ABB Relion Technical Manual page 128

Section 6
Differential protection
122
ANSI05000724 V3 EN
Figure 44: Zero sequence currents at an external ground fault
Uzs
ANSI05000725 V3 EN
Figure 45: Zero sequence currents at an internal ground fault
I
N
Uzs
I
N
1MRK 502 048-UUS A
ROA (Relay Operate Angle)
ROA = 60 deg
REFPDIF never operates for any faults
external to the protected zone.
Currents 3I and I are theoretically
o N
o
180 out of phase for any external
ground-fault.
Technical manual