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 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 component can be selected for that winding by setting the Zro
A elimination parameter.
Protection functions
1MRS759142 F
654 REX640
Technical Manual
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