IP approx A= ° + ° + × − °
( )
× ≤
−
2000
1
100 0 20 0 3 10 60 10 275
3
EQUATION1209 V2 EN-US (Equation 15)
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
37
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.
Section 6 1MRK 505 388-UEN B
Differential protection
86 Busbar protection REB650 2.2 IEC
Application manual
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