ABB RELION Series Technical Manual page 337

1MRS758755 A
REC615 and RER615
Technical Manual
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
I j I I
( )
+ ⋅ −
Rn eTot eFd
≈
U
ph
GUID-CAA0C492-20CF-406C-80AC-8301375AB454 V1 EN
Y Sum of the phase-to-earth admittances (Y
Bgtot
Y Admittance of the earthing arrangement (compensation coil and parallel resistor)
CC
I Rated current of the parallel resistor
Rcc
I Magnitude of the earth-fault current of the protected feeder when the fault resistance is zero ohm
eFd
I Magnitude of the uncompensated earth-fault current of the network when Rf is zero ohm
eTot
K Compensation degree, K = 1 full resonance, K<1 undercompensated, K>1 overcompensated
I Rated current of the neutral earthing resistor
Rn
Equation 16 shows that in case of a fault inside the protected feeder in unearthed
networks, the measured admittance equals the admittance of the background network.
I
)
−
eFd
, Y
BgA BgB
Section 4
Protection functions
, Y ) of the background network
BgC
(Equation 16)
(Equation 17)
(Equation 18)
(Equation 19)
(Equation 20)
(Equation 21)
331