2
Ipol = (IA+alpha IB+alpha IC)/3
×
×
ANSIEQUATION2406 V2 EN
(Equation 52)
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 53)
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 54)
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).
8.2.7.3
External polarizing for ground-fault function
The individual steps within the protection can be set as non-directional. When this setting
is selected it is then possible via function binary input BLKn(where x indicates the
relevant step within the protection) to provide external directional control (that is, torque
control) by for example using one of the following functions if available in the IED:
1MRK 502 048-UUS A
Section 8
Current protection
213
Technical manual
