ABB RELION 670 SERIES Applications Manual page 156

Section 7
Differential protection
150
in the unused taps, owing to auto-transformer action, voltages much
higher than design limits might be induced.
Basic data:
Current transformer ratio:
CT Class:
Secondary resistance:
Cable loop resistance:
Max fault current:
Calculation:
800
VR > × + =
(0.1 0.1) 8
20
EQUATION1768-ANSI V1 EN
TripPickup =30 V.
Select a setting of
The current transformer knee point voltage must be at least, twice the set operating voltage
(
VkneeANSI > +
2 0.1 100 0.7 147 V
EQUATION1779-ANSI V2 EN
TripPickup .
that is, greater than 2 ˣ
Check from the table of selected resistances the required series stabilizing resistor value
to use. Since this application requires good sensitivity, select R Series = 100 ohm, which
gives an IED current of 200 mA.
To calculate the sensitivity at operating voltage, refer to equation 23, which gives an
acceptable value, ignoring the current drawn by the non-linear resistor. A little lower
sensitivity could be selected by using a lower resistance value.
100
= × + ×
IP (200 2 30)
5
EQUATION1769-ANSI V1 EN
100/5 A (Note: Must be the same at all locations)
C200
0.1 Ohms (At 100/5 Tap)
<100 ft AWG10 (one way between the junction point and the farthest CT)
to be limited to approximately 0.1 Ohms at 75deg C
Note! Only one way as the tertiary power system grounding is limiting the
ground-fault current. If high ground-fault current exists use two way cable
length.
The maximum through fault current is limited by the reactor reactance and
the inrush will be the worst for a reactor for example, 800 A.
)
× × =
£
approx .5.2 A
1MRK 506 369-UUS -
(Equation 21)
TripPickup .
(Equation 22)
(Equation 23)
Line distance protection REL670 2.2 ANSI
Application manual