Low Voltage Customers Research Articles

Controlled Charging of Electric Vehicles to Minimize Energy Losses in Distribution Systems

Abstract: Controlled electric vehicle (EV) charging scenarios are proposed, each characterized with an algorithm and associated computational and communication requirements, to be adopted by an EV aggregator or system operator. The proposed scenarios include uniform, random, conditional-random, and valley-filling charging scenarios. Different from previous studies, this paper focuses on easy-to-implement charging scenarios. Further, a modeling framework is presented to investigate the impact of the proposed charging scenarios on energy losses in distribution systems, as compared to an uncontrolled charging scenario and a reference scenario with no EVs. The modeling framework considers uncertainties involved in the behavior of low voltage customers and EV charging loads. It is applied to a distribution system for various case studies, including different penetrations and combinations of EVs with various characteristics. As seen by the results, although the valley-filling charging algorithm represents the optimal solution from the perspective of energy losses, the uniform charging scenario emerges as a quasi-optimal solution, having lower computational and communication requirements, which makes it easier to be adopted by EV aggregators or system operators. Further, with appropriately selected coefficients, the conditional-random charging algorithm can also exhibit a performance comparable to that of the uniform charging algorithm.

Development of Low-Voltage Load Models for the Residential Load Sector

A bottom-up modeling approach is presented that uses a Markov chain Monte Carlo (MCMC) method to develop demand profiles. The demand profiles are combined with the electrical characteristics of the appliance to create detailed time-varying models of residential loads suitable for the analysis of smart grid applications and low-voltage (LV) demand-side management. The results obtained demonstrate significant temporal variations in the electrical characteristics of LV customers that are not captured by existing load profile or load model development approaches. The software developed within this work is made freely available for use by the community.

Influence of Socio-Economic Indicators on Electricity Consumption of Low Voltage Customers in Cameroon

In this paper, the demand of Low Voltage electricity customers in Cameroon using electricity as an energy source beginning from the period 1975 to 2011 is modeled. This approach aims to study the consumption determinants (macro- economic indicators, demographic indicators and lagged consumption of low voltage electricity) of low Voltage Customers and to analyze those determinants that have a strong influence on consumption. Parameters estimated by EVIEWS 7.2 software for linear and exponential (CooB-Douglas) models were used. The results show that CooB-Douglass models are better than the linear model. It also shows that: (i) the best linear model is a function of delayed consumption〖 C〗_(t-1) ; overall gross domestic product ((〖GDP_g)〗_t) and population (P_t ); (ii) the best model CooB-Douglas is a function of delayed consumption〖 C〗_(t-1) , the global gross domestic product ((〖GDP_g)〗_t) and the number of subscribers (S_t). It noticed that the macroeconomic indicators have a better influence on demographic consumer’s indicators and that the absence of the delayed consumption variable in a model causes autocorrelation of the residuals models.

Ecodesign of Ever Net-Load Microgrids

The European Union has promoted the process of electrical market liberalization, extended to residential/commercial buildings, and a strong encouragement toward the rational use of energy. The European energetic policy aims to promote the installation of small renewable power sources, the use of highly efficient cogeneration, and the Nearly Zero-Energy Buildings (NZEBs) that have to be pursued as much as possible by local generation sufficient to supply the residual amount of energy. To avoid future chaotic phenomena in the existing distribution network, this paper highlights that the power flow of local generators has to be maintained locally: The users have to remain net-loads organized in ever net-load microgrids at least in a first evolution. The actual distribution network for low-voltage customers appears inadequate to comply with these improvements, and it has to change in order to accept microgrids organized by the union of customer groups. The authors suggest the ecodesign of the microgrids able to constitute the NZEB and to accomplish the goals of enhanced safety, high local power quality, dc distribution systems, common emergency systems, efficient load shedding, and energy management. The microgrids guarantee a reduced impact as ever net-load on the net supply.

Analysis of the effect of distributed generation on life expectancy of power cables

Summary This paper presents a novel approach to quantify the effect of customer-owned distributed generation (DG) units on the life expectancy of power cables. Numerical results obtained from a realistic distribution system are presented and discussed under various scenarios, including different penetration levels of DG technologies. The results show that despite differences among various DG technologies, significant benefits can be realized in the area of power cable life extension, when DG units are installed by low-voltage customers. However, the extent of the benefits largely depends on the penetration level of DG units, the production pattern of DG technologies and the utilization factor of the analyzed cables. Copyright © 2013 John Wiley & Sons, Ltd.

