ABB RELION REX640 Technical Manual page 696

Protection and control

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Protection functions

Figure 397: Differential protection of a three-winding transformer and a transformer

with two output feeders

TR2PTDF can also be used for the protection of the power transformer feeding the

frequency converter. An interposing CT is required for matching the three-winding

transformer currents to a two-winding protection relay.

The fundamental frequency component is numerically filtered with a Fourier filter,

DFT. The filter suppresses frequencies other than the set fundamental frequency,

and therefore the protection relay is not adapted for measuring the output of

the frequency converter, that is, TR2PTDF is not suited for protecting of a power

transformer or motor fed by a frequency converter

1MRS759142 F

Technical Manual