Modern Power Distribution Systems Research Articles

Gas-sensing properties and mechanism of Pd-GaNNTs for air decomposition products in ring main unit

Ring main unit acts as an important role in modern power transmission and distribution systems. Partial electric discharge frequently occurs in ring main unit because of insulation faults. Along with the partial electric discharge, the air filled in ring main unit decomposes to various decomposition products, where NO, CO, O3, N2O4 are the characteristic products. This work devotes to detect the partial electric discharge by detecting these four characteristic gases. Based on first-principle calculation, Pd-modified gallium nitride nanotubes (Pd-GaNNTs) was proposed as a novel gas sensor for these gases detection. Pd atom doping greatly enhances the surface activity of GaNNTs. Gas-sensing properties and mechanism of Pd-GaNNTs to these four characteristic gases were analyzed based on adsorption energy, charge transfer amount, total density of states, projected density of states, and the molecular orbits calculations. The adsorption stability of Pd-GaNNTs to these gases ranked as: N2O4 > CO > O3 > NO, and the effect of gas adsorption on the conductivity is: O3 > NO > N2O4 > CO. Calculation results show that Pd-GaNNTs could be a promising material to prepare new generation gas sensor using in partial electric discharge detection in ring main unit.

Unit Template Based Control of PV-DSTATCOM

Background: In modern electrical power distribution systems, Power Quality has become an important concern due to the escalating use of automatic, microprocessor and microcontroller based end user applications. Methods: In this paper, power quality improvement has done using Photovoltaic based Distribution Static Compensator (PV-DSTATCOM). Complete simulation modelling and control of Photovoltaic based Distribution Static Compensator have been provided in the presented paper. In this configuration, DSTATCOM is fed by solar photovoltaic array and PV module is also helpful to maintain the DC link voltage. The switching of PV-STATCOM is controlled by Unit template based control theory. Results: The performance of PV-DSTATCOM has been evaluated for Unity Power Factor (UPF) and AC Voltage Control (ACVC) modes. Here, for studying the power quality issues three-phase distribution system is considered and results have been verified through simulation based on MATLAB software. Conclusion: Different power quality issues and their improvement are studied and presented here for harmonic reduction, DC voltage regulation and power factor correction.

An adaptive overcurrent protection system applied to distribution systems

In this paper, an innovative adaptive directional overcurrent protection system for electric power distribution systems with respect to distributed generation is proposed. The proposed system supervises network topology based on the monitoring functionality of numerical relays. The system detects any changes in the configuration and recalculates the directional overcurrent protection settings by using a microgenetic algorithm. The proposed system was evaluated for several operating scenarios and insertion levels of distributed generation, and then compared with both conventional and adaptive protection systems by means of a traditional genetic algorithm. The results showed that the performance of the proposed system is superior to the other two methods in terms of both speed and selectivity. This shows that this is a promising proposal for the protection of modern electric power distribution systems.

Decentralized Smart Grid Voltage Control by Synchronization of Linear Multiagent Systems in the Presence of Time-Varying Latencies

Modern power distribution systems require reliable, self-organizing and highly scalable voltage control systems, which should be able to promptly compensate the voltage fluctuations induced by intermittent and non-programmable generators. However, their deployment in realistic operation scenarios is still an open issue due, for example, to the presence of non-ideal and unreliable communication systems that allow each component within the power network to share information about its state. Indeed, due to technological constraints, time-delays in data acquisition and transmission are unavoidable and their effects have to be taken into account in the control design phase. To this aim, in this paper, we propose a fully distributed cooperative control protocol allowing the voltage control to be achieved despite the presence of heterogeneous time-varying latencies. The idea is to exploit the distributed intelligence along the network, so that it is possible to bring out an optimal global behavior via cooperative distributed control action that leverages both local and the outdated information shared among the devices within the power network. Detailed simulation results obtained on the realistic case study of the IEEE 30-bus test system are presented and discussed in order to prove the effectiveness of the proposed approach in the task of solving complex voltage control problems. Finally, a robustness analysis with respect to both loads variations and hard communication delays was also carried to disclose the efficiency of the approach.

