企业供电系统

三相三四五线等
IEC规定
TT (Terra-Terra) earthing system 地地系统
TN （TN-C TN-S TN-C-S）   Also called Neutral 中性中立者  C-combine S-separate
金属外壳和中性线联系在一块 所谓的接零保护
https://en.wikipedia.org/wiki/Earthing_system wiki说的比较清楚

 

 

"T" — Direct connection of a point with earth (Latin: terra)

"I" — No point is connected with earth (isolation), except perhaps via a high impedance.

The second letter indicates the connection between earth and the electrical device being supplied:

"T" — Direct connection of a point with earth

"N" — Direct connection to neutral at the origin of installation, which is connected to the earth

IT

The Letters used are as follows:

T – (French word “Terre” meaning Earth) – It means direct connection of a point to earth

I – It means that either no point is connected to Earth or it is connected via high impedance 高阻抗

N – It means that there is direct connection to neutral at the source of installation which is in turn connected to the ground

Based on a combination of these three letters, there are three families of Earthing arrangements proposed by IEC as below:

• TN Network
• TT Network
• IT Network

 IT系统是指在电源中性点不接地系统中，将所有设备的外露可导电部分均经各自的保护线PE分别直接接地，称之为IT供电系统。IT系统一般为三相三线制。
线路长就不安全，线路长分布电容慢慢聚集，形成高电压，设备在带电时就会形成回路，会有危险（分布电容继续查资料）