ABB RELION REB500 Technical Manual page 115

1MRK 505 406-UEN B
Assuming a grading time of 0.5 s at 6 times the base current I
each of the relays is given by,
k = 5 t
1
For operating times between 0.5 and 2.5 s, this results in the following settings for k
t [s]
0.5
1
1.5
2
2,5
The characteristics according to BS 142 are set as follows:
normal inverse:
very inverse:
extremely inverse:
long time earth fault:
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.
Bay protection functions REB500
Technical manual
k [s]
1
2.5
5
7.5
10
12.5
k = 0.14 s
1
k = 13.5 s
1
k = 80 s
1
k = 120 s
1
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Bay protection functions
is required, the factor k
B
1
Section 5
for
1
:
109