ABB Relion RES670, Technical Manual

Page: 207 / 934

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 ensures 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 the 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 a 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 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 the pre-set equivalent zero-sequence source impedance in order to
calculate the 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-US
(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).
1MRK 511 408-UUS A
Section 8
Current protection
Phasor measurement unit RES670 2.2 ANSI 201
Technical manual