Minimum ohms can be difficult to adjust due to the small value
compared to the total value.
Normally the voltage can be increased to higher values than the calculated
minimum U>Trip with a minor change of total operating values as long as this is
done by adjusting the resistor to a higher value. Check the sensitivity calculation
below for reference.
Table 10: 1 A channels: input with minimum operating down to 40 mA
Operating
voltage
U>Trip
Stabilizing
resistor R
ohms
Operating
current level
1 A
Stabilizing
resistor R
ohms
Operating
current level
1 A
20 V
500 0.040 A -- --
40 V 1000 0.040 A -- --
60 V 1500 0.040 A 600 0.100 A
80 V 2000 0.040 A 800 0.100 A
100 V 2500 0.040 A 1000 0.100 A
150 V 3750 0.040 A 1500 0.100 A
200 V 5000 0.040 A 2000 0.100 A
Table 11: 5 A channels: input with minimum operating down to 100 mA
Operating
voltage
U>Trip
Stabilizing
resistor R1
ohms
Operating
current level
5 A
Stabilizing
resistor R1
ohms
Operating
current level
5 A
Stabilizing
resistor R1
ohms
Operating
current level
5 A
20 V
200 0.100 A 100 0.200 A -- --
40 V 400 0.100 A 200 0.200 A 100 0.400
60 V 600 0.100 A 300 0.200 A 150 0.400 A
80 V 800 0.100 A 400 0.200 A 200 0.400 A
100 V 1000 0.100 A 500 0.200 A 250 0.400 A
150 V 1500 0.100 A 750 0.200 A 375 0.400 A
200 V 2000 0.100 A 1000 0.200 A 500 0.400 A
The current transformer saturation voltage must be at least 2 ˣ U>Trip to have
sufficient operating margin. This must be checked after calculation of U>Trip.
When the R value has been selected and the U>Trip value has been set, the
sensitivity of the scheme IP can be calculated. The IED sensitivity is decided by
the total current in the circuit according to equation
12.
( )IP n IR Ires lmag= × + +
å
EQUATION1747 V1 EN-US (Equation 12)
1MRK 505 388-UEN B Section 6
Differential protection
Busbar protection REB650 2.2 IEC 77
Application manual
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