I am modeling a hypothetical backup protection system for a power transmission grid and need to know if a directional relay can detect a fault if there are multiple lines and buses between the relay and the fault.

For example, in the below diagram of the IEEE 14-Bus System can a direction relay located on the Bus 2 side of line 2-4 detect a fault on line 13-14? enter image description here

  • \$\begingroup\$ Please provide a sketch. There's a built-in schematic editor on the toolbar. \$\endgroup\$
    – Transistor
    Nov 1, 2017 at 19:14
  • 1
    \$\begingroup\$ You need to clarify your terminology. The title of your question refers to a distance relay; the body of your question refers to a directional (overcurrent / earth fault) relay. These two types of relay work on very different principles. \$\endgroup\$ Nov 25, 2017 at 4:52

1 Answer 1


No a directional relay cannot detect a fault on line 13-14 (between buses 13 & 14).

Your relay has several buses between the fault location and the protective device in question. A directional relay only uses information from the circuit breakers that it is connected to (red boxes in your grid).

So in this case the relay does not know what is happening at the other relays/buses outside of its zone(s) of protection. You don’t have those zones shown but they are typically something like the following image.

Zones of Protection

The fault would most likely be detected by a relay on bus 13 and/or 14.


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