design and detailed documentation stage). They help improve the efficiency of electric power transmission by reducing additional losses caused by unbalanced loads.

Switching Operations in 110 kV Networks in the Context of Synchro-Check and Mitigation of Switching Stress by Utilizing Proper Control of Renewables and Energy Storages

Synchro-check (SC) relays are devices that control synchronization between different fragments of power system networks. Synchronism is monitored by controlling the voltage amplitude, angle, and frequency differences. The goal of monitoring is to avoid dangerous transients after the circuit breaker (CB) closing, which occur when the differences between the voltage, angle, and frequency at both sides of the CB are above the threshold. Although the idea of SC is straightforward, one needs to realize that blocking of the CB closing may cause even more severe issues, i.e., the deterioration of power system stability and safety. The conflicting goals of the switching operation result in many different interpretations, regarding the recommended settings and utilization of the SC relays in different locations of power system networks. The paper presents considerations connected with switching operations in power systems, in particular, in 110 kV networks. Different problems connected with switching operations are highlighted and described. Moreover, the switching-relevant parameters and switching constraints are provided. Further, the simulation results connected with switching operations are presented, the realistic possible voltage and angle differences before switching operations are provided, and the impacts of mitigation measures—renewables and energy storage—are estimated. Finally, the proposed procedures and algorithms of switching stress mitigation are provided.

Application of Artificial Neural Network Model for Improved Power System Protection in Port Harcourt 33 kV Network


 
 
 Electric power distribution networks are exposed to the environment due to their length, for this reason, they are mostly affected by faults. These faults disrupt the continuous flow of power supply. There is also an associated loss of power that is generated that also determines the state of the economy. In order to reduce system downtime, it is necessary to integrate a system that detects and classifies faults quickly in order to hasten its clearance. This will bring about improvement in the efficiency and integrity of the power network. The artificial neural network as proposed in this study is meant to detect, classify and locate fault on the Rukpokwu 33-kV
 feeder of Port Harcourt Electricity Distribution Company (PHEDC). Fault detector, classifier and locator, with feed-forward back propagation were employed in the research. Matlab Simulink software was used to model and simulate the distribution network. The model was trained using s values of voltages and currents. With the simulation results, the efficiency of the proposed network was demonstrated for fault detection, classification and location. Mean square error (MSE) and confusion matrix were used to evaluate the performance of the proposed model. Results showed that the acceptable MSE of 0.00000027736 and an accuracy of 100% were achieved, which is satisfactory.
 
 

ПІДВИЩЕННЯ ЕФЕКТИВНОСТІ РОЗПОДІЛЬНИХ МЕРЕЖ РАЙОНІВ МАЛОПОВЕРХОВОЇ ЗАБУДОВИ МІСТ

The article analyzes the methods of estimating the parameters and regimes of electrical distribution networks in areas of low-rise urban development. A method for optimizing the parameters of distribution networks of 0.38 kV under conditions of uncertainty of the initial information is proposed. It is shown that one of the unsolved problems of calculating the parameters of distribution electric networks of cities is the determination of the estimated load of utility consumers. Its dependence on the characteristics of consumers and their number connected to the lines of city transformer substations causes the low accuracy of calculations. In this case, the error of calculating the transformer substations load can reach 10-25%, and the error of calculating the cross-sections of 0.38 kV lines reaches 40%. In the assumption of the constancy of the total length of the lines of urban electric networks and the invariance of the distance between loads, calculation formulas for linear moments and load distribution coefficients are proposed, and based on them, models of intersection and power losses in lines are developed. Taking into account the developed models, we offer discounted cost models for 0.38 kV networks and transformer substations when calculating economic current density and allowable voltage costs. Keywords: optimization, distribution networks, uncertainty, efficiency, low-rise building, scheme.

Microgrid Design in Electricity Supply in Paper Factories

Renewable energy is growing, one of which is by controlling solar energy. A solar power plant (PLTS) is a power generation system that utilizes solar energy to become electrical energy through photovoltaic modules, which are included in environmentally friendly energy so that it becomes a renewable, effective, more efficient, and reliable plant. The research designing the modeling of PLTS on a grid was carried out on the roof of a gas power plant (PLTG) which generated 164.47 MWh / year. Analyzing modeling in the addition of the Rooftop Solar System that enters the network can reduce exhaust emissions from the use of other equipment for four years with an average of PLN by 99.29%, PLTG #1 by 99.06 and PLTG #2 by 99.11%. The impact of the addition of the PLTS Rooftop on the quality of power entering the 3.3 kV network system is seen that the feeder 2-panel bus has improved to 97.82% of the voltage drop of 72.67% in line with the PLN 3 panel, the improvement is made by providing capacitors of 3x4Mvar. Feeder 3 improved to 97.61% of the voltage drop of 78.87%, in line with the PLN 4 panel. The improvement was carried out by providing a capacitor of 2x4Mvar. Panel feeder four was seen to have improved to 99.21% from an excess voltage of 109.23% in line with the generating equipment, and the improvement was made by reducing capacitors by 0.1 Mvar from the used 5x0.1 Mvar.

