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Zero-sequence component elimination
If
Clock number
is "Clk Num 2", "Clk Num 4", "Clk Num 8" or "Clk Num 10", the vector
group matching is always done on both, winding 1 and winding 2. The combination results
in the correct compensation. In this case the zero-sequence component is always removed
from both sides automatically. The
Zro A elimination
parameter cannot change this.
If
Clock number
is "Clk Num 1", "Clk Num 5", "Clk Num 7" or "Clk Num 11", the vector
group matching is done on one side only. A possible zero-sequence component of the
phase currents at ground faults occurring outside the protection area is eliminated in the
numerically implemented delta connection before the differential current and the biasing
current are calculated. This is why the vector group matching is almost always made on
the star connected side of the "Ynd" and "Dyn" connected transformers.
If
Clock number
is "Clk Num 0" or "Clk Num 6", the zero-sequence component of the
phase currents is not eliminated automatically on either side. Therefore, the zero-sequence
component on the star connected side that is grounded at its star point has to be eliminated
by using the
Zro A elimination
parameter.
The same parameter has to be used to eliminate the zero-sequence component if there is,
for example, an grounding transformer on the delta-connected side of the "Ynd" power
transformer in the area to be protected. In this case, the vector group matching is normally
made on the side of the star connection. On the side of the delta connection, the elimination
of the zero-sequence component has to be separately selected.
By using the
Zro A elimination
parameter, the zero-sequence component of the phase
currents is calculated and reduced for each phase current:
I
I
x I
I
I
I
I
x I
I
I
I
I
x I
I
I
Am
A
A
B
C
Bm
B
A
B
C
Cm
C
A
B
C
=
−
+
+
(
)
=
−
+
+
(
)
=
−
+
+
1
3
1
3
1
3
((
)
GUID-BD8D0B4F-E3A9-4E58-834F-3736858F5430 V1 EN
(Equation 85)
In many cases with the grounded neutral of a "wye" winding, it is possible
to make the compensation so that a zero-sequence component of the phase
currents is automatically eliminated. For example, in a case of a "Ynd"
transformer, the compensation is made on the winding 1 side to
automatically eliminate the zero-sequence component of the phase
currents on that side (and the "d" side does not have them). In those cases,
explicit elimination is not needed.
Section 4
1MAC059074-MB A
Protection functions
504
615 series ANSI
Technical Manual
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