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1、为了使得导线相互隔离并且不接触到其他的物体，必须采取绝缘措施。在理想的条件下，绝缘应做到完全不导电，那样电流才能会完全束缚在计划的导体内。但事实上即使采用绝缘措施也会有少许漏电流，因此绝缘材料应当当作具有高电阻率的材料看待。在许多情况下，由于绝缘材料的导电性造成的漏电流很小，以致于可以忽略不计。在一些情况下，采用非常敏感的仪器测量的漏电流可以用来确定某种绝缘措施是否合适。尽管在正常情形下绝缘材料的性能会很稳定，但在极端情况下，比如电压过高、高温或在某种化学物质的作用下，绝缘材料的性能会遭到完全的破坏，绝缘材料的性能的改变会导致其成为良导体，由此而造成的不应有的电流会使得绝缘材料被强烈地导致其迅
2、速损坏。在电力系统中有相当比例的设备损坏是由于绝缘故障引起的。绝缘设计人员面临的问题包括选择合适的材料、合适的形状和尺寸，以及控制破坏性因素等。绝缘材料有许多绝缘材料应用于电力系统中，绝缘材料的选择取决于具体应用的需要和费用。在居民小区，分支线和电线中的导体可以采用橡胶或各种塑料材料绝缘。这些材料可以承受必要的弯曲，但其电器应力较低。高压电缆适用于较大的电气应力场合，在某种情况下，几百千伏的电压只采用几厘米厚的绝缘处理。这些绝缘材料必做成长形的，并且足够柔软，以便于将其穿进小口径的管道。绝缘材料可以是油浸纸质、浸漆麻纱或合成材料。发电机和电动机的绕组可以采用绝缘带绝缘。一些绝缘带是通过用胶将云
3、母片粘在一起而制成的，另一些是采用绝缘漆浸的玻璃纤维制成的。这些绝缘方式必须能够承受很高的温度、很强的机械力和振动。电力变压器的绕组的绝缘通常采用油浸纸带和压制纸板。纸在油的浸泡下，其绝缘强度大大增加，而且令油在管道中循环，还可以带走变压器中的欧姆损耗和铁芯损耗引起的热量。变压器绝缘要能经受高的电气应力和强的机械应力。在变压器的设计中，导电的金属不见的形状和布置必须特别考虑。架空线是通过瓷绝缘子绝缘的。在支撑件之间是采用空气绝缘的。选用陶瓷材料是用它在暴露于环境中时，具有抗变质能力，并且具有高的介电强度而且在雨中能够得到清洗。Insulation is required to keep ele
4、ctrical conductors separated from each other and from other nearby objects.Ideally，insulation should be totally no conducting，for then currents are totally restricted to the intended conductors.However，insulation does conduct some current and so must be regarded as a material of very high resistivel
5、y.In many applications，the current flow due to conduction through the insulation is so small that it may be entirely neglected.In some instances the conduction currents，measured by very sensitive instruments，serve as a test to determine the suitability of the insulation for use in service.Although i
6、nsulating materials are very stable under ordinary circumstances，they may change radically in characterstics under extreme conditions of voltage stress or temperature or under the action of certain chemicals.Such changer may，in local regions，result in the insulating material becoming highly conducti
7、ve.Unwanted current flow brings about intense heating and the rapid destruction of the insulating material.These insulation failures account for a high percentage of the equipment troubles on electric power systems.The selection of proper materials，the choice of proper shapes and dimensons and the c
8、ontrol of destructive agencies are some of the problems of the insulation-system designer.Insulating Materials 待添加的隐藏文字内容2Many different materials are used as insulation on electric-power system.The choice of material is dictated by the requirements of the particular application and by cost.In resid
9、ences，the conductors used in branch circuits and in the cords to appliances may be insulated with rubber or plastics of several different kinds.Such materials can withstand necessary bending，are relatively low electrical stress.High-voltage cables are subjected to extreme voltage stress：in some seve
10、ral hundred kilovolts are impressed across a few centimeters of insulation.They must be manufactured in long section，and must be sufficiently flexible as to permit pulling into ducts of small cross section.The insulation may be oil-impregnated paper，varnished cambric，or synthetic materials such as p
11、olyethylene.The coils of generators and motors may be insulated with tapes of various kinds.Some of these are made of thin sheets of mica held together by a binder，and others are of fiber glass inpreating with insulating varnish.This insulation must be capable of withstanding quite high operating te
12、mperatures，extreme mechanical forces，and vibration.The insulation on power-transformer windings is commonly paper tape and pressboard operated under oil saturates the paper，greatly increasing its insulation strength，and by circulating through ducts，serves as an agent for carrying a way the heat gene
13、rated due to losses and core losses in the transformer.The shape and arrangement of conducting metal parts is of particular concern in transformer design.Overhead lines are supported on porcelain insulators.Between the supports air serves as insulation.Porcelain is chosen because of its resistance to deterioration when exposed to the weather，its high dielectric strength，and its ability to wash clean in rain.
