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
(
)
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
in fault current to allow the use of only the AC components of the fault current in the above
calculations.
The voltage dependent resistor (Metrosil) characteristic is shown in Figure
Series resistor thermal capacity
SEMOD54734-336 v6
The series resistor is dimensioned for 200 W. Preferable the
U>Trip
2
/SeriesResistor should
always be lower than 200 W to allow continuous activation during testing. If this value is
exceeded, testing should be done with a transient faults.
1MRK 505 343-UEN B
Section 6
Differential protection
97
Application manual
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