Incremental Heuristic Approach for Meter Placement in Radial Distribution Systems

The evolution of modern power distribution systems into smart grids requires the development of dedicated state estimation (SE) algorithms for real-time identification of the overall system state variables. This paper proposes a strategy to evaluate the minimum number and best position of power injection meters in radial distribution systems for SE purposes. Measurement points are identified with the aim of reducing uncertainty in branch power flow estimations. An incremental heuristic meter placement (IHMP) approach is proposed to select the locations and total number of power measurements. The meter placement procedure was implemented for a backward/forward load flow algorithm proposed by the authors, which allows the evaluation of medium-voltage power flows starting from low-voltage load measurements. This allows the reduction of the overall costs of measurement equipment and setup. The IHMP method was tested in the real 25-bus medium-voltage (MV) radial distribution network of the Island of Ustica (Mediterranean Sea). The proposed method is useful both for finding the best measurement configuration in a new distribution network and also for implementing an incremental enhancement of an existing measurement configuration, reaching a good tradeoff between instrumentation costs and measurement uncertainty.

A Linear Power Flow Solution for Distribution Power System Including PV Bus and ZIP Load

The modern power distribution system (DPS) needs most urgently a robust and fast linear power flow (LPF) solution. The voltage controlled (PV) bus is much common in DPS with the high penetration of distributed generators (DGs) into DPS. Moreover, the conventional constant P type load should be converted into ZIP load in order to get closer to the practical load level. Thus, in this paper, with the several approximations on the voltage drop, link powers, voltage controlled bus and ZIP load, a loop-theory based linear power flow (LPLPF) was proposed with respect to voltage magnitude and phase angle under a polar coordinate system. The proposed method can account for ZIP loads, transformers, and PV type DGs in a balanced distribution network. The approximations have been tested in several distribution systems including radial, meshed and ill-conditioned (much heavy-loaded) large-scale systems. The effectiveness and advantages of the proposed LPLPF method were validated with the results of test systems and the proposed method was accurate enough and robust even in the bad voltage levels.

Spectral clustering for designing robust and reliable multi‐MG smart distribution systems

Reliability has become a key design aspect in modern energy system's planning. Owing to the higher fault rate in power distribution systems (PDSs), comparing with generation and transmission systems, considering reliability in PDSs' planning is very crucial. This study presents a novel robust approach to cluster the existing PDSs with intermittent distributed generators (DGs) into a set of reliable microgrids (MGs). For this purpose, first, a new reliability index is defined to evaluate the reliability of MGs in terms of real and reactive power adequacy as well as frequency and duration of interruptions. Then, the k -means algorithm, based on weighted graph partitioning method, is proposed for changing the system into a multi-MG system. Furthermore, a modified version of particle swarm optimisation approach is proposed and the Silhouette technique is used to determine the optimal location and sizes of DGs as well as the number of MGs. The design and sensitivity analysis performed by the proposed multi-objective optimisation algorithm on the well known IEEE 69-bus distribution system show the effectiveness and robustness of the proposed algorithms for constructing reliable MGs in modern PDSs.

Phase Coherence Index, HHT and Wavelet Analysis to Extract Features from Active and Passive Distribution Networks

The modern Power Distribution Systems (PDS) operate more and more often with distributed generators and the optimal operation of the utility distribution systems has to take into account the possibility of bi-directional energy flows, although this event may only occur for some of the PDS. For this reason, the analysis methods that are usually employed to investigate the electrical behavior of the PDS can be more or less effective, depending on the typology of electrical loads connected to the line and on the presence or absence of Renewable Energy Sources (RES). This paper proposes either a methodology to select the best performing mathematical tool to investigate the electrical behavior of the PDS—depending on their linearity and stationarity—either an index to discriminate the PDS on the basis of a different amount of PV penetration. The proposed approach is applied to three real cases of PDS with different characteristics: residential and commercial, in the presence or absence of PV plants. In addition, two indices that are able to characterize the PDS in terms of periodicity and disturbance of the electrical signal are considered, specifically the phase coherence between two arbitrary signals and the phase coherence between an arbitrary signal and a reference one. The combined use of these indices can give valuable information about the degree of non-linearity and can be a measure of the PV penetration in a distribution circuit.

