ABB REC670 Applications Manual page 134

Section 7
Differential protection
128
Table 17: 1 A channels: input with minimum operating down to 40 mA
Operating Stabilizing
voltage resistor R
U>Trip
ohms
20 V 500
40 V 1000
60 V 1500
80 V 2000
100 V 2500
150 V 3750
200 V 5000
Table 18: 5 A channels: input with minimum operating down to 100 mA
Operating Stabilizing
voltage resistor R1
U>Trip ohms
20 V 200
40 V 400
60 V 600
80 V 800
100 V 1000
150 V 1500
200 V 2000
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 14.
å
= × + +
IP n IR ( Ires
EQUATION1747 V1 EN-US
where:
n is the CT ratio
IP primary current at IED pickup,
IR IED pickup current (U>Trip/SeriesResistor)
Ires is the current through the voltage limiter and
ΣImag is the sum of the magnetizing currents from all CTs in the circuit (for example, 4 for
restricted earth fault protection, 2 for reactor differential protection, 3-5 for autotransformer
differential protection).
Operating Stabilizing
current level resistor R
1 A ohms
0.040 A --
0.040 A --
0.040 A 600
0.040 A 800
0.040 A 1000
0.040 A 1500
0.040 A 2000
Operating Stabilizing
current level resistor R1
5 A ohms
0.100 A 100
0.100 A 200
0.100 A 300
0.100 A 400
0.100 A 500
0.100 A 750
0.100 A 1000
lmag )
1MRK 511 401-UEN A
Operating
current level
1 A
--
--
0.100 A
0.100 A
0.100 A
0.100 A
0.100 A
Operating Stabilizing
current level resistor R1
5 A ohms
0.200 A --
0.200 A 100
0.200 A 150
0.200 A 200
0.200 A 250
0.200 A 375
0.200 A 500
(Equation 14)
Bay control REC670 2.2 IEC
Application manual
Operating
current level
5 A
--
0.400
0.400 A
0.400 A
0.400 A
0.400 A
0.400 A