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4.3.1.3
ANSI / IEEE Inverse Time Protection Curves
"IEEE (The Institute of Electrical and Electronics Engineers, Inc.) C37.112-2006: IEEE
Standard Inverse-Time Characteristic Equations for Overcurrent Relays - Description"
standard describes the protection curves named as below.
1. IEEE MI: IEEE Moderately Inverse Curve.
2. IEEE VI: IEEE Very Inverse Curve.
3. IEEE EI: IEEE Extremely Inverse Curve.
Universal trip time delay formula is given above, while ANSI / IEEE constants for various
curves are given on the below table.
t Trip delay (s).
A A constant for the characteristic (s).
I Momentary current (A).
Is Set current threshold (A).
α A constant for the characteristic (-).
B A constant for the characteristic (s).
TMS Time Multiplier Setting (-).
Curve Type
ANSI / IEEE MI
Moderately Inverse
ANSI / IEEE VI
Very Inverse
ANSI / IEEE EI
Extremely Inverse
A
t= [
+B] ×TMS
I
a
-1
(
)
I
s
Tripping Time Formula
0.0515 s
t= [
+ 0.114 ��] ×TMS
I
0.02
-1
(
)
I
s
16.91 s
t= [
+ 0.491 ��] ×TMS
I
2
-1
(
)
I
s
28.2 s
t= [
+ 0.1217 ��] ×TMS
I
2
-1
(
)
I
s
47
Reset Time Setting Range
DMT (0.04 - 100) s
or
RTMS (0.025 - 3.2)
DMT (0.04 - 100) s
or
RTMS (0.025 - 3.2)
DMT (0.04 - 100) s
or
RTMS (0.025 - 3.2)
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