Reactors

Introduction

With 40 years of successful fieldexperience, Trench is therecognized world leader in the design and manufacture of air core,dry type, power reactors for all utility and industrial applications.The unique, custom design ap-proach, along with fully integratedengineering and manufacturingfacilities in both North Americaand Europe have enabled Trench to become the technicalleader for high voltage inductorsworldwide.

A deep commitment to the powerindustry, along with extensive investment in engineering, manufacturing and test capabilitygive Trench customers the utmost in high quality, reliableproducts which are individually designed for each application. Trench reactor applications havegrown from small, distributionclass, current limiting reactors tocomplex EHV applied reactors surpassing 300 MVA per coil. Reactors are manufactured in accordance with ISO 9001 qualitystandard. Trench's highly develo-ped research and developmentprogram constantly addresses newtechnologies and their potential ap-plication in reactor products.Trench welcomes challenges fornew applications for power reactors.

This brochure outlines the features,capabilities and applications of Trench reactors. Although air-core, dry type reactors

represent the majority of reactorproduction volume, Trenchalso produces a highly successfulline of iron core/iron shielded andoil type reactors for specific appli-cation (eg. Resonance Grounding/Petersen Coils). These reactors arealso described in detail in othersections of the Trench product catalogue.

Design Features of Air-Core Dry Type Reactors

• Epoxy impregnated, fibreglassencapsulated construction

• Aluminum construction through-out with all current carryingconnections welded

• Highest mechanical and shortcircuit strength

• Essentially zero radial voltagestress, with uniformly gradedaxial voltage distribution between terminals

• Low noise levels are maintainedthroughout the life of the reactor

• Weatherproof construction, withminimum maintenance require-ments

• Design service life in excess of30 years

• Designs available in compliancewith ANSI/IEEE, IEC and othermajor standards.

Reactors

Fig. 1Three-phase stacked

current limiting reactor2

Series Reactors

Reactors connected in series withthe line or feeder. Typical uses arefault current reduction, load balancing in parallel circuits, limi-ting inrush currents of capacitorbanks, etc.

Reactor Applications

Fig. 2Schematic diagram

Fig. 4Current limiting reactor

Fig. 3Single phase series reactors

Trench reactors are utilized on transmission anddistribution systems. Although it is not possible to listall reactor applications, some of the most common aredescribed below.

Current Limiting Reactors,reduce the short circuit current tolevels within the rating of theequipment on the load side of thereactor.

Applications of current limiting reactors range from the simpledistribution feeder reactor to largebus-tie and load balancing reactorson systems rated up to 765 kV/2100 kV BIL.

Capacitor Reactors are designedto be installed in series with ashunt connected capacitor bank tolimit inrush currents due to switching, to limit outrush currentsdue to close in faults and to controlthe resonant frequency of the system due to the addition of thecapacitor banks. Reactors can beinstalled on system voltagesthrough 765 kV/2100 kV BIL.

When specifying capacitor reactors,the requested continuous currentrating should account for harmoniccurrent content, tolerance on capacitors and allowable systemovervoltage.

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Buffer Reactors forElectric Arc Furnaces (EAF).The most effective use of EAFs isachieved by operating the furnaceat low electrode current and longarc length. This requires the use ofa series reactor in the supply systemof the arc furnace transformer forstabilizing the arc.

Fig. 5Buffer reactor

for E.A.F.

Fig. 6Load flow control reactors

Duplex Reactors are current limiting reactors which consist oftwo half coils, wound in opposition.These reactors provide a desirablelow reactance under normal con-ditions and a high reactance underfault conditions.

Load Flow Control Reactors areseries connected on transmissionlines up to 800 kV.The reactors change the line impedance characteristic such thatload flow can be controlled, thusensuring maximum power transferover adjacent transmission lines.

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Filter Reactors

Filter Reactors are used in conjuctionwith capacitor banks to form series tuned harmonic filter circuits,or in conjunction with capacitorbanks and resistors to form broad-band harmonic filter circuits.

When specifying filter reactors,the magnitudes of fundamentaland harmonic frequency currentshould be indicated. If inductanceadjustment for fine tuning is required, the required tapping rangeand tolerances must be specified.

Many filter applications require aQ-factor which is very much lowerthan the natural Q of the reactor.This is often achieved by connectinga resistor in the circuit.An economical alternative is theaddition of a de Q'ing ring structureon a reactor. This can reduce theQ-factor of the reactor at tuningfrequency up to as much as onetenth without the necessity of in-stalling additional damping resi-stors. (see Fig. 9 below)

These rings, mounted on the reactorare simply coupled to the magnetic

Fig. 8Filter reactors

Fig. 9Filter reactors with

de Q’ing rings

Fig. 7Schematic diagram

Fig. 10Capacitor/filter protection relay

field of the reactor. This eliminatesthe concern of space, connectionand reliability of additional compo-nents such as resistors.

