ABB Relion 620 Series Applications Manual page 80

Section 4
Requirements for measurement transformers
74
pickup current settings have to be defined so that the relay operates with the minimum fault
current and it does not trip with the maximum load current. The settings for all three stages
are as in the figure above.
For the application point of view, the suitable setting for instantaneous stage (50P-3) in this
example is 3 500 A (5.83 x I
by the current transformer selection formula is fulfilled and also the relay setting is
considerably below the F
selected much lower than 10 VA for economical reasons.
). For the CT characteristics point of view, the criteria given
2n
. In this application, the CT rated burden could have been
a
1MAC308145-MB E
RER620
Application Manual