ABB RELION 611 Series Technical Manual page 223

1MRS757454 D
611 series
Technical Manual
GUID-AE532349-F4F6-4FF9-8A98-0C862162E208 V1 EN
Figure 101: Equivalent circuit when there is no fault or CT saturation
When there is no fault, the CT secondary currents and their emf voltages, E
are opposite and the protection relay measuring branch has no voltage or current. If an
in-zone fault occurs, the secondary currents have the same direction. The relay
measures the sum of the currents as a differential and trips the circuit breaker. If the
fault current goes through only one CT, its secondary emf magnetizes the opposite CT,
that is, E ≈ E .
1 2
R
m1
R
in1
U
E
1
E
1
GUID-CB3CACF7-A2D5-4D76-83B3-44F6AD6D2F9B V1 EN
Figure 102: Equivalent circuit in case of in-zone fault
R
m2
R
R
s
E
I
2
d
U
Section 4
Protection functions
in2
E
2
and E ,
1 2
217