ABB Relion 650 Series Technical Manual page 182

Section 6
Current protection
= ×
V 3 Vo
VPol
EQUATION2012-ANSI V1 EN-US
where:
VA, VB, VC
Note! 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 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
It shall be noted that –3V
required inversion of the polarizing voltage within the ground-fault function.
Current polarizing
When current polarizing is selected the function will use the residual current (3I
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).
•
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
using the following formula:
= ×
I 3 Io
Pol
EQUATION2019-ANSI V1 EN-US
where:
IA, IB and IC are fundamental frequency phasors of three individual phase currents.
The residual polarizing current is pre-processed by a discrete fourier filter. Thus the phasor of the
fundamental frequency component of the residual 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:
176
= + +
VA VB VC
are fundamental frequency phasors of three individual phase voltages.
is used to determine the location of the ground fault. This insures the
0
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)
= + +
IA IB IC
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from the first three inputs into the pre-processing block by
0
1MRK 506 326-UUS B
VpolMin .
) as polarizing
0
Line distance protection REL650
Technical manual
(Equation 30)
(Equation 31)