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Detection technology of composite insulator

Direct observation method
The composite insulator external physical defects are the most commonly used method is the method of direct observation, using double tube telescope to find common surface defects such as parts, sheath umbrella skirt, fittings and so there is no cracking in the tower, there is no erosion, powder, leakage of electricity, if the above phenomenon should be replaced insulator immediately. But the ground observation is not reliable enough, also need a plethora of detection and difficult to find internal insulation faults such as dendritic channel etc..
 
Ultraviolet imaging method
The small but stable surface partial discharge causes the composite insulator skirt and sheath to form carbonization channel or electric erosion loss. When the surface of the insulator formed carbide channel, its service life will be greatly reduced, even in the short term breakdown. Can live detection of composite insulator surface formed by partial discharge carbonized channel and erosion using electronic ultraviolet optical detector, its principle is: partial discharge of charged particles in the composite will emit ultraviolet, when forming a conductive carbide channel insulator surface, partial discharge increased. The disadvantage of this method is that it is required to operate in the nighttime and positive temperature environment. In addition, partial discharge is required during the test. However, the detection results are easily affected by the observation angle and the detection equipment is more expensive.
 
Infrared imaging method
Infrared imaging method can detect partial discharge, leakage current flowing through insulation material dielectric loss or resistance loss caused by insulator local temperature rise, can be used for online detection. SVA Group Foshan power supply branch of infrared temperature measurement of a large number of census, composite insulators found in any obvious local hot spots of the insulator, the hot spots to the surface of silicone rubber insulator were black, powder, brittle, hydrophobic basic loss, there are many small cracks and even some serious damage; some can not withstand power frequency withstand voltage test or steep wave impulse test to high voltage side of the hot spots, the hot spots for the internal insulation progress of partial discharge of the location of the interface. The instrument has high cost and measurement is vulnerable to sunlight, wind, humidity, ambient temperature and surface temperature of insulator can cause dramatic changes in factors are deficiency of infrared imaging method.
 
Ultrasonic method
A study at Tsinghua University to detect composite insulator core crack by ultrasonic method. Ultrasonic detection is the principle of ultrasonic reflection occurs, refraction and mode conversion in the two medium interface in the communication process into another medium from a medium based on the ultrasonic generator transmitting initial pulse into the insulator medium, when the insulator cracks, in time axis reflection wave of the crack to judge the defects in the insulator, by the time axis defect wave size and position can be. Ultrasonic detection of composite insulator mechanical defects with simple operation, safe and reliable, strong anti-interference ability. But due to the existence of coupling and attenuation of ultrasonic transducer in remote telemetry performance problems, yet there is a major breakthrough, not suitable for on-site monitoring, which is mainly used for on-line production testing and laboratory accreditation.
 
Electric field distribution method
There are a variety of composite insulator interface, at present, because the composite insulator metal end seal bad, moisture into the internal cause, the internal defects along the interface or mandrel rod of the development of electric carbon tracking is the most prone to failure of composite insulators is the most dangerous. Steep wave test can detect the internal insulation defects of composite insulators, but the method can not achieve on-site online detection. The electric field distribution method can detect the inner insulation defect of the composite insulator on line, and the instrument used in this method is simple, and it is very low for the weather and other external environment.
 
Under the normal condition, the curve of electric field intensity and potential along the insulator axis is smooth. When the insulator has conduction defects, the potential is a constant, so the electric field strength will reduce suddenly, the electric field distribution curve is not smooth, but the distortion in the corresponding position between both ends up sinking. So the measurement of axial electric field distribution of composite insulators can be found within the insulated conductive fault insulator.
 
Hydrophobicity detection method
At present, the measurement method of hydrophobicity applied to the site is mainly the water jet classification method proposed by the Swedish Transmission Research Institute. This method divides the hydrophobicity of composite insulator surface into 7 levels and gives classification criteria and standard pictures. The HC-1 and HC-7 levels correspond to the strongest and worst (i.e. completely hydrophilic) states of hydrophobicity. In the experiment, the sample surface with ordinary watering can spray water, water in the distribution of goods on the surface, comparative classification criterion and standard images, obtained status of hydrophobicity on the surface of the insulator.
 
The defect of water jet classification is a great dependence on subjective judgment. In recent years, the development of digital camera technology and computer digital image processing technology provides a new way to evaluate the hydrophobicity of composite insulators more objectively and accurately. The Swedish researchers measured the hydrophobicity grade by the water jet classification method for the simulated aging composite insulators, and took the digital gray image of the insulator surface after spraying. From a large number of digital gray image to extract a function value and HC level in mathematical monotone functions by using computer image processing technology (named hydrophobicity function), and through the hydrophobicity function as the hydrophobic level of insulators.
 
However, the study is only in the laboratory stage, the lack of complex surface analysis of complex situations; although on-site online testing to do a feasibility prediction, but did not put into practice. At present, North China Electric Power University (Beijing) and the research institute is engaged in the composite insulator surface hydrophobicity on-line detection method and spray method based on digital image processing technology has been the achievement of high voltage and EMC, all projects are expected to be completed in the first quarter of 2005.
 
Leakage current measurement
The leakage current measurement method is to use the principle of leakage current along the surface to form, in the insulator grounding side through the drainage card or current sensor, real-time measurement of leakage current, the signal processing unit calculates a period of time in the various statistical values of leakage current (such as the average peak value, peak value or high current pulse number). Through the combination of wireless transmission and cable transmission, transmits the data to the data terminal, using expert knowledge and self-learning algorithm of these three kinds of knowledge to conduct a comprehensive analysis to evaluate and forecast the status of contamination insulator, and provides the scientific basis for the realization of state maintenance. 
 
For composite insulators, due to its hydrophobicity and hydrophobicity transfer, the insulator is wet, at any moment can only participate in the conduction has dissolved all filth without loss of that part, called "effective pollution". Therefore, the leakage current along the surface of the composite insulator is related to the effective pollution degree, and is also related to the hydrophobicity. In addition, the leakage current is related to voltage level, insulator type, insulator number, environmental temperature, humidity and other factors. The research and application of this method are still controversial.