Excellence in Instrument Transformers

2The merger of these long-stand-ing, highly reputable high volt-age manufacturers, results in an unmatched source of HV andEHV expertise, and further en-hances our commitment totechnical excellence.

With combined expertise ofmore than 170 years Trenchprovides its customers withproven, highly reliable products.

Trench manufactures on a glob-al basis with manufacturingplants in North America, Europeand Asia. A worldwide salesnetwork ensures efficient,knowledgeable communica-tions with our customers.

Quality is our most importantgoal with particular emphasis onthe manufacturing processes.This is further enhancedthrough the use of our own in-house high voltage test labora-tories.

Trench

Switzerland

France

China

Austria

Canada

Germany

Canada

3Quality remains paramount for Trench.All products are manufactured with

compliance to international Quality Standard ISO 9001.

Was Formed by Three Member Companies

Current Transformers Voltage TransformersCombined Instrument Transformers

All of these products are charac-terized by high quality standards,superior technical features and afirst class price/performance rela-tionship. Competent customerservice is available worldwide.

Our customers have highest requirements regarding:

life expectancyreliabilityoperational security.

Our policies of design conser-vatism and quality assurance area direct result of our commit-ment to meet or exceed theserequirements.

In our day-to-day business weendeavor to always focus on theneeds of our customers. We treatour customers with fairness andrespect and our target is long-term partnership.

In instrument transformers, the expertise, experience andtechnology of each of the threeforming companies has beenbrought together and focusedon technology specialists actingas a team for the global market:

the former Trench Electric focusing on capacitive products

the former Haefely specializingin oil-insulated inductive instru-ment transformers

the former MWB focusing on SF6-insulated inductive instrument transformers.

Throughout the Trench Groupexcellence is built on a founda-tion of:

in-depth technical knowledgeand experienced people

close business and technical relationships built with our customers over many years

global service

strong innovation and qualityassurance demands

widely supported technologybase.

Our collective product scopecomprises instrument transform-ers for metering, protection andcontrol on HV and EHV systems:

4Instrument Transformer Technology

Electrical instrument transformerstransform high currents and voltages to standardized low andeasily measurable values whichare isolated from the high voltage.

When used for metering pur-poses, instrument transformers provide voltage or current signalswhich are very accurate repre-sentations of their transmissionline values in both magnitudeand phase. These signals allowaccurate determination ofrevenue billing.

When used for protection pur-poses, the instrument transformeroutputs must accurately representtheir transmission line values during both steady-state andtransient conditions. These criti-cal signals provide the basis forcircuit breaker operation underfault conditions and as such arefundamental to network reliabilityand security.

Instrument transformers used fornetwork control supply impor-tant information as to the stateof the operating conditions ofthe network.

For the above applications, the Trench Group supplies:

Current Transformers 72.5 kV through 800 kV and primary currents to 5000 A.

Inductive and Capacitive Voltage Transformers72.5 kV through 800 kV.

Combined Instrument Transformers72.5 kV through 800 kV andrated primary currents up to4000 A.

Highest Metering Accuracy Requirements Verified by:

CCAC in Canada

National Grid Company in England

EdF in France

PTB in Germany

SEV in Switzerland

Highest Protection Performance Requirements

In addition to both IEC and ANSIstandard protection cores, induc-tive current transformers can beprovided with TPS, TPX, TPY andTPZ cores in accordance with IEC standards, and Class X coresin accordance with British stan-dards.

The requirements of many othernational standards are also fullysatisfied on request.

Metering, Protectionand Control

5Reliability of an instrumenttransformer refers to its abilityto consistently satisfy prescribedperformance criteria over itsexpected useful lifetime underspecified operating conditions.

Security, refers to the accepta-bility and consequences of theinstrument transformer failuremode in the event that it doesfail, due either to reachingthe end of its expected servicelife or as a result of being sub-jected to stresses in excess ofthose for which it was designed.

The reliability and security characteristics of an instrumenttransformer are governed by theelectrical and insulation design,the manufacturing and processingtechnology used and the specificphysical arrangement.

The partial discharge performanceunder in-service conditions is akey determining factor in the lifeexpectancy and long-term reliabili-ty of an instrument transformer. IEC Standards require a P.D. valueof less than 10 pC at 1,2Umax.

Due to the demanding require-ments of todays HV and EHVnetworks, the Trench Group haselected to adopt even morestringent internal requirements.As such, Trench instrument trans-formers typically perform muchbetter than required by thesestandards.

