180000064-IEC19000469-1-en.vsdx
t
I
I
Start
I
B
t =
k1
I
I
B
c
1
tmin
IEC19000469 V1 EN-US
Figure 65: Tripping characteristic of Inverse time earth fault overcurrent protection
The
c-Setting can also be set to RXIDG, in which case the functions inverse characteristic
corresponds to that of the relay Type RXIDG:
[ ]
5.8 1.35
(
)
B
t s
Ln I I
The parameter
k1-Setting has no influence in this case.
Multiplier k1-Setting
The multiplier
k1-Setting enables the earth fault overcurrent inverse time characteristic to be
shifted. This is used for grading a series of relays along a line to achieve discrimination.
For example, in the case of the very inverse characteristic, the constant c = 1 and the factor k
1
≤
13.5. The operating time t is given by the equation:
1
0
3
1
B
k
t
I
I
Assuming a grading time of 0.5 s at 6 times the base current I
B
is required, the factor k
1
for
each of the relays is given by:
k
1
= 5 t
For operating times between 0.5 and 2.5 s, this results in the following settings for k
1
:
1MRK 505 406-UEN B
Section 5
Bay protection functions
Bay protection functions REB500
171
Technical manual
© Copyright 2019 ABB. All rights reserved