ABB RER615 - Page 823

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 86)
t [s] operate time in seconds
U measured voltage
U< the set value of the Start value setting
k the set value of the Time multiplier setting
Table 731: 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
1MRS758755 C General function block features
REC615 & RER615
Technical Manual
823