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Protection and Automation Functions
6.15 Sensitive Ground-Fault Detection
To prevent minor current fluctuations from leading to a maloperation of the function, the setting of the 3I0
delta pulse off-on parameter cannot be less than 5 %.
The setting of the 3I0 delta pulse off-on parameter can be calculated with the following formula:
[fo_3I0_delta_pulse_off-on, 1, en_US]
Where
K
f
C
s
ω
L
C
0Σ
C
0i
EXAMPLE
K
f
C
s
ω
L
C
0Σ
C
0i
Then the setting of the 3I0 delta pulse off-on parameter is calculated as follows:
[fo_delta calculate, 1, en_US]
If the network information for the setting calculation is not available, Siemens recommends using the default
setting of 10 %.
Parameter: No. of pulses for operate, Monitoring time(in pulses)
•
Default setting (_:107) No. of pulses for operate = 3
•
Default setting (_:108) Monitoring time(in pulses) = 5
With the No. of pulses for operate parameter, you determine the number of pulses to be detected
within the pulse monitoring time, so that the stage operates.
With the Monitoring time(in pulses) parameter, you define the pulse monitoring time, which is calcu-
lated via the following formula:
Pulse monitoring time = Value Monitoring time(in pulses) ⋅ (Value Pulse-on duration + Value
Pulse-off duration)
626
Safety factor
Siemens recommends applying the factor 0.6 to also detect high-impedance ground faults.
Capacitance of the switched capacitor
Angular frequency, which equals to 2πf, where f is the power frequency
Inductance of the arc-suppression coil
Zero-sequence capacitance of the whole network
Zero-sequence capacitance of the protected feeder
0.6
1.1 ⋅ 10
-6
F
314 rad/s
0.577 H
5.4297 ⋅ 10
-6
F
1.5502 ⋅ 10
-6
F
SIPROTEC 5, Overcurrent Protection, Manual
C53000-G5040-C017-8, Edition 07.2017
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