ABB Relion 670 Series RES670, Техническое руководство

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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
(Equation 18)
where:
IA, IB and 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 polarizing current is derived. This phasor is then
multiplied with pre-set equivalent zero-sequence source Impedance in order to calculate
equivalent polarizing voltage VIPol in accordance with the following formula:
( )
IPol
S Pol Pol
V Zo I RNPol j XNPOL
I
= × = + ×
×
EQUATION2013-ANSI V1 EN
(Equation 19)
which will be then used, together with the phasor of the operating current, in order to
determine the direction to the ground fault (Forward/Reverse).
In order to enable current polarizing the magnitude of polarizing current shall be bigger
than a minimum level defined by setting parameter
IPolMin .
1MRK 511 365-UUS A
Section 8
Current protection
Phasor measurement unit RES670 2.1 ANSI 201
Technical manual