Part B $-5$ points$)$

A$.$ For the system shown, a single line to ground fault occurs at $F_1.$ Find the phase current for the differential relay $(87)$ and the neutral relay current $(51$N$)$ for the grounding impedances as follows:

a$)R_N=0$

b$)R_N=1\mathrm{.}0$

c$)R_N=10\mathrm{.}0$