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Correlation analysis between ceramic insulator pollution and acoustic emissions

It is about Correlation analysis between ceramic insulator pollution and acoustic emissions. The investigation had shown that high quality electrical ceramic insulators can provide good pollution and acoustic emissions resistant.

 ceramic insulator

Abstract
Most of the studies related to insulator pollution are normally performed based on individual analysis among leakage current, relative humidity and equivalent salt deposit density (ESDD). This paper presents a correlation analysis between the leakage current and the acoustic emissions measured in a 230 kV electrical substations in the city of Barranquilla, Colombia. Furthermore, atmospheric variables were considered to develop a characterization model of the insulator contamination process. This model was used to demonstrate that noise emission levels are a reliable indicator to detect and characterize pollution on high voltage insulators. The correlation found amount the atmospheric, electrical and sound variables allowed to determine the relations for the maintenance of ceramic insulators in high-polluted areas.
In this article, the results on the behavior of the leakage current in ceramic insulators and the sound produced with different atmospheric conditions are shown, which allow evaluating the best time to clean the insulator at the substation. Furthermore, by experimentation on site and using statistical models, the correlation between ambient variables and the leakage current of insulators in an electrical substation was obtained. Some of the problems that bring the external noise were overcome using multiple microphones and specialized software that enabled properly filter the sound and better measure the variables.

Introduction
Electrical substations in high-polluted zones have major problems with reliability of the network. Ceramic insulators are commonly subjected to high level of contamination such as marine, industrial, sand, and other contaminants that reduce their performance and dielectric proper-ties. Pollution in insulators triggers an unfavorable reaction in the increase in leakage current, due to high pollution rates in the material.
Insulator washing is performed with energized lines to avoid disconnections, but the frequency of cleaning each element is still unknown for some places due to the local climate conditions. The cost of washing insulators is high, due to the amount of activities programmed during a year and the material such as water with conductivity greater than 1500cm (591inches).
Some pollutions problems have been previously reported in the city of Barranquilla, Colombia. The results showed that during the rainy period the pollution of insulators was low, but during the dry period the pollution was high. Few studies have been proposed to evaluate the severity of the pollution on insula-tors and more methods must be tested to identify the different behavior of insulators in high-polluted areas.
Currently, there are several methods to detect different levels of pollution. One of them is the equivalent salt deposit density (ESDD), which is the most direct measurement of conductive contaminants on the surface of the insulator. However, this procedure needs chemical tests and removing deposits from insulators, which is time and resource consuming.
Another reliable method to detect the levels of pollution in an electrical insulator is the monitoring of leakage current. The system usually consists of three components: the sensor, transducer and software. A microprocessor controls the gathering and processing of information and the data acquisition unit is connected to a computer or it is sent remotely using the serial port RS-232.
Another method used to detect anomalies in the insulators is the infrared image. Salt deposits or dirty insulators help the appearance of leakage currents and the temperature of the equipment increases. A thermography image can determine if the insulator is at an acceptable temperature. This procedure has been complemented using image processing to analyze hot spots.
Another method consists in the detection of arcs or partial discharge of insula-tor. The method uses an optical sensor with a link of fiber, a micro-computer con-trolled processing module, a link by satellite, and a solar panel with battery. The most important characteristics obtained from the leakage current signal are stored internally in the micro-controller and it enables to be transmitted through the communication link. Acoustic emissions have been used for several applications in engineering. Among the application in electrical engineering are: corona effect, electrical machines, and insulator monitoring.
This paper proposes the use of an acoustic emission method to identify the variation of leakage current with climate variables. The test was performed on a 230 kV substation and several models were obtained to correlate climate variables, leakage current and noise.

 

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