6. Determine the voltage setting of the high impedance residually connected relay shown in FIGURE 3 to protect the transformer...

6. Determine the voltage setting of the high impedance residually connected relay shown in FIGURE 3 to protect the transformer secondary winding against earth faults.  The 11 kV/415 V Delta/Star transformer rating is 2 MVA and X%  =  8%.  The source fault MVA is 25 MVA, the CT ratio is 1000/1 and its secondary resistance is 2.5 ohms.  The lead loop resistance to the neutral CT is 2 ohms.  Use a 1 MVA base.
FIG. 3