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The characteristics of external faults are: local temperature rise, easy to use infrared thermal imager to find, if not handled in time, the situation deteriorates quickly, easy to form an accident and cause losses. External faults account for a large percentage of faults.
The so-called high-voltage electrical equipment internal faults mainly refer to various faults caused by solid electrical insulation and electrical circuit failure inside the device housing and deterioration of the insulation medium. Since such failures occur inside the electrical equipment, the temperature rise of the reflected equipment surface is very small, usually only a few K. Detection of this type of fault has a high sensitivity to the detection equipment.
The characteristics of internal faults are: the fault ratio is small, the temperature rise is small, the hazard is great, and the requirements for infrared detection equipment are high.
According to the long-term measured data provided by relevant units and comprehensive statistics of a large number of cases, external thermal defects of power equipment generally account for 90% to 93% of the total index of equipment defects, and internal thermal defects only account for about 7% to 10%.
In the power industry, thermal imaging cameras have long been used in the safety overhaul of equipment, through its detection of thermal defects in electrical equipment and lines, such as transformers, bushings, circuit breakers, switches, transformers, power capacitors, Arresters, power cables, busbars, conductors, electrical appliances, insulator strings, low-voltage electrical appliances, and secondary circuits with current, voltage heating, or other heating effects, can be used to detect, treat, and prevent major accidents in time. To a very critical and effective role.
Depending on the reasons for the defects, we usually sum up to three kinds:
First, it is a part that is exposed to the air for a long time. Due to the influence of temperature and humidity, or the poor contact caused by the surface fouling, or the damage of the parts caused by the external force, the heat generated due to the reduction of the conductive cross-sectional area. If the joints are poorly connected, the bolts and washers are not compressed; corrosion and oxidation in long-term operation; corrosion caused by reactive gases and dust in the atmosphere;
Second, poor component materials, processing and installation process is not good cause conductor damage; mechanical vibration and other reasons caused by the reduction of the actual cross-section of the conductor; load current instability or excessive standards.
Third, it is due to the internal fault of the electrical appliance, such as excessive resistance due to poor connection of internal connection components; aging, cracking, and loss of insulation materials; dampening of internal components, increased loss of vital components, and blockage of cooling medium pipelines.
For those devices and vital components that can be observed directly, thermal imaging cameras can detect the heat hazard of all connection points. For those parts that cannot be seen directly because they are blocked, they can be analyzed based on the fact that their heat is transferred to the outer parts, which leads to the conclusion. Due to the fact that the actual situation on the scene is ever-changing, even if you get a picture with hot spots through the thermal imaging camera, in order to make an accurate judgment, it may be affected by many factors. Such as the current temperature, air volume, load, etc. We can make relevant analysis according to different characteristics and make corresponding judgments such as:
In order to ensure the safe and efficient operation of power production, higher requirements have been set for the state-of-the-art maintenance of power equipment. Because the status overhaul mainly depends on the status detection and on-line monitoring methods of the running equipment, the power equipment running status detection and on-line monitoring always play an important role in the power safety production. As a new technology, infrared imaging technology has unparalleled advantages in the detection of power equipment operation status. Infrared imaging is based on the distribution of the thermal state of the device to diagnose whether the device is operating properly or not. It has the features of non-stop operation, no contact, long-distance, quick and intuitive imaging of the thermal state of the device. Since the thermal image of the device is a true description of the thermal state and its temperature distribution in the operating state of the device, whether or not the thermal distribution of the electrical device in the operating state is normal is an important feature for determining whether the device state is good or not. The use of infrared imaging technology can diagnose the status of equipment and its hidden defects by analyzing the thermal image of the equipment.
Using infrared imaging technology can carry out the following power equipment status detection and fault diagnosis.
â— High-voltage electrical equipment operation status detection and internal and external center fault diagnosis:
â— Various types of conductive joints, clamps, wiring pile head oxide corrosion and poor connection defects;
â— All kinds of high voltage switch inner contact bad contact defect;
â— Isolation knife blade and contact and rotating cap and ball joint bad defects;
â— All kinds of CT inner-center and outer-center connection bad defects, defects in body and oil insulation, and abnormal inner core iron and coil abnormal heat trap;
â— All kinds of PT poor insulation defects, lack of oil and inner core, coil abnormal bad overheating defects;
â—Overheating of various types of capacitors, poor insulation of coupling capacitor oil, and lack of oil (low oil level) defects;
â— Various types of arresters have moisture defects in the center, aging of inner core components, or defects in non-linear characteristics.
â— All kinds of insulated porcelain surface contamination defects, zero-value insulator detection, deteriorating porcelain inspection;
â— Generator running status detection, brush and slip ring contact state detection, inner center overheating detection;
â— Abnormal overheating of the power transformer box, eddy current overheating, poor connection between the upper and lower ends of the high and low pressure bushings, and lack of oil (low oil level) defects in the oil filled bushing;
â— All kinds of motor bearing bushes are in poor contact and abnormally overheated inside and outside the body.
Thermal Imager Application in Power Industry
There are many kinds of failures in electrical equipment, but most are accompanied by fever. From the perspective of infrared diagnostics, it is usually divided into external faults and internal faults. It is well known that during the operation of a power system, current-carrying conductors can cause resistive losses due to current effects, and there are a large number of connectors, connectors, or contacts on the entire circuit of power transmission. In an ideal situation, the contact resistance of various connectors, connectors, or contacts in the power transmission loop is lower than the resistance of the connected conductor portion. Therefore, the heat loss at the connection portion will not be higher than that of the adjacent current-carrying conductor. However, once For some connectors, connectors or contacts, due to poor connection, the contact resistance increases, and the part will have more resistance loss and higher temperature rise, resulting in local overheating. This is usually an external fault.