ABB RELION REX640 Technical Manual page 654

Protection and control

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Protection functions

Figure 371: Connection example of current transformers of Type 2

Transformer vector group matching

Before differential and bias currents can be calculated, the phase difference of the

currents must be vector group matched based on the transformer connection type.

The vector group of the power transformer is numerically matched on the high

voltage and low voltage sides by means of the

Winding 2 type and Clock number settings. Thus no interposing CTs are needed if

there is only a power transformer inside the protected zone. The matching is based

on phase shifting and a numerical delta connection in the protection relay. If the

neutral of a star-connected power transformer is earthed, any earth-fault in the

network is perceived by the protection relay as a differential current. The elimination

of the zero-sequence component can be selected for that winding by setting the Zro

A elimination parameter.

Winding selection , Winding 1 type ,

Technical Manual

1MRS759142 F