Seg WIC1-W3 - Page 42

SEG Electronics GmbH Technical Manual WIC1
42 DOK-TD-WIC1E, Rev. M
Estimation of the tripping time at inverse characteristics
The setting and estimation by the use of an inverse characteristic will be explained at the following example.
Boundary condition:
Operating current of the load (IS) 72A
Selected CT ratio WIC1-W3, 32 A – 112 A
Characteristic Normal Inverse N-INV
Starting point of the characteristic I> x IS
Over current (I>): 1.4
Factor „a“ (tI>) 0.2
Short current (I>>) 1 kA
Delay time for I>> 100 ms
Primary test current value 150 A
Setting of the WIC1:
I
S
= 72 A
I> = 1.4
„a“ (tI>) = 0.2
I>> = 14 (1kA/72A = 13.88)
tI>> = 0.1s
Estimation of the tripping time from the characteristic curve
Starting point of the curve = 1.4 x 72 A = 100.8 A, this correspond to = 1 x I/I
S
x I>.
Primary testing current = 150 A, here for a factor as follows is calculated I/IS x I> = 150 A/100.8 A = 1.488
*Multiples of pick up setting =
*Multiples of pick up setting = Is * I>
From the curve a tripping time of 3.5s is estimated.
1 2 3 4 5 6 7 8 910 20
Multiples of pick up setting *
0.1
1
10
100
1000
t[s]
a =
0.05
0.1
0.2
0.3
0.4
0.5
0.6
0.8
1.0
10.0
1.4
2.0
3.0
4.0
6.0
8.0
1.488
3.5