Reliability Of Electric Networks Research Articles

Forecasting photovoltaics/concentrated photovoltaics at national level – Portugal experience

The solar power installed capacity all over the world is growing and this renewable energy technology is playing an important role to build a clean energy future. The solar forecast is a necessary tool for the transmission system operator in order to maintain the electricity network safety and reliability. This study aims to report the experience of R&D Nester in the solar forecast at national level in Portugal, forecasting for all solar plants connected to the very high voltage (400, 220 and 150 kV) and high voltage (60 kV) networks, providing this information to the Portuguese transmission system operator, REN. A novel approach to calculate cloud index from images from a sky camera is presented.

Influence of dispersed generation on reliability of electrical networks

Greater part of renewable sources of energy is represented by solar power plants (SPP). Their operation mode depends on natural conditions of the region, where they are located. That is why the problem of SPP stability estimation is important in the problem of covering the daily schedule of energy consumption. The system operator, in his study, emphasizes that photovoltaic and wind power plants are unreliable in terms of electrical power stability. Deviations from scheduled charts over the course of the day amount to more than 450 MW at a set power of 1217 MW. One more specific feature of the installation of renewable energy sources is their uneven distribution throughout Ukraine. Thus, the presence of one powerful source of up to 3 MW, or several less powerful ones up to 0.5 MW, connected to one substation of the distribution network (REM), makes it possible to consider REM as a local electrical system (LES). And for the local electric system, there are not yet clear legislative acts according to which renewable energy sources will function. Particularly acute for distributive electrical networks is the question of reliability and uninterrupted power supply. The article analyzes the pace of increase in the generation of photovoltaic stations in the context of the combined electricity system of Ukraine and the energy supply company of "Vinnytsyaoblenergo". The analysis of existing normative documents regulating the work of photovoltaic stations is carried out. Within the framework of the considered documents, the criteria for assessing the reliability of the operation of electric networks, namely SAIDI, are the length of long interruptions in the electricity supply of electricity consumers. The interconnection of changes in the reliability indices of electrical networks with the increase in the number and installed capacity of renewable energy sources, in particular photovoltaic stations, is shown. To increase the technical and economic efficiency of joint operation of distributed power sources and distribution electric networks, it is necessary to solve a number of tasks, which will allow to increase electricity generation of RES, reduce electricity losses in distribution electric networks, improve the quality and reliability of electricity supply to consumers.In order to efficiently exploit distributed energy sources and their integrated use in power grids, especially in the sense of improving the reliability of power supply, it is necessary to develop a method for restoring electricity supply to forest users, with a loss of centralized power supply

The influence of phase load asymmetry on power losses in power distribution network lines of oil and gas enterprises

The influence of phase load asymmetry on power losses in electric lines is investigated. The influence of phase load redistribution on power losses in three-phase three-conductor line with the insulated neutral is analyzed. It is demonstrated that additional power losses occur in this line which are in quadratic dependency on the relative change of phase loads. The influence of neutral conductor resistance in the four-conductor three-phase electric network on power losses in different asymmetry modes is investigated. It is shown that power losses in this network are much larger than in three-conductor network with identical phase load asymmetry and depend on the neutral conductor resistance. Significant economic effect can be obtained by increasing the cross-section of neutral conductor. At the same time, the simultaneous decrease of power losses and increase of the operational reliability of electric network are observed.

Increase of selectivity and reliability of electric transport traction networks

The paper describes methods for setpoints setting of digital protections (terminals) in traction DC networks. A technique for their improvement and protection settings in a complete scheme is proposed. Besides, the main technical characteristics of digital protection and automation devices are listed. Numerous network parameters, which include those affecting its service reliability, are also reviewed. The parameter factor evaluation of dc traction network servicing, including the random parameter affects, is given. The algorithm and the design procedure of the dc traction network are reported in the paper. Besides, a real operation circuit of traction network protection at the experimental site is considered.