Reliability and Security

6The reliability and security of Trench oil-insulated instrumenttransformers is based on the following features:

in-service experience spanningup to 50 years

in the event of internal insula-tion failure, a secure failuremode is achieved through:

For Inductive Type

The formation of fibre bridges inthe free oil between high voltageand ground electrodes is aknown potential failure mode ofinstrument transformers. In theTrench design this failure mode iseliminated through the use of abarrier construction design inthe free oil section. This ap-proach consists of inserting insulating barriers at strategicpoints through the free oil space - thereby preventing theformation of fibre bridges.

The behaviour of the in-strument transformer in the case of overvoltage,e.g. being struck by lightning: A rupture of the housing, in par-ticular of the hol-low insulator with built-in finely graded capacitor bushing is im-probable because of the overdimensioning of the bushing and the solid electricalconnection between the corehousing and the ground.

Should arcing occur, due to da-maged insulation, the best protection against severe pressurebuildup is guaranteed by:

the very thin welded elastichousing

the metal bellows for the oil expansion

Both the welded seam, whichconnects the upper and lowerportions of the head housing,and the metallic bellows are de-signed to act as pressure reliefpoints in the event of severe in-ternal pressure buildup. Since the unit has a normal internal oilpressure of approximately 1 bar

The Reliability and Securityof Oil-immersed...

absolute, it is possible to designthese pressure relief points torupture at very moderate pressures.For the ultimate in security inductive type oil-insulated instrument transformers can beequipped with a special additionalmonitoring systems:

Gas Detection System (GDS)

The gas detection system GDSmonitors the amount of gas col-lected at a specific collectiontank located in the head of theunit.

For CVTs

Pressure relief is provided by abellows puncture pin and throughthe use of porcelain which is sufficiently strong as to result inany rapid pressure rise being released through the seal platesat the ends of the porcelain ratherthan via explosion of the porce-lain itself.

Upon request oil-immersed instrument transformers canalso be supplied with compos-ite insulators.

7The reliability and security of Trenchgas-insulated instrument trans-formers is based on:

50 years experience as a manu-facturer of instrument trans-formers covering epoxy-resin,oil-paper and finally gas-insu-lated units

more than 10,000 gas-insulat-ed instrument transformers inservice under most differentenvironmental conditions

an explosion-proof design pro-viding maximum safety due tothe combination of SF6-gaswith a composite insulator

Explosion-proof Design

The present Trench gas-insulatedinstrument transformers are theresult of the development of anexplosion-proof design, whichmany customers asked for. Gas-insulation is particularly suitablefor this, as, in the event of an in-ternal flashover, the pressure in-crease will be linear and hencetechnically manageable.

A controlled pressure relief deviceat the head of the transformer(rupture disc) eliminates unac-ceptable mechanical stresses inthe housing; i.e. only the rupturedisc is released, gas escapes, butthe complete transformer remainsintact no explosion occurs.

Most reliable Insulation Properties

SF6-gas is the main insulationmedium between high voltageand ground potential. This gas due to its excellent features isa must for all GIS manufacturersof high voltage equipment.

A stable quality can be guaranteedby the use of SF6-gas acc. toANSI/DIN and the fact that thisinert gas shows no ageing evenunder the highest electrical andthermal stresses. The insulationproperties remain unchangedthroughout its lifetime.

...andGas-insulated Instrument Transformers

All the above features guaranteean operation period over manyyears without any control of theinsulation condition.

Full functional Security andMonitoring

The guaranteed SF6-leakage rateis less than 1% per year.The gas pressure can be checkedat site or by means of a remotecontrol device, i. e. a densimeterwith contacts for remote control.In the case of loss of SF6-pressure,the transformer still operates atrated pressure.

Environmentally beneficialunder most severe Conditions

SF6-gas is physiologically ab-solutely safe. It bears no ecologi-cally toxic potential and its de-composition products have noendangering effects on the envi-ronment, e.g. ground water pol-lution.This SF6-gas insulation mediumallows an easy waste manage-ment of the transformers.

Furthermore the hydrophobicfeatures of the composite insula-tor result in a problem-free serviceeven under salt-fog or pollutedconditions.

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Features

Head type design of lowweight and minimum oil volume

excellent seismic performanceas a consequence of optimizeddesign of flanges, porcelainand their interconnection

short, symmetrically arrangedlow reactance bar-type primaryconductor permits higher shortcircuit currents and avoids largevoltage drop across the primarywinding

excellent control of internaland external insulation stressesthrough the use of a propri-etary finely graded bushing sys-tem

hermetically sealed by stainlesssteel metallic bellows

uniformly distributed secondarywindings guarantee accuratetransformation at both ratedand high currents

essentially unaffected by strayexternal magnetic fields

stable accuracy over a long period of time

exclusive use of corrosion resistant materials

Composite insulators availableon request

1:1 A current ratio possible.

