Low voltage at the source of a fault

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mull982

Senior Member
Why does the voltage drop or become extremely low at the location of a fault during a fault?

Is it because the high magnitude of the fault current causes a large voltae drop across the rest of the system upstream, or is it because the fault weather its a L-L or L-G no longer has a voltage difference/reference between another line or ground depending on the type of fault?
 

beanland

Senior Member
Location
Vancouver, WA
Ohms Law

Ohms Law

You are right on both counts. The high current is caused by the low voltage between the two conductors (LL, LG). The upstream impedance limits the fault current but it is typically very low. For a 10K AFC, 120V/10,000A = 0.012 ohms
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
In a perfect short circuit the voltage across the short would be zero. It has little to do with the amount of fault current, and a lot to do with the voltage drop across a small amount of resistance.
 
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