Example 8.3 d A 25 MVA, 11 kV generator with X₁" = 20% is connected through a transformer to a bus that supplies three identical motors as shown in the following figure. Each motor has X" = 25% and X₁ = 30% on a base of 5 MVA, 6.6 kV. The three-phase rating of the step up transformer is 25 MVA 11/66 kV with a leakage reactance of 10% and that of the step down transformer is 25 MVA, 66/6.6 kV with a leakage reactance of 10%. The bus voltage of the motors is 6.6 kV when a three-phase fault occurs at the point F. For the specified fault, calculate the subtransient current at the fault point. Given the reactance of transmission line is 15% on a base 25 MVA, 66 kV. Choose a system base of 25 MVA and 11 kV at generator side and assume that the system is operating on no load. Mi 10/11/19 G T₁ Xine = 15% 25 MVA 11/66 kV X= 10% Dr. Mustafa BAYSAL T₂ उ 25 MVA 66/6.6 kV X= 10% F 5 MVA 6.6 kV M2 M3 X"=25%; X' = 30% 19