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In this paper, typical strengths, fault levels, and source impedances are thoroughly analyzed and calculated for the study of quality of supply in 230/400 V 50 Hz distribution systems. Considering all the disparity in distribution network design, this study is based on a comprehensive database containing typical arrangements and equipment in U.K./European systems, as well as on fully documented generic network models supplying four residential load subsectors in the U.K., i.e., from metropolitan to rural areas. Thus, this paper proposes an alternative method for determining reference values of network supply impedances and short-circuit fault levels at different points and locations of the medium-to-low voltage distribution system. The aim of this study is to provide a wider range of benchmark values than those stipulated in the IEC 60725 Standard, which only defines a single-reference threshold of public supply impedances for all types of distribution systems and residential customers. In order to assist network operators in the planning and design of their distribution systems, these values are further disaggregated and classified in this paper according to network/demand type.

With the integration of intermittent renewable generation, transmission voltage problems have become more dynamic. The deployment and tuning of numbers of VAr compensators at various locations may not be cost-effective. This paper presents an alternative method, which utilizes existing parallel transformers in distribution networks, to provide reactive power absorption services for transmission systems with low demands. The operation of parallel transformers in small different tap positions, that is, with staggered taps, can provide a means of absorbing reactive power. The aggregated VAr absorption from many pairs of parallel transformers could be used to provide voltage support to the upstream transmission network. This paper focuses on the economic and technical analyses of using the tap staggering method. For the economic analysis, the associated costs of applying the tap staggering technique are investigated through static load-flow studies. The IEEE Reliability Test System is used to carry out the studies and the results are compared with the installation of shunt reactors. In the technical studies, the dynamic impacts of tap staggering or reactor switching on transmission voltages are analyzed. From the results, the tap staggering technique has more economic advantages than reactors and can reduce the voltage damping and overshoots during the transient states.

Cable parameter extraction is needed for many practical purposes. The main motivation for this research came from a need to extract high-frequency properties of cables used for indoor electricity distribution because they can be utilized for transmission of communication signals, too, by means of the power-line carrier (PLC) technology. These cables have relatively high specific losses, so that indoor broadband PLC applications can use frequencies up to some 30 MHz. In this paper, cable features in the frequency range from 5 to 30 MHz, belonging to the high-frequency band, were studied. The purpose of this paper is to describe a practical method by which the cable parameters in the mentioned indicated frequency range can be extracted rather accurately from measured complex reflection coefficients at a cable end when the other end is terminated by precise open and short terminations, using very simple equipment. The parameters extracted in this way can be used for very precise modeling of real-life multiterminal distribution networks.

This paper presents the development of a prototype of a substation of 145 kV, BIL 650 kV, taking into account the decrease of the bus electrical insulation clearance, combined with the installation inside a metallic building. Only conventional equipment, usually found on the market, were applied in the prototype. During the preliminary approach, tests were carried out in the high-voltage laboratory, using different busbar configurations and equipment, as circuit breaker, current transformers, potential transformers, switches and insulators, applying models with metallic walls. The proposed prototype was then built and fully tested according to IEC recommendations, mainly from the point of view of lightning discharge withstand. The paper shows the layout and clearances used in the model. The result of the tests in the prototype of the compact substation for 145 kV, with BIL 650 kV, is also presented, proving the feasibility of the new proposal.

Electric power distribution system reliability is defined as the ability to deliver uninterrupted service to customers. Deregulation of the electric power industry has forced utilities to face new challenges and to evaluate the cost-benefit implications of providing an acceptable level of service. This paper presents a fuzzy knowledge-based approach for reliability planning purposes. This approach makes a direct assessment of the circuit configuration and hazards and assigns each section and feeder a relative risk index by expressing the configuration variables mathematically using fuzzy logic. Results obtained using the fuzzy model on actual utility feeder data are presented and the correlation between the fuzzy model results and actual feeder performance is obtained. Determination of the highest risk feeders and of the feeders which benefit the most from a given reliability improvement project are the major goals of the paper.

This paper presents an automatic faulted line section location method for distribution systems. It can be divided into two parts: faulted line section location method for medium-voltage distribution feeders and faulted area identification technique for low-voltage distribution systems. In the first part, an adjacency list that shows the adjacency relationship and status of fault indicating devices is developed. Then, an iterative search technique is devised to traverse the adjacency list to determine the faulted line section. In the second part, a relational table that shows the association relationship between smart meters, meter boxes, and distribution transformers is developed. Based on the table and the voltage of smart meters received from the customer electric information acquisition system, the faulted area can be located. Several test cases studied in a real distribution system demonstrate the effectiveness of the proposed method.

