Table of Contents
Advertisement
ABB Switzerland Ltd
+
Pr
PE
£
´
1.
n'
n
+
PB
n
: rated overcurrent factor (ALF = accuracy limit factor)
n'
: necessary effective overcurrent factor, as a function of
fault current IK, ( at nominal frequency and time constant of
the network)
PB
: connected burden at rated current
PE
: ct losses of secondary windings
Pr
: rated ct burden
I
: nominal current related to the protected object
N
and 2.
the dependence of the curves of fig 1, where:
for fault currents £ 3 * I
the exact boundary is at b*Ö3 (b = setting value of the characteristic).
n'
10
9
8
7
6
5
4
3
2
1
0
0
3
with 50% remanence
Figure 1:
Overcurrent factors
I
N
of
ct.
´
PE
I
N
the CT's should not saturate, respectively
N
4
6
without remanence
8
10
12
CH-ES 30-32.20 E
14
IK/ IN
3/3
Advertisement
Chapters
Table of Contents