Current TransformerOil-immersed Type

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Features

head type design

explosion-proof design by thecompressible insulation mediumSF6-gas and rupture disc

excellent seismic performancedue to the properties of thecomposite insulator

available for the full voltagerange 72.5 kV up to 800 kVand full current range 100 Aup to 4800 A

low reactance bar type primaryproviding optimal short-circuitperformance

optimum field grading is ac-complished by a fine condensergrading system especially developed for this application

multiple-turn primaries forsmall primary currents

uniformly distributed secondarywindings guarantee accuratetransformation at both ratedand high currents


perfect transient performance

exclusive use of corrosion-resistant materials

core changes after assembly donot require the destruction ofthe high voltage insulation

Current Transformer

Gas-insulated

12

Features

Low weight and minimum oilvolume

excellent seismic performanceas a consequence of optimizeddesigns of flanges, porcelainand their interconnection

excellent control of internaland external insulation stressesthrough the use of a proprietaryfinely graded bushing system


hermetically sealed stainlesssteel metallic bellows for unitsrated 123 kV and above



suitable for line discharging

exclusive use of corrosion-resistant materials.

Composite insulator availableon request

Inductive Voltage TransformerOil-immersed

13

Voltage Transformer Gas-insulated

Features

explosion-proof design by thecompressible insulation medi-um SF6-gas and rupture disc


available for the full voltagerange 72.5 kV up to 800 kV

optimum field grading is accomplished by a fine con-denser grading system especial-ly developed for this applica-tion

wide range ferroresonance freedesign without the use of anexternal damping device (please ask for details)

essentially unaffected by exter-nal stray magnetic fields


suitable for line-discharging

optimized high voltage coil as-sures identical electric stressesunder both transient and steadystate conditions

exclusive use of corrosion-resistant materials

14

Features

Capable of carrier coupling PLCsignals to the network

optimized insulation system design utilizing state-of-the-artprocessing techniques with either mineral oil or syntheticinsulating fluids

stability of capacitance andaccuracy over a long period oftime due to superior clampingsystem design

oil expansion by way of her-metically sealed stainless steelbellows assures the integrity ofthe insulation system over time

bellows puncture pin providesfor release of internal pressurein the event of severe serviceconditions leading to internaldischarges

extra high strength porcelainsprovide both superior seismicperformance and the ability tomount large line traps directlyon the CVT with correspondingsavings in installed cost

maintenance-free oil filled castaluminum basebox

superior transient responsecharacteristics

internal company routine testand quality requirements ex-ceed those of internationalstandards with impulse testsand partial discharge test beingperformed on a routine basis

not subject to ferroresonanceoscillations with the network or breaker capacitator

high capacitance CVTs, wheninstalled in close proximity toEHV circuit breakers, can pro-vide enhanced circuit breakershort line fault/TRV performance.

CapacitorVoltage Transformer

15

Trench offers special voltagetransformers for HVDC systems.

These units are primarly used tocontrol the HV valves of the rectifiers or inverse rectifiers. Themeasuring system consists of anRC voltage divider which providesinputs to a specially designed electronic power amplifier.The High Voltage Divider can be

ElectronicVoltage Measuring Systemfor HVDC

supplied either for outdooroperation or for installation intoSF6 gas-insulated switchgear(GIS).

The resulting system can accu-rately transform voltages withina defined burden range with lin-ear frequency response up to ap-proximately 10 kHz.

As such, the system is ideal formeasurement for dynamic andtransient phenomena and harmonics associated with HVDCsystems.

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Combined Instrument TransformerOil-immersed

Features

Low weight and minimum oilvolume

short symmetrically arrangedlow reactance bar-type primaryconductor permits higher shortcircuit currents and avoids largevoltage drop across primarywinding

excellent control of internaland external insulation stressesthrough the use of a proprietaryfinely graded bushing system

excellent seismic capability as a consequence of optimized design of flanges, porcelainand their interconnection

hermetically sealed by stainlesssteel metallic bellows

only one foundation requiredin the switchyard as a conse-quence of combining the voltageand current sensing functionsin one transformer

uniformly distributed secondarywindings guarantee accuratetransformation at both ratedand high current




suitable for line discharging

exclusive use of corrosion-resistant materials.

