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(1) Breakdown strength. Under the action of an electric field strength higher than a certain value, insulation materials will be damaged and lose their insulation performance, which is called breakdown. The electric field strength at which insulation materials are broken down is called breakdown strength, measured in kV/mm.
(2) Heat resistance. When the temperature increases, the resistance, breakdown strength, mechanical strength, and other properties of insulation materials will decrease. Therefore, it is required that the insulation material can work for a long time at the specified temperature and ensure reliable insulation performance. The heat resistance of insulation materials with different components varies, and the heat resistance level can be divided into 7 levels: Y, A, E, B, F, H, C, etc. The maximum operating temperature is specified for each level of insulation material.
Grade Y: The maximum working temperature is 90 ℃, for textiles such as wood, cotton yarn, paper fibers, acetate fibers, polyacrylates, and plastic insulation materials that are prone to thermal decomposition and low melting points.
Grade A: The maximum working temperature is 105 ℃, for insulation materials such as enameled wire, canvas, wire, oil-based paint, and asphalt.
Class E: The maximum working temperature is 120 ℃, and insulation materials such as glass cloth, oil-based resin paint, high-strength enameled wire, heat-resistant vinyl acetate enameled wire, etc.
Class B: The maximum working temperature is 130 ℃, such as polyester thin wax, mica treated with corresponding resin, glass fiber, asbestos, polyester paint, polyester enameled wire and other insulation materials.
F level: The maximum working temperature is 155 ℃, such as mica, glass fiber, asbestos, glass coating cloth, laminated products based on the above materials, mica, powder products, polyester and alkyd materials with good chemical and thermal stability, and composite silicone organic polyester paint after bonding or impregnation with F level insulation resin.
H-grade: The maximum working temperature is 180 ℃, such as thickened F-grade materials, mica, organosilicon mica products, silicone organic paint, silicone organic rubber polyimide composite glass cloth, composite film, polyimide paint, etc.
Class C: The maximum operating temperature is greater than 180 ℃. Refers to inorganic substances that do not use any organic adhesives or impregnating agents, such as quartz, asbestos, mica, glass, ceramics, and PTFE plastics.
(3) Insulation resistance. The resistance value presented by insulation materials is insulation resistance, which usually reaches several tens of megaohms or more in normal conditions. The insulation resistance may vary greatly due to temperature, thickness, and surface conditions (such as moisture and dirt).
The electrical resistivity of insulation materials is high, but under a certain voltage. There is always a small amount of current passing through, which is called leakage current.
(4) Mechanical strength. According to the specific requirements of various insulation materials, various strength indicators such as tensile, compressive, bending, shear, tear, and impact resistance are collectively referred to as mechanical strength.
(5) Other characteristic indicators. Some insulation materials are presented in liquid form, such as various insulation paints, whose characteristic indicators include viscosity, fixed content, acid value, drying time, and gelation time. Some insulation material characteristic indicators also involve permeability, oil resistance, elongation, shrinkage, solvent resistance, arc resistance, etc.