ABB RELION REB500 Technical Manual page 103

1MRK 505 406-UEN B
I > I of the protected unit: the protection permits maxi-mum utilization of the thermal
B1 N
capability of the protected unit
For example,
• Load current of protected unit I
• CT rated current I
I
N2
• Relay rated current I
Relay reference current I

I
B
An alternative is to adjust the characteristic to match the rated load of the protected unit and
set the reference current to its rated current instead of its load current.
Enabling the characteristic IStart
The characteristic is enabled when the current exceeds the setting
IStart is 1.1 I
Choice of characteristic c-Setting
The constant
standard characteristics according to BS 142 are:
normal inverse:
very inverse and long time earth
fault:
extremely inverse:
I
I Start
I B
IEC19000444 V1 EN-US
Figure 40: Operating characteristic of the inverse time overcurrent function
Bay protection functions REB500
Technical manual
= 1000 A
N1
= 5 A
= 5 A
N
-Setting:
B
I 5

N 2
I 800 A
B 1
I 1000
N 1
.
B
c-Setting determines the shape of the characteristic. The settings for the
t =
t
min
18000039-IEC19000444-1-en.vsdx
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= 800 A
B1
A

4 A
A
c = 0.02
c = 1.00
c = 2.00
k1
c
I
1
I B
t
Bay protection functions
Setting:
I 4 A
 
B
0.8
I 5 A
N
IStart . A typical setting for
Section 5
97