• For some special line protection applications, this dedicated IED CT
input can be connected to a parallel connection of current transformers in
all three phases (Holm-Green connection).
2. calculated from three phase current input within the IED (when the fourth
analog input into the pre-processing block, connected to EF4PTOC function
analog input I3PPOL, is NOT connected to a dedicated CT input of the IED in
PCM600). In such case, the pre-processing block will calculate 3I
0
from the
first three inputs into the pre-processing block by using the following formula:
IPol 3I IL1 IL2 IL3
0
= = + +
EQUATION2018 V2 EN-US (Equation 27)
where:
IL1, IL2 and IL3 are fundamental frequency phasors of three individual phase currents.
The residual current is pre-processed by a discrete fourier filter. Thus the phasor of
the fundamental frequency component of the polarizing current is derived. This
phasor is then multiplied with the pre-set equivalent zero-sequence source
impedance in order to calculate the equivalent polarizing voltage UIPol in
accordance with the following formula:
0s
UIPol Z IPol (RNPol j XNPol) IPol= × = + × ×
EQUATION1877 V2 EN-US (Equation 28)
which will be then used, together with the phasor of the operating current, in order
to determine the direction to the earth fault (forward/reverse).
In order to enable current polarizing, the magnitude of the polarizing current shall
be bigger than a minimum level defined by setting parameter IPolMin.
Dual polarizing
When dual polarizing is selected, the function will use the vectorial sum of the
voltage based and current based polarizing in accordance with the following
formula:
0s
UTotPol=UPol UIPol=UPol Z IPol UPol RNPol jXNPol Ipol
IECEQUATION2408 V2 EN-US (Equation 29)
UPol and IPol can be either zero sequence component or negative sequence
component depending upon the user selection.
Then the phasor of the total polarizing voltage UTotPol will be used, together with
the phasor of the operating current, to determine the direction of the earth fault
(forward/reverse).
Section 8 1MRK 505 394-UEN A
Current protection
194 Line differential protection RED650 2.2 IEC
Technical manual
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