I. Insulating materials, insulating materials
What is the insulating material
The insulating material commonly used in electrical engineering according to its different chemical properties, can be divided into inorganic insulating materials, organic insulating materials and mixed insulating materials. Commonly used inorganic insulating materials: mica, asbestos, marble, porcelain, glass, sulfur, etc., mainly used as motors, electrical winding insulation, switchboards and insulators. Organic insulating materials are: gum, resin, rubber, cotton, paper, hemp, rayon, etc., mostly used in the manufacture of insulating varnish, winding wire covered insulator. Mixed insulating materials from the above two materials are processed into a variety of molded insulating materials, used as the base of electrical appliances, shells and so on.
II. Application of insulating materials
The role of insulating materials is to separate the charged parts of the electrical equipment with different potentials. Therefore, the insulating material should first have a high insulation resistance and voltage strength, and can avoid leakage, breakdown and other accidents. Secondly, heat resistance should be good, to avoid aging and deterioration due to long-term overheating; in addition, there should also be good thermal conductivity, moisture resistance and lightning resistance and high mechanical strength, as well as easy processing and other characteristics. According to the above requirements, commonly used insulating materials performance indicators are insulation strength, tensile strength, specific gravity, coefficient of expansion.
III. Insulation voltage strength: the higher the voltage applied to the ends of the insulator, the greater the charge within the material is subjected to the electric field force, the easier it is to ionize the collision, resulting in breakdown of the insulator. Make the insulator breakdown of the lowest voltage is called the breakdown voltage of the insulator. Make 1 millimeter thick insulating material breakdown, need to add the voltage kilovolts is called the insulating material insulation withstand voltage strength, referred to as insulation strength. As insulating materials have a certain insulation strength, a variety of electrical equipment, a variety of safety equipment (electrician's pliers, tester, insulating gloves, insulating rods, etc.), a variety of electrical materials, manufacturers have stipulated a certain permissible use of voltage, known as the rated voltage. The use of the voltage shall not exceed its rated voltage value, in order to avoid accidents.
Four. Tensile strength: insulating material unit cross-sectional area can withstand the tension, for example, glass per square centimeter cross-sectional area can withstand 1400 newtons of tension.
v. Insulating material insulation performance and temperature has a close relationship. The higher the temperature, the worse the insulating properties of the insulating material. In order to ensure the insulating strength, each insulating material has an appropriate maximum allowable working temperature, below this temperature, can be used safely for a long time, more than this temperature will be rapidly aging. According to the degree of heat resistance, the insulation material is divided into Y, A, E, B, F, H, C and other levels. For example, the maximum allowable working temperature of A-class insulation materials for 105 ℃, the general use of distribution transformers, electric motors in the insulation material mostly belongs to A-class.
VI. Insulating material heat resistance rating and grading
1 Theme content and scope of application
This standard specifies the insulation of electrical products, heat resistance grading, determines the heat resistance of the assessment and grading principles and tasks.
This standard applies to electrical products and their insulation heat resistance grading, also applies to a particular occasion of application of insulation materials, simple combinations and insulation structure of heat resistance grading.
2 Referenced standards
GB 11026.1 Guidelines for determining the heat resistance of electrical insulating materials Part I: Development of thermal aging test methods and evaluation of test results of the general protocol
3 General
3.1 Thermal class
3.1 Thermal class
The service life of the insulation of electrical products is subject to a variety of factors (eg, temperature, electrical and mechanical stresses, vibration, Hazardous gases, chemicals, humidity, dust and irradiation, etc.), and temperature is usually a factor that dominates the aging of insulating materials and structures. Therefore, there is a practical, world-recognized heat resistance classification method, that is, the heat resistance of electrical insulation is divided into a number of heat-resistant grade, the heat-resistant grade and the corresponding temperature values are as follows:
Heat-resistant grade Temperature, ℃
Y 90
A 105
E 120
B 130
F 155
H 180
200 200
220 220
250 250
If the temperature exceeds 250°C, the heat-resistance class is set accordingly at 25°C intervals.