Technological and operational reliability of power supply system

The article is devoted to choosing ways to improve the technological reliability of regional electric network (REN) to ensure reliable power supply. At the operational stage, the task of increasing operational reliability is assigned to the enterprise asset management system of the territorial network organization (TNO), as a REN operator. Technological reliability is ensured by an operational dispatch control system, which uses the existing reserves in the network to support the technological process of electricity supply to electricity consumers in case of network equipment failures. The relevance of improving the technological and operational reliability of power supply system (PSS) requires the development and improvement of methods for analyzing and assessing the TNO's readiness to provide power transmission services. The indicators adopted in Russia reflect the level of technological reliability of PSS. However, these indicators do not reflect the technical condition of the equipment, or identify causal relationship between an equipment failure and an interruption of power supply. The research is aimed at identifying “bottlenecks” from the technological reliability standpoint and substantiating maintenance and repair, and technical re-equipment and reconstruction measures to improve operational reliability. A PSS model is proposed reflecting the technical condition of the network equipment, the operational readiness of automation systems, the availability of structural, functional and load redundancy in the REN. A method is suggested for calculating the PSS reliability indicators, where the developed indices reflect the degree of development of the network technical potential and the role of the aforesaid nodes in the PSS. The method makes it possible to identify the network parts, where it is necessary to introduce new technologies. In contrast to a well-known method, which is based on expert estimates of probabilities of different circuit-mode states of the network and on the calculation of normal and post-emergency modes, a less timeconsuming formalized procedure for analyzing and evaluating the network structural and functional reliability is proposed. The results obtained allow to increase the validity of the decisions made both at the operational stage and the design stage.

An improved sag detection approach based on modified Goertzel algorithm

ABSTRACTPower quality is one of the key features in developing electric networks. It has been noticed because of its impact on economy and reliability of electrical networks. There are several power quality phenomena which are categorised in recent standards and literatures. Among them, voltage sag is more common and destructive for electric networks and consumers. This article presents a new detection method to monitor voltage sag in different electric network conditions. Goertzel algorithm is shown to be effective and simple for sag measurement compared to available sag detection methods.In order to increase the detection speed and response time, the Goertzel algorithm is modified. This modification will add to the speed of sag detection. The feasibility of the proposed method is justified through a measurement set-up developed using the dSPACE R1104 Digital Signal Processor Platform. The experimental results prove that sag measurement speed is improved by twice using the proposed modified Goertzel algorithm in comparison with the original method and some established methods. The results also verify that the sag detection of the proposed method is not affected by harmonic distortion of the voltage waveform.

Toward reliable interpretation of power transformer sweep frequency impedance signatures: experimental analysis

Power transformers play a significant role in maintaining the reliability of electrical power transmission and distribution networks. The probability that a transformer will fail increases with the aging of its insulation system [1]. Core deformation and winding movement may be caused by severe electromagnetic forces generated during short circuit faults [2]–[5]. Although a transformer may still work normally with minor axial or radial winding deformations, accumulating effects of these deformations may lead to sudden catastrophic failure of a transformer [6]. According to an international CIGRE survey conducted on power transformers covering the period 1996 to 2010, 19.4% of transformer failures during this period were attributed to windings- related problems [7]. It is therefore essential to assess the mechanical integrity of transformers which have been exposed to severe short circuit faults or lightning, or relocated, and take appropriate remedial action.

Phase Balancing in Power Distribution Network with Data Center

High degree of unbalance in electric distribution feeders can significantly affect power quality, damage electrical equipment, and result in tripping of protective devices. If not properly managed, integration of new data center and distributed energy resources into the power distribution network will exacerbate the problem. This paper proposes a new paradigm which coordinates the operation of data center and distributed energy resources to reduce phase unbalance and improve the reliability and efficiency of electric distribution networks. The coordination scheme is implemented within the framework of a distribution system operator managed electricity market. The proposed phase balancing algorithm with data center is validated using a modified IEEE distribution test feeder. The simulation results show the proposed data center and distributed energy resources coordination scheme not only significantly reduces the degree of unbalance of distribution feeders but also results in sizable reduction in data center electricity costs.

Application of UHF sensors for PD measurement at power transformers

The reliability of electrical energy networks depends on both, the quality and reliability of its electrical equipment, e.g. power transformers. Local failures inside their insulation may lead to breakdowns and hence to high outage and penalty costs. Power transformers can be tested on partial discharge (PD) activity before commissioning and monitored during service in order to prevent these events. In the first part, this contribution presents different types of ultra-high frequency (UHF) sensors for PD measurement. Various applications of UHF sensors and proper sensor installation are discussed. The second part of the contribution is about the necessity of UHF measurement comparability and reproducibility. Therefore, a new calibration procedure for the UHF method is proposed and discussed in respect of the procedure for the IEC 60270 compliant conventional electric method. The characterization of UHF sensors is a key precondition for the UHF calibration process in order to obtain calibration for the full measurement path. Sensor characteristics are described by the antenna factor (AF) which is determined under inside transformer conditions in an oil-filled Gigahertz Transversal Electromagnetic cell (GTEM cell). In addition to the calibration procedure, the performance of the installed sensor has to be determined. The evaluation is based on the concept of transmitting electromagnetic waves through the transformer tank from one UHF sensor to another. This performance check procedure is used in this contribution for the examination of the influence of the sensor's insertion depth into the tank. These results are compared to the reference GTEM cell measurement used for calibration.

