Detailed explanation of creepage distance and electrical clearance

Suppose there is a three-phase five wire AC electric vehicle charging pile , It is necessary to determine the creepage distance and electrical clearance .

Ⅰ： Electrical clearance

First determine the impact withstand voltage level

To make a choice , See what level the device belongs to ？

Category I： The transient overvoltage protection device is installed and controlled within a sufficiently low range .

Category II： Energy consuming equipment powered by the above fixed installation equipment , Such as home appliances , Mobile electric tools, etc ;

Category III： Fixed installation and certain requirements for reliability , Such as fixed installation switch , Plug socket , Permanent installation equipment for industrial use ;

Category IV： Primary power grid equipment , Such as electricity meter , Primary overvoltage protection, etc ;

Or see if there are any product standards .

Electric vehicle charging piles can be classified III;

Next , Comparison table

three-phase , So line voltage 230, Phase voltage 400V, Looking up the table, the rated impulse voltage is 4KV.

Then look up the table

The rated impulse voltage of the first column is 4KV.

Second column ： Two options ,caseA Non uniform electric field ,caseB Uniform electric field . choose caseA, Because in a uniform electric field , The electric field intensity at each point , In the same direction , The working environment of the charging pile is not satisfied .

Next is the pollution level ;

class of pollution 1: No pollution or only dry non-conductive pollution .

class of pollution 2: Generally, there is only non-conductive pollution , However, temporary conductivity caused by accidental condensation must be considered .

class of pollution 3： Conductive contamination , Or due to the expected condensation, the dry non-conductive pollution becomes conductive . 

  
class of pollution 4： Cause persistent conductive contamination , For example, pollution caused by conductive dust or rain and snow .

Unless otherwise specified in relevant product standards , Industrial electrical appliances are generally selected for pollution grade 3 Level environment , Household and similar electrical appliances are generally selected for pollution grade 2 Level environment .

Pollution grade we choose grade 3;

The electrical clearance obtained is 3mm;

It's not over yet .

If the design altitude requirements of electric vehicle charging pile 4000M.

Then look up the table

Therefore, the electrical clearance shall not be less than 3*1.29=3.87mm.

The above is basic insulation , If the insulation is required to be strengthened , To check the table, select the next level .

Ⅱ Creepage distance

Look up the table

The voltage in the first column is the working voltage ： We choose 400V

Second column ： class of pollution 3

Next, look at the material group , Explain the following

IEC Species are divided into I、II、IIIa、IIIb、-- Five kinds ,
The corresponding relation is 0 Yes I;1 Yes II、2/3 Corresponding IIIa、4 Corresponding IIIb、5 Corresponding --.

FR-4 board CTI The value is 175 The micro environmental pollution level used to determine the electrical clearance or creepage distance can be divided into 4 level .

nothing CTI When making a statement , Generally, the worst grade is selected III, Requirements for selecting creepage distance .

Therefore, the creepage distance can be obtained as 6.3mm.

If PCB Limited size , The creepage distance can be increased by trenching .

For the detailed description of electrical clearance and creepage distance, please refer to IEC60664-1.