Jose Maria de Carvalho Filho

Analysis of power system performance under voltage sags

Abstract The aim of this work is to provide both utility and customer planning engineers a methodology for aiding them to achieve compatibility between industrial processes requirements and the quality of the electrical supply, taking into account the influence of voltage sag on the latter one. By applying this approach, new indices for both supply system and load buses can be drawn. They can be used by end-users planning engineers to choose the best location in the supply system, where new sensitive load consumers are to be connected. The paper also presents an example, based on a real case, which illustrates the applicability of such a methodology.

Alternative methodology for characterization of industrial process sensitivity to voltage sags

This paper proposes an alternative methodology for the characterization of industrial process sensitivity to voltage sags using a power quality (PQ) monitoring system. Several methodologies have been used for voltage sag characterization as can be seen in the literature. The load behavior is classified for each event registered by PQ monitors. Several characterization methods are analyzed to select the most consistent methodology for the characterization of load sensitivity.

Validation of Voltage Sag Simulation Tools: ATP and Short-Circuit Calculation Versus Field Measurements

Two methods to calculate voltage sags are validated against actual measurements. One of the methods is a short-circuit calculation program resulting directly in sag magnitude during the fault. The other is an electromagnetic transient program resulting in voltage waveform as a function of time. Individual sag characteristics and system performance obtained by deterministic simulation and measurement are compared. The influence of the random variables (prefault voltage, fault location and fault impedance) is investigated.

Differences in Voltage Dip Exposure Depending Upon Phase-to-Phase and Phase-to-Neutral Monitoring Connections

Voltage dip indices are estimated for a set of simulated and measured events. The simulated dips are obtained applying the method of fault positions on a large transmission network and the measured dips come from a one-year survey. The indices estimated to compare phase-to-phase and phase-to-neutral dips are SARFI-90, SARFI-70, SARFI-ITIC, and average voltage dip amplitude. Furthermore, the results are analyzed in terms of the cumulative distribution frequency of the voltage dip amplitude. The comparison of phase-to-phase and phase-to-neutral indices indicates that, at transmission level, phase-to-neutral dips are more frequent and more severe than phase-to-phase ones. However, these differences are reduced at the load connection level, where the phase and line voltages show similar performance for the monitored system

Comparative analysis between measurements and simulations of voltage sags

This paper shows a comparative analysis between voltages sags measurements and simulations that were carried out between the years of 1999 and 2001 in a Brazilian transmission subsystem. Firstly, a brief description of the methodology to obtain, analyze and process the data is presented. Then the model/software is deterministically tested by comparing the results of measurements to the results of simulations where all the variables as fault impedance and fault localization were known. Finally the model/software is statistically tested by using a combination of measurements and simulations of events.

Analysis of the relation between voltage sags severity and fault characteristics

This work presents some advances on analysis of voltage sags based on the load variation and the non delivered energy. The power flow variation measured at the transmission level is proposed as an index to evaluate the severity of voltage sags. The correlation between the loss of load and the sag source characteristics, such as type of fault, cause of the fault, location of the fault, fault resistance, season and part of the day each fault happens, can be used for the optimization of transmission network planning and maintenance. Data obtained from actual measurements confirm that correlation and suggest new priorities for utility planners.

Electrical Power Quality and the Challenges Faced by Power Assemblies Applications in Petrochemical Industry

The use of power switchgear and controlgear assemblies in typical electrical power distribution systems of petrochemical industries, both in medium voltage and low voltage levels, has faced different challenges related to their specification and operation in order to deliver solutions that ensure the quality of electricity to be distributed. Many of these problems are related to the equipment used for both switching and protection. Components such as circuit breakers, protective relays, current transformers, and voltage transformers require careful analysis of the electrical system in question. The philosophies adopted for electrical protection, type of neutral grounding, and topographic conditions (arrangement) of the circuits can create conditions, which are unacceptable from the point of view of electrical power quality. Currently, in many of the analyses related to power quality in electrical installations, basic care in the definition and use of the internal components of the power assemblies is often not considered. This paper discusses actual case studies of different power assemblies installations in the industry, aiming in this way to introduce basic guidelines that can help in the specification and installation of new equipment or modernization of existing equipment for industrial facilities.

Use of computational system for analysis of power quality in smart grid

This paper presents the use of a computational system, MATLAB/Simulink SimPowerSystem, as a tool for analysis of power quality (PQ) including distributed generation (DG) connected to smart girds. An electrical circuit model for DG, recloser, photovoltaic system-PV and loads located downstream and upstream from recloser is proposed in this study. The paper shows that this system allows to understand the operational consequence of loads in the grid. In addition, based on simulations in which loads represent the consumer, it is possible to understand, analyze and conclude in terms of power quality.

Implementation of an economic model for the electricity market evaluation of public policies in smart grids

This paper presents the application of an economic model of the electricity market, representing economic flows the concessionaire and the consumer, which allows quantifying the key variables (consumption, price, income and quality) and establish a connection between the innovations made possible by the intelligent network environment (smart grids) on one hand, and parameters of social efficiency and sustainability on the other. The solution to this optimization problem leads to quantitative results for consumption, income, price or tariff for electricity and quality, items needed for evaluation of public policies, such as in the case of sustainable distributed generation incentives for low-income consumers.

Real Time Digital Simulation of utility and industrial co-generation system interconnection - Evaluating a new approach of voltage sag source locator

This paper presents a case study of voltage sags on a utility and industrial co-generation system interconnection. The system was simulated through a Real Time Digital Simulator (RTDS) and a new voltage sag source locator is evaluated. This new approach is capable of locating voltage sags source based on power flow behavior. The proposed algorithm calculates the positive, negative, and zero sequence voltages and currents and the apparent power flowing, before and after the voltage sag detection. The proposed approach uses a robust Boolean logics based on the power flow expected behavior at the system. A real industrial system composed by five turbo-generators and approximately 70MW of loads were simulated even as the interconnected utility system composed by two 138kV transmission lines. The voltage sag source location, when fault occurrences, were evaluated.