A substation operating at 33kv is divided into sections A and B. Section A consist of three...

Question

A substation operating at 33kv is divided into sections A and B. Section A consist of three generators 15MVA each having a reactance of 15% and section B is fed from the grid through a 75MVA transformer of 8% reactance. The circuit breakers have each a rupturing capacity of 750MVA.Determine the reactance of the reactor to prevent the breakers being overloaded if a symmetrical short circuit occurs on an outgoing feeder connected to A.

David · Accepted Answer

Solution:
Refer to the Figure 1 for the substation system. 
 
Section B power rating is,  bS 75 MVA

Substation operating voltage is,  bV 33 kV

Short circuit capacity (SCC) or short circuit level (SCL) in per unit (p.u.) quantity is,

A substation operating at 33kv is divided into sections A and B. Section A consist of three generators 15MVA each having a reactance of 15% and section B is fed from the grid through a 75MVA...

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