How to calculate creepage distance of an insulator?

Two pictures let you know how to calculate the insulator creepage distance and what should be pay attention to?

Creepage distance:
The creepage distance of an insulator is the most important parameter, which decide the electrical performance. This should be confirmed by the end user, if the insulator is used on coastal side and more polluted area, they should use high creepage distance insulators.
Sometimes the end user will give creepage distance per KV, such as the standard has several, 16mm/kv, 25mm/kv, 31mm/kv, 52mm/kv. For example, if a nominal voltage 33kv distribution lines, and need 31mm/kv, we should use the system voltage 36kv, to multiply 31, the creepage distance is 1116mm.

            Calculate the creepage distance when design by CAD
How to design the creepage distance?
When the insulator manufacturer knows the creepage distance value or the creepage distance per kv, then they can use this to design the profile of the insulator sheds. After drawing, if design by auto CAD, we should use command “pedit” to join the multiple segments into one segment, and then use command “di” to check the segment length.
If you use CAXA CAD, then it will be easy, just click the tool-circumference, then the value will be multiple segments.  
How to calculate the creepage distance when inspect the insulators?
After the production of the insulator, before shipment, the insulators should be performed routine test and sample test. Then how to calculate the creepage distance?

Inspect the insulator creepage distance
First, you should prepare one tape, glue the tape from one end of the insulation part to the other end, and then mark the two ends of the tape, take off the tape, and measure the length of the marking distance.
Tolerance of the creepage distance:
Since creepage distance is as bigger as better, some people think the creepage distance is no tolerance. In fact, in the international standard IEC60383, it states the creepage distance also has tolerance, if the client prefer bigger creepage distance, should add “minimum” before creepage distance.

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