ABB RED615 Technical Manual page 322

Section 4
Protection functions
316
For example, in a 15 kV compensated network with the magnitude of the earth-
fault current in the protected feeder being 10 A (Rf = 0 ohm), the theoretical value
for the measured admittance during an earth fault in the reverse direction, that is,
outside the protected feeder, can be calculated:
I
10
eFd
Yo ≈ − ⋅ j = − ⋅ j
U
15
ph
GUID-E2A45F20-9821-436E-94F1-F0BFCB78A1E3 V1 EN
The result is valid regardless of the neutral earthing method.
In this case, the resistive part of the measured admittance is due to leakage losses
of the protected feeder. As they are typically very small, the resistive part is close
to zero. Due to inaccuracies in the voltage and current measurement, the small real
part of the apparent neutral admittance may appear positive. This should be
considered in the setting of the admittance characteristic.
Fault in the forward direction, that is, inside the protected feeder:
Unearthed network:
Yo Y
=
Bgtot
GUID-5F1D2145-3C0F-4F8F-9E17-5B88C1822566 V1 EN
 
I − I
eTot eFd
≈ ⋅ j
 
 
U
ph
 
GUID-0B7C9BA9-B41B-4825-9C1B-F8F36640B693 V1 EN
Compensated network:
Yo Y Y
= +
Bgtot CC
GUID-F3810944-D0E1-4C9A-A99B-8409F4D3CF05 V1 EN
(
( )
I + ⋅ j I ⋅ − K
1
Rcc eTot
≈
U
ph
GUID-208EA80C-62B6-46E0-8A5B-DC425F0FE122 V1 EN
High-resistance earthed network:
Yo Y Y
= +
Bgtot Rn
GUID-F91DA4E4-F439-4BFA-AA0D-5839B1574946 V1 EN
A
= − ⋅ j 1 15 . milliSiemens
3 kV
)
− I
eFd
1YHT530004D05 D
(Equation 20)
(Equation 21)
(Equation 22)
(Equation 23)
(Equation 24)
(Equation 25)
615 series
Technical Manual