grounded and ungrounded system

[kimrichi]

i asked this question couple days ago and i am i couldnot understand the answerit is two-part question
in a grounded system how grounding stabilize the system
in ungrounded system why firet fault ground the system and dont open the overcurrent device
i appreciate it if somebody could explain it to me in more details

 

[jumper]

i asked this question couple days ago and i am i couldnot understand the answerit is two-part question
in a grounded system how grounding stabilize the system
in ungrounded system why firet fault ground the system and dont open the overcurrent device
i appreciate it if somebody could explain it to me in more details

Not to be rude, but it would help if you rewrote the post with grammar, spelling, and punctuation.

This is for clarity, not condemnation. It is really hard to read what you typed.

 

[ActionDave]

Read this and see if it helps.
http://forums.mikeholt.com/showthread.php?t=89023&p=708650#post708650
It will not completely answer your questions but will give a basic understanding of a grounded system. Then come back and ask more questions.

 

[SG-1]

i asked this question couple days ago and i am i couldnot understand the answerit is two-part question
in a grounded system how grounding stabilize the system
in ungrounded system why firet fault ground the system and dont open the overcurrent device
i appreciate it if somebody could explain it to me in more details

You may find this link interesting if you have power point or access to power point.
http://www.tirebiter.net/downloads/ludecke.html

It is from the Grounding vs Bonding Forum, The Big Picture.

In the ungrounded system the first ground fault does not open the OCPD ( over-current protective device ) because the only fault current that can flow is the system charging current. That will only be 3 or 4 amps in a medium voltage system. The current cannot find a low impedance path back to it's source. Remember the electrons are not trying to find the earth, they are seeking to return to the source that produced them. That source in this case is not connected to earth, so the electrons cannot even use the dirt for a return path. They can only use the capacitance that exists in the system. Things like arrestors & cables that are capacitively coupled to ground.