Modelling and Simulation of Current Source Converter based Dynamic Voltage Restorer for Voltage Regulation cum Harmonics Mitigation

The modern electric power distribution system faces lots of power quality (PQ) problems such as short and long duration voltage variations, voltage imbalance, waveform distortions, impulsive and oscillatory transients and voltage flicker etc. The custom power devices (CPD) have been designed and developed with the aim of mitigating these problems. The major CPDs introduced so far include distribution-static synchronous compensator (D-STATCOM), dynamic voltage restorer (DVR), unified power quality conditioners (UPQC), active power filters (APF) etc. However, most of these CPDs are designed and implemented using voltage source converter (VSC) topology. Although lots of research works have been carried out for realizing DVR system based on VSC topology, not much research work has been reported on the application of CSC topology in DVR system over the last one decade. Through this paper, it has been attempted to develop a model of DVR system based on CSC topology capable of performing dual power quality enhancement tasks viz. voltage regulation and harmonics mitigation at a power distribution system catering power to a variety of loads. The DVR system has been modeled and simulated in the MATLAB / Simulink platform and the simulation results reveal the effectiveness and validity of the proposed model for use in power distribution system.

Generating capacity adequacy evaluation of large-scale, grid-connected photovoltaic systems

Large-scale, grid-connected photovoltaic systems have become an essential part of modern electric power distribution systems. In this paper, a novel approach based on the Markov method has been proposed to investigate the effects of large-scale, grid-connected photovoltaic systems on the reliability of bulk power systems. The proposed method serves as an applicable tool to estimate performance (e.g., energy yield and capacity) as well as reliability indices. The Markov method framework has been incorporated with the multi-state models to develop energy states of the photovoltaic systems in order to quantify the effects of the photovoltaic systems on the power system adequacy. Such analysis assists planners to make adequate decisions based on the economical expectations as well as to ensure the recovery of the investment costs over time. The failure states of the components of photovoltaic systems have been considered to evaluate the sensitivity analysis and the adequacy indices including loss of load expectation, and expected energy not supplied. Moreover, the impacts of transitions between failures on the reliability calculations as well as on the long- term operation of the photovoltaic systems have been illustrated. Simulation results on the Roy Billinton test system has been shown to illustrate the procedure of the proposed frame work and evaluate the reliability benefits of using large-scale, grid-connected photovoltaic system on the bulk electric power systems. The proposed method can be easily extended to estimate the operating and maintenance costs for the financial planning of the photovoltaic system projects.

Advanced fault location strategy for modern power distribution systems based on phase and sequence components and the minimum fault reactance concept

A generalized strategy for fault location in modern power distribution systems, which normally include distributed generation, is presented in this paper. The fault location method considers the phase and sequence network parameters and voltage and current measurements at the main substation and at the distributed generators, in pre-fault and fault steady states. The fault distance is estimated from the analysis of all section lines, which is required to determine if the fault is located in a radial or non-radial zone of the power distribution feeder; next, a specific equation is used to determine the exact location. The proposed methodology is validated in the IEEE 34-node test power system, where single-phase to ground, phase-to-phase and three-phase faults were tested, considering 51 different and optimally determined operational conditions. The proposed method has range of estimation errors from −2.8% to 3.2%.

