Phase to Phase Fault calculation
Phase to Phase Fault calculation
(OP)
What would the correct formula to use to determine the multiples of a transformers rated OA current and then calculate into actual ampheres?
Transformer:
10 MVA
impedance 8.5%
rated phase to phase voltage (secondary side) 12.47 kV
Supply side capacity 650 MVA
assume impedence angles are the same
assume phase-to-phase voltage at the secondary terminals (prior to the fault) is 12.47kV.
Transformer:
10 MVA
impedance 8.5%
rated phase to phase voltage (secondary side) 12.47 kV
Supply side capacity 650 MVA
assume impedence angles are the same
assume phase-to-phase voltage at the secondary terminals (prior to the fault) is 12.47kV.






RE: Phase to Phase Fault calculation
Transformer short circuit MVA :
10MVA / 0.085Zpu = 117.65 SC MVA
650MVA entrance in series with the 117.65 SCMVA is capable of supplying 99.62 SC MVA (X/R assumed to be equal)
Assuming equal 1 and 0 sequence network impedances and X/R ratios, both SCMVA1 and SCMVA2 equal to the 99.62 SCMVA.
The series combination of SCMVA1 and SCMVA2 results in 99.62 / 2 = 49.81 SCMVA.
Ia1 = 49.81 / (1.73 x 12.47) = 2.3kA.
Ia2 = - Ia1 for phase to phase fault.
Assuming B to C fault:
Ib = -Ic = a x a x Ia1 + a x Ia2 + Ia0 =
(-0.5 - j0.866) x Ia1 - (-0.5 + j0.866) x Ia1 + 0 =
-j x 1.73 x Ia1 = 3.98 kA
RE: Phase to Phase Fault calculation
RE: Phase to Phase Fault calculation