Thytronic DMC3S - Appendix; Dmc3 S - Inverse Time Curves

98
DMC3S - Manual - 08 - 2021
7 APPENDIX
— DMC3S - INVERSE TIME CURVES
General formula
The general formula, pursuant to IEC 60255-3/BS142, is:
[1]
Where:
• t = operating time (in seconds).
• t
>inv
= operating time regulation (in seconds).
• I = measured current.
• I>
inv
= trip threshold regulation.
Constant α
• α = 0.02 for the IEC type A normal inverse curve.
• α = 1 for the IEC type B very inverse curve.
• α = 1 for the IEC type LTI long time inverse curve.
• α = 2 for the IEC type C extremely inverse curve.
Coefficient K
• K = 0.14 for the IEC type A normal inverse curve
• K = 13.5 for the IEC type B very inverse curve.
• K = 120 for the IEC type LTI long time inverse curve.
• K = 80 for the IEC type C extremely inverse curve.
The following applies to all inverse time characteristics:
• The asymptotic reference value (minimum trip current ) is 1.1 time the set threshold.
• The minimum operating time is 0.1 s.
• The characteristics are defined between 1.1 and 20 times the set threshold
[2][3]
For all the following thresholds, with exception of the threshold relating to protections 59 and 59 N,
[4]
normalised IEC type A, B, B-LI and C curves can be set.
Protection Functions Thresholds Operating time
46
I2> DEFINITE/INVERSE
I2>> DEFINITE/INVERSE
50/51
I> DEFINITE/INVERSE
I>> DEFINITE/INVERSE
I>>>> DEFINITE/INVERSE
50N/51N IE> DEFINITE/INVERSE
51N(E) INe> DEFINITE/INVERSE
51N(Eme) IEeme> DEFINITE/INVERSE
51(SQL) ISQL> DEFINITE/INVERSE
59 U> DEFINITE/INVERSE
59N UE> DEFINITE/INVERSE
59N(Eme) UEeme> DEFINITE/INVERSE
67
IPD> DEFINITE/INVERSE
IPD>> DEFINITE/INVERSE
IPD>>>> DEFINITE/INVERSE
67N
IED> DEFINITE/INVERSE
IED>>a DEFINITE/INVERSE
Note 1 The formula uses the symbols relating to the overcurrent function. The full description of the symbols used in the inverse time curves for protec-
tions 50/51 and 50N/51N are given in 4.4 PROTECTION FUNCTIONS
Note 2 When the threshold regulation exceeds 2.5 In for protection 50/51 and 0.5 IEn for protection 50N/51N, the upper limit of the measurement range
is limited to 30 In and 10 IEn respectively
Note 3 when the threshold regulation exceeds 20 times the threshold, the operating time is limited to the value corresponding to 20 times the threshold
Note 4 The trip characteristic is given in the paragraph describing the operation of the system (Chapter 4)
t =
t>
inv
·
[(I/I>
inv
)
α
-1]
K