ABB Relion 670 Series Technical Reference Manual page 407

1MRK505222-UUS C
7.4.2.2
Technical reference manual
take I2 from same SMAI AI3P connected to I3PDIR input (same SMAI AI3P
connected to I3P input)):
If zero sequence current is selected,
= × = + +
I 3 Io IA IB IC
op
EQUATION2011-ANSI V1 EN
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.
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 or the negative sequence voltage -3V
0
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
three inputs into the pre-processing block by using the following formula:
Current protection
as polarizing quantity V3P.
2
Section 7
(Equation 82)
from the first
2
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