SOLUTION

• In a short transmission line, the most common fault is the line to ground fault hence reactance type relay is used because more of the line can be protected at high speed.
• In the case of the short transmission line, the protection due to arc resistance is the major factor. hence, the relay should be selected which is less affected by arc resistance. and according to R-X diagram of impedance and reactance relay, the area of reactance relay is more and it is less affected by arc resistance fault but impedance relay is moderately affected due to arc resistance

Note:- In the case of short lines, power surges remain for a shorter period, and hence, their effect is unimportant. The predominant factor is, therefore, the effect of arc resistance. The effect of power surges stays for a longer period in the case of long lines and hence, a relay that is least affected by power surges is preferred for the protection of long lines. The MHO unit is less affected by power surges than the impedance and reactance relays and hence, it is best suited for the protection of long lines against phase