P1max = 100 MVA , Z1% = 10
P2max = 150 MVA , Z2% = 9
P3 max = 150 MVA, Z3% = 8
P2max = 150 MVA , Z2% = 9
P3 max = 150 MVA, Z3% = 8
From the previous data, the expected maximum power available is
P1max + P1max + P3max = 100 + 150 + 150 = 400
Actually:
Assume the total required load to be 400 MVA. The participation of each transformer can be calculated from the formula
Where:Pi : Power taken from transformer no. ( i )
Pt : Total required power
Then P1 can be calculated as
Similarly
P2 = 146.7889
P3 = 165.137 ( overloaded )
But, P3 must not exceed 150 MVA
So, let P3 = 150 MVA
According to the new value of P3 , new values of P1, and P2 can be calculated from the formula
In this case, the maximum available power from the three transformers is equal to
80 + 133.3 + 150 = 363.3 MVA
Comparing this value with the total required power ( 400 MVA ). The available power in this case is only ( 90.8% ) from the required power.
Note :
For high differences between percentage impedances of power transformers, the ratio between the available power to the summation of the total MVA of the transformers will decrease to very small values. So, the differences between percentages impedances of transformers connected in parallel must not exceed 10% from the mean value of them.