Section 4 1MAC308145-MB E
Requirements for measurement transformers
74 RER620
Application Manual
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
2n
). For the CT characteristics point of view, the criteria given
by the current transformer selection formula is fulfilled and also the 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.
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