ABB RELION REB500 Technical Manual page 114

Section 5
Bay protection functions
An alternative is to adjust the position of the characteristic to match the rated load of the
protected unit and set the base 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
The settings for the standard characteristics according to BS 142 are:
normal inverse:
very inverse and long time
earth fault:
extremely inverse:
I
I Start
I B
IEC19000447 V1 EN-US
Figure 43: Operating characteristic of the directional overcurrent inverse time function
Multiplier k
The multiplier
shifted. This is used for grading a series of relays along a line to achieve discrimination.
For example, in the case of the
13.5. The operating time t is given by the equation:

t
108
.
B
c-Setting determines the shape of the characteristic.
c = 0.02
c = 1.00
c = 2.00
t
min
-Setting
1
k1-Setting enables the directional overcurrent inverse time characteristic to be
k
1
 
I

  1
 
I
B
© Copyright 2019 ABB. All rights reserved
k1
t =
c
I
1
I B
t
18000042-IEC19000447-1-en.vsdx
very inverse characteristic, the constant c = 1 and the factor k
1MRK 505 406-UEN B
IStart . A typical setting for
Bay protection functions REB500
Technical manual
≤
1