Study of detecting defect porcelain insulators using infrared imaging technique
Qiu Changtao, Sun Xintiang
NE China Institute of Electric Power Engineering
Jitin City 132012, China
Hou Shanjing
Xian Laboratory of Thermal Power Engineering
Xian 710032, China
Abstract
The detection of defect porcelain insulators on high voltage transmission lines is a very important problem for guaranteeing operating security. In order to investigate the thermal imaging characteristics of defect porcelain insulators, an AC simulation experiment under the laboratory condition and a field testing were carried out by using the infrared imaging technique. The insulators were energized at 110KV. The instrument used is an infrared detector, AGENA-870. Also, a DC simulation experiment at the laboratory for porcelain insulators of 500KV was performed by using the same infrared detector.
Results show that the infrared imaging technique is a new effective and simpler technique for detecting the AC defect porcelain insulators, but it is not feasible for DC defect porecelain insulators.
Introduction
The operating security of transmission lines is a very important problem concerning the reliable and economical operation of power systems. According to the statistical data in large power networks over the world, the contingency caused by defect insulators is about 85 percent of the whole transmission line contingency. At present, the insulators used in transmission systems in China are almost porcelain. So electrical engineers do still pay their attention to the detection of defect porcelain insulators. Traditional detecting methods, such as, sparking gap method, isolation resistance method, impulse corona current method etc., can not meet the need of site detection owing t their deficiency of tower crimbingm strong laboring, low efficiency or too much environmental influence etc. Since the infrared imaging technique was applied to power-to-power system, many organizations and authors in China have been engaging in experiment research work or on site testing. In this paper, by using the infrared imaging technique, an AC simulation experiment at the laboratory and a field-testing for porcelain insulators of 110KV were carried out. The instrument employed was an infrared detector, AGENA-870. Also, a simulation experiment at the laboratory for DC porcelain insulators of 500KV was performed using the same detector.
Results show that the infrared imaging technique is a new effective and simpler technique for detecting the AC defect porcelain insulators, but it is not feasible for defect DC porcelain insulators.
Infrared imaging detection methods
A body whose temperature is higher than 0°K must radiate infrared energy of 0.75-100
mm. The relationship between the radiation energy and the temperature of the body must comply with stephen-Bolzmannian theorem, i.e.,
W = e-dT4
Where
W - Radiation power per unit area;
d - Radiation Rate of the body;
T - Absolute temperature of the body;
e - Stephen-Boizmannian Constant.
According to the value of insulation resistance, the insulators on high voltage transmission lines can be divided into two kinds, normal insulator whose insulation resistance is higher than 300M
W, and defect insulator whose insulation resistance is less than 300M
W. The defect insulators can also be divided into two kinds, low resistance insulator whose insulation, resistance is between 10-300M
W and zero resistance insulator whose insulation resistance is tower than 10M
W.
For on-line operation insulators, there exists a voltage aross each of them some teak age. currents and dielectric polarization currents would be caused and flow through its body. this may produce dissipation of energy and makes their temperature higher than ambient temperature. however,. each insulator is under different environment, so it has different temperature. We can use the infrared imaging detector to identify the defect insulators from their thermal images. this is so called infrared imaging detection.
