ABB RELION REX640 Technical Manual page 572

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Protection functions

GUID-903978C2-D0AC-4737-89DA-0BEA9CB30B9B V1 EN

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 selection, Winding 1 type, 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

1MRS759142 C

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