Vector group of the
transformer
Winding 1 type
Winding 2 type
Phase shift
Zero sequence
current elimination
ZNz10
ZN
z
10
(Automatic)
ZNzn10
ZN
zn
10
(Automatic)
Zzn10
Z
zn
10
(Automatic)
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 automatically
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, a 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 eliminated by using the Zro A elimination
parameter.
By using the Zro A elimination parameter, the zero-sequence component of the local
phase currents is calculated and reduced for each phase current:
I
I
I
I
I
LOC
A
LOC
A
LOC
A
LOC
B
LOC
C
−
−
−
−
−
=
− ×
+
+
_
_
_
_
_
1
3
GUID-7C504C11-31C0-47A2-8253-E05020CA1CF7 V1 EN
(Equation 76)
I
I
I
I
I
LOC
B
LOC
B
LOC
A
LOC
B
LOC
C
−
−
−
−
−
=
− ×
+
+
_
_
_
_
_
1
3
GUID-6FEF478B-7DA1-4012-9F59-43B21AF813E3 V1 EN
(Equation 77)
Section 4
1MAC059074-MB A
Protection functions
478
615 series ANSI
Technical Manual
Summary of Contents for Relion 615 series
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