Analysis of methods for monitoring the technical condition of high-voltage electronic measuring transformers

The objectives of the present study included an analysis of statistical data on the failure causes of highvoltage equipment with a particular focus on current and voltage measuring transformers; a study of factors affecting the technical and functional condition of measuring transformers; a review of available methods for monitoring the technical condition of high-voltage electronic measuring transformers; the development of the basic principles of a stationary system for monitoring the technical capabilities of electronic measuring transformers. A review of available scientific publications and copyright objects on the aforementioned problems was conducted. The results were processed using the principles of systematic approach, as well as induction, deduction, classification and abstraction methods. The existing methods for monitoring the technical condition of high-voltage electronic measuring transformers were analyzed. The influence of various regimes and external factors on the technical and functional state of measuring transformers was investigated. The main principles for developing a stationary system for monitoring the technical condition of electronic measuring transformers were formulated. It was established that the failure of measuring transformers in medium voltage networks accounts for 6% of all failures. In 110 kV and higher-voltage networks, this level reaches 7%. It was found that the majority of accidents is associated with damaged insulation, poor-quality manufacturing and installation of the equipment, the impact of operating parameters and external factors on the technical and functional state of measuring transformers. Based on the considered methods for monitoring the technical condition of high-voltage equipment, a functional scheme of a stationary system for monitoring the technical capabilities of electronic measuring transformers at a digital substation is proposed.

Transient overvoltage transfer and amplification in a 400 kV network – A case study

The paper investigates overvoltage propagation in a 400 kV network within the National Grid Electricity Transmission system in the UK. The studies were triggered by a replacement project for two parallel 400 kV cables and the installation of an additional one. The network in the vicinity of the cables has historical issues of flashover and circuit breaker failures. Electromagnetic transient studies were performed to simulate energisation and fault inception and clearance for the three new cables to examine compliance against overvoltage standards and limits. Studies were performed using the DIgSILENT analysis tool. Studies show that due to resonance in a specific frequency range, switching overvoltage propagated and amplified at remote nodes to a level close to the equipment's rated switching voltage. As mitigation, surge arresters with characteristics different from the National Grid recommended surge arresters were proposed and found suitable to bring the overvoltage values within the design limits for temporary overvoltage.

A Method and an Algorithm for Implementing Relay Protection of 6(20)/0.4 kV Step-down Transformer Substations

The article discusses a method and an algorithm for implementing the protection system for a 6(20)/0.4 kV transformer substation, using which its reliable operation is secured regardless of the grid configuration and operation mode and the operation parameters of higher-level electrical installations. The proposed method makes it possible to clear any fault in the 0.4 kV network with minimal time delays. To this end, it is necessary to supplement the 0.4 kV network with current transformers (if they are not available) and forward the algorithm control output to the circuit breaker tripping coils. To ensure short-range backup protection, the circuit breakers protective functions remain in operation. Based on the existing electrical network, the approximate pickup parameters of the proposed method are pointed out, and recommendations for their optimization are given. Various contingencies in the 0.4 kV electrical network are considered to verify the correct functioning of the proposed relay protection method and algorithm.

Ensuring the Serviceability of 0.4 kV Electric Networks in Case of Breaks of the Combined Neutral and Earth Conductor

