## 1 Introduction  
Wherever any cause generates heat, thermal imaging measurements become an indispensable diagnostic tool [1; 2; 3]. Thermal imaging can be an effective method for tracking various processes whose course is associated with changes in emissivity or temperature over time or with variations in the thermal images of individual objects [4; 5]. To assess, for example, the type of damage in electrical installation based on thermograms, it is additionally necessary to carry out numerous tests and comparative analyses. A comparison with X-ray methods comes to mind here, where, without being a specialist, it is not possible to properly interpret an X-ray image. In the field of thermal imaging measurements, as in X-ray, specialization is also required, considering the characteristics of the individual fields of application and the ability to perform examinations and interpret the results correctly [6; 7]. In general, the thermal imaging measurements in power engineering, among others, used for testing indoor or outdoor installations and equipment are listed below [8]:  
* The detection of thermal bridges in the insulation of electric furnaces, and overheating points due to damage to the insulation of chamber furnaces, continuous furnaces, melting furnaces, dryers, boilers, and pipelines;
* The testing of internal combustion engines and turbines;
* Wind turbine integrity testing;
* Tests on electroencephalections elements to determine heat distribution and assess the components' cooling conditions [1; 2];The surveillance of the operation and the detection of overheating points on rotating machinery and equipment, bearings, gears, shafts, couplings, drive belts, chains, conveyors, compressors, and pumps [3];
* The detection of overheating points in electrical equipment and installations, such as fuses, contacts, switchgear and circuit breakers, busways and distribution panels, stationary batteries and chargers, emergency and Diesel generators [9], UPS, overhead and cable lines, substations, transformers, thyristors, motors, insulators, and electrical circuits [10; 11; 12];
* Testing photovoltaic panels and installations [13]. Electrical devices designed for the power industry are intended for power transmission. Generally, being loaded with rated power and occasional short-term overloads do not significantly affect their technical condition. However, excessive power will cause the device to overheat, shortening its life cycle and performance. An uncontrolled increase in temperature results in damage to devices, often resulting in significant costs and an unplanned interruption in energy supply. In many cases, fires even occur, affecting not only the device itself but also buildings or neighboring facilities. The effects of a seemingly minor damage can be huge. When inspecting and assessing the condition of power line components, thermal imaging measurements can furthermore be used to, among other things:
* Detecting overloads, damage, or partial ruptures of cables;
* The detection of load asymmetry;
* The detection of leakage occurring on the insulation surfaces;
* The ongoing monitoring of the correct functioning of transformers. It should be noted that the lists given above are not fully exhaustive. The fault reason can be:  
* Surface and internal cracks and material inhomogeneities;
* Insulation deterioration and aging [12];
* Weak mechanical connection;
* Partial short circuits;
* Induced eddy current;
* Cooling system failure;
* The wear of electric brushes;
* Semiconductor failure (photovoltaic panels) [13]. Some of the factors are independent of the device itself and related to the conditions of heat exchange. These factors can be external pollution, excessive ambient temperature, the obstruction of ventilation inlets, the presence of other hot objects, etc. It is not possible to include a full description of possible applications within the limited framework of this article. Some of these examples, particularly those related to electrical power engineering, are discussed in more detail below.