Edson Guedes da Costa

Voltage sag performance of a distribution system and its improvement

The voltage sag performance of a distribution system has been investigated. A Monte-Carlo procedure has been used to construct the sag density table and estimate the number of unacceptable sags per annum at a sensitive load bus. The subtransmission lines and distribution feeders that largely contribute to the unacceptable sags have been identified. It has been shown that proper protective relay coordination and adequate maintenance of the critical lines and feeders result in significant improvement of the voltage sag performance of the distribution system.

Self-organizing maps applied to monitoring and diagnosis of ZnO surge arresters

In this work a monitoring and diagnostic technique for ZnO surge arresters is proposed. This technique is based on a special kind of Artificial Neural Network (ANN) known as Self-Organizing Maps (SOM), which is a network, trained using unsupervised learning. The proposed technique performs the thermal profile analysis of ZnO surge arresters when submitted to their operating voltage. From this analysis, the SOM network can determine the status of the surge arrester. So, this technique may be a very useful tool to power system utilities in their predictive monitoring activities, as well as to the manufactures, assisting the project of more robust surge arresters.

Transmission line shunt conductance from measurements

In this work, sensitivity studies were performed using electromagnetic transients program (EMTP)-type programs in order to show how shunt conductance values affect the characteristic impedance and the propagation function of overhead transmission lines. Time-domain simulations were carried out using modal and phase-domain line models. It is shown that, in some situations, simulation results are very sensitive to shunt conductance values. Laboratory measurements were carried out to provide better estimates for overhead line shunt conductances. Measurements were carried out for two voltage classes, considering different insulator types and arrangements. The estimated values can be used as default values for overhead transmission lines in EMTP-type programs.

MOSA Monitoring Technique Based on Analysis of Total Leakage Current

Currently, the majority of metal-oxide surge arrester (MOSA) monitoring techniques are based on total leakage current decomposition of their capacitive and resistive components. However, these techniques are subject to some financial, technical, and practical limitations, which can hamper their usage on the field. In this paper, a new monitoring technique for the zinc-oxide surge arrester is proposed. The technique is based on the feature extraction of measured total current signals and on the analysis of these characteristics by artificial neural networks. The measured total currents were obtained from station class surge arresters submitted to their maximum continuous operating voltage. In the lab tests, six different kinds of failures were simulated on the tested MOSA with the purpose of evaluating the capacity of the technique to distinguish different operating conditions of surge arresters. Hit ratios greater than 98% were obtained in the identification of the operating conditions. The results show the viability of the technique on MOSA monitoring procedures.

ZnO Surge Arresters Diagnosis Using Microcontroller

Surge arresters are equipments used for the power electrical systems protection. They limit the voltage level during the occurrence of switching and atmospheric surges. A surge arrester failure can cause the equipments insulation breakdown or flashover, or even the surge arrester explosion. To avoid this problem, the maintenance of these equipments is made by means of regular monitoring. Measurement of the resistive leakage current and analysis of its harmonic components is one of the most used techniques to evaluate the degradation level of metal oxide surge arresters. In this paper is presented a new measurement technique for the resistive component of leakage current based on the orthogonal position between this component and the capacitive component. The technique is accomplished by means of inductive current sensors based on nanocrystalline alloys and a PIC microcontroller to provide the measurement of the first, third and fifth harmonic components of the resistive leakage current in the arrester.

Thermal behavior analysis of ZnO polymeric surge arrester using the finite elements method

Surge arresters are used to protect electrical systems against switchgear and atmospheric surges. A defective or bad-dimensioned arrester may cause failures or damage to substation apparatus. Routine and type tests are used to evaluate the surge arresters operating capacity. Moreover, one of the techniques used in monitoring and diagnosis of arresters is the thermal imaging. For the correct use of thermal imaging, it becomes necessary to know the acceptable temperatures level of the materials that compose the arrester. Computational simulations have been used to analyze electro-thermal model. This technique presents several advantages, i.e. possibility of previous analyses before the manufacturing and presents lower cost when compared with the tests in laboratory. In this paper, the surge arrester thermal behavior will be analyzed. The surge arrester that was analyzed has a polymeric housing and 120 kV nominal voltage. Tests based on IEC and ANSI standards were computationally simulated using COMSOL Multiphysics®, which is based on Finite Elements Method. The temperature behavior of the varistor blocks and housing was determined and analyzed.

Evaluation of surge arrester models for overvoltage studies

This work aims to determine a model which represents efficiently real surge arresters behaviour, when submitted to fast surge current impulses and lightning current impulses. It presented a comparative study among nine arrester models. The experimental data of a zinc-oxide (ZnO) block with rated voltage of 4 kV was used in comparisons. Each model response was compared with experimental data in order to specify which model produces better results. This comparison was performed in relation of voltage peak, absorbed energy and coefficient of determination (R2), which was used to compare the voltage waveform similarity between experimental and simulation results. Thus, representation efficiency of each model was verified. The impulsive currents waveforms applied to arrester blocks were 2/6 μs, 4/10 μs and a standard lightning current impulse of 8/20 μs.

Fault location in distribution systems using the voltage sag-duration table

A fault location technique based on the voltage sag-duration table has been described. The technique is simple to apply and has the potential to be implemented on-line. It needs the data from power quality meters installed at a few measuring stations. The technique has been demonstrated by simulating faults in realistic distribution networks.

Monitoring and Diagnosis of ZnO Arresters

Surge arresters are part of the protection system of electrical substations and transmission and distribution networks. They avoid damages in equipments of main importance for the electric system, such as power transformers, not allowing them to be reached by overvoltages. An arrester presenting any kind of failure may not actuate in a satisfactory way during the occurrence of an electric surge. As a consequence, it will present an overheating which can lead to its complete degradation and exposing the system that should be protected and bringing risk to those who are working nearby [1]. In order to avoid this kind of problem, several monitoring techniques are used. The measurement of leakage current and the thermal analysis are the most used of these techniques. A work being developed in the High Voltage Laboratory of the Universidade Federal de Campina Grande together with the Companhia Hidreletrica do Sao Francisco has the main purpose of developing a technique to be used for arrester monitoring by means of continuous analysis of its leakage current and variations on its thermal patterns, resulting in a useful tool for the diagnosis and preview of failures in ZnO arresters.

Evaluation of Current in Composites PVAL/Ceramics for Detection of Leakage Current Generated in Electrical Insulators

This research aims to prepare composites of polyvinyl alcohol (PVAL) with ceramic nanoparticles loads (NPs) of Ti1.95Eu 0.05O2; ZnAl2O4 and Ni0.5Zn0.5Fe2O4 to evaluate the detection of leakage current generated in electrical insulator. The composites were prepared in the proportion of 6/1.5 g of the PVAL/ceramics and characterized by XRD, FTIR, SEM and measurements of the current as a function of applied voltage. The results show for the composites with Ti1.95Eu0.05O2 and ZnAl2O4 a homogeneous morphology, while the structure of the composite formed by Ni0.5Zn0.5Fe2O4 resulted in a heterogeneous and porous morphology. The determination of the current as a function of the applied voltage has shown that there is a dependence of morphology and the semiconductor characteristic of the load used and the best results are therefore assigned for the composite produced with the Ti1.95Eu0.05O2 load with homogeneous morphology and high current values as a function of the applied voltage.