Easy Way to Understand Creepage and Clearance
It is essential to avoid or prevent electrical noise and isolation failures in a battery system. Hence, we must consider freedom from electrical interference when making an electrical hardware design or a mechanical structure design. If two conductive paths are too close to each other, we may create an electrical conductivity between them, depending on the pollution degree. Hence, it requires a minimum distance between them; therein, Creepage and Clearance come into play. Creepage represents the shortest distance between two conductive parts through the surface from one to another, while Clearance does the one between them through the air. As seen in Figure 1, the dashed arrow shows the shortest path in the air between two conductive points, representing clearance. On the other hand, Creepage corresponds to the shortest path from one end to the other through the surface of the insulated area. In this case, creepage is longer than clearance.
Creepage distance is calculated, given a battery working voltage, a material group, and a pollution degree. The working voltage refers to the maximum system voltage of the battery, and the material group measures the Component Tracking Index, which appears in the material specification of insulators. Finally, we determine the pollution degree based on the IP rating of an isolated area. Simply speaking, IP54 or less sets the pollution degree to 3, while IP54+ does it to 2.
Clearance distance additionally requires determining impulse voltage rating and altitude correction for calculation. It also depends on the field type and the pollution degree, which is either homogeneous or inhomogeneous. Thus, clearance distance requires a little more math and is straightforward as follows the standard steps. There is also an online calculator for you; you just set all the above parameters, and then it returns basic and reinforced distances for each Creepage and Clearance. Figure 1 shows a screenshot of the calculator. Next, you go to the Creepage Clearance Calculator link and play out.
In conclusion, we need to design a high-voltage battery pack with Creepage and Clearance properties incorporated. These properties are vital to gain a degree of isolation from any high-voltage exposure.
Reference: IEC 60364 1–41 and IEC 60664
