Seg WI Series User Manual

The operating current should be in the rated CT current range. The WIC1 system
can be loaded continuously up to 2.5 times of the upper rated CT current. (See ╚═▷
“3.3.2.1 Current Ranges of the WIC1-CTs”.)
This has no e󰊞ect on the measurement of the overload. But due to the limitation of
the measurement to 20 times the upper rated CT current, the short-circuit protection
is limited.
•
Accuracy of current measurement:
•
For low current, the accuracy is better if »In,relative« (see ╚═▷ “11.1.3 Setting of the
Rated CT current In”) may be set to a higher value, which means a preference for
W3, especially if low protection thresholds are planned.
For high phase currents, however, and/or if DC o󰊞set signals are possible, the
accuracy is better if »In,relative« is low, which means a preference for W4,
especially with respect to CT saturation e󰊞ects and to reliability of inrush blocking.
•
Trip times:
•
Trip times, as measured for an initially switched o󰊞 WIC1, may be slightly faster for
a higher »In,relative« because collecting enough electrical energy for a trip pulse is
faster. This is especially true if a DiggiMEC is connected that also drains a little bit of
energy. This would be a preference for W3.
The calculated nominal current In = 92.4 A is settable in the WIC1, see ╚═▷ “11.1.3 Setting
of the Rated CT current In”.
• W3: 92.4 A = 2.887 ⋅ In
,min
,•
• W4: 92.4 A = 1.443 ⋅ In
,min
.•
We listed several criteria in favor of W3 and W4 above. Since these depend on the individual
preferences of the application it is not possible to give a general rule that meets all aspects.
From our experience we can conclude that most real-life applications should select a CT such
that »In,relative« is within the range In
,min
… 2.5⋅In
,min
. This would prefer the “higher” CT in
our example, i. e. W4, and the related setting »In,relative« = 1.443 ⋅ In
,min
. Of course, this
setting value cannot be set exactly with DIP or HEX switches, for these WIC1 variants the
best settable value is »In,relative« = 1.5 ⋅ In
,min
.
71WIC1WIC1-1.0-EN-MAN
3 Hardware
3.3.2.3 Selection of the CT Transformation Voltage Ratio

Seg WI Series Specifications

General

Brand	Seg
Model	WI Series
Category	Relays
Language	English