Thair I. A. H. Mustafa

Comparison of simulated and recorded transients for travelling wave fault location

In order to assist in the location of EHV transmission line faults using travelling wave transients a program has been devised where the transients are simulated and compared with those recorded. The simulation scheme is based on the well-known ATP program, which has been found to be satisfactory for sample step times of 800 ns. The fault transients have been recorded at a 800 ns sample rate via a current probe attached to the secondary circuit of the current transformers. An offline analysis program has been written in Matlab/spl trade/ which then converts the simulated transients into a form that allows direct comparison with the recorded transients and also provides extra analysis routines. This greatly improves the confidence in a given fault location estimate. Example faults recorded on the ScottishPower EHV transmission system are given which demonstrate the utility of this scheme.

Study of the correlation between weather conditions and protection trips in a 230 kV transmission line in southern Brazil

This paper presents a study of investigation of possible correlation between weather conditions and protection trips of a 230 kV transmission line in southern Brazil. This transmission line has a history of outages during winter, ever since its initial operation in 1974. Most of these outages are caused by single phase faults randomly located along the line. In consequence, many studies have been done to identify the main reason for these events, including now the investigation of the influence of the relative humidity of the air, rainfall index and wind direction in this region to justify these problems that affect the reliability of the protection systems of this transmission line. Thus, preliminary results shown in this work allows to identify a correlation between faults and local weather conditions.

The role of the distribution transformer in the transference of voltage surges

Distribution transformer is a very important equipment that allows the delivery of electricity with a high degree of capillarity. As a consequence, all of the conductors of a distribution network become a way for bringing into a transformer voltage surges, especially those yielded by lightning. These effects have been intensively studied along the last decade in attempt to clarify how a transformer allows transference of voltage surges as well as to understand what happens inside it. One of the most used methodologies for its analysis is based on its frequency response. Thus, the aim of this work is to analyze some of the most usual premises for experimental tests of frequency response, by discussing their applicability as well as its usefulness. An experimental case is presented

Study of occurrence of overvoltage along power transmission lines with acceptable end voltage

For studies of insulation coordination at industrial frequency transmission line must be modelled with much more details than for other studies, like load flow and short circuit analyses. In other words, that usual representation of the transmission line by a single quadrupole Pi circuit is not applicable. In fact, all of the three-phase conductors must be analyzed separately though the determination of individual voltage profile for several conditions of load. This is so because it is possible that voltage to ground of each conductor presents itself as satisfactory at its ends whereas overvoltage may occur along some points in between them. Thus, an alternative and feasible way for modelling the transmission line is proposed by the authors. Although the proposed method is not new, it is has not been usual. For showing the importance of the proposed method a real 230 kV/197 km transmission line are taken and simulated results do show how the occurrence of overvoltage is possible, not only under fundamental frequency but also for harmonics. All the presented results are a clear evidence of the need in reevaluating some conceptions of insulation coordination for power transmission lines.

Methodologies for implementing improvements in maintenance of power transmission lines

This article describes and analyzes the historical incidence of defects along overhead power transmission lines over the area of the state utility company CEEE-GT, in Southern Brazil in order to suggest improvements for the program of maintenance of this company that may applicable to several other similar companies. To this end, two methods are presented: the first one classifies the defects in accordance with their risks to system functionality, in view of establishing a guideline for the corrective maintenance program. The second method establishes the frequency with which rigid detailed inspections should be done in accordance with historical incidence of defects along the power transmission line.

A tool for analysis of fault location in transmission lines based in estimated transients

This paper presents a tool based on MATLAB™ program that has been devised to reproduce the observed and simulated transients of the high voltage (HV) power system network on the ATP program. The graphical interface can to help in the interpretation of high frequency travelling waves. Therefore, the analysis of these transients can be used to assist in the fault location in transmission lines. The practicality of this tool is demonstrated applying a methodology for estimating voltage transients from current transients, based on the properties travelling waves instigated on transmission line as a result of a fault. The application of this analysis tool will be demonstrated through some simulated cases on the CEEE-GT 230 kV transmission system of Brazilian power system.

An analysis of the performance of power circuit breakers using a non-invasive system

Some researches have shown that arcing produces impulsive radio-frequency radiation and through timing analysis of the received and recorded impulses, the switching times of circuit breakers can be measured and utilized in order to ensure the safe operation and reliability of these equipments. In this context, this paper presents a performance evaluation of power circuit breakers (CBs) using an antennas-based system along with signal processing techniques. The signals obtained from the arc created during the switching process are captured by the antennas and then processed aiming to characterize the operation process of the CB. Results of this analysis are shown for field measurements performed on CBs attached to shunt reactor of a substation in the southern Brazil.

An analysis of the performance of surge suppression devices applying the TLM method

This work presents an analysis of the performance of surge suppression devices that currently are applied in power distribution network. Based on the Transmission Lines Method - TLM, numerical models for these devices have been created and their computational implementation made by using MATLAB™ codes. These models were simulated with some types of power surges and a comparison of results is made with measurements of actual devices and other methods of simulation obtained in the literature for verifying the efficiency of the proposed methodology. Also, it is presented some advantages over other methods for analysis of power distribution network, subjected to the effects of fast transients.

An analysis of the overvoltage in the secondary network, considering a transient grounding resistance.

This work presents an analysis of the overvoltage in the secondary network caused by lightning discharges that are transferred from the primary through the transformer. Numerical simulations using TLM- Transmission Line Modeling and ATP- Alternative Transients Program are presented to show and to establish comparisons between two models for the grounding resistance of the transformer and customer: the traditional model with constant resistance and the model proposed in this work, considering a transient resistance.

Analysis of the overvoltage in the power distribution networks using two models of the grounding resistance: The traditional model with constant resistance and considering a transient resistance

This work presents an analysis of the overvoltage in the distribution network caused by lightning discharges. Numerical simulations using TLM- Transmission Line Modeling and ATP- Alternative Transients Program are presented to show and to establish comparisons between two models for the grounding resistance of the transformer and customer: the traditional model with constant resistance and considering a transient resistance.