1. Subject content and scope of application: This standard stipulates the classification of heat resistance of electrical product insulation, and determines the principles and tasks of heat resistance assessment and classification. This standard applies to the classification of heat resistance of electrical products and their insulation, and also applies to the classification of heat resistance of insulating materials, simple combinations and insulating structures applied in a specific occasion.

2. Refer to the standard GB 11026.1 Guidelines for determining the heat resistance of electrical insulating materials, Part I: General regulations for formulating thermal aging test methods and evaluating test results

3 General Remarks 3.1 The service life of thermal insulation of electrical products is affected by a variety of factors (such as temperature, electrical and mechanical stress, vibration, harmful gases, chemicals, moisture, dust and irradiation, etc.), and temperature is usually the dominant factor for the aging of insulating materials and insulation structures. Therefore, there is a practical and world-recognized method of heat resistance classification, that is, the heat resistance of electrical insulation is divided into several heat resistance grades, and the corresponding heat resistance levels and corresponding temperature values are as follows:

Heat resistance class temperature, °CY 90A 105E 120B 130F 155H 180200 200220 220250 250 If the temperature exceeds 250 °C, the heat resistance level will be set accordingly at an interval of 25 °C. It is also possible to indicate the heat resistance class without letters, but the above correspondence must be followed. For equipment used under special conditions and with special requirements (as described in clause 3.1.5), the above classification methods may not be applicable, and other identification classification methods may be used. The heat resistance rating indicated on an electrical product generally indicates the maximum temperature that the product can withstand when it reaches its expected useful life under rated load and other specified conditions. Therefore, in electrical products, the temperature pole of the insulation used at the highest temperature should not be lower than the temperature corresponding to the heat resistance class of the product (otherwise see clause 3.1.2). Due to customary reasons, the term "heat resistance class" is currently used in general terms for insulating materials, insulating structures, and electrical products. However, the trend in the future is to recommend the use of the terms "temperature index" and "relative temperature index" for insulating materials, the term "identification mark" for insulating structures, the "identification mark" for insulation structures only in relation to the specific product for which it is designed, and the term "heat resistance class" for electrical products. 3.1.1 Operating conditions have been proved by experience: if the standard of electrical products (such as rotating electrical machines, transformers, etc.) is based on the temperature listed in Article 3.1 and due consideration of the specific factors of the product, then the electrical products designed and manufactured according to such standards can have a satisfactory and economical service life under normal operating conditions. 3.1.2 The insulating material in the insulating structure indicates that an electrical product is a certain heat-resistant grade, which in no way means that each insulating material in the insulating structure of the product has the same temperature limit. The temperature limit of an insulating structure may not be directly related to the temperature limit of each insulating material in it. In insulating structures, the temperature limit of the insulating material may be increased by the protection of other constituent materials, or the temperature limit of the insulating structure may be lower than that of the individual constituent materials due to incompatibility between the materials. All of these questions should be investigated through functional testing. 3.1.3 Temperature and temperature riseThe temperature listed in this standard refers to the maximum temperature that the insulation in the electrical product bears, and is not the allowable temperature rise of the electrical product. Temperature rise is usually specified in electrical equipment standards but not temperature. The following factors should be taken into account when determining the measurement method and allowable temperature rise in such standards, such as the characteristics of the structure, the thermal conductivity and thickness of the insulation, the ease of detection of each insulating part, the ventilation method, the load characteristics, etc. 3.1.4 Other influencing factors: The ability of insulation to retain its utility, in addition to thermal factors, is also affected by certain conditions (such as mechanical stresses exerted on the insulation and its supporting structure) and certain factors (such as vibration and different thermal expansion). As the size of the product increases, the influence of vibration and thermal expansion factors becomes more important. The temperature of the atmosphere, as well as the presence of dust, chemicals, or other pollutants, can also have harmful effects. These factors should be taken into account when designing a particular product. For details, please refer to the guiding materials for evaluating and identifying the insulation structure of electrical equipment. 3.1.5 The actual service life of the electrical product depends on the specific conditions in operation. These conditions can vary greatly depending on the environment, duty cycle, and product type. In addition, the expected service life depends on the product size, reliability, the expected service life of the equipment in question, and the economic requirements. For some electrical products, due to their specific application purposes, the service life of their insulation is required to be lower or higher than the normal value, or due to special operating conditions, the temperature is higher or lower than the normal value, and the temperature of the insulation is extremely higher or lower than the normal value. The life of an insulation is largely determined by how well it is insulated from oxygen, humidity, dust and chemicals. Properly protected insulation will last longer at a given temperature than insulation that is freely exposed to the atmosphere, so the use of chemically inert gases or liquids for cooling or protective valence can extend the life of the insulation. 3.1.6 Limitation of working temperatureIn addition to aging, some materials will soften or undergo other deterioration when heated more than a certain temperature, but they will return to their original properties after cooling. Care should be taken when working with these materials to ensure that they operate within the appropriate temperature range. 3.2 The selection of insulation and the determination of the research, design and manufacturing unit of electrical products should select the appropriate insulation materials and insulation structures according to the temperature limit of the insulation. The basis for determining a reasonable temperature limit for insulation can only be operational experience or suitable, acceptable tests. Operational experience is an important basis for the selection of insulation materials and insulation structures. However, when it comes to the selection of new materials and structures, suitable testing is the basis for this choice