Siemens 7SJ85 - Page 635

Parameter Value Description
I
2
/I
rated, obj
The negative-sequence current is referred to the rated current of the
protected object. This is a preferred normalization for electrical machines,
because the permissible limiting values are indicated exclusively referred to
the machine rated current. You can also use this normalization for other
applications.
I
2
/I
1
The normalization of the negative-sequence system to the positive-
sequence system yields a higher sensitivity. Use this normalization when
detecting interruptions in the primary system.
Set the parameter depending on the application.
Parameter: Current limitation Imax, Maximum phase current
•
Default setting (_:2311:107) Current limitation Imax = no
•
Recommended setting value (_:2311:101) Maximum phase current = 10.0 A at 1 A
If the protection function needs a maximum current limitation, set the value of the Current limitation
Imax parameter from no to yes. With the parameter Maximum phase current, you set the upper limit of
the phase current. CT saturation will cause negative-sequence current in the secondary system. To avoid over-
function due to the CT saturation, a suitable phase-current limit value is 10 times of the rated protection-
object current.
Parameter: Release current
•
Recommended setting value (_:2311:104) Release current = 0.05 A at 1 A
For the safe calculation of negative-sequence currents, the current in at least one phase must be greater than
5 % of the secondary rated device current. For a 1-A device, the value of Release current is 0.05 A (0.25 A
for a 5-A device).
Protection and Automation Functions
6.17 Negative-Sequence Protection
SIPROTEC 5, Overcurrent Protection, Manual 635
C53000-G5040-C017-8, Edition 07.2017