You cannot post a reply to this discussion. If you have a question start a new discussion
Reactance and impedance of 300 mm2 Aluminium 4-core cable
Former Community Member
I am doing 6.3.4 example in the IET Electrical installation design guide: calculations for electricians and designers. in part 2: three-phase to earth fault current at C, it says a 100m of 300 mm2 cable aluminium SWA thermosetting (Table F7A). but the table does not have x value, only r value. where and how to find these values to help in calculating the prospective fault current ?
Note that those figures you have highlighted are not for voltage drops in SWA but relate to unarmoured cable with cores only.
In the case of the phase to phase to phase fault this is partly correct, as there is only voltage drop in the line conductors, not in the return path.
However, the X part is likely to be a bit off, as in the 3 core SWA, the magnetic fields of the 3 cores cancel, making the transmission line inductance rather less than the sum of the individual lines .
Note that those figures you have highlighted are not for voltage drops in SWA but relate to unarmoured cable with cores only.
In the case of the phase to phase to phase fault this is partly correct, as there is only voltage drop in the line conductors, not in the return path.
However, the X part is likely to be a bit off, as in the 3 core SWA, the magnetic fields of the 3 cores cancel, making the transmission line inductance rather less than the sum of the individual lines .