Breaks of the neutral conductor are among the most common failures in 0.4 kV networks. At present, to ensure the electrical safety of personnel, grounding loops with standard values of grounding resistance in compliance with Electrical Installation Code (PUE) are set up. Such grounding loops do not have any significant impact on the power quality indicators. Moreover, their construction is quite expensive and requires significant material costs. To maintain power quality parameters within the permissible limits, grounding loops with much lower resistance values are needed, which, however, are much more expensive. One of the ways for solving the problem under consideration is the use of natural grounding conductors for temporarily maintaining the standard electric power quality. The article addresses the problem of ensuring the electric power quality in case of breaks of the neutral conductor and a decrease of its conductance with reference to voltage unbalance. The ways of solving this problem are briefly outlined, in particular, by laying an additional conductor or using the TN-C-S grounding system. One of the alternative solutions to the problem considered is the use of natural grounding conductors, for example, a reinforced concrete foundation or a metal fence. The grounding resistances of such grounding conductors were calculated, the estimated values of which have confirmed the possibility of using them to comply with the PUE requirements. Practical recommendations for implementing the suggested proposals are given. One of them is to develop a device for monitoring the state of the neutral protective and main conductors. The key related issue of the problem considered is to ensure the electrical safety of both personnel and all people staying in the territory in which the grounding is temporarily used as the main neutral conductor. This issue will be addressed in the subsequent publications.

Cost Effective Reliability Improvements in 33kV/11kV Electricity Distribution Networks – A Case Study in Western Province South 1, CEB, Sri Lanka

Electricity Distribution system in Sri Lanka consists of 33 kV, 11 kV and LV (400V/230 V) networks. Providing reliable supply to the end user is a challenging task to any utility. Therefore, utility is committed to develop its network to provide reliable supply to electricity users by investing in system developments. In this research, a methodology is introduced for selecting cost-effective solutions to improve the reliability of the 33 kV and 11 kV distribution systems among different proposals. Improvement of conductor, its insulation and protection of short duration faults are focused to develop the system in this research. Part of the method developed includes a software tool (named as DisFeeRIA) to analyse the reliability indices and economic parameters for the relevant proposal. Database of the DisFeeRIA software tool includes failure rate improvement, mean time to repair and costing of each option under consideration. Medium Voltage Underground Cable (MVUGC), Medium Voltage Aerial Bundle Conductor (MVABC), Medium Voltage Covered Conductor (MVCC), Room Temperature Vulcanizing (RTV) Si-R coating on existing bare overhead line ceramic insulators are considered as options for improving conductor and its insulation. One of the latest and innovative technologies used in distribution network, Pulse Closing Technology, is used to reduce short duration faults (momentary interruptions) and enhance the lifetime of the equipment used in distribution networks. Developed tool and method were tested by a case study done for distribution network in Western Province South – 01 of Ceylon Electricity Board (CEB). Three (03) feeders were selected in different areas from Urban, Coastal and Rural for this purpose. MVCC and RTV Si-R coating for existing Medium Voltage Bare Overhead lines can be used for improving the reliability of Coastal, Urban and Rural distribution feeders in a cost-effective manner after proper analysis, based on technical and economic aspects. However, depending on the safety concerns, MVUGC or MVABC can be used irrespective of the economical aspect. Intelirrupter pulse closers can be used to replace traditional auto recloses, especially with MVUGC, MVABC and MVCC in rural feeders. It helps to reduce momentary interruption failures and enhance the equipment lifetime by reducing thermal and mechanical stress on all distribution equipment and cables. Furthermore, it improves the power quality of the system.

Investigation of the impact of PSO, ABC, BFO and Cuckoo search optimization techniques on UPFC device for sustainable voltage stability margin improvement

This paper investigates the enhancement of voltage stability margin using Unified Power Flow Control (UPFC) device tuned with Particle Swarm Optimization (PSO), Artificial Bee Colony (ABC), Bacterial Foraging Optimization (BFO) and Cuckoo Search techniques (CS) on Nigerian 330 kV 56-bus practical network. In order to have a voltage stable power system, it is good to keep voltages within the acceptable limits. This is achieved using continuation power flow embedded in Power System Analysis Toolbox (PSAT). The optimal location and tuning of the UPFC device is determined using line stability index and the met-heuristics techniques. The effects of UPFC and the proposed optimizing techniques on voltage stability margin are examined. The results so obtained for tuning PSO, ABC, BFO and Cuckoo Search with UPFC device are compared to know the technique that yields the best loading parameter for Nigerian 56- bus power system for voltage stability margin enhancement. It is found that UPFC tuned with Cuckoo Search outperforms the other techniques in terms of the increased loading parameter of the Nigerian power system with margin improvement of 86.6%, 90% and 88.6% for Adiabor (Bus 45), Jalingo (Bus 34) and Jos (Bus 13). The tuned UPFC device has proved beyond reasonable doubt that it can improve voltage stability margin of the entire Nigerian 330 kV Network as envisaged from results before and after optimization.

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.