Adaptive differential search algorithm for optimal location of distributed generation in the presence of SVC for power loss reduction in distribution system

Optimal location and sizing of multi type of distribution generations in a distribution system is of great importance for experts and industries to achieve the desired technical-economic objectives. This paper aims to develop a new planning strategy for modern power distribution system using a flexible variant based differential search (DS) algorithm named adaptive DS. The proposed algorithm investigated for solving the optimal location and sizing of multi distributed generation (DG). The total power losses have been optimized considering the cost component of DG for real power, and the cost of energy losses. The robustness of the proposed planning strategy was validated on a two practical test system, 33-Bus and 69 Bus at normal situation and considering specific loading margin stability. The results show the importance of installing the suitable size of DG at the suitable location in the presence of SVC compensators.

Guest Editorial Enabling Technologies and Methodologies for Knowledge Discovery and Data Mining in Smart Grids

The advance in the research of Smart Grid methodologies opens the doors toward the conceptualization of new tools aimed at effectively addressing most challenging issues of modern power distribution systems, including the massive pervasion of renewable power generators, the strictest power quality limits, the complex interactions with the energy markets, the raising levels of security and reliability constraints, and the need for maximizing the exploitation of existing electrical infrastructures

A framework for classification of non-linear loads in smart grids using Artificial Neural Networks and Multi-Agent Systems

This paper proposes a general framework that uses the Artificial Neural Networks (ANNs) as a classification tool of nonlinear loads in a simulated smart grid environment by using Multi-Agent Systems (MAS). The increasing of communication and computation infrastructure on devices installed on modern power distribution systems allows new automated and coordinated control actions. This is mainly due to the ability to manage and process information and deploy actions in real-time mode. One important measurement tool is the smart meter, which will be present with all customers. Besides the measurement function, it has the communication feature and also some computational processing capability. Considering this base structure, the objective is to present methods to classify/identify nonlinear loads based only on current or voltage profiles measured by smart meters in this distributed computing environment. In this work, the MAS will manage the data and the tasks related to the classification and the ANN will perform the classification, both tools have been developed in JADE/JAVA and Matlab environment, respectively. Test case using 4000 input signals distributed in eight classes corresponding to nonlinear medical electromedical loads have been used and 98.7% of the samples have been identified correctly.

A Single-Stage Solid-State Transformer for PWM AC Drive With Source-Based Commutation of Leakage Energy

A solid-state transformer is a three-phase ac/ac converter with a high-frequency transformer. Due to advanced features like high power density, on demand var support and frequency regulation, solid-state transformer is an enabling technology for the modern power distribution system. It can also find application in high-power-density motor drives. The single-stage solid-state transformer considered in this paper is capable of bidirectional power flow and open loop power factor correction. This topology uses a minimum amount of copper and has relatively few semiconductor switches. One major problem in this converter is the commutation of leakage energy which results in power loss, reduction in switching frequency, loss of output voltage, and additional common-mode voltage switching. This paper presents a source-based commutation strategy along with a novel modulation technique resulting in elimination of additional snubber circuits, minimization of the frequency of leakage inductance commutation, recovery of the leakage energy, and soft switching of the output converter. The topology and its proposed control have been analyzed. Simulation and experimental results confirm the operation.

Extraction of Frequency Domain Dielectric Characteristic Parameter of Oil-paper Insulation for Transformer Condition Assessment

In modern power transmission and distribution systems, power transformers are critical components and their electrical properties together with service lives are determined by the insulation property of oil-paper insulation. To better apply the frequency domain spectroscopy technique to assess transformer insulation condition, a series of experiments were performed under controlled laboratory conditions. First, this article presents the frequency domain dielectric response measurement results of oil-paper insulation samples under different moisture contents and aging states, and then the extracted frequency dielectric characteristic parameters determined from the imaginary part of relative permittivity (ϵr′′) and dielectric dissipation factor (tanδ) curves are used to assess the moisture contents and aging states of oil-paper insulation. Finally, the quantitative relationships among dielectric characteristic parameters, moisture content, and degree of polymerization are also established. Results show that in the frequency range of 10–3–102 Hz, ϵr′′ and tanδ obviously increase as the moisture content of oil-paper insulation rises, while ϵr′′ and tanδ are very sensitive to aging only in 10–3–10–1 Hz. Consequently, ϵr′′ and tanδ in different frequency ranges can be used to distinguish the influences of moisture content and aging state on frequency domain spectroscopy measurement results.

