Diogo Salles

Assessing the Collective Harmonic Impact of Modern Residential Loads—Part I: Methodology

The proliferation of power-electronic-based residential loads has resulted in significant harmonic distortion in the voltages and currents of residential distribution systems. There is an urgent need for techniques that can determine the collective harmonic impact of these modern residential loads. These techniques can be used, for example, to predict the harmonic effects of mass adoption of compact fluorescent lights. In response to the need, this paper proposes a bottom-up, probabilistic harmonic assessment technique for residential feeders. The method models the random harmonic injections of residential loads by simulating their random operating states. This is performed by determining the switching-on probability of a residential load based on the load research results. The result is a randomly varying harmonic equivalent circuit representing a residential house. By combining multiple residential houses supplied with a service transformer, a probabilistic model for service transformers is also derived. Measurement results have confirmed the validity of the proposed technique. The proposed model is ideally suited for studying the consequences of consumer behavior or regulatory policy changes.

Assessing the Collective Harmonic Impact of Modern Residential Loads—Part II: Applications

This paper studies the harmonic impact of modern residential loads on the secondary power distribution systems. Several issues of concern to utilities, such as the neutral-to-earth voltage rise, the overloading of service transformers, the impact of compact fluorescent lights (CFL), and the benefits of adopting IEC 61000-3-2 limits, have been investigated. A bottom-up probabilistic harmonic assessment method proposed in the companion paper was applied to conduct the study. Several interesting results have been obtained. For example, the adoption of CFLs based on market trend could result in an increase of voltage total harmonic distortion by about 10% per year over the next couple of years. Adopting the IEC limits on CFLs will drop the growth rate to 2% per year. In addition to the results of interest to utility companies, this paper demonstrates the usefulness and necessity of a bottom-up-based approach to conduct harmonic assessment for residential loads.

Nondetection Index of Anti-Islanding Passive Protection of Synchronous Distributed Generators

Synchronous distributed generators are prone to operate islanded after contingencies, which usually is not allowed due to safety and power quality issues. Thus, there are several anti-islanding techniques; however, most of them present technical limitations so that they are likely to fail in certain situations. Therefore, it is important to quantify and determine whether the scheme under study is adequate or not. In this context, this paper proposes an index to evaluate the effectiveness of anti-islanding frequency-based relays commonly used to protect synchronous distributed generators. The method is based on the calculation of a numerical index that indicates the time period that the system is unprotected against islanding considering the global period of analysis. Although this index can precisely be calculated based on several electromagnetic transient simulations, a practical method is also proposed to calculate it directly from simple analytical formulas or look-up tables. The results have shown that the proposed approach can assist distribution engineers to assess and set anti-islanding protection schemes.

A Practical Method for Nondetection Zone Estimation of Passive Anti-Islanding Schemes Applied to Synchronous Distributed Generators

Unintentional islanding detection is a primary requirement for the interconnection of synchronous distributed generators (DGs). For this purpose, voltage and frequency-based relays are largely employed due to their low cost and simplicity However, these devices are not totally reliable due to their associated nondetection zone (NDZ). The NDZ is an effective tool to evaluate the performance of these relays against islanding occurrence. In this context, this paper presents a simple and practical analytical method to estimate the NDZ of frequency and voltage-based relays without relying on numerous, time-consuming electromagnetic transient (EMT) simulations. The main contribution is that one can easily estimate the NDZ of these protection systems based on a few analytical expressions. The effectiveness and generality of the analytical method are verified by comparing its results with those obtained by repeated, intensive EMT simulations for different power distribution networks and different relay types.

A Practical Second-Order Based Method for Power Losses Estimation in Distribution Systems With Distributed Generation

Power losses estimation under time-varying distributed generation (DG) conditions usually demands several power flow simulations, which is a time-consuming task. To handle this issue, this paper proposes a method that uses the information of only one (base case) power flow to estimate the total power losses of distribution networks for any new DG condition. The method is based on the second-order power flow sensitivities, which are suitable to model the nonlinear nature of power losses. As a result, the method has the potential to speed up the solution of power losses reduction optimization problems, such as DG allocation problems, in which several DG configurations need to be considered. Moreover, a practical index is proposed to quantify the responsibility of each DG for the total power losses in a multi-DG scenario. The test results verified the validity of the proposed concept and method.

An Intelligent Control Strategy for Power Factor Compensation on Distorted Low Voltage Power Systems

Due to the proliferation of harmonic producing-loads, harmonic resonance has become a major hurdle for performing power factor compensation in commercial power systems, such as office towers and shopping complexes. This paper presents an intelligent power factor compensation controller that can perform power factor correction without exciting harmonic resonance under varying demand conditions. Practical and robust control algorithms are proposed for the purpose of easy implementation in a micro-controller. In addition, the controller relies on common low cost sensing devices and does not require additional measurements. As a result, the proposed controller can be constructed as a retrofitting device to replace existing power factor correction controllers with little effort. Analysis of representative case studies is conducted to illustrate how the proposed controller performs.

Method to assess the power quality impact of plug-in electric vehicles

This paper presents a probabilistic harmonic simulation method to study the power quality impact of electric vehicles (EV). The proposed method takes into account the random operating characteristics of the vehicles, such as random charging time, charging duration and vehicle locations. A multi- phase model of the primary and secondary systems is used to represent the study system. Extensive case studies have been conducted using the method and the measured EV data. The results reveal that the current versions of plug-in hybrid EVs have no significant harmonic impact on power systems. However, the Level 1 charger can increase the neutral to earth voltage at homes which could lead to increased stray voltage incidents.

Review of international guides for the interconnection of distributed generation into low voltage distribution networks

Technological development, energy source diversification, environment concerns, financial incentives have driven the increasing interest on the interconnection of small scale distributed generators (SSDG) into low voltage (LV) distribution networks. This practice allows homeowners and others to contribute to the energetic matrix without having to implement expensive modifications to the grid. In this context, this paper presents a review of the requirements adopted by distribution companies worldwide to facilitate the connection of SSDG units while maintaining the integrity of the public low voltage distribution network, both in terms of safety and supply quality. Issues like disconnect switch, protection, metering, and power quality are examined.

Information extraction from PQ disturbances — An emerging direction of power quality research

Power quality is a field that deals with all sorts of power disturbances. Past power quality research and development activities have been focused on the harmful aspects of the disturbances. With the wide spread use of power quality monitoring tools, more and more users and developers start to realize that power disturbances can carry valuable information about the conditions of a system and its equipment. As a result, initiatives that explore the “useful” aspects of power disturbances have emerged. For example, short-circuit caused voltage sag disturbances have been exploited for fault location purposes, characteristics of capacitor-switching transients are used to determine and locate which feeder capacitors are operating normally. Such information-oriented use of power disturbance data and monitoring techniques could emerge as an important field of the future smart grid. The objective of this paper is to present some of the example developments in this interesting field. We hope this survey/review paper will help to stir up broader research interests in the field and serves as a step stone for PQ disturbance researchers.

Investigation of the islanding detection of induction generators

This paper provides an analysis of the performance of the under/over frequency and under/over voltage relays for islanding detection of squirrel-cage induction generators. This analysis is based on the nondetection zones, which are determined by extensive dynamic simulations using PSCAD/EMTDC. The presented nondetection zones are constructed considering different reactive power compensation and different detection times. Analysis on the nondetection zones is developed, and the influence of the required detection time and of the reactive power compensation on the nondetection zone is highlighted.