Ashida ADR141C - Inverse Time Curves Explained

NUMERICAL OC/EF PROTECTION RELAY ADR141C/241C
ASHIDA Electronics Pvt. Ltd.
Ref: Manual / ADR141C / 241C
Issue: 04D
Date : 10.07.2014
Page 8/86
the minimum guaranteed value of the operating current for all the curves with the inverse time
characteristic is 1.1Is (with a tolerance of ± 0.05Is).
4.2 Inverse Time Curves :-
The each stage thresholds for phase (earth) over current can be selected with an Inverse
Definite Minimum Time (IDMT) characteristic. The time delay is calculated with a
mathematical formula
where
t = operation time
a = constant
I = Input current
I
ref = Current threshold setting
b = Constant
K = Time multiplier setting or Time dial Setting
Curve Type Description a b
C1 Standard Inverse_1 0.14 0.02
C2 Standard Inverse_2 0.06 0.02
C3 Very Inverse 13.5 1
C4 Extremely inverse 80 2
C5 Long Time Inverse 120 1
C6 Define Time Inst 99.9 Sec
K * a
I
b
Iref
[ ]
- 1
t =