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

pulsing, lock-out contact output and so on, is performed. The

binary inputs are heavily stabilized against disturbance to

prevent incorrect operations at for example dc system

capacitive discharges or DC earth faults.

The binary inputs are heavily stabilized against disturbances

to prevent incorrect operations during for example during DC

system capacitive discharges or DC earth faults.

Distance protection functionality for phase-to-phase and/or

phase-to-earth faults is available as back-up protection for

faults within the transformer and in the connected power

system.

Versatile phase, earth, positive, negative and zero sequence

overcurrent functions, which can optionally be made

directional and/or voltage controlled, provide further

alternative backup protection. Thermal overload with two timeconstants, volts per hertz, over/under voltage and over/under

frequency protection functions are also available.

A built-in disturbance and event recorder provides valuable

data to the user about status and operation for post-fault

disturbance analysis.

Breaker failure protection for each transformer breaker allows

high speed back-up tripping of surrounding breakers.

The transformer IED can also be provided with a full control

and interlocking functionality including Synchrocheck function

to allow integration of the main and/or a local back-up control.

Out of Step function is available to separate power system

sections close to electrical centre at occurring out of step.

The advanced logic capability, where user logic is prepared

with a graphical tool, allows special applications such as

automatic opening of disconnectors in multi-breaker

arrangements, closing of breaker rings, load transfer logic

and so on. The graphical configuration tool ensures simple

and fast testing and commissioning.

Serial data communication is via optical connections to

ensure immunity against disturbances.

The wide application flexibility makes this product an

excellent choice for both new installations and the

refurbishment of existing installations.