The percentage differential relay solves this problem without sacrificing sensitivity. The schematic
arrangement is shown in Figure 7.3. This scheme has already been introduced in section 2.2.
Depending upon the specific design of the relay, the differential current required to operate this
relay can be either a constant or a variable percentage of the current in the restraint windings. The
constant percentage differential relay operates, as its name implies, on a constant percentage of the
through or total restraint current. For instance, a relay with a 10% characteristic would require at
least 2.0 A in the operating winding with 20 A through-current flowing in both restraint windings.