ABB RED615 Technical Manual page 368

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Protection functions

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

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:

GUID-7C504C11-31C0-47A2-8253-E05020CA1CF7 V1 EN

GUID-6FEF478B-7DA1-4012-9F59-43B21AF813E3 V1 EN

GUID-D5203A0B-D0A0-4147-B1F0-06C2B78B288B V1 EN

Fail safe function

To prevent malfunction during communication interference, the operation of

LNPLDF is blocked when the protection communication supervision detects severe

interference in the communication channel. The timer reset stage is activated in

case the stabilized stage is started during a communication interruption. The

protection communication supervison is connected internally from PCSRTPC to

LNPLDF (dotted OK line).

1YHT530004D05 D

(Equation 39)

(Equation 40)

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