1MAC050144-MB C
Section 4
Protection functions
615 series ANSI
341
Technical Manual
restraining 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 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:
(Equation 39)
Compensation of tap changer position
The position of the tap changer used for voltage control can be compensated and the
position information is provided for the protection function through the tap position
indication function 84T.
Typically, the tap changer is located within the high voltage winding, that is, winding 1,
of the power transformer. The
Tapped winding
parameter specifies whether the tap
changer is connected to the high voltage side winding or the low voltage side winding.
This parameter is also used to enable and disable the automatic adaptation to the tap
changer position. The possible values are “Not in use”; “Winding 1”; “Winding 2.”
The
Tap nominal
parameter tells the number of the tap, which results in the nominal
voltage (and current). When the current tap position deviates from this value, the input
current values on the side where the tap changer resides are scaled to match the currents
on the other side.
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.
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