Calculation:
EQUATION1207 V2 EN-US
(Equation 16)
Select a setting of
U>Trip=200 V.
The current transformer saturation voltage must be at least twice the set operating voltage
U>Trip.
(
)
5
20 6.2 20 524
E P
V
>
+
×
=
EQUATION1208 V1 EN-US
(Equation 17)
that is, bigger than 2
ˣ
U>Trip
Check from the table of selected resistances the required series stabilizing resistor value to
use. As this application requires to be so sensitive select
SeriesResistor= 2000 ohm, which
gives an IED operating current of 100 mA.
Calculate the primary sensitivity at operating voltage using the following equation.
IP
approx
A
=
° +
° + ×
−
°
(
)
×
≤
−
2000
1
100 0
20 0
3
10
60
10
275
3
EQUATION1209 V2 EN-US
(Equation 18)
where
100 mA is the current drawn by the IED circuit and
10 mA
is the current drawn by each CT just at pickup
20 mA
is current drawn by metrosil at pickup
The magnetizing current is taken from the magnetizing curve for the current transformer
cores which should be available. The current value at
U>Trip is taken. For the voltage
dependent resistor current the peak value of voltage 200
ˣ
√2 is used. Then the RMS current is
calculated by dividing obtained current value from the metrosil curve with√2. Use the value
from the maximum metrosil curve given in Figure
It can clearly be seen that the sensitivity is not so much influenced by the selected voltage level
so a sufficient margin should be used. The selection of the stabilizing resistor and the level of
the magnetizing current (mostly dependent of the number of turns) are the most important
factors.
6.1.4.4
Tertiary reactor protection
M16850-118 v5
Reactive power equipment (for example shunt reactors and/or shunt capacitors) can be
connected to the tertiary winding of the power transformers. The 1Ph High impedance
differential protection function HZPDIF can be used to protect the tertiary reactor for phase
faults as well as earth faults if the power system of the tertiary winding is direct or low
impedance earthed.
1MRK 505 343-UEN B
Section 6
Differential protection
103
Application manual
Summary of Contents for Relion 670 series
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