ABB RELION REX640 - Page 684

I
I I
I
I I
I
I I
L mHV
L L
L mHV
L L
L mHV
L L
1
1 2
2
2 3
3
3 1
3
3
3
=
−
=
−
=
−
(Equation 159)
Example 2
But if vector group is Yd11 and CT connection type is according to type
1, the compensation is a little different. The Winding 1 type setting is ”Y”,
Winding 2 type is “d” and Clock number is “Clk Num 11”. This is compensated
internally by giving winding 1 internal compensation value 0° and winding 2
internal compensation value -30°;
I
I I
I
I I
I
I I
L mLV
L L
L mLV
L L
L mLV
L L
1
1 3
2
2 1
3
3 2
3
3
3
=
−
=
−
=
−
(Equation 160)
The "Y" side currents stay untouched, while the "d" side currents are
compensated to match the currents actually flowing in the windings.
In this example there is no neutral current on either side of the transformer
(assuming there are no earthing transformers installed). In the previous
example, however, the matching is done differently to have the winding 1
neutral current compensated at the same time.
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
Protection functions
1MRS759142 F
684 REX640
Technical Manual