Transformer protection RET670

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 vector group 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 earth-fault protection function is

available as a complimentary sensitive and fast main

protection against winding earth 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 earth fault or, as three functions

are included, also as differential protection on

autotransformers, as differential protection for a tertiary

connected reactor, as T-differential protection for the

transformer feeder in a mesh-corner or ring arrangement, as

tertiary bus protection and so on.

Tripping from pressure relief/Buchholz and temperature

devices can be done through the transformer IED where