Effect of Distributed Generations on Aging Failure Probability of Distribution Transformers

This article presents a methodology to investigate the effect of customer-owned distributed generation units on the probability of transition to aging failure of distribution transformers. It is based on a probabilistic view to the aging failure of transformers. The proposed methodology is applied to realistic distribution transformers supplying residential and commercial customers. The results show that adopting a distributed generation solution by low-voltage customers may bring about a 45% reduction in aging failure probability at old ages of the examined transformers. It should be noted that micro-turbines and wind turbines represent superior results among the examined distributed generation technologies.

Determining Maximum Impedance Limits At A Point of Connection For Different Current Capacity Installations

Modern customers use many power electronics based devices that are often sensitive to power quality (PQ) related disturbances. Those devices produce current harmonics that in combination with the network’s impedance at a customer’s point of connection (POC) influence the network’s voltage quality. With a distorted supply voltage, many devices produce more current pollutions. Therefore, the network’s impedance at a POC is quite important and can have significant impact on the network’s power quality. At present some standards specify requirements of the voltage and/or current quality at a POC. However, only few requirements are given for the network’s impedance (short circuit power) which can highly influence the PQ performance at a POC. In this paper, estimation is made to determine the maximum impedance limits at the medium voltage (MV) and the low voltage (LV) customer’s POC. The network operators should be responsible to limit the maximum impedance value at a POC while approving a specific capacity connection to a customer.

低圧配電システムの雷過電圧

The portion of the faults of a medium-voltage line, cause by lightning, tends to increase with often reaching beyond 30%. However, due to the recent progress of the lightning protection design, the number of faults has decreased to 1/3 of that at 30 years ago. As for the low-voltage distribution line, the fault rate has been estimated primarily, although the details of the overvoltages have not been studied yet. For the further development of highly information-oriented society, improvement of reliability of electric power supply to the appliance in a low-voltage customer will be socially expected. Therefore, it is important to establish effective lightning protection design of the low-voltage distribution system, defined to be composed of lines having mutual interaction on the customers' electric circuits, such as a low-voltage distribution line, an antenna line and a telecommunication line. In this report, the author interprets the recent research on the lightning overvoltage on a low-voltage distribution system.

Flicker propagation and emission coordination study in a simulated low voltage network

AbstractVoltage flicker is an irritating problem especially for the low voltage (LV) customers. It is mainly caused by the loads having repetitive cycle of operation. During the past years, the network operators around the world have registered many complaints from the customers about flicker related problems. Presently, there is no common standard value for the flicker planning level available globally. Moreover, in some countries (for example, in the Netherlands), the existing networks are not even based on a specific planning level value for flicker. Therefore, it is necessary to discuss the flicker planning level values in different voltage levels to overcome flicker related problems. In this paper a typical LV network is simulated to analyze the flicker propagation behavior in the network. The effects of switching LV disturbing loads (such as elevator, welding machine, etc.) on flicker generation at different customer's installations are studied by using synchronized measurement technique. Also, the impacts of the background flicker pollution transferred from the upstream to the downstream networks are analyzed. The simulation results give an overview of the flicker pollution levels at the LV customer's installations in the presence of background flicker. This paper estimates the maximum value of flicker emission share at different customer's point of connections (POC), considering the impact of background flicker pollution. Finally, planning level values of flicker in different voltage levels are suggested that can be useful for the network operators in designing their future networks. Copyright © 2009 John Wiley & Sons, Ltd.

Implementation of a systematic distribution transformer load management in Taipower

The practice of transformer load management (TLM) in Taipower to determine the daily power profile and the peak loading of distribution transformers by integration of customer information systems (CISs) such as, automated mapping/facilities management/geographic information system and load survey system is presented. The load survey study is conducted by selecting 672 customers for installation of digital power meters to measure the customer power consumption within 15 min intervals. The typical load patterns of low-voltage residential, commercial and industrial customer classes are derived by executing statistic analysis of power consumption of test customers. A narrow-band power line carrier-based identifier is developed to identify all of the customers served by each distribution transformer. The hourly power consumption of each customer is determined by allocating the monthly energy consumption according to the typical load pattern of the corresponding customer class. The peak loading of each distribution transformer is then estimated by integrating the power consumption of all customers served. The overloading flags and peak loading levels of all transformers are then displayed on the digital mapping system. The TLM program proposed in this study has effectively assisted Taipower distribution engineers to identify the potentially overloading transformers for load reduction to mitigate the transformer damage during the hot summer season.

A non-linear multivariable regression model for midterm energy forecasting of power systems

The objective of this paper is to describe a non-linear multivariable regression method for midterm energy forecasting of power systems in annual time base. This method performs an extensive search in order to select the appropriate transformation functions of input variables, the weighting factors and the training periods to be used, by taking into consideration the correlation analysis of the selected input variables. With this procedure the best forecasting model is formed. Results are presented that are obtained applying the described method for the Greek power system and for different categories of low voltage customers. These results are also compared to those obtained from the application of standard regression methods.

