LG earth fault current of DG set
LG earth fault current of DG set
(OP)
Solidly gorunded DG set contributes say xkA for L-G fault.
This values comes assuming ground grid resistance as 0.
If the ground grid resistance which is normally 1-5 ohms for earthing calculations, is added to zero sequence impedance of DG L-G fault value reduces drastically.
Is it possible to consider ground grid resistance for L-G faults?






RE: LG earth fault current of DG set
During a ground fault the current does not necessarily flow through the "earth" or the grounding electrode. Draw a diagram and review.
The generator frame/ground bus is normally bonded through the equipment grounding conductors with the circuit. The neutral is solidly bonded to the ground bus. So the most likely impedance of the ground circuit in case such as you describe would be much less than 0.5 ohm (same as impedance of the equipment grounding conductors).
The 1-5 ohms earthing resistance is the resistance of the grounding electrode to the remote earth and not necessarily part of a ground fault circuit. Unless you do not install any equipment ground conductors, which is a code violation.
Rafiq Bulsara
http://www.srengineersct.com