Insulation materials are divided into three categories:
(1) Gas: The air distance in the transformer is often used as a safety distance for insulation. The safety distance between the primary and secondary stages of a high-frequency transformer is generally 7mm.
(2) Liquid: There are two main types of motor insulation materials: mineral and synthetic insulating oil.
(3) Solid: mainly divided into organic and inorganic.
Common organic solid insulation high-frequency transformers include insulating varnish (Varnish), insulating glue (Epoxy), insulating paper (Nomex), insulating fiber (FR4), plastic (PBT, Bakelite), casing (Teflon, Thermal casing), film (PI, Mylar), adhesive tape (Mylar, Kapton, PET), etc. Inorganic solid insulation includes mica, glass, ceramics, etc.
3. Performance and specifications of insulating materials:
Insulating materials are related to safety and reliability. The main specifications of insulating materials include breakdown strength, temperature resistance, insulation resistance, voltage resistance and mechanical stress strength. Insulation materials must meet the certification of electrical insulation. Common electrical insulation systems generally refer to the combination of winding insulation materials for electrical products such as transformers, motors, and coils, such as the testing and certification services provided by UL.
(1) Breakdown strength: When the voltage strength is higher than the specification parameter value, the voltage strength that will cause insulation damage and short circuit is called the breakdown strength, and the unit is V/mm.
(2) Heat resistance: When the temperature is higher than the specification, the performance of the insulating material will be reduced. The temperature resistance of the insulating material can work for a long time at the specified temperature and ensure reliability. The heat resistance grade is divided into Y and A , E, B, F, H, N, R and other 8 grades.
• CALSS Y: temperature limit 90 ℃. Insulators such as epoxy resin adhesives or plastic particles with low melting points.
• CALSS A: temperature limit 105 ℃. Such as enameled wire, varnished cloth, lacquered wire, oily paint and other insulating materials.
• CALSS E: temperature limit 120 ℃. Such as glass cloth, oily resin paint, enameled wire and other insulating materials.
• CALSS B: temperature limit 130 ℃. Such as epoxy resin adhesive, enameled wire, three-layer insulated wire, plastic pellets, insulating tape and other insulating materials.
• CALSS F: temperature limit 155 ℃. Such as epoxy resin adhesive, glass fiber, plastic pellets, insulating tape, enameled wire, three-layer insulated wire.
• CLASS H: The temperature limit is 180℃, such as epoxy resin adhesive, glass fiber, plastic pellets, insulating tape, enameled wire, three-layer insulated wire, motor wire, flat wire.
• CLASS N : The temperature limit is 200℃.
• CLASS R : The temperature limit is 220℃.
(3) Insulation resistance: The resistance value of the insulating material is the insulation resistance, and the unit is Ω. The resistivity of the insulating material is generally greater than 1010Ω·m, and the insulation resistance will vary due to the difference in the ambient temperature and surface condition of the insulating material.
For general objects, the relationship between resistance R, resistivity ρ, length I and cross-sectional area A is as follows
In the above formula,
• Resistance R in ohms
• Length l in meters
• Sectional area A is in square meters
• The unit of resistivity ρ is ohm·meter
(4) Mechanical stress strength: According to different insulating materials, various reliability verifications such as stretching, compression, bending, shearing, impact, fatigue, etc. are defined accordingly, which are called mechanical stress strength.
(5) Other specifications: Insulation materials can be solid or gel-cured. For example, the specifications of gel-cured insulating materials include viscosity, hardness, expansion coefficient, curing time and curing temperature. The specifications of solid insulating materials also include permeability, oil resistance, elongation, shrinkage, solvent resistance, and voltage resistance.