E. G. da Costa

Influence of Emissivity and Distance in High Voltage Equipments Thermal Imaging

Thermographic inspection is a very safe and noninvasive monitoring technique, widely used in electrical substations and other power plants. Using an infrared camera, a thermal image can be obtained presenting abnormal heating regions on power equipment. The heating can indicate a failure on this system/equipment or an unusual electrical situation as over voltage or a poor contact. The precision of an infrared cam is based on some parameters that must be evaluated during the inspection. This work presents a study done with thermal images obtained from different materials. Different values measured when the correct emissivities and distance are not used during inspection and/or analysis of the thermal image. The results show that differences larger than 10% can be obtained for the temperature when the emissivity varies in a range from 1 to 0.75, which includes the value of 0.85 used for most companies

Partial Discharge Location using Unsynchronized Radiometer Network for Condition Monitoring in HV Substations - A Proposed Approach

A location estimation system for online Partial Discharge (PD) detection is proposed as a low-cost approach to real-time condition monitoring, asset management and operation optimization in future smart grid. Some early progress in the development of subsystems (specifically the antenna, radiometer device, PD emulator and PD generator) for a proof-of-principle prototype system is described. The proposed PD Wireless Sensor Network (WSN) uses a novel approach to PD location which obviates the need for synchronization between sensors thereby improving scalability.

A virtual bridge to compute the resistive leakage current waveform in ZnO surge arresters

The measurement and the harmonic analysis of the resistive leakage current present is an efficient parameter for determining the degradation level of metal oxide surge arresters. In this paper, the methodology and results of a novel circuit for measuring the resistive leakage current in metal oxide surge arresters is described. The technique requires the digital acquisition of the voltage applied to the surge arrester and the total current of the arrester. A virtual bridge has been implemented in software Matlab/sup /spl reg// to eliminate the capacitive component. In this implementation the resistive leakage current waveform is computed without the need for an expensive high voltage capacitor. The implementation suggested in this paper agrees well with measurements obtained with a coupling capacitor.

Electro-thermal simulation of ZnO arresters for diagnosis using thermal analysis

Surge arresters are equipment of great importance for the protection of electrical systems. Their choice for a specific substation line or equipment must follow a rigid selection and testing. The maintenance of this equipment by the realization of regular monitoring also plays a major role for the system integrity. Arrester failure may result in an its explosion or system turn off. Thermographic inspection is one of the most used techniques for monitoring high voltage devices. It registers the temperature gradient along the equipments surface, indicating overheat. For zinc oxide (ZnO) arresters, this technique presents a limitation. Because of the low thermal conductivity of the porcelain or polymeric housing there is no direct relation between the temperatures on the housing surface and the temperatures on the varistors. A solution for this limitation is the development of computational routines to make this correlation. This paper presents a program based on finite difference techniques that makes the heat transfer over all the arrester indicating the temperature of any desired point. It considers both ceramic and polymeric housed arresters and can be used to simulate electrical tests defined in technical normative and to estimate the inner arrester temperatures when the outside temperatures are measured. A comparison between thermal dissipation for porcelain and polymeric insulated arresters is also presented.

Characterization of contacts degradation in circuit breakers through the dynamic contact resistance

Static resistance measurement of circuit breakers has been a crucial technique to assess the state of contacts, supporting maintenance procedures. However, in many cases, the obtained results do not provide accurate data for correct diagnosis, since the test examines only the main contact. This article discusses the application of the contact dynamic resistance measurement (DRM) in the evaluation of main and arcing contacts. The DRM is a contact resistance test, and the resistance is determined during the opening of contacts, analyzing the main and arcing contacts. The research objective is to get the DRM parameters that can assist in the contacts diagnosis. The obtained results indicate that DRM has presented more qualitative parameters than the static resistance test in the evaluation of contacts. The resistance tests were performed applying a direct current with 300 A of amplitude.amplitude.amplitude.

Wavelet transform processing applied to partial discharge evaluation

Partial Discharge (PD) is characterized by high frequency current pulses that occur in high voltage (HV) electrical equipments originated from gas ionization process when damaged insulation is submitted to high values of electric field [1]. PD monitoring is a useful method of assessing the aging degree of the insulation, manufacturing defects or chemical/mechanical damage. Many sources of noise (e.g. radio transmissions, commutator noise from rotating machines, power electronics switching circuits, corona discharge, etc.) can directly affect the PD estimation. Among the many mathematical techniques that can be applied to de-noise PD signals, the wavelet transform is one of the most powerful. It can simultaneously supply information about the pulse occurrence, time and pulse spectrum, and also de-noise in-field measured PD signals. In this paper is described the application of wavelet transform in the suppression of the main types of noise that can affect the observation and analysis of PD signals in high voltage apparatus. In addition, is presented a study that indicates the appropriated mother-wavelet for this application based on the cross-correlation factor.

Failure Analysis in ZnO Arresters Using Thermal Images

ZnO arresters are protective devices of electrical power systems. An arrester with some kind of failure is not able to operate properly during an electrical surge. As a consequence it present an excessive heating which can lead to a thermal runaway. Thermographic inspection is a widely used method to monitor surge arresters preventing their failure. When an arrester is substituted due to some abnormality detected by means of thermal inspection, no further analysis is done, so that the causes of the problem cannot be evaluated. Tn addition, there is no study indicating which are the main causes of failures in ZnO arresters or if there is another alternative to the substitution of them. This work presents a study done with 96 kV ZnO arresters presenting the most common failures detected in substations and their effects on the thermal image

Intelligent acoustic detection of defective porcelain station post insulators

This work presents an intelligent acoustic methodology for detection of defective porcelain station post insulators, which are widely used in substations in the form of column presenting several sheds. The acoustic emission inspection aims to detect cracks or fissures in a particular shed, which will have its insulating capacity severely decreased, if cracked. The test is done by gently striking the shed with an appropriate instrument, connected to the tip of an insulated pole. The resulting acoustic emissions are recorded at the substation. A database is created with these audio files and two approaches are considered in order to emphasize the important attributes and to compact the information: Wavelet Energy Coefficients and Spectral Subband Centroid Energy Vectors. Finally, to add reliability, automation and ability to generalize and to adapt to new situations, an Artificial Neural Network is employed. The average classification accuracy is above 62% when using Wavelet Energy Coefficients and above 98% when using Spectral Subband Centroid Energy Vectors.

A new approach for optimal design of corona ring

In this research several optimization methods were used to determine the optimal design for a corona ring. The following methods were utilized: Nelder-Mead, COBYLA and BOBYQA. In addition, a software based on the Finite Element Method was used to perform electric field simulations. Results show that the optimized corona ring provides a reduction of 79.6% on the electric field when compared to the manufacturers ring. It was also possible to determine the performance of the optimization methods, and the Nelder-Mead method was found as the most suitable for the problem solution. The methodology presented in this paper, can be generalized to any insulators with different voltage levels and has some advantages over other presented in the literature.

Experimental impulse response of grounding systems

This work aims at proposing a methodology to perform an experimental evaluation of energized grounding grid systems, subjected to current impulses. By using an impulse generator (80 kJ/100 kV) impulses were generated 8/20 μs waveforms that were injected into the soil through a copper coated steel electrode. The applied voltage signal and the propagated signal in the soil were acquired by using a digital oscilloscope. The transient impedance and impulse coefficient were used as parameters to verify the grounding grid system performance.