Investigation of the Transfer Capability of the Nigerian 330 kV, 58-bus Power System Network using FACTS Devices

Over the years, the Nigerian power system is beset with lingering problems, which include severe power losses, as well as very low transfer capability of the transmission network to evacuate power from generating stations to the load at the distribution level. Presently, the Nigerian power industry is undergoing restructuring, especially in the generation and distribution systems. In view of the deregulation of electricity distribution and marketing, the traditional practices of the Nigerian power system are undergoing changes to address the identified problems in the existing power system. Specifically, better utilization of the existing power transmission network to improve on the system transfer capability and minimize cost is one of the key focuses of the deregulation agenda. This work deals with the enhancement of transfer capability of Nigerian 58-bus, 330kV network using FACTS (Flexible Alternating Current Transmission System) devices. FACTS devices are used for controlling transmission voltage, power flow, reducing reactive power losses, and damping of power system oscillations for high power transfer capability. Three FACTS devices; Thyristor Controlled Series Compensator (TCSC), Unified Power Flow Controller (UPFC), and Interline Power Flow Controller (IPFC) were used to investigate the transfer capability of the Nigerian 58-bus power system network. NEPLAN was employed in this work to model the Nigerian 58-bus system and optimally placed the FACTS devices at the weakest buses that were found out through the computation for available transfer capability (ATC) after continuation power flow (CPF) simulation was completed. MATLAB codes were developed and used to calculate power transfer capability of the network without and with FACTS devices. Comparing the three FACTS devices, the results obtained showed that UPFC enhanced the power transfer capability of the network than TCSC and IPFC.

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.

Modeling Power Flows and Electromagnetic Fields Induced by Compact Overhead Lines Feeding Traction Substations of Mainline Railroads

The ongoing re-equipment of electric power systems is based on the use of smart grid technologies. Among the key tasks that are solved on this basis are increasing the capacity of power transmission lines, reducing losses, and improving power quality. To address these issues, one can use compact power transmission lines. Such lines are notable for their complex split-phase designs and close together placement of current-conducting parts, so as to keep the distance to a permissible minimum, which is achieved by the use of insulating spacers. This article reports the results of computer-aided simulations performed for a standard railroad power supply system, the traction substations of which were connected to 220 kV networks through compact overhead lines (COHLs). The purpose of the study was to calculate the values of quantitative metrics that measure power quality and energy efficiency as well as electromagnetic safety. Modeling was performed in the three-phase reference frame with the use of techniques and algorithms implemented in the Fazonord software package. We considered a power supply system with 25 kV overhead contact systems. It was assumed that the external network used three different designs of COHLs: with coaxial, linear, and sector-shaped arrangements of conductors. Based on the results obtained, we concluded that (1) when using COHLs, the voltages on bow collectors of electric rolling stock were stabilized and did not exceed permissible limits; (2) losses in the traction network were reduced; and (3) the parameters of power quality and electromagnetic safety conditions in external power supply systems of railroads were improved, if judged in terms of electric and magnetic field strengths. Out of the eight types of COHLs considered, compact lines with the three-segment and concentric arrangement of conductors had the best performance, and the use of COHLs with the vertical arrangement of conductors made it possible to reduce electric field strengths. However, the designs of such transmission lines are quite complex and entail higher construction costs.

Analysis of the Causes of Outages in the Distribution System of Lagos State, Nigeria

The distribution system is essential in the provision of electricity for all consumers. However, outages occasioned by faults are a major setback in ensuring a regular supply of electricity to consumers in a populous state like Lagos. This study analyses the outage causes, their cost, energy loss, and duration of outages experienced by electricity consumers in the distribution systems of Lagos State. The fault reports of Eko Electricity Distribution Company (EKEDC) and Ikeja Electricity Distribution Company (IKEDC) were used for the analysis. The analysis revealed that the main causes of outages on the network are transient faults (356.78 occurrences per month) and jumper cuts (352.83 occurrences per month). The average monthly cost impacts of the outages on the network are estimated to be between ₦631m & ₦837m and ₦837m & ₦1.66b for the 11kV and 33kV networks of the State respectively. The average monthly energy lost due to outages on the network for the period under review is significant (100,415.34 MWh in total) while the average monthly duration of the outages is notably high (28,463.34 hours in total). To minimise outages and their impacts, faults should be cleared on time while the lines are patrolled and maintained regularly. The jumpers should be replaced with metal line taps or bi-metal line taps while intermediate poles are introduced in over-spanned lines to minimise transient fault on the network of the State.