Simplified model for estimation of lightning induced transient transfer through distribution transformer

In this work a simplified procedure for the formulation of distribution transformer model for studying its response to lightning caused transients is presented. Simplification is achieved by the way with which the model formulation is realised. That is, by consolidating various steps for model formulation that is based on terminal measurements of driving point and transfer short circuit admittance parameters. Sequence of steps in the model formulation procedure begins with the determination of nodal admittance matrix of the transformer by network analyser measurements at the transformer terminals. Thereafter, the elements of nodal admittance matrix are simultaneously approximated in the form of rational functions consisting of real as well as complex conjugate poles and zeros, for realisation of admittance functions in the form of RLCG networks. Finally, the equivalent terminal model of the transformer is created as a π-network consisting of the above RLCG networks for each of its branches. The model can be used in electromagnetic transient or circuit simulation programs in either time or frequency domain for estimating the transfer of common mode transients, such as that caused by lightning, across distribution class transformer. The validity of the model is verified by comparing the model predictions with experimentally measured outputs for different types of common-mode surge waveform as inputs, including a chopped waveform that simulate the operation of surge arresters. Besides it has been verified that the directly measured admittance functions by the network analyser closely matches the derived admittance functions from the time domain impulse measurements up to 3 MHz, higher than achieved in previous models, which improves the resulting model capability of simulating fast transients. The model can be used in power quality studies, to estimate the transient voltages appearing at the low voltage customer installation due to the induced lightning surges on the high voltage side of the transformer. The procedure is general enough to be adapted for any two-port devices that behaves linearly in the frequency range of interest.

Impacts Over the Distribution Grid From the Adoption of Distributed Harmonic Filters on Low-Voltage Customers

This work presents a study of distributed passive harmonic filter design to minimize harmonic distortions caused by nonlinear loads in residential customers. The main objectives in this study are: 1) to improve the power factor, 2) to reduce current and voltage distortions to standard limits, and 3) to reduce electrical losses. In this sense, several measurements that were carried out in some domestic customers of the metropolitan distribution grid of Belem City, in the North of Brazil, have characterized as the main harmonic distribution current sources the third, fifth, and seventh harmonic components. According to the results obtained and considering the impacts caused in the distribution grid, a distributed filtering strategy is proposed using passive-tuned filters of low costs to be installed in the customers.

Voltage sag distributions caused by power system faults

Voltage sag distributions caused by faults at different voltage levels and experienced by low-voltage customers were established for four different power system areas. The shares of different fault types at each voltage level and the sag propagation throughout the power system were taken into account. The results show that the origin of sags in urban and rural areas tends to be different. These data are needed when, for example, planning measures for sag mitigation in different parts of the power system.

Load profile assignment of low voltage customers for power retail market applications

To facilitate retail choice in a competitive power market, the knowledge of hourly load shape by customer class is necessary. Requiring a meter as a prerequisite for lower voltage customers to choose a power supplier is not considered practical at the present time. A technique which uses load research and customers’ monthly energy usage data for a preliminary screening of customer load profiles is presented. Two data mining techniques, namely, the fuzzy c-means (FCM) method and an artificial neural network (ANN) based pattern recognition technique, are utilised in this work. The proposed method can be used by the Energy Service Provider (ESP) to assign customers to specific load profiles with certainty factors. Customers with less certainty in the assignment will need meter installation or further investigation in order to determine which classes they belong to. Test data are from actual measurement and the customer information system (CIS) of Taiwan Power Company (TPC). Promising results on assigning existing under 220 V customers to their proper load profiles are illustrated.

Design and cost analysis of an automatic meter reading system for Electricité du Liban

This paper summarizes the results of a study for modernizing the electricity metering, billing and collection processes for Electricité du Liban (EDL), the national power company of Lebanon. The objective of this study is to provide EDL with the best alternatives for modernizing their electricity metering of low-voltage customers. These customers are currently being metered using a variety of old and new electromechanical meters. The metering process at EDL is manual, and prone to errors. The existing system does not provide EDL with reliable methods to readily check bills, identify problematic customers, and reduce fraud. Therefore, EDL’s modernization requirements include an automated system capable of enhancing current metering processes, minimizing fraud, and maximizing revenue collection. This paper will describe the functional requirements of EDL and investigate the feasibility of using Automatic Meter Reading (AMR) technology to satisfy these requirements. Both procedural and equipment modernization techniques will be identified and assessed. The proposed modernization system will make EDL’s metering activities as advanced as those of modern utilities. Most importantly, with the modernized system, EDL will regain the confidence of its customers, and would become a highly reputable and revenue generating organization.