I
0
t
I
I
N
I - Setting
Delay
18000040-IEC19000445-1-en.vsdx
IEC19000445 V1 EN-US
Figure 41: Operating characteristic of the definite time over-current detector
Where the rated CT current I
N1
differs from the rated current I
GN
of the protected unit,
compensating the measurement to achieve a match is recommended. This is done by
correcting either the reference value of the A/D input or the setting.
For example, assuming I
GN
= 800 A and I
N1
= 1000 A, the setting to pick up at 1.5 I
GN
= 1200 A
should be:
1
800
1.5
1.5
1.2
1000
GN
N
I
A
I
A
Characteristic angle
Determining the phase-angle of the current provides an additional criterion for preserving
discrimination compared with non-directional overcurrent protection. The directional
sensitivity is ±180° in relation to the reference voltage. This is illustrated in the following
diagram.
Section 5
1MRK 505 406-UEN B
Bay protection functions
102
Bay protection functions REB500
Technical manual
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