What Is Creepage Distance?

Creepage distance refers to the charged area between two conductive parts measured along the insulation surface, due to the electrification of the insulation material around the conductor under different use conditions.

Creepage distance is the shortest path between two conductive parts or between a conductive part and the protective interface of the device, measured along an insulating surface. That is, in different use cases, the insulating material around the conductor is electrified, which causes the insulating material to appear charged.

UL, CSA, and VDE safety standards emphasize the safety requirements for creepage distances. This is to prevent fire between devices or between devices and ground, which threatens personal safety.

The creepage distance of the insulator refers to the shortest distance or the shortest distance between the two parts of the insulator that normally carry the operating voltage along the insulation surface. ^[1]

The meaning of creeping can be seen as the shortest distance that an ant must go from one charged body to another, which is the creeping distance.

Electrically, the requirements for the minimum creepage distance are related to the voltage between the two conductive parts, the leakage resistance index of the insulating material, and the pollution level of the environment in which the appliance is located.

The limitation on the minimum creepage distance is to prevent the creepage phenomenon between the two conductive bodies and the pollutants that may appear on the surface of the insulating material.

Creepage distance In use, the shortest insulation distance between two live conductors to be installed is greater than the minimum allowed creepage distance.

When determining the electrical clearance and creepage distance, various use conditions and environmental factors such as rated voltage, pollution status, insulation material, surface shape, location direction, and duration of withstand voltage should be considered, which are included in advanced equipment and product standards. This specified value.

Specifically, in different use cases, the insulating material around the conductor is electrified, which causes the insulating material to appear charged. The radius of this charged area (when the conductor is circular and the charged area is annular) is the creepage distance. The size of the creepage distance is directly related to the working voltage and insulation materials. At the same time, pay attention to the different use environments, such as air pressure and pollution.

Creepage distance and electrical clearance are two concepts that must be met at the same time when judging, and cannot be replaced with each other. The size of the electrical clearance depends on the peak value of the working voltage, and the overvoltage level of the power grid has a greater impact on it. Depending on the effective value of the working voltage, the CTI value of the insulating material has a great influence on it. Both conditions must be met at the same time, so by definition, the creepage distance must not be less than the electrical clearance at any time. Of course, for two charged bodies, it is usually impossible to design a creepage distance smaller than the clearance. ^[1]

Traditional manual measurement of the creepage distance of transporting equipment requires the use of herringbone ladders or aerial work vehicles to perform aerial work when the equipment is out of power, and requires at least two people to measure and cooperate with multiple people. Valuable equipment power failure maintenance time, and there is a risk of personal and equipment safety when working at high altitudes. The use of 3D laser scanning technology can be performed at any time without power failure of the equipment. The measurement can be completed by as few as one person, and the measurement speed is fast. Batch measurement can be performed on multiple devices at the same time. Each of the tested devices can be 3D modeled separately for comprehensive data analysis. Therefore, 3D laser scanning technology has great advantages in terms of work development, personal safety, equipment safety, and work efficiency. At present, the ex-factory value and field measurement values of the external insulation creepage distance data of the transformer equipment are generally obtained by manual tape measure methods. There is an error with the actual value of the equipment. In the process of researching the new technology of 3D scanning of creepage distance, I used 3D scanning data and manual measurement data to compare the data, so the comparison error has certain limitations. The new technology of 3D scanning has established a more scientific and effective Method, and can quickly, accurately and comprehensively carry out a comprehensive survey and information collection of the device, without the need for power outage of the device, this technology is worth popularizing and applying. ^[2]