12.5 a. Apply and set distance-type relays at Stations H and R for the protection of line HR in the system in Figure P12.5. Set zone 1 units for 90% of the protected line, zone 2 to reach 50% into the next line section beyond the protected line, and zone 3 for 120% of the next line section. b. Plot this system on an RX diagram with the origin at bus H. Plot the relay settings of part 1 using mho-type characteristics. The mathematical formula for a circle through the origin or relay location is where Zs is the relay setting at 758:

The first term is the offset from the origin at 758 and the second term is the radius. This when f is 758, Z0, the relay location; when f is 2558, ZZs the forward reach.

c. What is the maximum load in MVA at 87% pf. that can be carried over line HR without the distance relays operating? Assume that the voltage transformer ratio RV1000 and the current transformer ratio Rc80.