ABB REF615 G - Page 322

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:
Yo j
I
U
j
A
kV
j
eFd
ph
≈ − ⋅ = − ⋅ = − ⋅
10
15 3
1 15. milliSiemens
GUID-E2A45F20-9821-436E-94F1-F0BFCB78A1E3 V1 EN (Equation 20)
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 (Equation 21)
≈ ⋅
−








j
I I
U
eTot eFd
ph
GUID-0B7C9BA9-B41B-4825-9C1B-F8F36640B693 V1 EN (Equation 22)
Compensated network:
Yo Y Y
Bgtot CC
= +
GUID-F3810944-D0E1-4C9A-A99B-8409F4D3CF05 V1 EN (Equation 23)
≈
+ ⋅ ⋅ −
( )
−
( )
I j I K I
U
Rcc eTot eFd
ph
1
GUID-208EA80C-62B6-46E0-8A5B-DC425F0FE122 V1 EN (Equation 24)
High-resistance earthed network:
Yo Y Y
Bgtot Rn
= +
GUID-F91DA4E4-F439-4BFA-AA0D-5839B1574946 V1 EN (Equation 25)
Section 4 1YHT530004D05 D
Protection functions
316 615 series
Technical Manual