Example 8.3 A 25 MVA, 11 kV generator with X4" = 20% is connected through a transforme bus that supplies three identical motors as shown in the following figure. Each has Xa" = 25% and X4' = 30% on a base of 5 MVA, 6.6 kV. The three-phase rat the step up transformer is 25 MVA 11/66 kV with a leakage reactance of 10% of the step down transformer is 25 MVA, 66/6.6 kV with a leakage reactance o The bus voltage of the motors is 6.6 kV when a three-phase fault occurs at the For the specified fault, calculate the subtransient current at the fault point. Give reactance of transmission line is 15% on a base 25 MVA, 66 kV. Choose a syst of 25 MVA and 11 kV at generator side and assume that the system is operatin load. MI T2 Xiine = 15% M2 25 MVA 25 MVA 11/66 kV 66/6.6 kV M3 X=10% X= 10% 5 MVA 6.6 kV X"= 25%; X' = 30%

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Example 8.3
A 25 MVA, 11 kV generator with X4" = 20% is connected through a transformer to a
bus that supplies three identical motors as shown in the following figure. Each motor
has Xa" = 25% and X4' = 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
T2
Xiine = 15%
M2
25 MVA
25 MVA
11/66 kV
66/6.6 kV
M3
X=10%
X= 10%
5 MVA
6.6 kV
X"= 25%; X' = 30%
Transcribed Image Text:Example 8.3 A 25 MVA, 11 kV generator with X4" = 20% is connected through a transformer to a bus that supplies three identical motors as shown in the following figure. Each motor has Xa" = 25% and X4' = 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 T2 Xiine = 15% M2 25 MVA 25 MVA 11/66 kV 66/6.6 kV M3 X=10% X= 10% 5 MVA 6.6 kV X"= 25%; X' = 30%
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