TB XRI1-IE 11.01 E
11
4.4
Requirements on the main
current transformers
The current transformers have to be rated in such a
way, that a saturation should not occur within the fol-
lowing operating current ranges:
Independent time overcurrent function: K1 = 2
Inverse time overcurrent function:
K1 = 20
High-set function:
K1 = 1.2 - 1.5
K1 = Current factor related to set value, at which the
C.T. is not yet saturated
Moreover, the current transformers have to be rated
according to the maximum expected short circuit cur-
rent in the network or in the protected objects.
The low power consumption in the current circuit of
XRI1-IE
, namely <0.2 VA, has a positive effect on the
selection of current transformers. It implies that, if an
electromechanical relay is replaced by
XRI1-IE
, a
high accuracy limit factor is automatically obtained by
using the same current transformer.