The Research Of Infrared Diagnosis For High Voltage Electric Equipment

With the increasing request for electrical equipment reliability and the rapid growth of infrared technology, infrared thermography has become an interesting method in electrical equipment detection and gained more attention among researchers. But there are some problems in infrared detection for electrical equipment: the first is what factors will affect the accuracy of the infrared detection and how much the influence are respectively, followed by how the load affect the infrared detection for equipment heating by current, the third is how to determine the defects of equipment heating by voltage. To solve above problems, theoretical analysis and experimental research were made on the influence factors of infrared detection, the heating characteristics of the equipment heating by current and the temperature statistical characteristics of the equipment heating by voltage.Firstly, experiments were applied according to the principle of infrared thermal imager to analyze the influence of emissivity, detection distance, detection angle and solar radiation on infrared detection. The infrared measurements of surface with different emissivity under same temperature showed that the emissivity would affect the temperature measure results. Then the infrared measurements of the gap of the metal contact position at different temperatures was carried out. The results showed that the emissivity of the gap was higher than its components. The infrared measurements of targets with different sizes in different distances showed that atmosphere would absorb infrared radiation and the distance affect the attenuation degree, so the distance will have a certain impact on the infrared temperature measurement. If the target was too far from the infrared thermal imager that its size was below the minimum measurement size of the infrared thermal imager, the measurement result was not accurate due to the influence of the background temperature. The infrared measurements of targets with different sizes under different angles showed that the detection angle had little influence on infrared measurement results if the temperature is uniform on the measured surface. But if the detection angle is too large, the measured area of instantaneous field of view can be changed greatly, and the background temperature may be introduced into the infrared detection. The temperature of the mirror image of the sun on the surface with different emissivity were measured by infrared thermal imager. The result showed that the reflection of the solar radiation could make the infrared temperature measurement result higher than it really was. And the infrared detection of an arrester just after sunset showed that the sun would heat the equipment and caused additional temperature rise, this would have impacts on inferred diagnosis.Secondly, the heating characteristics of the electrical equipment heating by current were studied theoretically and experimentally. Theoretical analysis showed that the temperature rise of the equipment heating by current was related to load current. And the temperature of equipment would change with time exponentially when the load current was changed, the speed of temperature change was related to the thermal time constant of the equipment. The infrared measurements of the contact and the terminal of the isolation switch in the substation showed that both thermal time constant were in the range of 15~25s. And the steady-state temperature rise have functional relation with load current.Finally, the method of statistics were applied to study the temperature characteristics of the equipment heating by voltage. Temperature statistical analysis of three typical equipment heating by voltage including 220 kV Zinc Oxide arrester, 110 kV Zinc Oxide arrester and 220 kV coupling capacitor are carried out. The research revealed that temperature rise probability distribution of the concerned equipment obey the Weibull model, while interphase temperature difference probability distribution of concerned equipment obey the normal model. Then the range of temperature rise and interphase temperature difference for normal operation of these equipment were calculated at the 0.05 significant degree.This study may provide reference for infrared diagnosis of electric equipment.