Siemens SIPROTEC 7SS60, Manual

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Functions
5-11
7SS60 Manual
E50417-G1176-C132-A2
Normal earth
current sensitivity In a connection circuit as shown in Figure 5-10, the sensitivity to the earth current is
less pronounced than in the circuit shown in Figure 5-6. It should be considered for
power systems with low-resistant or solid earthing of the starpoints where due to the
transformer design sufficiently high short-circuit currents can be expected in case of
1-phase earth faults.
Figure 5-10 Connection circuit of the summation current transformer for normal earth
short-circuit sensitivity
The effective number of turns in the winding and fault detection ranges are listed in the
following table.
Figure 5-11 Summation transformer currents in a 1-pole earth fault in a power system with earthing only on the consumer
side; connection as per 5-10
Short-circuit Affected phases Effective number
of turns
Fault detection
range
Multiple of I
N
3-phase L1–L2–L3
√
3 0.20 to 2.50
2-phase L1–L2
L2–L3
L3–L1 1
2
1 0.35 to 4.33
0.18 to 2.17
0.35 to 4.33
1-phase L1–E
L2–E
L3–E 2
1
3 0.18 to 2.17
0.35 to 4.33
0.12 to 0.72
more
devices