In distribution power systems, feeder voltages can be very sensitive to changes in load and/or distributed generation. This paper introduces a solid-state-transformer-based local voltage-control strategy to reduce variability distribution system bus voltages. An online dynamic volt-var control (VVC) algorithm is proposed to regulate bus voltages by injecting or absorbing reactive power through a solid-state transformer (SST). The proposed algorithm does not require any communication between the SST and the substation and makes control decisions locally. The main goal of the voltage-control algorithm is to enforce strict voltage constraints on the system voltages. The proposed control algorithm is validated in a radial and meshed distribution system using PSCAD.

Low-voltage direct-current (LVDC) distribution is a promising solution whose benefits are large power transfer capacity with low voltage, high cost savings potential, and improvements to reliability and voltage quality. Tests by the pilot implementation in the distribution system operator (DSO) Elenia Oy have given promising results. The power transfer capacity of the system has been calculated in this paper using voltage drop and maximum load of cable as boundaries. The branches of the medium-voltage network that can be replaced by LVDC distribution are determined based on the calculations and mass computation of the entire distribution area of Elenia Oy. Based on the electrotechnical and customer outage costs (COC) analyses made, it can be inferred that LVDC distribution has good utilization potential. Based on the power transfer capacity calculations, it is technically possible to replace branch lines up to 8 km long by LVDC distribution which means about 20% of the total medium-voltage network length in the distribution area of Elenia Oy. This means also huge potential in improving the overall reliability of electricity supply and in reducing outage costs of customers which are these days taken into account in the regulation of network business.

Customer satisfaction counts very much to the electric power distribution companies. The improvement of reliability indices is an effective way to achieve this goal. The optimal placement of power switches is a desirable procedure because while it reduces investment in network assets, it also reduces the number of customers not supplied by outages and, accordingly, improves system reliability. This paper proposes a multiobjective optimization approach for switch placement based on the particle swarm optimization method applied to radial distribution networks of power utilities. The proposed algorithm gives a set of solutions instead of a single one. It intends to be a valuable and flexible tool for planning modern and reliable power distribution networks. Simulation results when using the IEEE 123-node test system and the Roy Billinton Test System are presented as testbeds.

Due to load growth, aging infrastructure, and a competitive environment, innovative solutions are required by electrical utilities to enhance the utilization of transformers which are cost intensive. This paper proposes a demand response optimization model based on transformer hottest-spot temperature. The optimization model quantifies the improvement of transformer utilization through DR. The proposed model is applied to a typical Finnish residential primary and secondary distribution transformers for case studies of load with and without DR. The results show that the loading on the transformers can be significantly increased without sacrificing the life of transformers. The gain in utilization depends on the DR capability of the load. Significant monetary benefits can be achieved with the deployment of the proposed model in a real system.

This paper presents an investigative study on the impact of unified power-quality conditioner (UPQC) allocation on radial distribution systems. A design approach for UPQC, called sag-based design for phase-angle control for UPQC (UPQC-SPAC) is proposed. The phase-angle shifting of the load voltage required to mitigate a given value of voltage sag is determined and the same is used during a healthy operating condition in order to provide the reactive power compensation of a distribution network. To study the impact of the UPQC-SPAC allocation on distribution systems, it is placed at each node, except the substation node, one at a time. The load-flow algorithm for radial distribution systems is suitably modified to incorporate the UPQC-SPAC model. The simulation results show that a significant amount of power-loss reduction, under voltage mitigation, and the enhancement of voltage stability margin can be obtained with an appropriate placement of the UPQC-SPAC in a distribution network. The performance comparison of the UPQC-SPAC with one previously reported design approach shows that it is more efficient in undervoltage mitigation. An appropriate allocation of the UPQC-SPAC is also found to be beneficial for the networks with distributed-generation units.

Distribution network designers use a transformer load-management system to estimate and examine the historical and current loads occurring on transformers and test proposed load situations. Due to a lack of measurements at the feeders and distribution transformers, the confidence on the transformer load-management reports was low in the past. Intelligent equipment and advanced information and communication technology are now being integrated into distribution networks at an unprecedented speed. The technology advancement provides an opportunity to enhance transformer load modeling and management. In this paper, a framework using synchronized measurements obtained from different information systems via a utility's enterprise service bus is proposed to calculate the actual load profiles of distribution transformers and reflect changing system conditions. Network analyses resulting from using improved system models based on distribution state estimation allow the system operators and designers to make informed decisions concerning where new loads can be added and when new transformer capacity must be included.