Reliability and cost optimisation of complex electric power networks using ant colony algorithm

The article presents a new approach towards reducing an overall cost of electric power network with maintaining its reliability. Goals are achieved by implementing an ant colony algorithm with a cut-set method as a method for reliability evaluation. The algorithm solves the problem of multi-objective optimisation, where both the network cost and network reliability index, known as unavailability, should be minimalised. The network cost is considered as a linear function of overall length of network’s connections. For reliability evaluation in the cut-set method, real empiric data of hazard rate for overhead power lines are used. Parallel-series network structure, equivalent by means of reliability to analysed network, is generated through the cut-set method to compute unavailability of trial solutions. Sections of the structure are generated on the basis of minimum cut set, found by the algorithm for finding one- and two- minimum cuts. As used algorithm for finding minimum cuts has linear complexity, the evaluation of trial solutions is computationally effective. An example, presented in this article, provides figure of optimal network configurations found by the algorithm.

Stochastic assessment of investment efficiency in a power system

The assessment of investment efficiency plays a critical role in investment prioritization in the context of electrical network expansion planning. Hence, this paper proposes new criteria for the cost-efficiency investment applied in the investment ranking process in electrical network planning, based on the assessment of the new investment candidates impact on active-power losses, bus voltages and line loadings in the network. These three general criteria are chosen due to their strong economic influence when the active-power losses and line loadings are considered and due to their significant impact on quality of supply allowed for the voltage profile. Electrical network reliability of supply is not addressed, since, this criterion has already been extensively applied in other solutions regarding investment efficiency assessment. The proposed ranking procedure involves a stochastic approach applying the Monte Carlo method in the scenario preparation. The number of scenarios is further reduced by the K-MEANS procedure in order to speed up the investment efficiency assessment. The proposed ranking procedure is tested using the standard New England test system. The results show that based on the newly involved investment assessment criteria indices, system operators will obtain a prioritized list of investments that will prevent excessive and economically wasteful spending.

Effect of Islanding and Telecontrolled Switches on Distribution System Reliability Considering Load and Green-Energy Fluctuations

To improve electrical distribution network reliability, some portions of the network could operate in autonomous mode, provided that the related technical issues are addressed. More specifically, when there is not a path from those portions to the primary substation due to a fault in the network, such portions could be disconnected from the main network and supplied by local generation only. Such a mode of operation is known as “intentional islanding” and its effectiveness, in terms of adequacy, depends on the ability of the local generation to meet the island’s load. In fact, the ratio between the available local generation and load demand can frequently change during islanding due to load variations and, especially, due to the strongly irregular behavior of the primary energy sources of renewable generators. This paper proposes an analytical formulation to assess local generation adequacy during intentional islanding, accounting for the aforementioned variations. More specifically, the fluctuations of load and green-energy generators during islanding are modeled by means of Markov chains, whose output quantities are encompassed in the proposed analytical formulation. Such a formulation is used by the analytical equations of load points’ outage rate and duration. The evaluation of the reliability indices accounts for a protection scheme based on an appropriate communication infrastructure. Therefore, a brief overview on the telecommunications technologies has been presented with reference to their suitability for the specific application. In particular, distribution network safety issues have been considered as the main concern. The results show that neglecting load and generation fluctuations leads to a strong overestimation of the ability of distributed generators to meet the island load. Through a case study it is observed that the error on the load point outage rate is greater than the one affecting the outage duration.

Analyzing Distributed Generation Impact on the Reliability of Electric Distribution Network

With proliferation of Distribution Generation (DG) and renewable energy technologies the power system is becoming more complex, with passage of time the development of distributed generation technologies is becoming diverse and broad. Power system reliability is one of most vital area in electric power system which deals with continuous supply of power and customer satisfaction. Distribution network in power system contributed up to 80% of reliability problems. This paper analyzes the impact of Wind Turbine Generator (WTG) as a distribution generation source on reliability of distribution system. Injecting single WTG and close to load point has positive impact on reliability, while injecting multiple WTGs at single place has adverse impact on distribution system reliability. These analyses are performed on bus 2 of Roy Billinton Test System (RBTS).

Electrical network reliability and system blackout development simulations

The main regulations of the author’s model of electrical network reliability and system blackout development are stated. The model allows one to analytically determine the main technical and economic parameters indicators of reliability of electrical network operation, taking into account the generating power dislocations and electric loads, operation conditions, and dynamic and static stability of operation, while simultaneously calculating short circuit currents. The model also considers open-phase modes at singlephase short circuits and allows one to choose the most efficient operation conditions. The calculations are finished with an estimate of the annual averages of undersupply of energy and economic losses of customers due to their power supply interruptions.

