Petru Postolache

Customer characterization options for improving the tariff offer

This paper deals with the classification of electricity customers on the basis of their electrical behavior. Starting from an extensive field-measurementbased database of customer daily load diagrams, we searched for the most appropriate indices or sets of indices to be used for customer classification. We propose two original measures to quantify the degree of adequacy of each index. Using the indices as distinguishing features, we adopt an automatic clustering algorithm to form customer classes. Each customer class is then represented by its load profile. We use the load profiles to study the margins left to a distribution company for fixing dedicated tariffs to each customer class. We take into account new degrees of freedom available in the competitive electricity markets, which increase flexibility in the tariff definition under imposed revenue caps. Results of a case study performed on a set of customers of a large distribution company are presented.

Analysis of Three-Phase Systems With Neutral Under Distorted and Unbalanced Conditions in the Symmetrical Component-Based Framework

This paper introduces an original and rigorous formulation for computing the unbalance and distortion components of phase and neutral currents in the framework of the symmetrical component transformation. The proposed formulation extends recent literature results, in which different matrices were used for unbalance characterization in the presence of distorted waveforms and provides, at the same time, an innovative interpretation of the neutral current waveform components. New indicators are also defined to combine the effects of unbalance and waveform distortion, extending the set of indicators currently adopted in the power-quality standards. A set of illustrative examples is presented to show the applicability of the proposed approach. These include four circuits, two real-case applications, and an example taken from the IEEE trial-use standard 1459-2000

Electric energy customer characterisation for developing dedicated market strategies

This paper deals with the classification of the electricity customers for building up dedicated tariff structures based on their electrical behaviour. Starting from the results of field measurements, the load patterns are characterised by a set of indices representing the shape of the load curves. An automatic clustering algorithm is used to form the customer classes. Each customer class is then represented by its load profile. The load profiles are used to study the margins left to the utility company for fixing dedicated tariffs to each customer class, according to new rules introduced in the liberalised electricity market, which increase the flexibility in the definition of the tariffs under imposed price caps. Results of a case study performed on a set of customers of a distribution company are presented.

New nested evolutionary programming approach for voltage control optimization with distributed generation

This paper addresses the optimization of voltage control in distribution systems in the presence of distributed generation. The objective is minimizing the voltage deviations at the load nodes with respect to specified reference values. The optimization is solved by means of a new approach based on nested evolutionary programming. Results are shown on a test system including controls at the HV/MV and MV/LV substations, and voltage-controlled local generation sources.

The connection to the grid of wind turbines

With a view to the integration in national power system of new power plants based on renewable energy sources, such as wind energy, this paper presents the technical requirements related to the connection of the wind power plants to the main grid. Grid connected wind turbines may cause power quality problems, such as voltage variation and flicker, and therefore, the connection of wind farms requires new connecting rules to avoid negative effects on the existing electrical system. System operators usually issue these rules in the form of grid codes. The paper should be helpful to facilitate the orientation in finding of adequate type of wind turbines that can be installed in the intended sites, dependent on specific conditions.

Efficient iterative refinement clustering for electricity customer classification

Customer classification is aimed at providing to the electricity suppliers a sound information on the electricity consumption, to be used for formulating dedicated tariff structures. Different clustering methods can be adopted for assisting the process of electricity customer classification. Previous studies have identified two methods - hierarchical clustering and follow-the-leader - as most promising in terms of clustering validity for classifying the customers on the basis of the shape of their load patterns. However, the above methods exhibited some limitations in terms of the possibility of preassigning the number of clusters (for the follow-the-leader) or improving the cluster formation by reassigning the load patterns to the clusters already formed (for the hierarchical clustering). This paper presents the new iterative refinement clustering (IRC) method, originally developed in order to overcome these limitations. The performance of the IRC method has been compared to the one of other clustering methods by means of suitable clustering validity indicators. The results obtained on a set of over 200 non-residential customers are presented in the paper to show the effectiveness of the proposed IRC method.

Experimental Evaluation of Unbalance and Distortion Indicators in Three-Phase Systems with Neutral

The characterization of three-phase systems with neutral under unbalanced operation in the presence of waveform distortion is a key aspect in the power quality studies. This paper presents the application to a number of real cases of a unified framework providing a set of synthetic indicators capable to explain the individual effects of unbalance and harmonic distortion. The use of specific indicators extending the notion of total harmonic distortion to the case of unbalanced systems, and the notion of unbalance to the systems with distorted waveforms is illustrated and discussed on various sets of data gathered from real-time measurements on office and laboratory feeders and on a photovoltaic system.

Analysis of the Steinmetz compensation circuit with distorted waveforms through symmetrical component-based indicators

This paper deals with the use of a set of indicators defined within a symmetrical component-based framework to study the characteristics of the Steinmetz compensation circuit in the presence of waveform distortion. The Steinmetz circuit is applied to obtain balanced currents in a three-phase system supplying a single-phase load. The circuit is analyzed without and with harmonic distortion of the supply voltages. The compensation effect is represented by the classical unbalance factor and by the Total Phase Unbalance (TPU) indicator defined in the symmetrical component-based framework. Comparing the two indicators, it is shown that the classical unbalance factor is insufficient to represent the effect of voltage distortion and fails to detect the lack of total unbalance compensation occurring with distorted waveforms. Correct information is provided by calculating the TPU indicator.

Voltage estimation in power distribution networks. A case study on data aggregation and measurement uncertainty

The paper presents a real case study of uncertainty evaluation in case of data aggregation. The analysis is related to the half period rms voltage time aggregation stated by IEC 61000-4-30 for voltage measurement and it is based on selected data gathered during more than one year. In order to perform the measurements campaign, the special facility (OSC function) of custom designed equipment called MOT was used. The mix of measurement uncertainty, data aggregation and non-stationarity of data make the search of relevant information difficult.

Cluster analysis of half-cycle duration measurements to classify local and network events

This paper presents a real case study of the half-cycle duration measurement and classification. The study is based on data gathered at three different low voltage locations. In order to carry out the measurements, a special facility (OSC function) of a custom designed equipment called MOT was used. After the introductory aspects concerning the regulation for frequency measurement, the paper presents the structure of the MOT equipment and illustrates the characteristics of the data gathered. These data are then analysed through a hierarchical clustering method to identify and classify the events. The results obtained and the main ideas for future developments are illustrated and discussed in the paper.