The
Minimum operate time setting defines the minimum operate time possible for
the IDMT mode. For setting a value for this parameter, the user should carefully
study the particular IDMT curve.
11.3.2.1
Standard inverse-time characteristics for undervoltage protection
The operate times for the standard undervoltage IDMT curves are defined with the
coefficients A, B, C, D and E.
The inverse operate time can be calculated with the formula:
t s
k A
B
U
U
U
C
D
E
=
⋅
× < −
<
−
+
(Equation 401)
t [s]
Operate time in seconds
U
Measured voltage
U<
Set value of the
Start value
setting
k
Set value of the
Time multiplier
setting
Table 1655: Curve coefficients for standard undervoltage IDMT curves
Curve name
A
B
C
D
E
(21) Inverse
Curve A
1
1
0
0
1
(22) Inverse
Curve B
480
32
0.5
0.055
2
1MRS759142 F
General function block features
REX640
Technical Manual
1903