composite insulators availableon request

17

Features

head type design with voltagetransformer section located ontop of the current transformer

low weight and compact SF6-design

explosion-proof design by thecompressible insulation medi-um SF6-gas and rupture disc


the single-section high voltagecoil (not cascaded) of the volt-age transformer section en-ables a product range for com-bined instrument transformersup to 800 kV

optimum field grading is ac-complished by a fine condensergrading system especially de-veloped for this application

wide range ferroresonance freedesign without the use of anexternal damping device (please ask for details)

low reactance type primaryconductor allows for highshort-circuit currents and covers all core standards

less foundation space requiredcompared to the use of individ-ual current transformers andvoltage transformers

suitable for line-discharging

essentially unaffected by exter-nal stray magnetic fields

exclusive use of corrosion-resis-tant materials

Combined TransformerGas-insulated

18

in addition to the measure-ment of the voltages and cur-rents best discharge capabilitiesfor HV-lines

custom-designed instrumenttransformers for each specificapplication and extended func-tion designs comply with di-mensional restrictions, flangesizes and insulator require-ments

standard designs for single-and three-phase units

meets all national and interna-tional standards with regard topressure vessel codes

prevention of occurrence ofsustained ferroresonance by integrated ferroresonance suppression

Instrument Transformerfor GIS Switchgear

shielded against transient over-voltages in accordance withIEC standards. Special additionalshielding is available.

guaranteed SF6-leakage rate ofless than 1% per year

equipped with pressure reliefdisc and deflection device

all components designed andtested for mechanical stress towithstand up to at least 20 g

accuracy classes in accordanceto DIN VDE 0414, IEC 60044,ANSI: IEEE C57.13, AS 1243(other standards or classes onrequest)

shock indicators warningagainst inadmissible accelerationduring transportation

Voltage transducer 145 kV series RCT (active part) for HV GIS

RC TypeInductive Type

RC divider for voltage measure-ments

conform to microprocessorbased secondary technology

ferroresonance free

able to withstand voltage teston site

1 phase or 3 phase system

significant size and weight reduction

19

LoPoThe Low Power Transducers

Voltage transducer principlediagram

Voltage transducer 24 kV series LPVT

Voltage transducer 36 kV series LPVTG for MV metalcladswitchgears

Current transducer for MV applications, series LPCT and LPLS

Current transducer principle diagram, iron core design

The low power current and voltage transducers canbe used for a wide range of medium and high voltageapplications where they replace the conventionalmeasuring transformers for measurement and protection purposes.

The Voltage Transducers arebased on resistive as well as resistive capacitive dividers

The Current Transducers arebased on an iron core or an aircore design and provide a secondary voltage which represents the primary current

Standard cables and connec-tors; twisted pair and doubleshielded cable

Connection capability for mul-tiple protection and measuringdevices

Metalclad housing ensuringoperator safety

Immune to all methods of on-line switchgear and cable test-ing

Current Transducers provide alinear transmission up to shortcircuit current

Completely EMC shielded, immune to RFI/EMI

Advantages System conforms to low power digital microprocessor based

technology for protection and metering

Simple assembly with compact size and low weight No secondary circuit problems; Voltage Transducers are short circuit

proof, Current Transducers can have an open secondary

Voltage Transducers are ferroresonance free

Environment friendly (no oil)

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Trench is your partner of choice for your Instrument Transformer solutions today;and for the development ofyour new technology solutions of tomorrow.

Modifications reserved

04.2000

E210.10

Trench Austria GmbHPaschinger Strasse 49, Postfach 13A-4060 Linz-Leonding/AustriaPhone +43.732.6793-0Fax +43.732.671341E-Mail [email protected]

Trench Brasil LTDAVia Expressa de Contagem, 2685CEP: 32370-485Cpmtagem, MG - BrasilPhone 55. 31. 391-5959Fax 55. 31. [email protected]

Trench LimitedCoil Product Division71 Maybrook Drive, ScarboroughOntario, Canada M1V 4B6Phone (416) 298-8108Fax (416) 298-2209E-Mail [email protected]

Trench LimitedInstrument Transformer Division390 Midwest Road, ScarboroughOntario, Canada M1P 3B5Phone (416) 751-8570Fax (416) 751-6952E-Mail [email protected]

Trench France S.A.16, rue du Gnral CassagnouB.P. 70F- 68302 St-Louis Cedex/FrancePhone +33.3.89 70 23 23Fax +33.3.89 67 26 63E-Mail [email protected]

Trench Germany GmbHNrnberger Strasse 19996050 Bamberg/GermanyPhone +49.951.1803-0Fax +49.951.1803-224E-Mail [email protected]

Trench Switzerland AGLehenmattstrasse 353CH - 4028 Basel/SwitzerlandPhone +41.61.315 5111Fax +41.61.315 59 00E-Mail [email protected]

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Excellence in Instrument Transformers