ISA T1000 PLUS User Manual page 40

DOC. MIE91093 Rev. 1.34 Page 40 of 145
Characteristic Angle
MTA
Operating zone
Non Operating zone
Limits between operating and a non operating zone are at
around +115° and +285°. This limits can be found with an
angle search, starting from the non operating zone (I =
R
180°) towards the operative zone, until the relay trips. Prior to
this, we have to make sure that the relay operates.
Also, the earth directional relay shouldn't trip for all values of
voltage and current. It is widely accepted that a directional
relay characteristic can run inside the dotted line area, as
shown in the figure.