The safety standards of UL, CSA and VDE emphasize the safety requirements of creepage distance, that is, to prevent fire between equipment or between equipment and the ground, thus threatening personal safety.
The creepage distance of insulators refers to the shortest distance or the sum of the shortest distances along the insulation surface between two insulators that normally bear working voltage.
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Practical application:
In electricity, the requirement for the minimum creepage distance is related to the voltage between two conductive parts, the anti-leakage index of insulating materials, and the pollution degree of the environment where electrical appliances are located.
The purpose of limiting the minimum creepage distance is to prevent creepage between two conductors from passing through possible pollutants on the surface of insulating materials.
Creep distance In operation, the shortest insulation distance between two live conductors to be installed is greater than the minimum allowable creepage distance.
When determining the electrical clearance and creepage distance, various operating conditions and environmental factors such as rated voltage, pollution status, insulation material, surface shape, position and direction, and withstand voltage time should be considered, which are stipulated in advanced equipment and product standards.
Specifically, under different use conditions, the insulating material around the conductor is polarized, which leads to the phenomenon that the insulating material is charged. The radius of this charged area (when the conductor is circular, the charged area is annular) is the creepage distance.
The creepage distance is directly related to the working voltage, insulation materials and so on. At the same time, we should pay attention to different use environments, such as air pressure and pollution.
Creep distance and electrical clearance are two concepts, which must be satisfied at the same time and cannot be replaced by each other. The size of electric gap depends on the peak value of working voltage, and the overvoltage level of power grid has a great influence on it. The creepage distance depends on the effective value of working voltage, and the CTI value of insulating material has great influence on it.
The two conditions must be met at the same time, so by definition, the creepage distance cannot be less than the electrical gap at any time. Of course, for two charged bodies, it is usually impossible to design the creepage distance less than the electrical gap.
References:
Baidu encyclopedia-crawling distance