Application of infrared thermal imager in power equipment fault detection

There are various types of faults in electrical equipment, but most of them are accompanied by heating. From the perspective of infrared diagnosis, it is usually divided into external faults and internal faults. *In the operation of power systems, current carrying conductors will experience resistance losses due to current effects, and there are numerous connectors, joints, or contacts throughout the entire circuit of electrical energy transmission. In an ideal situation, the contact resistance of various connectors, joints, or contacts in a transmission circuit is lower than the resistance of the connected conductor parts. Therefore, the loss and heat generation of the connection parts will not be higher than that of the adjacent current carrying conductors. However, once some connectors, joints, or contacts increase in contact resistance due to poor connection, there will be more resistance loss and higher temperature rise in that part, resulting in local overheating. This type is usually an external fault.

The characteristics of external faults are: local temperature rise, easily detected by infrared thermal imaging cameras. If not dealt with in a timely manner, the situation deteriorates quickly and can easily lead to accidents and losses. External faults account for a large proportion of faults.

The internal faults of high-voltage electrical equipment mainly refer to various faults caused by electrical circuit faults and insulation medium degradation enclosed in solid insulation and equipment casing. Due to the occurrence of such faults inside electrical equipment, the temperature rise reflected on the surface of the equipment is very small, usually only a few K. Detecting such faults requires high sensitivity of the detection equipment.
The characteristics of internal faults are: small fault proportion, low temperature rise, high harm, and high requirements for infrared detection equipment.

According to 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 equipment defect index, while internal thermal defects only account for about 7% to 10%.

In the power industry, thermal imagers have been used for equipment safety maintenance for a long time. Through their detection of thermal defects in electrical equipment and lines, such as transformers, bushings, circuit breakers, disconnectors, transformers, power capacitors, lightning arresters, power cables, busbars, wires, composite appliances, insulator strings, low-voltage electrical appliances, and secondary circuits of equipment with current, voltage heating effects or other heating effects, they can play a crucial and effective role in timely detection, handling, and prevention of major accidents.

The so-called thermal defects in electrical equipment usually refer to the heating phenomenon caused by internal or external reasons detected through certain means.

According to the different causes of defects, we usually classify them into three types: one is the poor contact caused by long-term exposure to air, such as temperature and humidity, or surface scaling, or component damage caused by external forces, resulting in a decrease in conductive cross-sectional area and heat generation. If the joint connection is poor, the bolts and washers are not tightened; Long term operation corrosion oxidation; Corrosion caused by reactive gases and dust in the atmosphere; Poor material of electronic components and poor processing and installation technology result in conductor damage; The actual cross-sectional area of a conductor decreases due to various reasons such as mechanical vibration; Unstable or excessive load current, etc.

Another type is due to internal electrical faults, such as poor contact of internal connecting components causing excessive resistance; Aging, cracking, and detachment of insulation materials; Internal components are affected by moisture, resulting in increased wear and tear of the primary components; Blockage of cooling medium pipelines, etc.

For devices and components that can be directly observed, infrared thermal imagers can detect thermal hazards at all connection points. For those parts that cannot be directly seen due to obstruction, conclusions can be drawn based on the analysis of their heat transfer to external components. Due to the ever-changing actual situation on site, even if you obtain a hot spot image through a thermal imager, making an accurate judgment may be influenced by many factors. Such as current temperature, air volume, load, etc. We can conduct relevant analysis and make corresponding judgments based on different characteristics, such as:

To ensure the safe and efficient operation of power production, higher requirements have been put forward for the status maintenance of power equipment. Due to the fact that condition based maintenance mainly relies on the status detection and online monitoring of operating equipment, the operation status detection and online monitoring of power equipment always play an important role in power safety production. Infrared imaging technology, as a new technology, has unparalleled versatility in detecting the operating status of power equipment. Infrared imaging is based on the thermal distribution of equipment to diagnose whether the equipment is in good operating condition. It has the functions of non-stop, non-contact, long-distance, fast, and intuitive imaging of the equipment's thermal state. Due to the fact that the thermal image of the equipment is a true description of the thermal state and temperature distribution of the equipment during operation, and the normality of the thermal distribution of power equipment during operation is an important feature to determine whether the equipment is in good condition, therefore. The use of infrared imaging technology can diagnose the status and hidden defects of equipment by analyzing its thermal images.

The use of infrared imaging technology can carry out the following power equipment status detection and fault diagnosis work.

● High voltage electrical equipment operation status detection and internal and external center fault diagnosis:

Various types of conductive joints, wire clamps, and wiring pile heads are subject to oxidation, corrosion, and poor connection defects;

Poor contact defects of central contacts in various high-voltage switches;

Defects in the connection between the isolation knife switch blade and the contact piece, as well as between the rotating cap and the ball head;

Various types of CT have poor connections between the inner and outer centers, poor insulation of the body and oil, and abnormal overheating of the inner center iron core and coil;

Various PT insulation defects, oil shortages, and abnormal overheating defects in the inner center iron core and coil;

Overheating of various capacitors, poor oil insulation of coupling capacitors, and oil shortage (low oil level) defects;

Various types of lightning arresters have defects such as moisture damage to the center, aging of the central components, or abnormal nonlinear characteristics;

Surface contamination defects on various types of insulating porcelain bottles, zero value insulator detection, and degraded porcelain bottle detection;

● Generator operation status detection, brush and collector ring contact status detection, internal center overheating detection;

Abnormal overheating of the power transformer box, eddy current overheating, poor connection between the upper and lower ends of the high and low voltage bushings, and oil deficiency (low oil level) defects in the oil filled bushing;

Poor contact of various motor bearings and abnormal overheating of the inner and outer centers of the body.