REG 316*4 1MRB520049-Uen / Rev. F ABB Switzerland Ltd
3-63
Compensating any difference between the rated currents of c.t.
I
N1
and protected unit I
GN
is recommended. This is achieved with
the aid of the reference value of the A/D channel or by correcting
the overcurrent setting.
For example, for I
GN
= 800 A and I
N1
= 1000 A, the setting for a
pick-up current of 1.5 I
GN
= 1200 A would have to be
2.1
A1000
A800
5.1
I
I
5.1
1N
GN
==
CurrentInp
An interposing c.t. in the input is essential for current settings
lower than < 0.2 I
N
.
Delay
The delay is used to achieve discrimination of the overcurrent
function. It is set according to the grading table for all the over-
current units on the power system. The zone of protection of our
overcurrent function extends to the location of the next down-
stream overcurrent relay.
Should the downstream relay fail to clear a fault, the overcurrent
function trips slightly later as a back-up protection.
Setting MaxMin
This parameter enables the following operating modes to be
selected:
· MIN (3ph): Pick-up when the highest phase current also
falls below the setting. This setting is not per-
mitted for single-phase measurement.
· MIN (1ph): Pick-up when the lowest phase current falls
below the setting.
· MAX (3ph): Pick-up when the lowest phase current also
exceeds the setting. This setting is not permit-
ted for single-phase measurement.
· MAX (1ph): Pick-up when the highest phase current ex-
ceeds the setting.
· MAX-Inrush: Blocking of inrush currents when a phase
current exceeds the setting.
To Next Page
Loading...
