ABB Relion 670 Series Applications Manual page 121

1MRK 511 358-UUS A
Setting example
Basic data:
Current transformer ratio:
CT Class:
Secondary resistance:
Cable loop resistance:
Max fault current:
Calculation:
>
VR
EQUATION1751-ANSI V1 EN-US
Select a setting of
The current transformer saturation voltage must be at least twice the set operating voltage
TripPickup .
VkneeANSI
EQUATION1752-ANSI V1 EN-US
that is, bigger than 2 ˣ
Check from the table of selected resistances the required series stabilizing resistor value to use.
As this application requires to be so sensitive select
operating current of 200 mA.
Calculate the primary sensitivity at operating voltage using the following equation.
2000
=
IP
EQUATION1887-ANSI V1 EN-US
where
100 mA is the current drawn by the IED circuit and
10 mA
20 mA
Application manual
It is strongly recommended to use the highest tap of the CT whenever high
impedance protection is used. This helps in utilizing maximum CT capability,
minimize the secondary fault current, thereby reducing the stability voltage limit.
Another factor is that during internal faults, the voltage developed across the
selected tap is limited by the non-linear resistor but in the unused taps, owing to
auto-transformer action, voltages induced may be much higher than design limits.
2000/5A
C800 (At max tap of 2000/5A)
0.5 Ohm (2000/5A tap)
2
Equal to switchgear rated fault current 40 kA
40000
( )
× + =
0.5 0.4 90 V
400
TripPickup =100 V.
> + × =
(0.5 8) 100 * 0.7 595 V
TripPickup
(
° + × - ° ×
200 0 3 50 60
5
is the current drawn by each CT just at pickup
is current drawn by metrosil at pickup
R Series = 500 ohm, which gives an IED
)
- £
3
10 approx .100 A
Section 6
Differential protection
(Equation 16)
(Equation 17)
(Equation 18)
115