In the GB/T 2900.18-2008 standard for electrical terminology, the creepage distance is defined as the shortest distance between two conductive components along the surface of a solid insulating material.
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The meaning of crawling can be seen as the shortest distance that an ant must travel from one charged body to another, which is the crawling distance.
The creepage distance of an insulator refers to the shortest distance or the sum of the shortest distances along the insulation surface between two components that normally carry the operating voltage of the insulator.There are specific regulations in the national standard, and the calculation method for creepage distance is different for insulation of different shapes. The limitation on the minimum creepage distance is to prevent the occurrence of creepage phenomena caused by pollutants that may occur on the surface of insulating materials between two conductors.
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Application:
In electrical engineering, the minimum creepage distance requirement is related to the voltage between two conductive components, the leakage resistance index of insulation materials, and the pollution level of the environment in which the electrical appliance is located.
In application, the minimum insulation distance between the two live conductors to be installed should be greater than the allowed minimum creepage distance.
When determining electrical clearances and creepage distances, various usage conditions and environmental factors such as rated voltage, pollution conditions, insulation materials, surface shape, position and direction, and duration of withstand voltage should be considered. These values are specified in advanced equipment and product standards.Specifically, in different usage scenarios, due to the polarization of the insulation material around the conductor, the insulation material exhibits a charged phenomenon. The radius of this charged area (when the conductor is circular, the charged area is circular) is the creepage distance. The size of the creepage distance is directly related to the working voltage, insulation material, etc. At the same time, it should be noted that different usage environments may also have an impact, such as air pressure, pollution, etc.Creepage distance and electrical clearance are two concepts that must be met simultaneously when making judgments and cannot be replaced by each other. The size of electrical clearance depends on the peak value of the working voltage, and the over voltage level of the power grid has a significant impact on it. The creepage distance depends on the effective value of the working voltage, and the CTI value of the insulation material has a significant impact on it. Both conditions must be met simultaneously, so according to the definition, the creepage distance cannot be less than the electrical clearance at any time.
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calculation:
Firstly, there is a creepage distance, which is divided into levels 0-4 based on the pollution level of the environment. For example, when there is a third level pollution, the creepage distance of the equipment in the power plant substation is 2.88cm/kV (based on the rated voltage), followed by the rated voltage of the equipment, such as 220kV.
So, the creepage distance is 2.88cm/kV * 220kV=6336mm.
That is to say, we require the creepage distance between the live part and the grounded part of this equipment to be greater than 6336mm.