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 method may not be applicable and other methods of identification and classification may be used.
The thermal rating indicated on an electrotechnical product usually indicates the maximum temperature to which the product can be subjected when it reaches the end of its intended service life at the rated load and under other conditions specified. Therefore, the temperature pole of the insulation used at the highest temperature in an electrotechnical product should not be lower than the temperature corresponding to the thermal class of the product (otherwise see clause 3.1.2).
For customary reasons, the term "thermal class" is currently used generically for insulating materials, insulating structures and electrical products. However, the future trend is to recommend the use of insulation materials, "temperature index" and "relative temperature index" of the two terms; insulation structure is recommended to use the "identification mark" of the term The term "identification mark" for insulation structures is only associated with the specific product for which it is designed; while the term "thermal class" is retained for electrical products.
3.1.1 Operating conditions
Experience has shown that if the standards for electrical products (e.g., rotating electric motors, transformers, etc.) are formulated on the basis of the temperatures listed in Article 3.1, with due regard to factors specific to the product, then electrical products designed and manufactured in accordance with such standards will have a satisfactory and economical service life under normal operating conditions.
3.1.2 Insulating materials in insulating structures
The labeling of an electrical product as a thermal class does not in any way imply that every insulating material in the insulating structure of the product has the same temperature limit.
The temperature limit of an insulation structure may not be directly related to the temperature limit of each of the insulating materials in it. The temperature limit of the insulating material may be increased by the protection of other constituent materials in the insulation structure, or the temperature limit of the insulation structure may be lower than that of the individual constituent materials due to incompatibility between the materials. All these issues should be investigated by functional tests.
3.1.3 Temperature and temperature rise
The temperatures listed in this standard are the maximum temperatures to which the insulation is subjected in an electrical product, not the permissible temperature rise of the electrical product.
Temperature rise, but not temperature, is often specified in standards for electrical equipment. In determining the measurement method and allowable temperature rise in such standards, the following factors should be considered, such as the characteristics of the structure, the thermal conductivity and thickness of the insulation, the ease of detection of each insulated part, ventilation methods, load characteristics.
3.1.4 Other Influences
The ability of insulation to maintain its utility is affected by certain conditions (e.g., mechanical stresses applied to the insulation and its supporting structure) and by certain factors (e.g., vibration and varying thermal expansion) in addition to thermal factors. As the size of the product increases, the effects of vibration and thermal expansion factors become more important. Atmospheric temperatures, and the presence of dust, chemicals or other contaminants can also have harmful effects. All of these factors should be considered when designing a particular product. See the guidance material for evaluating and identifying the insulation structure of electrical equipment for more details.
3.1.5 Useful life of insulation
The actual useful life of an electrical product depends on the specific conditions of operation. These conditions can vary greatly with the environment, duty cycle, and type of product. In addition, the expected service life depends on the requirements of product size, reliability, the expected service life of the equipment in question, and economics.
For some electrical products, due to its specific application purpose, the requirement of its insulation life below or above the normal value, or due to the special operating conditions, the provisions of its temperature rise above or below the normal value, while the temperature of its insulation is extremely higher or lower than the normal value.
The service life of insulation depends largely on the degree of insulation against oxygen, humidity, dust and chemicals. At a given temperature, the service life of properly protected insulation will be longer than that of insulation freely exposed to the atmosphere, and therefore, the use of chemically inert gases or liquids for cooling or protection can extend the service life of the insulation.
3.1.6 Limitations on operating temperature
In addition to insulation being subjected to aging, some materials soften or otherwise deteriorate when subjected to heat above a certain temperature, but then regain their original properties when cooled. Be careful when using such materials, be sure to make them work in the appropriate temperature range.
