ABB Relion 620 Series - Page 484

The polarity of the polarizing quantity (residual voltage) can be changed
(rotated by 180 degrees) by setting the Pol reversal parameter to "True"
or by switching the polarity of the residual voltage measurement wires.
Fault direction determination
If an earth fault is detected by the GFC module, the fault direction is evaluated
based on the calculated sum admittance phasor
Y
osum
obtained from the Multi-
frequency admittance calculation module. To obtain dependable and secure fault
direction determination regardless of the fault type (transient, intermittent,
restriking, permanent, high or low ohmic), the fault direction is calculated using
a special filtering algorithm, Cumulative Phasor Summing (CPS) technique. This
filtering method is advantageous during transient, intermittent and restriking earth
faults with dominantly non-sinusoidal or transient content. It is equally valid during
continuous (stable) earth faults.
The concept of CPS is illustrated in Figure 248 . It is the result of adding values of
the measured sum admittance phasors together in phasor format in chronological
order during the fault. Using the discrete sum admittance phasors
Y
osum
in different
time instants (t
1
...t
5
), the corresponding accumulated sum admittance phasor
Y
osum CPS_
is calculated. This phasor is used as directional phasor in determining the
direction of the fault.
Y t Y t
osum CPS osum_
( ) ( )
1 1
=
(Equation 50)
Y t Y t Y t
osum CPS osum osum_
( ) ( ) ( )
2 1 2
= +
(Equation 51)
Y t Y t Y t Y t
osum CPS osum osum osum_
( ) ( ) ( ) ( )
3 1 2 3
= + +
(Equation 52)
Y t Y t Y t Y t Y t
osum CPS osum osum osum osum_
( ) ( ) ( ) ( ) ( )
4 1 2 3 4
= + + +
(Equation 53)
Y t Y t Y t Y t Y t Y
osum CPS osum osum osum osum osu_
( ) ( ) ( ) ( ) ( )
5 1 2 3 4
= + + + +
mm
t( )
5
(Equation 54)
Protection functions
1MRS757644 H
484 620 series
Technical Manual