ABB RELION 670 Series Technical Manual page 127

1MRK 502 066-UUS B
I_A_W3
I_B_W3
I_C_W3
Vn_W1
Vn_W2
Vn_W3
A, B and C
Values of the matrix A, B and C coefficients depend on:
1. The Power transformer winding connection type, such as wye (Y/y) or delta (D/d)
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2. The Transformer phase shift such as Yd1, Dy11, YNautod5, Yy0d5 and so on, which introduce
phase displacement between individual windings currents in multiples of 30°. Since the HV
and LV winding voltages are in phase for wye/wye or Delta/Delta transformers, the same is
represented in IEC as represented as Dd0, Yy0. Polarity reversal in one of the windings would
give 180 degree phase displacement which can be represented by clock position 6. Such
transformers can thus be represented as Dd6 or Yy6. It is also possible to rename the phases
ABC to CAB or BCA, giving 120 or 240 degree displacements, represented by clock positions 4
& 8 . Polarity reversals in one of the windings would provide clock positions 10 & 2. These can
all be represented for example: Yy0, Yy2, Yy4, Dd0, Dd6. ANSI wye/Delta or Delta/wye
transformers have the HV winding leading the LV winding by 30degrees. This can be
represented by Yd1 or Dy1. Again considering polarity reversals and renaming of phases gives
rise to other clock positions 4,7,5,11
3. The Settings for elimination of zero sequence currents for the individual windings.
When the end user enters all these parameters, transformer differential function automatically
calculates the matrix coefficients. During this calculations the following rules are used:
For the phase reference, the first winding with set wye (Y) connection is always used. For example,
if the power transformer is a Yd1 power transformer, the HV winding (Y) is taken as the phase
reference winding. If the power transformer is a Dy1, then the LV winding (y) is taken for the phase
reference. If there is no wye connected winding, such as in Dd0 type of power transformers, then
the HV delta winding (D) is automatically chosen as the phase reference winding.
The fundamental frequency differential currents are in general composed of currents of all
sequences, that is, the positive-, the negative-, and the zero-sequence currents. If the zero-
sequence currents are eliminated (see section
then the differential currents can consist only of the positive-, and the negative-sequence
currents. When the zero-sequence current is subtracted on one side of the power transformer,
then it is subtracted from each individual phase current.
As it can be seen from equation
ampere level reference (current magnitudes from all other sides are always transferred to W1 side).
In other words, within the differential protection function, all differential currents and bias current
are always expressed in HV side primary Amperes.
Technical manual
is the fundamental frequency phase current in phase A on the W3 side
is the fundamental frequency phase current in phaseB on the W3 side
is the fundamental frequency phase current in phaseC on the W3 side
is transformer rated phase-to-phase voltage on the W1 side (setting parameter)
is transformer rated phase-to-phase voltage on the W2 side (setting parameter)
is transformer rated phase-to-phase voltage on the W3 side (setting parameter)
are three by three matrices with numerical coefficients
Note! The capitalized letter Y or D is used to represent the high voltage (HV) side of the
transformer and the smaller letter y or d to represent lower voltage(LV) level. When
neutral bushing of a wye winding is brought out, the same may be represented as YN or
yn depending on whether the winding is HV or LV.
1 and equation
"Optional Elimination of zero sequence
2 the first entered winding (W1) is always taken for
Section 6
Differential protection
currents"),
121