3.2 Selection and determination of insulation
The research, design and manufacture of electrical products should be based on the insulation of the temperature limit to select the appropriate insulation materials and insulation structure. The basis for determining a reasonable temperature limit value for insulation can only be operational experience or suitable and acceptable tests. Operational experience is an important basis for the selection of insulation materials and insulation constructions. However, when new materials and constructions are selected, suitable tests are the basis for such selection (see clause 4.2).
4 Evaluation of thermal resistance
4.1 Evaluation of thermal resistance of insulating materials
Many insulating materials of the same genus can have very different thermal resistance. Therefore, it is not appropriate to determine the thermal resistance of insulating materials based on the chemical name of their genus.
Various insulating materials used in the insulating structure of electrical products, their respective heat resistance may be affected by other materials. In addition, the thermal resistance of various materials depends to a large extent on the specific function they perform in the insulation structure.
As far as the use of insulating materials in electrical products is concerned, material evaluation has two purposes: one is the evaluation of a material as part of an electrical insulation structure, and the other is the evaluation of a material used alone or as part of a simple combination of components that make up the insulation structure.
In general, evaluation tests and operating experience are recognized as an acceptable basis for evaluating the thermal resistance of insulation materials.
When using operating experience as a basis, it is important to note that the experience must be applicable. However, it may often be appropriate to transfer one experience to another application under certain circumstances. A suitable methodology should be developed to determine the relationship between operational experience.
Significant progress has been made in the study of test methods for material evaluation. The determination and expression of the thermal resistance of insulating materials has been improved, which can be found in GB 11026.1, and other parts of the guidelines will be developed.
To can a material, using different properties (such as electrical, mechanical, etc.), methods and failure criteria for heat map, it is possible to get a different temperature index and half-difference. Different temperature indices and half-differences indicate differences in heat resistance, and from the citation determines the way the material is used and the function it can assume.
The results obtained with standardized specimens may differ from the results obtained when the material is tested in its actual form of use. Insulation construction is closer to the actual situation. Therefore, the results of the insulation structure test can prove the suitability of the material for the application in question.
4.2 Evaluation of thermal resistance of insulating structures
The evaluation of the thermal resistance of insulating structures is best based on relevant operating experience. In the absence of such operational experience, suitable functional tests should be carried out. For this purpose, it is necessary to use a structure proven by operational experience as a reference insulating structure. The heat resistance of the new insulation structure is evaluated by comparison with it. Insulation research institutes and electrical product research, design, manufacturing, testing and utilization institutes shall design and conduct appropriate tests. In the design of appropriate tests and the development of standardized test procedures for the evaluation of heat resistance, should refer to the evaluation of the insulation structure of the relevant information.
In the selection of the components of the insulating structure, reference may be made to the results of the thermal resistance evaluation of a single material (see clause 4.1).
The suitability of a particular insulating material for a particular insulating structure can be determined as long as it has been demonstrated by tests on suitable insulating structures or by operating experience that the material has satisfactory operating characteristics. There is no need to consider the heat resistance of the material itself.
For very simple and subjected to single stress insulation structure, can be decided on a case-by-case basis, is the need to carry out the insulation structure of the functionality of the test; or more simply based on the material's thermal data to make an evaluation, you can get a satisfactory result. If it is necessary to evaluate the applicability of a material for a particular electrical product, the material has been proven by the appropriate operating experience as a reference material, the test should be carried out. In this case, the organization concerned should provide information on the material that has been proven in operation in a specific application. Also, guidelines on how to evaluate the operating experience should be provided to enable proper grading of the material.
Standardized test protocols for comparative evaluation should be developed. In the absence of such standardized test protocols, the insulation research unit and the research, design, manufacture, testing, and use of electrical products should select the appropriate test protocols for testing.
5 Classification
The classification of electrical products and their insulation for heat resistance is given in clauses 3.1 (especially 3.1.5 and 3.1.6) and 4.2.
If it is shown by tests or operational experience that an insulating material, a simple combination or an insulating structure, for a particular application, can work reliably at a particular temperature, it may be assigned an appropriate thermal class in accordance with clause 3.1.