RET670 1MRK002246-BD Transformer protection

RET670 provides fast and selective protection, monitoring and control for two- and three-winding transformers,
autotransformers, generator-transformer units, phase shifting transformers, special railway transformers and shunt reactors.
The transformer IED is designed to operate correctly over a wide frequency range in order to accommodate power system
frequency variations during disturbances and generator start-up and shut-down.
A very fast differential protection function with settable CT ratio matching and phase shift compensation makes this IED the
ideal solution even for the most demanding applications. Since RET670 has very low requirements on the main CTs, no
interposing CTs are required.It is suitable for differential applications with multi-breaker arrangements with up to six
restraint CT inputs. The differential protection function is provided with 2nd harmonic and wave-block restraint features
to avoid tripping for magnetizing inrush current, and 5th harmonic restraint to avoid tripping for overexcitation.

The differential function offers a high sensitivity for low-level internal faults. The unique and innovative sensitive differential
protection feature of the RET670 provides the best possible coverage for winding internal turn-to-turn faults, based on the
theory of symmetrical components .
A low impedance restricted ground-fault protection function is available as a complimentary sensitive and fast main protection
against winding ground faults. This function includes a directional zero-sequence current criterion for additional
security.
Additionally a high impedance differential function is available. It can be used as restricted ground fault or, as three functions are
included, also as differential protection on autotransformers, as
differential protection for a tertiary connected reactor, as Tdifferential protection for the transformer feeder in a

meshcorner or ring arrangement, as tertiary bus protection and so on.