ABB RED615 Technical Manual page 434

Section 4
Protection functions
428
GUID-124047A0-9B33-4D2F-9519-75D98C0A4534 V1 EN
Figure 228: Connection of the current transformers of Type 2. The phase
currents and the neutral current have equal directions at an
external earth-fault situation.
Internal and external faults
LREFPNDF does not respond to any faults outside the protected zone. An external
fault is detected by checking the phase angle difference of the neutral current and
the sum of the phase currents. When the difference is less than 90 degrees, the
operation is internally restrained or blocked. Hence the protection is not sensitive
to an external fault.
I
zs1
A
I
zs1
B
I
zs1
C
Uzs
Operate for
internal fault
GUID-FAC5E4AD-A4A7-4D39-9EAC-C380EA33CB78 V2 EN
Figure 229: Current flow in all the CTs for an external fault
zone of
protection
Io
For external fault
Restrain for
external fault
1YHT530004D05 D
I
a = 0
I I
b = 0 b = 0
I I
c = 0
I
N
Io
I
N Reference is Neutral
Current
Technical Manual
a
b
c
615 series