ABB Relion 650 Series Applications Manual page 73

1MRK 505 287-UUS B
Basic data:
Rated knee
point Ek
Cable loop
resistance:
Max fault
current:
Calculation:
Select a setting of
V.
The rated knee point Ek of the current transformer shall fulfill the following conditions:
>
E 0, 8 2
k
The requested conditions are fulfilled because Ek = 300 V.
Check from the table of selected resistances the required series stabilizing resistor value to use.
Since this application it is not required to be so sensitive, select
IED current of 400 mA.
To calculate the sensitivity at operating voltage, refer to equation
value; in fact in this example the sensitivity is about 13% of the nominal current of the CT:
Busbar protection REB650
Application manual
300 V
Note! Only one way as the system grounding is limiting the
ground-fault current. If high ground-fault current exists use two
way cable.
One way as the system earthing is limiting the
earth-fault current. If the neutral solidly
grounded, then a high-earth- fault current
exists, and a two way cable is considered for
the loop
Loop lenght: <50 m; cross section of the cable: 2.5 mm2 (one
W ×
r
=
0, 021
Cu
way)
l
=
r ×
=
R 0, 021
sec
A
= =
R R 0,42
loop sec
The maximum through fault current given by the transformer
reactance for example, 28 kA.
TripPickup =60
× × = × =
U 1, 6 82, 9 132, 64
R
© Copyright 2013 ABB. All rights reserved
2
mm
°
at 75 C
m
50
× W °
=0,42 at 75 C
2, 5
W
(
> × >
V 2 U TripPickup
E k
Differential protection
)
= × =
2 100 200 V
R series =150 ohm, which gives an
10 which gives an acceptable
Section 6
67