A Review of Considered Factors to Penetrate Renewable Energy Resources in Electrical Power System

<p>As an increasing of load demand, scarcity of fossil fuel and penetration of greenhouse gasses (GHG) effect, utilization of renewable energy resources (RER) such as wind, solar, biomass and tidal are rising drastically. Distributed generation (DG) is a technology giving opportunity to integrate RER into power system network. These integrations are needed optimal long term planning. Those planning, hopefully, can increase reliability of electrical power system network while saving environment from GHG with minimum infestation, operation and maintenance cost. The aim of this paper is reviewing factors should be consider when preparing, operating and evaluating electrical power system with integration of RER. By this planning, it is expected that its integration is effective and efficient in a lifetime of project. Finally, this review can help government, researcher, engineer and private sector to make policies to preparing hybrid power system-DGs. </p><p><strong>Keywords</strong>: <em>Penetration of renewable energy resources, electrical power system, long term planning, distributed generation, policies </em></p>

Power Quality Analysis of Smart Grid Pilot Project, Puducherry

Abstract The concept of smart grid lies in the integration of information and communication technologies into the existing power system infrastructure to get maximum benefit to the end-user. The objective of implementing smartness in the grid is to increase the reliability, efficiency, customer satisfaction and power quality of the vast electrical distribution network. This paper presents the power quality analysis of a smart grid pilot project of utility in Puducherry implemented under collaboration of Power Grid Corporation of India Limited. The analysis has been done by data collected via power analyser at several locations in the smart grid pilot project. Analysis includes harmonics, sub-harmonics, total harmonic distortion and other various components of power quality. Instead of using only voltage parameters, current parameters are also considered for analysis.

Multiobjective planning of distribution networks incorporating switches and protective devices using a memetic optimization

A multi-objective planning approach for the reliability of electric distribution networks using a memetic optimization is presented. In this reliability optimization, the type of the equipment (switches or reclosers) and their location are optimized. The multiple objectives considered to find the optimal values for these planning variables are the minimization of the total equipment cost and at the same time the minimization of two distribution network reliability indexes. The reliability indexes are the system average interruption frequency index (SAIFI) and system average interruption duration index (SAIDI). To solve this problem a memetic evolutionary algorithm is proposed, which combines the Non-Dominated Sorting Genetic Algorithm II (NSGA-II) with a local search algorithm. The obtained Pareto-optimal front contains solutions of different trade-offs with respect to the three objectives. A real distribution network is used to test the proposed algorithm. The obtained results show that this approach allows the utility to obtain the optimal type and location of the equipments to achieve the best reliability with the lower cost.

Monte Carlo simulation-based probabilistic assessment of DG penetration in medium voltage distribution networks

Abstract With the growing use of renewable energy sources, Distributed Generation (DG) systems are rapidly spreading. Embedding DG to the distribution network may be costly due to the grid reinforcements and control adjustments required in order to maintain the electrical network reliability. Deterministic load flow calculations are usually employed to assess the allowed DG penetration in a distribution network in order to ensure that current or voltage limits are not exceeded. However, these calculations may overlook the risk of limit violations due to uncertainties in the operating conditions of the networks. To overcome this limitation, related to both injection and demand profiles, the present paper addresses the problem of DG penetration with a Monte Carlo technique that accounts for the intrinsic variability of electric power consumption. The power absorbed by each load of a medium voltage network is characterized by a load variation curve; a probabilistic load flow is then used for computing the maximum DG power that can be connected to each bus without determining a violation of electric constraints. A distribution network is studied and a comparison is provided between the results of the deterministic load flow and probabilistic load flow analyses.

Hierarchical fair competition algorithm for optimization of reliability of complex electric power networks

Hierarchical fair competition algorithm for optimization of reliability of complex electric power networks

On the Transient Behavior of Large-Scale Distribution Networks During Automatic Feeder Reconfiguration

The paper presents an in-depth analysis of the automatic reconfiguration and self-healing principles of the next generation (3G) smart grid of a real metropolitan distribution network. The large network is to be divided dynamically and remotely controlled into three smaller subnetworks to further increase the reliability of electrical power distribution secondary networks. When one subsection is experiencing difficulties, there is no longer the need to de-energize the entire network. A time-domain (EMTP) model has been developed and validated by comparing simulations with recordings of actual transient events. Different switching and fault scenarios are investigated using this model. Analysis of the results provides important conclusions on equipment rating, relay protection coordination, voltage regulation, switching and operation strategies which are discussed in the paper. A subset of these results is presented for illustration. This extensive study of a complex urban network suggests that: 1) before implementation of smart grid principles, it would be prudent to supplement steady-state analysis with time-domain analysis to avoid problems, such as installation of improperly rated equipment, and improper relay-protection coordination; and 2) EMTP-type programs may be used to conduct the time-domain analysis, despite the enormous number of elements contained in an urban network.