ABB 615 Series - IDMT Curves for Undervoltage Protection

11.3.2 IDMT curves for undervoltage protection
In the inverse-time modes, the trip time depends on the momentary value of the voltage,
the lower the voltage, the faster the trip time. The trip time calculation or integration starts
immediately when the voltage goes below the set value of the Pickup value setting and the
PICKUP output is activated.
The TRIP output of the component is activated when the cumulative sum of the integrator
calculating the undervoltage situation exceeds the value set by the inverse-time mode. The
set value depends on the selected curve type and the setting values used. The user
determines the curve scaling with the Time multiplier setting.
The Minimum trip time setting defines the minimum trip 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 trip times for the standard undervoltage IDMT curves are defined with the
coefficients A, B, C, D and E.
The inverse trip time can be calculated with the formula:
t s
k A
B
V V
V
C
D
E






=
⋅
×
<
<
−






+
-
GUID-4A433D56-D7FB-412E-B1AB-7FD43051EE79-ANSI V2 EN (Equation 181)
t [s]
trip time in seconds
V measured voltage
V< the set value of the Pickup value setting
k the set value of the Time multiplier setting
Table 947: 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
1MAC059074-MB A Section 11
General function block features
615 series ANSI 1119
Technical Manual