0 10 20 30 40 50 60 70 80 90 100
0
10
20
30
40
50
60
70
80
90
100
Total earth fault current (A), Rf = 0 ohm
Re
si
d
ua
l v
o
lt
ag
e
(%
)
Resonance, K = 1
0 10 20 30 40 50 60 70 80 90 100
0
10
20
30
40
50
60
70
80
90
100
Total earth fault current (A), Rf = 0 ohm
Re
si
d
ua
l v
o
lt
ag
e
(%
)
Over/Under-Compensated, K = 1.2/0.8
0 10 20 30 40 50 60 70 80 90 100
0
10
20
30
40
50
60
70
80
90
100
Total earth fault current (A), Rf = 0 ohm
Re
si
d
ua
l v
o
lt
ag
e
(%
)
Unearthed
Rf = 500 ohm
Rf = 2500 ohm
Rf = 5000 ohm
Rf = 10000 ohm
Figure 226: 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 larger than the absolute value of the capacitive reactance of the network.
Parallel resistor of the compensation coil is assumed to be disconnected.
0 10 20 30 40 50 60 70 80 90100
0
10
20
30
40
50
60
70
80
90
100
Total earth fault current (A), Rf = 0 ohm
R
es
id
ua
l v
ol
ta
ge
(%
)
Resonance, K = 1
0 10 20 30 40 50 60 70 80 90100
0
10
20
30
40
50
60
70
80
90
100
Total earth fault current (A), Rf = 0 ohm
R
es
id
ua
l v
ol
ta
ge
(%
)
Over/Under-Compensated, K = 1.2/0.8
0 10 20 30 40 50 60 70 80 90 100
0
10
20
30
40
50
60
70
80
90
100
Total earth fault current (A), Rf = 0 ohm
R
es
id
ua
l v
ol
ta
ge
(%
)
Unearthed
Rf = 500 ohm
Rf = 2500 ohm
Rf = 5000 ohm
Rf = 10000 ohm
Figure 227: 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 larger than the absolute value of the capacitive reactance of the network.
Parallel resistor of the compensation coil is assumed to be disconnected.
0 10 20 30 40 50 60 70 80 90 100
0
10
20
30
40
50
60
70
80
90
100
Total earth fault current (A), Rf = 0 ohm
R
es
id
ua
l v
ol
ta
ge
(%
)
Resonance, K = 1
0 10 20 30 40 50 60 70 80 90 100
0
10
20
30
40
50
60
70
80
90
100
Total earth fault current (A), Rf = 0 ohm
R
es
id
ua
l v
ol
ta
ge
(%
)
Over/Under-Compensated, K = 1.2/0.8
0 10 20 30 40 50 60 70 80 90100
0
10
20
30
40
50
60
70
80
90
100
Total earth fault current (A), Rf = 0 ohm
R
es
id
ua
l v
ol
ta
ge
(%
)
Unearthed
Rf = 500 ohm
Rf = 2500 ohm
Rf = 5000 ohm
Rf = 10000 ohm
Figure 228: 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 larger 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
Voltage start value setting must be set above the maximum healthy-
state Uo of 10%×Uph with a suitable margin.
1MRS757644 H
Protection functions
620 series
Technical Manual
449