The popularity of underground cables to replace overhead lines is increasing. This is partly a consequence of the requirement for better reliability and supply security. In some countries, the authorities have set maximum interruption durations for distribution system operators to steer the operators to avoid the use of overhead lines. However, although faults are typically of a rare occurrence in underground cable networks, they cannot be completely avoided. Since the fault repair process in an underground cable network is time consuming, the distribution network should be meshed, and the rate of disconnecting switches should be high enough. However, this is not always possible or economically feasible and, therefore, other opportunities to restore the electricity supply should also be considered. This is especially the case for branch lines without a backup option. Yet, the power should be restored in a reasonable amount of time, which emphasizes the significance of an appropriate switch placement strategy and reserve power planning. This paper proposes a methodology to analyze the costs of different reserve power strategies and to optimize the reserve power arrangements. The reserve power strategies under consideration are the application of reserve power cables and reserve power generators and looping of the existing branch lines.

This paper investigates the power frequency electric fields around a 1000-kV ultra-high voltage (UHV) substation which is located in Jingmen, China. Detailed field measurements around this substation as well as numerical results in a 1000-kV area are provided. Most values observed are below the reference level indicated in the relevant national design guideline. Therefore, we can conclude that the power frequency electric fields around this UHV substation are safer for working personnel.

In the context of incentive regulation applied to electricity distribution companies, reference network models (RNMs) can be a valuable tool to estimate their efficient costs. These models have to plan large-scale electricity distribution areas with different voltage levels. This paper describes the planning algorithms proposed to optimize the location, size, and supply area of the medium-voltage/low-voltage transformer substations in an RNM that has to plan a network from scratch (Greenfield planning). The presented methodology aims to divide the entire planning area into small zones with a nonpredetermined area so that each one can be optimized separately. Then, a heuristic process based on k-means algorithm seeks to find the set of clusters that minimize the cost function, considering the cost of the transformer substations, as well as the LV and MV network costs. The presented case studies show the benefits of applying the proposed methodology.

Islanding detection methods can be divided into communication-based and local detection-based methods. Proposed local passive detection methods have traditionally been dependent on the distributed generation unit type. A large nondetection zone (NDZ) near a power balance situation and unwanted distributed generation tripping due to other network events have also been major drawbacks of traditional, passive local islanding detection methods. In this paper, a new passive local multicriteria-based islanding detection algorithm with fault detection and islanding verification logic is presented. This new islanding detection algorithm, measuring voltage unbalance and voltage total harmonic distortion from all phases, is able to detect very fast and selectively islanding situations in a perfect power balance without NDZ with a simultaneous utilization of the available fault detection information and novel islanding verification logic. In addition to the new multicriteria-based islanding detection method, the fault detection information and islanding verification logic could also be used together with any other known passive islanding detection methods, that is, parameters which are not specified in the fault-ride-through (FRT) requirements of the future grid codes, to improve the performance of these methods in terms of reliability and speed of detection.

In recent years, there was an increase of ancillary service loads, such as signaling systems, inspection robots, surveillance cameras, and other monitoring devices distributed along high-voltage transmission lines which require low-power dc voltage supplies. This paper investigates the use of the induced voltage in the shield wires of an overhead 525 kV transmission line as a primary power source. Since phase current variations throughout the day affect the induced voltage in the overhead ground wire, a step-down dc-dc converter is used after rectification of the ac voltage to provide a regulated dc output voltage. The initial encouraging results obtained indicate that this form of power supply can be a feasible and cost-effective alternative for feeding small ancillary service loads. The simulation results are validated by field measurements as well as the installation of a 200 W voltage stabilization system prototype.

Electric power distribution systems of many commercial and industrial sites often employ variable frequency drives and other loads that internally utilize dc. Such loads are often based on front-end line-commutated rectifiers. The detailed switch-level models of such rectifier systems can be readily implemented using a number of widely available digital programs and transient simulation tools, including the Electromagnetic Transient (EMT)-based programs and Matlab/Simulink. To improve the simulation efficiency for the system-level transient studies with a large number of such subsystems, the so-called dynamic average models have been utilized. This paper presents the average-value modeling methodologies for the conventional three-phase (six-pulse) front-end rectifier loads. We demonstrate the system operation and the dynamic performance of the developed average models in discontinuous and continuous modes, as well as under balanced and unbalanced operation.

This paper discusses some of the electromagnetic-compatibility issues concerning the use of power lines for communication. Based on a series of measurements performed in a laboratory environment and in the field, five different types of interactions between communication and end-user equipment are distinguished. Measurement examples are shown for several of these types. It is concluded that the creation of a low-impedance path by end-user equipment is the main cause of interference.

