Voltage Distribution Network Research Articles

分散型電源の大量導入が発電出力に与える影響と電圧調整制御による効果

Japanese government has declared that the amount of the Photovoltaic cells (PV) will be 53GW by 2030 in national area. It is about 40 times of the amount of PV in 2005. It means that 30 to 40 percent of detached residential houses will have PV systems. It results in many issues such as voltage fluctuation in distribution systems. Voltage in distribution network might rise because of the reverse power flow from many PV systems. PV generation outputs suppression method is being considered to avoid the voltage problem in case of high insolation. However, the output of PV generation should not be suppressed from the viewpoint of efficient energy utilization.It is also probable that fuel cell cogeneration systems will be introduced in many residential houses. In this paper, the operating method of fuel cells for relieving PV generation outputs suppression under high penetration conditions is studied. It is shown that PV outputs can be increased by the operation of fuel cells.

The search for optimal feature set in power quality event classification

The significance of detection and classification of power quality (PQ) events that disturbs the voltage and/or current waveforms in the electrical power distribution networks is well known. Consequently, in spite of a large number of research reports in this area, the problem of PQ event classification remains to be an important engineering problem. Several feature construction, pattern recognition, analysis, and classification methods were proposed for this purpose. In spite of the extensive number of such alternatives, a research on the comparison of “how useful these features with respect to each other using specific classifiers” was omitted. In this work, a thorough analysis is carried out regarding the classification strengths of an ensemble of celebrated features. The feature items were selected from well-known tools such as spectral information, wavelet extrema across several decomposition levels, and local statistical variations of the waveform. The tests are repeated for classification of several types of real-life data acquired during line-to-ground arcing faults and voltage sags due to the induction motor starting under different load conditions. In order to avoid specificity in classifier strength determination, eight different approaches are applied, including the computationally costly “exhaustive search” together with the leave-one-out technique. To further avoid specificity of the feature for a given classifier, two classifiers (Bayes and SVM) are tested. As a result of these analyses, the more useful set among a wider set of features for each classifier is obtained. It is observed that classification accuracy improves by eliminating relatively useless feature items for both classifiers. Furthermore, the feature selection results somewhat change according to the classifier used. This observation shows that when a new analysis tool or a feature is developed and claimed to perform “better” than another, one should always indicate the matching classifier for the feature because that feature may prove comparably inefficient with other classifiers.

Multiple Distributed Generators for Distribution Feeder Voltage Support

Inclusion of voltage support distributed generation (VSDG) can reinforce the feeder voltage of distribution networks, especially in rural/remote areas where voltage dip and frequent blackouts are significant concerns for power utilities. However, installation of multiple distributed generators within a distribution grid system may introduce technical problems in network operation and control, including control interaction and/or voltage instability. This paper addresses the network issues that may occur during multiple VSDG inclusion in the network and presents analytical models and solutions to develop design criteria of VSDG installation in the networks. Voltage sensitivity of lines is investigated and the effect of DG real (P) and reactive (Q) power injections with Q priority is developed for optimal use of VSDG in correcting the network voltage. Interaction among VSDG controllers has been explored and a generalized model is presented to analyze this interaction between any number of VSDGs in the network. The model is tested on a sample VSDG system and test results are presented. The issue of which VSDG must be started recognizing the costs of starting is addressed using an inverse definite minimum time (IDMT) model. A prioritization and coordination scheme for start discrimination of multiple VSDGs is proposed which avoids hunting between multiple generators.

Scaling Analysis of On-Chip Power Grid Voltage Variations in Nanometer Scale ULSI

This paper presents a detailed scaling analysis of the power supply distribution network voltage drop in DSM technologies. The effects of chip temperature, electromigration and interconnect technology scaling (including resistivity increase of Cu interconnects due to electron surface scattering and finite barrier thickness) are taken into consideration during this analysis. It is shown that the voltage drop effect in the power/ground (P/G) distribution network increases rapidly with technology scaling, and that using well-known countermeasures such as wire-sizing and/or decoupling capacitor insertion which are typically used in the present design methodologies may be insufficient to limit the voltage fluctuations over the power grid for future technologies. It is also shown that such voltage drops on power supply lines of switching devices in a clock distribution network can introduce significant amount of skew which in turn degrades the signal integrity.

Application of a genetic algorithm in the reduction of loss and control of the voltage of distribution networks using the real optimization of fixed and switched capacitors

For a long time, reduction of the loss and control of the voltage of electric distribution networks have been considered to be some of the most important problems of such networks. The importance of these two features arises from the fact that they are directly related to the loss of electric energy. One of the essential and effective methods in solving these two problems is the use of fixed and switched capacitors. In this paper, a new method has been presented on the basis of a genetic algorithm aimed at reducing the loss and controlling the network voltage by using fixed and switched capacitors in the form of real optimization. By real optimization in this method, we mean the use of the range of low- and medium-voltage capacitors available in the market with their real prices and by modelling the load at its different levels, the real model of the network is also taken into consideration. With due regard to the above facts and considering the large number of variables of optimization, the use of the genetic algorithm is an important factor in finding the real optimal method in the application of capacitors. Copyright © 2005 John Wiley & Sons, Ltd.

