sepam 20 user manual - Schneider Electric

3
DE51629
DE51630
DE50755
Protection functions General
Tripping curves
Example.
Detection of restriking faults with adjustable timer hold.
Timer hold dependent on current I. Constant timer hold.
3/38
Setting of IDMT tripping curves, time delay T or TMS factor
The time delays of current IDMT tripping curves (except for customized and RI
curves) may be set as follows:
b time T, operating time at 10 x Is
b TMS factor, factor shown as T/β in the equations on the left.
13.5
Example: tI () --------------
T
= × TMS where TMS = ------- .
I
---- – 1
1.5
Is
The IEC curve of the VIT type is positioned so as to be the same with
TMS = 1 or T = 1.5 s.
Timer hold
The adjustable timer hold T1 is used for:
b detection of restriking faults (DT curve)
b coordination with electromechanical relays (IDMT curve).
b Timer hold may be inhibited if necessary.
Equation for IDMT timer hold curve
T1
Equation: t where .
r
() I
1 ⎛ I
---- ⎞
⎝Is⎠ T1 = timer hold setting (timer hold for I reset = 0 and TMS = 1)
T = tripping time delay setting (at 10 Is)
b = basic tripping curve value at .
2
----------------------
–
T T
= × -- -- = T M S
β β
k
10 α -----------------
– 1
DE50754
PCRED301005EN - 06/2008