Estácio T. Wanderley Neto

Methodology for fast fault location in overhead distribution networks by the application of temporary georeferenced fault indicators

Most of the electricity distribution companies in Brazil, especially in rural areas, usually spend a long time to locate shunt faults in overhead lines. The major cause of the excessive time spent in the fault location process is the lack of appropriate tools. In spite of the existence of some tools that could be applied to aid the fault location, as permanent fault indicators, they are usually not installed by the companies because of the high cost and vandalism. In order to shorten this time, a new methodology has been developed aiming especially long networks in rural areas. This methodology consists in installing temporary georeferenced fault indicators in the branches after the fault occurrence. These devices communicate with a computer via mesh network, allowing a diagnostic software to indicate the path of the fault, and its location, in the overhead line map.

Feasibility for the utilization of 5 kA distribution arresters

This paper presents the initial stages of development of an arrester based on real current discharge values and failure rate estimative. The results indicate that, for most cases, the utilization of 5 kA arresters, instead of the usual 10 kA ones, presents some advantages related to costs, unnecessary replacement and possibly to the security level of power transformers. One innovation of these arresters is the lower cost compared to conventional ones, incentivizing its usage and resulting in smaller expenses to distribution companies and costumers.

Artificial rain accelerated aging test of HDPE pin insulators for medium voltage distribution in Brazil

High density polyethylene (HDPE) is a polymer commodity widely used in manufacturing of polymer pin insulators (PIN) for medium voltage distribution. The major problem to be faced in the use of HDPE by PIN manufacturers is their low resistance to oxidative degradation in the processing step and/or the prolonged exposure of HDPE-PIN to weathering and operation voltage for a long time. This work presents the experimental results on artificial ageing test of 15 kV commercial HDPE-PIN specimens for distribution system application in Brazil. Attenuated total reflectance Fourier transform infrared spectroscopy (FTIR/ATR) for chemical analysis, UV-visible diffuse reflectance spectroscopy (DRUV-Vis) for band-gap (Eg) evaluation, contact angle (CA) for determination of polar surface tension (γΡ) components and scanning electron microscopy (SEM) for morphological surface analysis were conducted on aged and unaged specimens. Chemical analysis results of ATR/FTIR confirmed the occurrence of oxidation reactions with significant increase of polar groups C=O at tested HDPE-PIN specimens. It was also observed a significantly increase on the contribution of γp to the surface energy for all HDPE-PIN after 500 hours of accelerated aging time. The experimental values of Eg for aged commercial HDPE-PIN samples suggest that the accelerated aging test produces structural defects in commercial HDPE-PIN samples. The SEM micrographs reveal cracks, pinholes and degradation in the form of crystals and cavities after 3,500 hours of accelerated aging test in all HDPE-PIN specimens. The physicochemical performance of the aged commercial HDPE-PIN specimens analyzed in this work indicates that the HDPE resin was not formulated to be suitable for performing in tropical medium voltage environments.

Assessment of lightning overvoltages on lines with different voltages sharing the same structures

The objective of this paper is to evaluate the lightning overvoltages that appear on a conventional 69 kV line, a compact overhead distribution line (spacer cable system) rated 11.4 kV and a low voltage line rated 220 V sharing the same tower. The simulations were performed using the software ATP (Alternative Transient Program) considering lightning strikes at the top of the tower, the mid span of the ground wire and one of the phases of the high voltage line.

Lightning withstand of medium voltage cut-out fuses stressed by nonstandard impulse shapes experimental results

This paper aims at evaluating the lightning withstand voltage of cut-out fuses designed for overhead distribution lines of 15 kV and 25 kV. For this purpose, it is used the critical flashover voltage (CFO) and the V-t curves parameters. These two parameters are usually derived for 1.2 × 50 μs impulse shape, which represents overvoltages originated by direct lightning strikes on phase conductors or shield wires of transmission and distribution lines. In order to assess the lightning withstand levels with respect to induced overvoltages, it has been chosen five nonstandard impulse shapes with front and tail times of 0.5 × 5 μs, 0.5 × 20 μs, 1.2 × 10 μs, 3 × 16 μs and 5 × 50 μs. The standard impulse shape 1.2 × 50 μs results are also provided for the purpose of comparison with nonstandard ones. The tests for determining the CFO and V-t curves were performed on dry condition, for positive and negative polarities. The CFO and V-t curves results show an important issue considering lightning withstand of cut-out fuses. For both test methods and impulse shapes, the lowest withstand values are observed on negative polarity. Considering porcelain insulators and manual disconnectors for distribution systems, it means a change on the critical polarity with impacts on insulation coordination procedures.

Chopped Impulses for Distribution Transformers Their Importance for Dimensioning and Performance Evaluation

Impulse tests on distribution transformers are requested by all main international standards as IEC, IEEE and ANSI. They are also adopted by most national standards and normative. These tests consists in the application of a sequence of impulses, including chopped ones, to evaluate the insulation withstanding of the equipment, mainly failures on paper and windings. Although the chopped impulses are of main importance in this evaluation process, there is a discussion in some countries considering removing them from the test sequence. This paper discusses the importance of the chopped impulses and how they aid in the evaluation of the transformer failure probability.

Resonant grounding networks: A new perspective for the utilization of MOSA with series spark gaps

This paper presents a new appraisal for the utilization of series spark gaps with metal oxide surge arresters aiming at networks with resonant grounding. For these networks, single phase faults can lead to enduring overvoltages on the sound phases, stressing equipments like arresters. Usually, this is not a problem when the network is planned to operate with resonant grounding. But the situation changes when a solidly grounded network is adapted to operate with a resonant grounding. In this case, the natural solution is the replacement of the arresters by equipments with higher rated voltages, implying in higher costs and raising the residual voltage on arresters during a current surge. The utilization of spark gaps allows keeping lower rated voltage arresters as though as avoids the occurrence of high residual overvoltages from the arresters.