ABB RELION REX640 Technical Manual page 602

Section 4
Protection functions
596
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 earth 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 earthed 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 earthing 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:
1
I I I I I
(
L m 1 = L 1 − ⋅ L 1 + L 2 +
3
1
I I I I
(
L m 2 = L 2 − ⋅ L 1 + L 2 +
3
1
I I I I
(
L m 3 = L 3 − − ⋅ L 1 + L 2 +
3
GUID-B8E1C9C7-76EE-4054-812C-B08C7409B023 V1 EN
In many cases with the earthed 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.
)
L 3
I
)
L 3
I
)
L 3
1MRS759142 C
(Equation 108)
REX640
Technical Manual