Fault current

[edetaen]

Good day Folks,

Can anyone tell me the difference between Asymmetrical and symmetrical RMS fault current and how to determine its values for a ring main unit

 

[cranky108]

Do you know your X/R value?

What is a ring main unit? Is it part of a generator brush works, or is it a part of a ring bus?

 

[ScottyUK]

Cranky108,

An RMU is a piece of distribution switchgear comprising two HV disconnectors and an HV switch-fuse or breaker in one piece of apparatus. In the UK they're commonplace at the bottom end of the distribution chain, typically serving relatively small loads from the 11kV network. Older ones were often oil-filled. Here's an example of a modern SF₆ one:

http://hemhub.com/wp-content/uploads/2015/08/ELE093-Img-02.jpg

 

[cranky108]

The picture dos not give a clue to the purpose. Is it like a network protector?

 

[wroggent]

I think they're similar to S&C Vista gear commonly used in the US. Consists of gang operated switch (open/close/ground) and a vacuum bottle for fault interruption, or if it has fuses instead of vacuum bottle then it would be like S&C PME/PMH switches.