Time to connect [distributed generation

This paper discusses the wide range of issues related to the connection and operation of distributed electricity generation in the UK. A key development is the concept of the active network composed of integrated devices communicating with each other as well as two-way power flows taking place between the generator and customer. Investigations into active network management are underway to examine how additional further renewable energy generation connections could be made to distribution networks such as the Orkney electricity network. While many efforts are taking place on active networks, changes to the technical, regulatory and commercial framework that governs today's industry have to be made to recognize the growing numbers of sustainable technologies connected at distribution network voltages.

Voltage and current sensitivities of radial distribution network: a new approach

A new method is proposed for determination of voltage and current sensitivities at different buses and branches of a radial power distribution network. First-order sensitivity expressions for bus voltage and branch current with respect to bus power load have been developed. These sensitivities expressions are then used to evaluate sensitivity constants at different buses and for various branches with respect to load variation at various buses. The method has been applied to a 33 KV, 41-bus practical distribution system. The results are compared with the conventional Jacobian method and almost negligible error has been observed. The evaluated voltage and current sensitivities for the 41-bus system are then used to determine the optimised limits of the existing network for forecast load to demonstrate the application of derived sensitivities. The method proposed here greatly reduces the computational effort compared to other existing methods.

Network voltage controller for distributed generation

Present distribution network voltage design practice limits the distributed generation capacity that can be connected to 11 kV networks. It has been shown previously that adoption of a more active approach to network voltage control can significantly increase distributed generation capacity. One way to do this is to control the target voltage of automatic voltage control relays at primary substations. A basic design for a controller to do this has been created, comprising three algorithms. A statistical state estimation algorithm estimates the voltage magnitude at each network node supplied by the primary substation, using real-time measurements, network data and load data. The estimate accuracy depends on the number and placement of real-time measurements. Studies using an 11 kV feeder model showed that an acceptable accuracy could be obtained with one or two measurements. The state estimator uses pseudo measurements for unmeasured loads. A load model was constructed using load profiles to calculate the pseudo measurements. The calculated pseudo measurements were inaccurate, but it was found that acceptable state estimate accuracy could be obtained with inaccurate pseudo measurements. A control algorithm alters the AVC relay target voltage, based on the maximum and minimum node voltage magnitude estimates. A simulation on a four-feeder network showed that the algorithm enabled the generator power export to be more than doubled.

A study of voltage and reactive power control methods for high-efficiency operation of distribution networks

Transformers with on-load tap changer and step voltage regulators are most often used for regulating the distribution network voltage. Their use, however, creates certain problems, namely, the voltage control is in discrete steps and the response time is not satisfactory enough. In addition, the power factor (p.f.) compensation relies on capacitors installed by electricity users which creates additional problems manifesting themselves in unexpected overvoltages during light load and increase of power losses. To solve these problems, the authors have proposed a new voltage and p.f. control system for distribution networks based on sophisticated power electronics technology. This paper describes our study on the operating theory of inverter-controlled regulators and thyristor-controlled reactors, which play important roles in this system, and the results of simulation through which the usefulness of these equipment has been ascertained. © 1999 Scripta Technica, Electr Eng Jpn, 130(1): 76–87, 2000

GA・NNを適用した配電系統電圧・無効電力制御手法の開発

GA・NNを適用した配電系統電圧・無効電力制御手法の開発

Distribution system voltage and reactive power control based on probabilistic load flow analysis

The paper presents a method for the adjustment of voltage and reactive power control devices in distribution networks based on probabilistic constrained load flow. The overall control problem is decoupled into subproblems characterised by the reaction speed of the control devices. The algorithm takes into account the effects of load variations within the time period considered, and provides setpoints for control devices satisfying constraints for the whole planning period.

Parallelogram theory for solution of distribution network voltage problems by computer

The application of the theory of voltage regulation on a distribution network to the problem of optimising the various voltage control facilities available is generally assumed to be well understood. However, with complex network arrangements, the wide variety and numbers of distribution transformers, and differing load patterns, a distribution engineer is faced with a major problem when attempting to optimise the voltage performance of a distribution network, while maintaining the voltages supplied to consumers within declared limits. The paper covers a theoretical approach to distribution network voltage performance, leading to the derivation of a parallelogram theory linking primary substation source busbar voltage and the tap setting on each distribution transformer on the network. Based on this parallelogram theory, a computer program has been developed which enables distribution networks to be surveyed in greater depth, thus enabling engineers to more readily identify problem areas. Overall the program provides a powerful and efficient means of assessing and optimising the voltages on existing networks, or modifying networks to accommodate additional loads, or for designing new networks. The program is adaptable for use on any MV/LV distribution network. The paper thus provides both a theoretical and practical approach to the problem of improving the voltage performance of distribution networks.

Some Considerations on the High Harmonic Phenomena of the Voltage and Current in Transmission and Distribution Networks

Some Considerations on the High Harmonic Phenomena of the Voltage and Current in Transmission and Distribution Networks

Erratum to : Some Considerations on the High Harmonic Phenomena of the Voltage and Current in Transmission and Distribution Networks

Erratum to : Some Considerations on the High Harmonic Phenomena of the Voltage and Current in Transmission and Distribution Networks