Table 12: 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 13: 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 15.
( )IP n IR Ires lmag= × + +
å
EQUATION1747 V1 EN-US (Equation 15)
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).
It should be remembered that the vectorial sum of the currents must be used (IEDs, Metrosil
and resistor currents are resistive). The current measurement is insensitive to DC component
1MRK 511 358-UEN A Section 6
Differential protection
89
Application manual
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