This paper proposes a new algorithm for localizing phase to ground faults in an electric power distribution system. Fault-originated traveling waves propagate along the distribution paths in both directions away from the fault point and are reflected at line terminations, junctions between feeders, laterals, and the fault location. Depending on the paths which traveling waves reciprocate through, the transient signal at each node contains certain path characteristic frequencies (PCFs). Energy spectrum of the transient signal has high density around the path characteristic frequencies. On this basis, the transient voltage is decomposed by a wavelet filter and its energy spectrum is decomposed into different levels. Depending on the bandwidth of the wavelet filter and the path characteristic frequencies, the decomposed signal in each level contains a certain percentage of energy. Then, a neural network-based methodology is proposed as a power distribution line fault locator. Energy percentage in each level is the candidate feature for training the artificial neural network. Simulations and the training process for the neural network are performed respectively using ATP/EMTP and MATLAB. It is shown that the results of the proposed algorithm are quite satisfactory.

This paper shows a new hybrid method for risk assessment regarding interruptions in sensitive processes due to faults in electric power distribution systems. This method determines indices related to long duration interruptions and short duration voltage variations (SDVV), such as voltage sags and swells in each customer supplied by the distribution network. Frequency of such occurrences and their impact on customer processes are determined for each bus and classified according to their corresponding magnitude and duration. The method is based on information regarding network configuration, system parameters and protective devices. It randomly generates a number of fault scenarios in order to assess risk areas regarding long duration interruptions and voltage sags and swells in an especially inventive way, including frequency of events according to their magnitude and duration. Based on sensitivity curves, the method determines frequency indices regarding disruption in customer processes that represent equipment malfunction and possible process interruptions due to voltage sags and swells. Such approach allows for the assessment of the annual costs associated with each one of the evaluated power quality indices.

Two different fuzzy approaches to voltage control in electric power distribution systems are introduced in this paper. The real-time controller in each case would act on power transformers equipped with under-load tap changers. Learning systems are employed to turn the voltage-control relays into adaptive devices. The scope of this study has been limited to the power distribution substation, and the voltage measurements and control actions are carried out on the secondary bus. The capacity of fuzzy systems to handle approximate data, together with their unique ability to interpret qualitative information, make it possible to design voltage-control strategies that satisfy the requirements of the Brazilian regulatory bodies and the real concerns of the electric power distribution companies. Fuzzy control systems based on these two strategies have been implemented and the test results were highly satisfactory.

Because traditional electric power distribution systems have been designed assuming the primary substation is the sole source of power and short-circuit capacity, DR interconnection results in operating situations that do not occur in a conventional system. This paper discusses several system issues which may be encountered as DR penetrates into distribution systems. The voltage issues covered are the DR impact on system voltage, interaction of DR and capacitor operations, and interaction of DR and voltage regulator and LTC operations. Protection issues include fuse coordination, feeding faults after utility protection opens, impact of DR on interrupting rating of devices, faults on adjacent feeders, fault detection, ground source impacts, single phase interruption on three phase line, recloser coordination and conductor burndown. Loss of power grid is also discussed, including vulnerability and overvoltages due to islanding and coordination with reclosing. Also covered separately are system restoration and network issues.

In this paper, a technique based on nondominated sorting genetic algorithm-II (NSGA-II) is presented for solving the service restoration problem in an electric power distribution system. Due to the presence of various conflicting objective functions and constraints, the service restoration task is a multiobjective, multiconstraint optimization problem. In contrast to the conventional genetic-algorithm (GA)-based approach, this approach does not require weighting factors for the conversion of such a multiobjective optimization problem into an equivalent single objective function optimization problem. In this work, various practical distribution system operation issues, such as the presence of priority customers, presence of remotely controlled, as well as manually controlled switches, etc. have also been considered. Based on the simulation results on four different distribution systems, the performance of the NSGA-II-based scheme has been found to be significantly better than that of a conventional GA-based method. Besides, to reduce the software runtime of the NSGA-II algorithm, a faster version of NSGA-II has also been implemented.

In this paper, a fuzzy logic-based algorithm to identify the type of faults in radial, unbalanced distribution system has been developed. The proposed technique is able to accurately identify the phase(s) involved in all ten types of shunt faults that may occur in an electric power distribution system under different fault types, fault resistance, fault inception angle, system topology and loading levels. The proposed method needs only three line current measurements available at the substation and can perform the fault classification task in about half-cycle period. All the test results show that the proposed fault identifier is well suited for identifying fault types in radial, unbalanced distribution system.