ABB Relion 670 series, Technical Manual

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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:
VPol=3V0=(VA +VB +VC)
EQUATION2012 V1 EN-US
(Equation 127)
where:
VA, VB, VC are fundamental frequency phasors of three individual phase voltages.
In order to use this, all three phase-to-ground voltages must be connected to three
IED VT inputs.
The residual voltage is pre-processed by a discrete fourier filter. Thus, the phasor of the
fundamental frequency component of the residual voltage is derived.
This phasor is used together with the phasor of the operating directional current, in order to
determine the direction to the ground fault (Forward/Reverse). In order to enable voltage
polarizing the magnitude of polarizing voltage shall be bigger than a minimum level defined by
setting parameter VpolMin.
It shall be noted that residual voltage (-3V
0
) or negative sequence voltage (-3V
2
) is used to
determine the location of the ground fault. This insures the required inversion of the polarizing
voltage within the ground-fault function.
Current polarizing
When current polarizing is selected the function will use an external residual current (3I
0
) as
polarizing quantity IPol. This current can be:
1. directly measured (when a dedicated CT 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 I3PPOL). This dedicated IED CT input is then typically connected to one single current
transformer located between power system WYE point and ground (current transformer
located in the WYE point of a WYE connected transformer winding).
•
For some special line protection applications this dedicated IED CT input can be
connected to 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 (51N/67N) 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:
3
= × = + +
Pol
I Io IA IB IC
EQUATION2019-ANSI V1 EN-US
(Equation 129)
where:
IA, IB and IC are fundamental frequency phasors of three individual phase currents.
1MRK 502 066-UUS B Section 8
Current protection
481
Technical manual