(1)
1-phase earth fault
(2)
2-phase short circuit
The standardization is based on the transformer rated object current (Reference value = rated current).
If the pickup value on the HV side is 12 % (46-n Setting = 0.12) of the transformer rated current, this corre-
sponds to 0.1 A on the secondary side. With this the following currents and sensitivities are reached.
1-phase short circuit
[fo_function46ShortCircuit1-phase, 1, en_US]
Sensitivity
[fo_function46ShortCircuit1-phaseSensitivity, 1, en_US]
2-phase short circuit
[fo_function46ShortCircuit2-phase, 1, en_US]
Sensitivity
[fo_function46ShortCircuit2-phaseSensitivity, 1, en_US]
Since this is the short circuit on the low-voltage side, the time delay must be coordinated with the times of
subordinate protection devices.
Line or Cable Networks
In line or cable networks, the function Negative-sequence protection is used to detect weak current caused by
unbalanced faults. In the unbalanced fault, the pickup values of the overcurrent protection is not reached.
The current is based on the rated object current (Reference value = rated current).
Therefore:
The 2-phase short circuit with the current I leads to a negative-sequence current:
[fo_function46ShortCircuit-2phaseLineNetwork, 1, en_US]
The 1-phase short circuit with the current I leads to a negative-sequence current:
[fo_function46ShortCircuit-1phaseLineNetwork, 1, en_US]
If the protection works exclusively with short circuits, the protection must be set via the value for 2-phase
operation. Then a 2-phase short circuit can be assumed with more than 60 % of the rated object current. Set
the standardization on the rated object current. To avoid over-function with overload, Siemens recommends a
pickup value of approximately 65 %. Coordinate the time delays with the network grading for phase short
circuits.
Protection and Automation Functions
5.7 46 Negative-Sequence Overcurrent Protection
Reyrolle 7SR5, Transformer Protection Device, Device Manual
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C53000-G7040-C015-1, Edition 11.2019
