ABB RED615 Technical Manual page 324

Section 4
Protection functions
318
E
A
E
B
E
C
R
n
Uo
L
cc
R
cc
Forward fault,
unearthed network:
Yo ≈ j*(I -I )/U
eTot eFd
Reverse fault:
Yo ≈ -j*I
GUID-5DB19698-38F9-433E-954F-4EBDBA5B63BD V1 EN
Figure 158: Admittance calculation during a forward fault
When the network is fully compensated in compensated networks,
theoretically during a forward fault the imaginary part of the
measured admittance equals the susceptance of the protected feeder
with a negative sign. The discrimination between a forward and
reverse fault must therefore be based on the real part of the
measured admittance, that is, conductance. Thus, the best
Io
A B C
~
~
~
high resistance earthed network:
Im(Yo)
ph
/U
eFd ph
Forward fault, compensated network:
Yo ≈ (I + j*(I *(1-K) - I
rcc eTot
1YHT530004D05 D
Protected feeder
Y
Fd
I
eFd
Background network
Y
Bg
Forward fault,
Yo ≈ (I +j*(I -I ))/U
Rn eTot eFd ph
Under-comp. (K<1)
Re(Yo)
Resonance (K=1)
Over-comp. (K>1)
))/U
eFd ph
Technical Manual
Forward
Fault
I
eTot
(I - I )
eTot eFd
615 series