ABB Relion 670 series, Technical Reference Manual

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take I2 from same SMAI AI3P connected to I3PDIR input (same SMAI AI3P
connected to I3P input)):
If zero sequence current is selected,
op
I 3 Io IA IB IC
= × = + +
EQUATION2011-ANSI V1 EN
(Equation 82)
where:
IA, IB, IC 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 residual current is derived. The phasor
magnitude is used within the EF4PTOC (51N/67N) protection to compare it with the
set operation current value of the four steps (
Pickup1 , Pickup2 , Pickup3 or Pickup4 ). If
the residual current is larger than the set operation current and the step is used in non-
directional mode a signal from the comparator for this step is set to true. This signal
will, without delay, activate the output signal PUSTx (x=step 1-4) for this step and a
common PICKUP signal.
7.4.2.2 Internal polarizing
A polarizing quantity is used within the protection in order to determine the direction
to the ground fault (Forward/Reverse).
The function can be set to use voltage polarizing, current polarizing or dual polarizing.
Voltage polarizing
When voltage polarizing is selected the protection will use either the residual voltage
-3V
0
or the negative sequence voltage -3V
2
as polarizing quantity V3P.
This voltage can be:
1. directly measured (when a dedicated VT input of the IED is connected in PCM600
to the fourth analog input of the pre-processing block connected to EF4PTOC (51N/
67N) function input V3P). This dedicated IED VT input shall be then connected to
open delta winding of a three phase main VT.
2. calculated from three phase voltage input within the IED (when the fourth analog
input into the pre-processing block connected to EF4PTOC (51N/67N) analog
function input V3P is NOT connected to a dedicated VT input of the IED in
PCM600). In such case the pre-processing block will calculate -3V
2
from the first
three inputs into the pre-processing block by using the following formula:
1MRK505222-UUS C
Section 7
Current protection
401
Technical reference manual