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hi there Can anybody help with the following question A factory is supplied from a substation containing two 500 kVA, 11 kV/400 V transformers connected in parallel, each having a reactance of 0.08...

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hi there

Can anybody help with the following question

A factory is supplied from a substation containing two 500 kVA, 11 kV/400 V transformers connected in parallel, each having a reactance of 0.08 pu. A 750 kVA generator with 0.12 pu reactance also supplies the 400 V busbars which in turn supply a 400 V feeder having an impedance of XXXXXXXXXXj0.015)Ohm /ph.

Calculate the short-circuit current in the feeder and the voltage of the 400 V busbars when a symmetrical three-phase fault occurs at the far end of the feeder. That fault level of the 11 kV system is 100 MVA.

Many thanks

Answered Same Day Dec 23, 2021

Solution

Robert answered on Dec 23 2021
113 Votes
A factory is supplied from a substation containing two 500 kVA, 11 kV/400 V
transformers connected in parallel, each having a reactance of 0.08 pu. A 750 kVA
generator with 0.12 pu reactance also supplies the 400 V busbars which in turn supply
a 400 V feeder having an impedance of (0.01 + j0.015)Ohm /ph.
Calculate the short-circuit cu
ent in the feeder and the voltage of the 400 V busbars
when a symmetrical three-phase fault occurs at the far end of the feeder. That fault
level of the 11 kV system is 100 MVA.
Solution:
Let the base MVA of 11kV system be 500kVA
Hence reactance will be:












Hence now making single line diagram:
Now to calculate the per unit impedance of the line we find the base...
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