sepam 20 user manual - Schneider Electric

3
Protection functions General
Tripping curves
Presentation of tripping curve operation and
settings for protection functions using:
b definite time
b IDMT
b timer hold.
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MT10911
DE50666
Definite time protection
The tripping time is constant. The time delay is started when the set point is overrun.
t
T
Definite time protection principle.
IDMT protection
The operation time depends on the protected value (phase current, earth fault
current, etc.) in accordance with standards IEC 60255-3, BS 142 and IEEE C-37112.
Operation is represented by a characteristic curve, e.g.:
b t = f(I) curve for the phase overcurrent function
b t = f(I0) curve for the earth fault function.
The rest of the document is based on t = f(I); the reasoning may be extended to other
variables I0, etc.
The curve is defined by:
b its type (standard inverse, very inverse, extremely inverse, etc.)
b current setting Is which corresponds to the vertical asymptote of the curve
b time delay T which corresponds to the operation time for I = 10 Is.
These 3 settings are made chronologically in the following order: type, Is current,
time delay T.
Changing the time delay T setting by x % changes all of the operation times in the
curve by x %.
t
T
Is
type 1
type 1,2
1 1,2 10 20 I/Is
IDMT protection principle.
The tripping time for I/Is values less than 1.2 depends on
the type of curve selected.
I
Name of curve Type
Standard inverse time (SIT) 1, 2
Very inverse time (VIT or LTI) 1, 2
Extremely inverse time (EIT) 1, 2
Ultra inverse time (UIT) 1, 2
RI curve 1
IEC inverse time SIT / A 1
IEC very inverse time VIT or LTI / B 1
IEC extremely inverse time EIT / C 1
IEEE moderately inverse (IEC / D) 1
IEEE very inverse (IEC / E) 1
IEEE extremely inverse (IEC / F) 1
IAC inverse 1
IAC very inverse 1
IAC extremely inverse 1
b when the monitored value is more than 20 times the set point, the tripping time is
limited to the value corresponding to 20 times the set point.
b if the monitored value exceeds the measurement capacity of Sepam (40 In for the
phase current channels, 20 In0 for the residual current channels), the tripping time is
limited to the value corresponding to the largest measurable value (40 In or 20 In0).
PCRED301005EN - 06/2008