ABB Relion 620 Series - Page 1172

that the protection relay operates with the minimum fault current and it does not
operate with the maximum load current. The settings for all three stages are as in
Figure 625 .
For the application point of view, the suitable setting for instantaneous stage
(I>>>) in this example is 3 500 A (5.83 × I
2n
). I
2n
is the 1.2 multiple with nominal
primary current of the CT. For the CT characteristics point of view, the criteria given
by the current transformer selection formula is fulfilled and also the protection relay
setting is considerably below the F
a
. In this application, the CT rated burden could
have been selected much lower than 10 VA for economical reasons.
Requirements for measurement
transformers
1MRS757644 H
1172 620 series
Technical Manual