ABB RELION REX640 Technical Manual page 510

Protection functions
100
90
80
70
60
50
40
30
20
10
0
Total earth f ault current (A), Rf = 0 ohm
Figure 292: Influence of fault resistance on the residual voltage magnitude in 10 kV
unearthed and compensated networks. The leakage resistance is assumed to be 30
times higher than the absolute value of the capacitive reactance of the network.
Parallel resistor of the compensation coil is assumed to be disconnected.
100
90
80
70
60
50
40
30
20
10
0
Total earth f ault current (A), Rf = 0 ohm
Figure 293: Influence of fault resistance on the residual voltage magnitude in 15 kV
unearthed and compensated networks. The leakage resistance is assumed to be 30
times higher than the absolute value of the capacitive reactance of the network.
Parallel resistor of the compensation coil is assumed to be disconnected.
100
90
80
70
60
50
40
30
20
10
0
Total earth f ault current (A), Rf = 0 ohm
Figure 294: Influence of fault resistance on the residual voltage magnitude in 20 kV
unearthed and compensated networks. The leakage resistance is assumed to be 30
times higher than the absolute value of the capacitive reactance of the network.
Parallel resistor of the compensation coil is assumed to be disconnected.
Example
In a 15 kV, 50 Hz compensated network, the maximum value for Uo during
the healthy state is 10%×Uph. Maximum earth-fault current of the system is
100 A. The maximum earth-fault current of the protected feeder is 10 A (Rf
= 0 Ω). The applied active current forcing scheme uses a 15 A resistor (at
15 kV), which is connected in parallel to the coil during the fault after a 1.0
second delay.
Solution: As a start condition for the admittance-based earth-fault
protection, the internal residual overvoltage condition of EFPADM is used.
The
state Uo of 10%×Uph with a suitable margin.
510
Unearthed
Rf = 500 ohm
Rf = 2500 ohm
Rf = 5000 ohm
Rf = 10000 ohm
0 10 20 30 40 50 60 70 80 90 100
Unearthed
Rf = 500 ohm
Rf = 2500 ohm
Rf = 5000 ohm
Rf = 10000 ohm
0 10 20 30 40 50 60 70 80 90 100
Unearthed
Rf = 500 ohm
Rf = 2500 ohm
Rf = 5000 ohm
Rf = 10000 ohm
0 10 20 30 40 50 60 70 80 90100
Voltage start value setting must be set above the maximum healthy-
Resonance, K = 1
100
90
80
70
60
50
40
30
20
10
0
0 10 20 30 40 50 60 70 80 90 100
Total earth f ault current (A), Rf = 0 ohm
Resonance, K = 1
100
90
80
70
60
50
40
30
20
10
0
0 10 20 30 40 50 60 70 80 90100
Total earth f ault current (A), Rf = 0 ohm
Resonance, K = 1
100
90
80
70
60
50
40
30
20
10
0
0 10 20 30 40 50 60 70 80 90 100
Total earth f ault current (A), Rf = 0 ohm
1MRS759142 F
Over/Under-Compensated, K = 1.2/0.8
100
90
80
70
60
50
40
30
20
10
0
0 10 20 30 40 50 60 70 80 90 100
Total earth f ault current (A), Rf = 0 ohm
Over/Under-Compensated, K = 1.2/0.8
100
90
80
70
60
50
40
30
20
10
0
0 10 20 30 40 50 60 70 80 90100
Total earth f ault current (A), Rf = 0 ohm
Over/Under-Compensated, K = 1.2/0.8
100
90
80
70
60
50
40
30
20
10
0
0 10 20 30 40 50 60 70 80 90 100
Total earth f ault current (A), Rf = 0 ohm
Technical Manual
REX640