Thermography can be described as the science that deals with reproducing images based on the emission of infrared radiation. Thermographic cameras detect the electromagnetic spectrum and reproduce images of this radiation, which we call Thermograms.
Infrared radiation is emitted by any object according to the blackbody radiation law, and thermography makes it possible to see and analyze objects and environments with or without visible light. The radiation emitted by an object is proportional to its temperature; however, thermography also allows the analysis of temperature variations. When viewed through a thermographic camera, hot objects stand out compared to surfaces or environments at lower temperatures.
Through thermal images, we can easily locate overheating in connections, cables, busbars, transformers, motors, and other equipment, providing a reliable indication of defects and allowing the elimination of potential problems before they become more serious.
It is important to understand that thermal images actually show the amount of infrared energy emitted, transmitted, and reflected by a given object. Because of this, accurately determining the temperature of an object also requires evaluating the environment (temperature, air humidity) as well as analyzing the material from which the object is made.
It is known that:
Incident Energy = Emitted Energy + Transmitted Energy + Reflected Energy. Where Incident Energy is the energy presented in the thermal image. Emitted Energy is the quantity we aim to measure, as it is proportional to temperature; Transmitted Energy comes from another heat source; and Reflected Energy is the amount of energy reflected from the surface of a heat source.
If the object is radiating at a higher temperature than the surrounding objects, heat transfer will occur from hot to cold, following the second law of thermodynamics. Therefore, if a surface appears cold in the thermogram, that surface is absorbing the radiation emitted by the hot object. The property of objects and surfaces to absorb or emit radiation is called emissivity. In outdoor environments, cooling due to wind should also be considered to obtain a more accurate temperature reading.
These properties make thermographic inspection in electrical and mechanical systems an excellent tool for improving the maintenance of these systems, provided that the use of this technology is carried out with proper care regarding the camera settings and the techniques used for capturing the images. Without these precautions, camera users can easily make errors in their evaluations.
– Only projects designed based on the provisions of these standards can ensure an installation that is considered efficient and reliable. However, this efficiency will never reach 100%, and even these installations remain subject to protection failures. The most common failures are the damage to small sections of facade coatings or to the building’s edges.
Emissivity is the factor that represents each material’s ability to emit radiation. Each material has a different emissivity, and its precise determination is not an easy task, since many objects to be analyzed are made of various types of materials and metal alloys, which in many cases are also affected by aging and environmental aggressiveness (such as oxidation). The emissivity of materials can vary from 0 to 1, where 0 means the object does not emit any radiation.
For measuring the temperature of a given object, the thermal imager must be set according to its respective emissivity. This way, the camera itself will correct the acquired data using the emissivity to calculate a temperature that most closely approximates the object’s actual contact temperature.
Main Advantages of Thermography:
– Enables visual analysis of images with their respective temperatures;
– Allows identification of imminent problems in electrical and mechanical systems;
– Enables analysis of hard-to-reach or high-risk areas;
– It is a non-destructive testing method, as there is no direct contact with the system being measured;
– Does not require a high level of lighting at the location to capture images.
Created in the 1960s, Thermography is the science of acquiring and analyzing thermal information using thermal imaging devices. It is a technique that extends human vision into the infrared spectrum, which is a range of electromagnetic frequencies naturally emitted by any body, with an intensity that is in some way related to its temperature.
The images that show the temperature distribution of the focused surface are called thermograms. This technique establishes a form of predictive maintenance through thermographic inspection in mechanical, electrical, and process systems; it can be performed with the issuance of technical reports indicating operational distortions, illustrated with the respective thermograms and photographic records. As a subsequent procedure, image processing techniques can be employed to enhance the analysis. Thus, thermography can contribute by indicating relevant corrective actions.
Due to the absence of physical contact between the measuring instruments and the installations, thermography establishes a data collection and thermal analysis process that is completely safe. This method avoids interference with production since the work is done with equipment fully operational. Another advantage is the good inspection yield, as it enables coverage of a reasonable number of devices in a short period.
Thermographic inspection evaluates the normal operating condition of equipment according to its nature. Thus, some electrical and electronic equipment in operation naturally present some type of heating according to their design, construction characteristics, and load at the time of inspection. Certain equipment such as insulator columns, lightning arresters, transformer bushings, and bushings must have thermal profiles in their normal state based on predefined criteria.
In this sense, applying thermographic inspection to electrical equipment can offer the following benefits:
• Predictive maintenance: Helps prevent damage that could cause high repair costs;
• Inventory: Prevention of potential problems allows for reduced stock investment;
• Energy consumption: Enables correction of issues causing energy loss and excessive consumption; any overheating results in abnormal consumption;
• Time: Inspection of a large number of devices in a shorter period;
• Load evaluation on panels: Simplifies diagnosis during equipment operation;
• Support for maintenance teams: Assesses the quality of executed services;
• Planning: Allows prior planning before service completion, optimizing time;
• Service life: Detecting problems early prevents unnecessary burnout or loss of devices.
The equipment used to acquire thermograms in this work is called a thermal imager. It is capable of producing an image highlighting the thermal profile of a component, enabling detection of any abnormal heating outside the object’s thermal standard. To specify an appropriate thermal imager for a given application in terms of cost and performance, it is important to understand certain technical definitions used in the field of thermography.
All objects emit radiation due to the thermal agitation of the atoms and molecules that constitute them. The higher the temperature of the object, the more radiation it emits. Most thermal radiation is emitted in the form of infrared light, which is invisible to the naked eye. Thermal imagers (thermal cameras) are sensitive to the infrared radiation emitted by objects, providing thermal images of the inspected objects called thermograms. Thus, through these thermal imagers, it is possible to measure the distance and the surface temperatures of the inspected objects.
A thermal imager measures the infrared radiation emitted by objects and reproduces corresponding images. Since the radiation results from the surface temperature of the object, the camera can calculate and display this temperature. However, the radiation measured by the camera does not depend solely on the object’s temperature; it is also a function of emissivity. Additionally, the total infrared energy leaving the surface of an object is the sum of the transmitted, emitted, and reflected components of the infrared radiation.
Thermal imagers, infrared cameras, or thermographic cameras aim to convert the captured infrared radiation into thermal information. They operate by reading wavelengths around 14 µm. Various types of systems have been developed, differing in how they scan the scene, the type of detector used, and the way the captured information is presented. The result of the information captured by thermal imagers is the presentation of a thermal image showing the heat distribution of the objects being studied. Generally, a thermal imager consists of a camera unit and a video (display) unit.