ABB Relion 670 series, Техническое справочное руководство

Страница: 408 / 1232

VPol=3V0=(VA +VB +VC)
EQUATION2012 V1 EN
(Equation 84)
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:
Section 7
1MRK505222-UUS C
Current protection
402
Technical reference manual