ABB REB650, Technical Manual

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2
Ipol = (IA+alpha IB+alpha IC)/3
× ×
ANSIEQUATION2406 V2 EN
(Equation 12)
where:
IA, IB and IC are fundamental frequency phasors of three individual phase currents.
alpha
phasor with an angle of 120 degrees.
The polarizing 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 13)
which will be then 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 current polarizing the magnitude of polarizing current shall be bigger
than a minimum level defined by setting parameter
IPolMin .
Dual polarizing
When dual polarizing is selected the function will use the vectorial sum of the voltage
based and current based polarizing in accordance with the following formula:
( )
0 s
VTotPol=VVPol VIPol=VPol Z IPol VPol RNPol jXNPol Ipol
+ + × = + + ×
ANSIEQUATION2408 V1 EN
(Equation 14)
Vpol and Ipol can be either zero sequence component or negative sequence component
depending upon the user selection.
Then the phasor of the total polarizing voltage VTotPol will be used, together with the
phasor of the operating current, to determine the direction of the ground fault (Forward/
Reverse).
7.2.7.3 Operating directional quantity within the function
The function can take either the residual current or the negative sequence current for its
operating directional quantity. The residual 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
Section 7
1MRK 505 277-UUS C
Current protection
92
Technical Manual