ABB RELION REB500 Technical Manual page 108

Section 5
Bay protection functions
I
0
IEC19000445 V1 EN-US
Figure 41: Operating characteristic of the definite time over-current detector
Where the rated CT current I
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
should be:
I
GN
1.5
I
N
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.
102
I - Setting
I
I
N
Delay
differs from the rated current I
N1
= 800 A and I
GN
800 A
 
1.5 1.2
1000 A
1
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t
18000040-IEC19000445-1-en.vsdx
= 1000 A, the setting to pick up at 1.5 I
N1
1MRK 505 406-UEN B
of the protected unit,
GN
= 1200 A
GN
Bay protection functions REB500
Technical manual