ABB RED615 Technical Manual page 339

1YHT530004D05 D
615 series
Technical Manual
Example
In a 15 kV, 50 Hz compensated network, the maximum value for Uo during the
healthy state is 10%xUph. Maximum earth-fault current of the system is 100 A.
The maximum earth fault current of the protected feeder is 10 A (Rf = 0 ohm). The
applied active current forcing scheme uses a 15 A resistor, which is connected in
parallel to the coil during the fault after a 1.0 second delay.
Solution: As a start condition for the neutral admittance protection, the internal
residual overvoltage condition of EFPADM is used. The Voltage start value setting
must be set above the maximum healthy-state Uo of 10%xUph with a suitable margin.
Voltage start value = 0.15 xUn
According to Figure 170, this selection ensures at least a sensitivity corresponding
to a 2000 ohm fault resistance when the compensation degree varies between 80%
and 120%. The greatest sensitivity is achieved when the compensation degree is
close to full resonance.
An earth-fault current of 10 A can be converted into admittance.
10 A
Y = ≈ ⋅ j 1 15 .
Fdtot
15 kV 3
GUID-3631BAB9-7D65-4591-A3D6-834687D0E03C V1 EN
A parallel resistor current of 15 A can be converted into admittance.
15
A
= ≈ 1 73 milliSiemens
G .
cc
15 3
kV
GUID-4B7A18DE-68CB-42B2-BF02-115F0ECC03D9 V1 EN
According to Equation 18, during an outside fault EFPADM measures the
following admittance:
Yo = − Y ≈ − ⋅1 15 j . milliSiemens
Fdtot
GUID-AD02E209-1740-4930-8E28-AB85637CEF0D V1 EN
According to Equation 23, during an inside fault EFPADM measures the
admittance after the connection of the parallel resistor:
(
Yo Y = + Y ≈ 1 73 .
Bgtot CC
GUID-28AF4976-1872-48A1-ACC7-7CC3B51CD9D8 V1 EN
Where the imaginary part of the admittance, B, depends on the tuning of the coil
(compensation degree).
The admittance characteristic is selected to be the combined overconductance and
oversusceptance characteristic with four boundary lines:
Operation mode = "Go, Bo"
Directional mode = "Non-directional"
milliSiemens
)
+ ⋅ j B milliSiemens
Section 4
Protection functions
333