Protection And Reset Curves - DEMA 400 Series User Manual

switched on and off separately. For example, when the Phase Overcurrent protection is
selected, it appears to have 3 thresholds for the corresponding protection. Phase overcurrent
protection for these thresholds separately can be activated by assigning protection settings. On
the screen below, somon colored cell shows the selected treshold. By pressing the button
'Change Threshold' in the device you can choose the thresholds.
4-22 Illustration of protection thresholds
4.3.1

Protection and Reset Curves

DEMA 400 Series Digital Protection Relays can employ and run IEC and IEEE / ANSI
protection and reset curves, as well as a wide range of special curves that are mostly used
when 400 Series units are used in the same selectivity scheme with older models of protection
relays such as electromechanical relays. The wide setting ranges make 400 Series compatible
with most of the protection and selectivity schemes currently in use worldwide.
400 Series protection and reset curves, and formulas, parameters and setting ranges belonging
to these are given in the below table. The Thermal Overload Protection Function is studied in
detail in its dedicated section - for this, parameters and other information for thermal
overcurrent protection is not given in the table.
A
t= [ +B] ×TMS
I
a
-1
( )
I
s
Universal Formula for Protection Curves
42