1. The premise of selecting an electrical insulation material
You should be clear before selection an insulating material: ① the structure of electrical equipment which use this material, the location and fixation of materials in the device.② working status of this equipment and the effect of the material in this state. ③how the insulating material is processed in this electrical equipment.④ how many insulating material in the device and which kind of insulation systems are they composed
2 Basic selection principles
(1) the force field the materials in. In addition to ensuring the safe operation of electrical insulating materials, insulating material may also be affected by centrifugal force, extrusion, compression, tension, stretch, shear, bending, or other force of repeated bending, some of these forces are stationary on the structure of the present device, others are generated when devices rotated, heated and other working conditions.
(2) the temperature field the materials in. Most electrical devices generate heat during operation the temperature rises, and some electrical equipment is to work for the purpose of heating, these will make the insulating material inside a specific temperature field. Selection of materials should calculate the temperature distribution of the device while operating, clear at what temperature insulating materials (including start-up, long-term and abnormal heat shock), combined with the life of the equipment, refer to Table 1 – 2, then consider the special case, select the appropriate heat-resistant grade of the material. It should also be noted here that the life of the device itself, such as general electrical equipment’s life is 15 years of continuous operation, but some devices may only work a few weeks or even a few hours, some work intermittently. All factors should be taken into account.
(3) the electromagnetic field material in. Electric and magnetic fields of different electrical equipment vary considerably, consequences resulting in electrical aging is also very different, such as voltage, current, AC, DC, low frequency, high frequency, frequency, electromagnetic waves of different shape, sine wave, square wave, steep waves, steep wave pulse, even within the insulating material has the electric field distribution. In addition, under high or special high voltage corona field, leakage, and the resulting partial discharge ozone and ionized particles impact, cracking, etc. Furthermore, in different power states, such as large current or no electric current, the electromagnetic field (electrostatic), etc. These all made for a very different requirements on insulating materials, must be selected.
(4) Material compatibility with the surrounding material. In the electrical equipment and components, the insulation material must work together with other materials, such as conductors, other insulators (gas, liquid, solid) as well as other mechanical materials and chemical materials. In most cases, an insulating structure may also be composed of several insulation materials. These materials, at room temperature or lower temperature, due to the role of the electric and thermal field, each occur physical, chemical reactions, such as dissolution, swelling, surface chemical reactions, mutual penetration, ion exchange, or by the reaction of new substances. These reactions by materials working together and what kind of positive or negative consequences the selected materials working in electrical equipment will bring, must also be evaluated in the selection.
(5) The process of the material. Materials used in electrical equipment, may be processed in two ways: first, make hold of the products, second, to be processed in the manufacture of construction equipment. This should be known when design (or repair). The materials must be able to not only withstand these processes, but its performance also to adapt the technologic requirement during processing and processed by electrical equipment finally. These processes include forming, cutting, punching, cutting, winding, impregnation, compound, pressing, baking, drying, off the assembly line, the line corrosion, bonding, coating, coating, wrapping, casting, extrusion, injection molding, molding, coating, welding, fitting, impact, etc., but also an important intermediate parts should be tested prior to assembly, or even simulated working conditions or under more severe conditions for type test or evaluation test. Material must be able to adapt to these processes.
(6) special environment material in. In recent years, electrical environments work in more extreme are increasing, such as the deep cold, ultra-high temperature, humidity, vacuum, high pressure, high altitude, deep sea diving, submersible, submersible water, space, underground, super frequency, intense pulsed , strong nuclear radiation, cosmic radiation, bad weather and unprotected work, etc., special attention is needed in the election insulating material.
(7) economy, easy access and friendly environmental. Economy, easy access to any material that is environmentally friendly is universal principles of selecting any material. Economy should include the price of the material itself and the additional value during process of obtaining (such as communications, transportation, storage and other additional costs), so a small amount of material downgrade is to be frequent occurrence. Besides, modern environment-friendly is the factor of selection, such as materials solvent-free, flame retardant, conducive to environmental protection, in line with environmental laws, regulations, decrees and standard.
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