Andres Pavas

Discussion on existing methodologies for the Responsibilities Assignment Problem

This paper introduces the responsibilities assignment problem (RAP) and discusses existing methodologies by theory and examples. The RAP can be understood as the evaluation and determination of the power quality disturbances and of the power quality conditions detriment concerning source and amount. Selected details of this problem are presented in this paper, in order to provide a conceptual background to understand the problem itself and to interprete the characteristics of the currently available assessment methodologies. The existing methodologies are summarized, their principles, characteristics, and application are illustrated by means of an example. From the application results, a comparison of the mentioned methodologies is shown to point out advantages and differences. In the framework of the conference this paper could start and support a discussion about the assigment of responsibilities related to power quality disturbances propagation and improvements of the existing methodologies.

Method of Disturbances Interaction: Novel approach to assess responsibilities for steady state power quality disturbances among customers

A new method to decompose currents in electrical circuits in order to analyze stationary power quality disturbances is presented in this paper. A set of reference conditions allows the definition of the desirable load behavior regarding power quality. The decomposition permits to analyze separately three stationary phenomena, waveform distortion, asymmetry and phase displacement. A discussion about the problem is responsibilities is presented as well.

Impact Assessment of Power Quality Limits in Colombia: a Regulatory Approach

In order to improve present regulations about power quality (PQ) in Colombia, an impact assessment of PQ limits among utility companies and customers is presented in this paper. This evaluation takes into account results obtained from a previous project of PQ measurements in Bogota-Colombia (PQB) over a representative sample of end users. This paper evaluates the percentage of users that would be surpassing some proposed limits for PQ disturbances such as: THD, TDD, individual harmonics, unbalance voltage, flicker and unbalance current. This analysis was carried out for industrial and commercial facilities taking into account that these users require higher levels of power quality and therefore may inquire in bigger costs in case of poor power quality conditions compared to other type of users such as residential customers. The results achieved in this work show that for some disturbances is possible to apply a regulation based on international standards as IEC and IEEE but in other parameters their application could become very expensive for utilities and end users

Web based management system for power quality assessment and detection of critical zones

The implementation of a web system information management for assessment of power quality indices and detection of critical zones on a distribution system is proposed in this paper. The proposed system was implemented on a APACHE server platform, consisting of three main parts. The first part registers, pre-processes and stores power quality measurements on an open source data base using MySQL. In the second part power quality indices are calculated for each substation, such indices allow the evaluation of disturbances like voltage sags, voltage swells, voltage flicker (Pst) and voltage unbalance. Finally, in the third part the indices are displayed as power quality maps by means (Google Maps) tools, where critical zones are identified for each disturbance according to disturbance activity and severity criteria. This is a low cost, useful and easy to implement tool by the network operator, also can be implemented by the regulatory body for end user consultations.

A new methodology for the comparative analysis of sags among substations in a distribution network in Colombia

In this paper, a new methodology to achieve comparative analysis of sags among substations in large distribution networks is proposed. The proposed methodology consists in three stages as follows. First, data acquired from a Power quality measurement system is considered. Second, sags disturbances are classified and quantified according to a proposed level of severity. Third, an index called Sags Activity index-SAI is proposed allowing to weight and rank the severity of sags among the affected substations. The results show that this index might be easily used by both, the electric companies and the regulator entities to establish limits for sags disturbances.

Power quality assessment of the Bogotá distribution network focused on voltage sag analysis

Power quality assessment of the Bogotá distribution network has been performed using four different statistical methods. Data was collected during two years by CODENSA, the largest Colombian electricity utility. The strategies have been divided as quantitative and qualitative approaches. Quantitative strategies are based on the study of probability density functions as well as the analysis of principal components (PCA). Probability density functions of voltage sag magnitudes have been used to better characterise their occurrence. PCA has been used to improve the analysis of sags based on coordination charts. On the other hand, qualitative approaches are focused on two sag related indices: the sag activity index (SAI index) and the amount of not delivered when the disturbance occurs. Those methods have been applied to assess power quality of 249 substations.

Modeling of a distribution transformer performance operating under harmonic polluted conditions

This paper shows the results obtained from the simulated study case about the impact of harmonics on a distribution transformer useful life. These results depend on the supplied energy level (power variation along the time) under three different demand profiles with the same harmonics level. It will be presented that the transformer overload affects the transformer useful life subjected to the presence of peaks and valleys in the weekly demand profile, providing period times to the transformer for the temperature increase (peaks) or decrease (valleys). These temperature variations will affect directly the transformer loss of life and will show that not only the harmonic presence on the transformer operation will accelerate its aging, but also other conditions allow a slow aging and even a useful life beyond the rated expectation. The possible effects of more complex disturbing scenarios, like unbalanced currents and high reactive power feeding, are presented as discussion.

Current supraharmonics identification in commonly used low voltage devices

This paper presents the measurement and characterization of current supraharmonic emission levels caused by commonly used electronic devices. A system setup was developed and signal processing techniques were proposed to identify lower and higher frequency phenomena, emission frequency bands and distortion indicators. Finally, a summary of emission levels is presented.

Impact assessment of distributed generation on the power quality and reliability of distribution grid

This paper presents the development of a methodology aimed to assess the impact of distributed generation, specifically Photovoltaic systems (PV) and battery storage, on the power quality and reliability within a distribution network. Reliability is evaluated by means of SAIFI and SAIDI indicators, evaluation of power quality is performed reviewing voltage drops, sags and fluctuations indicators. As different PV and storage penetration scenarios were considered, the amount of generation capable of improving the system power quality performance could be determined. The generation limits represent the amount of distributed generation above which the network performance begins to be undesirable. These limits were determined by means of the recently published concept of hosting capacity (HC). Finally the paper shows that some scenarios of GD penetration reduce potential interruptions but increase voltage sags.

Insulation temperature increase in power transformers due to stationary disturbances: Comparison of methods

This paper presents the comparison of two methods to estimate the insulation temperature increase and lifetime reduction in power transformers due to the presence of stationary power quality disturbances. The internal insulation can suffer an accelerated aging by temporary increases of rms values of currents caused by waveform distortion (harmonic current). The recurrent presence of increase in rms values during long time periods will produce a cumulative effect that degrade the dielectric material. Models for insulation aging are employed. A discussion about the effects on insulation lifetime is presented.