Standard inverse-time characteristics for undervoltage protection - Arc protection - Motor protection - Feeder protection - Back-up protection - Technical Manual - REX610 Protection and control - 1.2 - IEC - ANSI - 17.02.2023

REX610 Technical Manual

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:
Figure 1. Equation
image/svg+xml
t [s]Operate time in seconds
UMeasured voltage
U<Set value of the Start value setting
kSet value of the Time multiplier setting
Table 1. 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
Figure 2. : Inverse curve A characteristic of undervoltage protection
Figure 3. Inverse curve B characteristic of undervoltage protection