ABB RELION REX640 Technical Manual page 660

Protection and control

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Protection functions

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

automatically 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.

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:

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 PCSITPC to

LNPLDF (dotted OK line).

1MRS759142 F

(Equation 152)

(Equation 153)

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