4800V Ground Fault

[Mike01]

If I have a 4800V-3W+grd. system the voltage to ground would be 4800/sqrt(3), with that being said how an the LG fault be zero? Does this mean that on a L-G fault you would not operate the OCPD you would need a L-L-G fault?

 

[charlie b]

If I have a 4800V-3W+grd. system the voltage to ground would be 4800/sqrt(3), with that being said how an the LG fault be zero?

I presume you mean that the LG fault current is zero.

If the system is 3 wire, then this is a Delta connected system. As such, the voltage to ground is not established at any given value. The 4800/1.732 value would apply only on a WYE system for which the center point is connected to planet Earth. On the Delta system, if you connect one corner (intentionally or by virtue of a fault condition) to planet Earth, then that point gets established as "zero voltage reference." No current will flow, because you do not yet have a complete path. As you pointed out, if there is a L-L-G fault, then that establishes a complete path for fault current to flow, and the OCPD will trip.

 

[Mike01]

L-G Voltage

L-G Voltage

SoSo with that being said is the L-G voltage of a 4800V-3W+Grd. Circuit is zero?

 

[charlie b]

I am not completely sure I understand the question. But let me offer this, and tell me if it has your answer: If there is no intentional connection between a point on the electrical system and planet Earth, then the voltage between any given point anywhere in the system, with respect to planet Earth, can be anything, and can vary from second to second.