ABB REL650 series Technical Manual page 230

Section 7
Current protection
224
The negative sequence current can be calculated from the three-phase current input within
the IED by using the pre-processing block. The pre-processing block will calculate the
negative sequence current from the three inputs into the pre-processing block by using the
following formula:
2 ×
Ipol = (IA+alpha IB+alpha IC)/3
ANSIEQUATION2406 V2 EN
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:
(
= × = + ×
V Zo I RNPol
S Pol
IPol
EQUATION2013-ANSI V1 EN
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:
+
VTotPol=VVPol VIPol=VPol
ANSIEQUATION2408 V1 EN
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).
×
)
×
I
j XNPOL
Pol
(
+ × = +
Z IPol VPol RNPol
0s
1MRK 506 335-UUS A
)
+ ×
jXNPol Ipol
Technical manual
(Equation 52)
(Equation 53)
(Equation 54)