ABB RELION REX640 - 11.3.2.1 Standard inverse-time characteristics for undervoltage protection

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