Responsive demand to mitigate slow recovery voltage sags

SUMMARYIt is expected that in the future, customers will play a much more active role in modern power distribution systems. Instead of being passive agents, customers will be encouraged to participate in many other functions, such as frequency and voltage control, by providing a rapid, active, and reactive power reserve for peak load management through price responsive methods and also as energy providers through embedded generation technologies. This article introduces a new technology, called demand as voltage‐controlled reserve, which can help mitigation of momentary voltage sags. The technology can be provided by thermostatically controlled loads as well as other types of load. This technology has proven to be effective in distribution systems with a large composition of induction motors, when voltage sags present slow recovery characteristics because of the deceleration of the motors during faults. This article presents detailed models, discussion, and simulation tests to demonstrate the technical viability and effectiveness of the demand as voltage‐controlled reserve technology for mitigating voltage sags. Copyright © 2011 John Wiley & Sons, Ltd.

Ground-fault detection in multiple source solidly grounded systems via the single-processor concept for circuit protection

Modern power distribution systems often contain multiple power sources integrated within one system. A simple variant may be the common double-ended substation, which can be further complicated by an additional emergency or alternate sources. This presents significant complexity to the designer attempting to design a protection system that will not be fooled by circulating neutral currents. The authors describe how the "single processor concept for circuit breaker protection and control" (M. E. Valdes et al., Proc. PCIC, 2003, pp. 267-275) provides ways to address this sensing problem. One such method is described in further detail. Handling of resistance-grounded systems will be the subject of a related paper.

Simplified bidirectional-feeder models for distribution-system calculations

The paper presents three novel distribution-feeder models to simplify complicated distribution-system calculations. These equivalent models are developed to simulate the total series voltage drop at the end of the given feeder accurately, the total copper loss of the given feeder accurately, and a hybrid to simulate both voltage drop and feeder loss accurately. In addition, all of the proposed models are bidirectional. This means that power infeed can be at either end and the model is accurate. In contrast, unidirectional models previously developed are accurate only when power infeed is at the end specified by the model. This feature is important for a modern power-distribution system in which the power infeed of the switched feeder may change from one end to the other during service restoration or feeder reconfiguration. These bidirectional feeder models are illustrated by examples and applied to an actual feeder. The simulation results show that it is possible to reduce many complex feeders to simple equivalent models in the study of feeder-voltage profiles and losses with negligible error, even if the power infeeds of the given feeders are changed.

An Evaluation of High-Voltage Cable-Coupler Performance for Underground Mine Power Systems

High-voltage cable couplers are convenient and widely used accessories in modern coal-mine power distribution systems for aiding in the extension and retraction of power-feeder cables throughout a mine. Coupler design has tried to keep pace with the industry's desire to move to higher distribution levels, but the increase in recorded failures of 15 kV-class couplers, which serve the distribution levels of 12.47 kV and above, have inhibited this transition. The problems associated with high-voltage cable couplers are analyzed. Manufacturing, testing, and mounting practices are reviewed. A discussion of a coupler's operating environment is also included. On the basis of the aforementioned conditions, a testing standard is developed and various coupler designs are subjected to its requirements. An analysis of the test results is provided. Although new couplers can satisfy the performance requirements of the cables to which they are mounted, partial discharge appears to be the failure mechanism of concern. The effects of partial discharge are magnified where voids, either in the insulation, cable termination, or potting compound, occur. In this regard, it is shown that the quality of installation of a coupler onto cable is quite critical. By slightly altering the mounting procedure, satisfactory partial-discharge readings are produced on a test coupler.