The Capacitor/Filter ProtectionRelay CPR 04 is a microprocessorbased protection relay speciallydesigned for optimized protectionof shunt banks and harmonic filtercircuits.

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Static VAR Compensators are used on transmission systems to improve the overall reliability, correct forvoltage fluctuations and power factor as well as increasing the transmission capability and reducing losses.

Shunt Reactors

Shunt Reactors are used to compensate for capacitive VARsgenerated by lightly loaded trans-mission lines or underground cables. They are normally connectedto the transformer tertiary windingbut can also be directly connectedon systems up to 115 kV.

Fig. 11Schematic diagram

Fig. 14Thyristor controlled reactor

Fig. 12Tertiary connected

shunt reactors

Fig. 13Thyristor controlled shunt reactors and filter

reactors in a Static VAR Compensator

Thyristor Controlled Shunt Reactors are extensivelyused in static VAR systems, wherereactive VARs are adjusted by thyristor circuits. Static VAR compensator reactor applicationsnormally include:

• Thyristor controlled shunt reactors(TCR). The compensating poweris changed by controlling thecurrent through the reactor bymeans of the thyristor valves.

• Thyristor switched reactors (TSR)

• Thyristor switched capacitor reactors (TSC)

• Filter reactors (FR)

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HVDC-Reactors

HVDC lines are used for long distance bulk power transmission

Fig. 15Schematic diagram

Fig. 17HVDC-Smoothing reactor

Fig. 16AC-Filters

a) AC - PLC b) AC - FR c) HVDC - SMR d) DC - FR e) DC - PLC

as well as back-to-back inter-connections between differenttransmission networks.HVDC Reactors normally include

Smooting Reactors, AC and DCHarmonic Filter Reactors as well as AC and DC PLC Noise Filter Reactors.

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Smoothing Reactors

Smoothing reactors are used to reduce the magnitude of the ripplecurrent in a DC system. They areused in power electronics applications such as variable speeddrives and UPS systems. They arealso required on HVDC transmissionlines for system voltages up to500 kV. Several design and constructiontechniques are offered by Trench.

Fig. 18Schematic diagram

Fig. 19Iron core,

forced air cooled reactor

Fig. 20Air core,

encapsulated winding design

Fig. 21Iron core,

water cooled reactor

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Test Lab Reactors

Test Lab Reactors are installed inhigh voltage and high power testlaboratories. Some typical applications include current limiting,synthetic testing of circuit breakers,inductive energy storage, artificiallines, etc.

Fig. 22Schematic diagram

Fig. 23Reactor bank for the

voltage circuit for synthetic testingof circuit breakers; 32 kA peak to peak,

0,318 mH to 353,6 mH, up to 1600 kV BIL

Fig. 25Short circuit test reactor

Fig. 24Adjustable

current limiting reactor

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Neutral Grounding Reactors

Neutral Grounding Reactors limitthe line to ground fault current tospecified levels. Specificationshould also include unbalancedcondition continuous current andduration.

Fig. 26Schematic diagram

Fig. 27Arc suppression coil 110 kV

Fig. 28Standard arc suppression coil

Arc Suppression Coils

Single-phase neutral grounding(earthing) reactors (arc suppressioncoils) are intended to compensatefor the capacitive line-to-groundcurrent during to a single phaseground-fault.The arc suppression coil (ASC) represents the central element ofthe Trench earth fault protection system.

Since the electric system is subjectto changes, the inductance of theASC used for neutral earthingmust be variable.

The earth fault detection systemdeveloped by Trench utilizes theplunger core coil (moveable coredesign). Based on extensive experi-ence in design, construction andapplication of ASCs, Trenchproducts can meet the most strin-gent requirements for earth faultcompensating techniques.

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A Trench air core dry type reactorconsists of a number of parallelconnected, individually insulated, aluminum (copper onrequest) conductors. These conductors can be small wire orproprietary cables custom designedand manufactured.

The size and type of conductorused in each reactor is dependanton the reactor specification. Thevarious styles and sizes of conductors available ensure optimum performance at the mosteconomical cost. The windings aremechanically reinforced withepoxy resin impregnated fibreglass,which after a carefully definedoven cure cycle produces an encapsulated coil. A network ofhorizontal and vertical fibreglassties coupled with the encapsulationminimizes vibration in the reactorand achieves the highest availablemechanical strength.

The windings are terminated ateach end to a set of aluminum barscalled a spider. This constructionresults in a very rigid unit capableof withstanding the stresses developed under the most severeshort circuit conditions.

Exceptionally high levels of terminalpull, tensile strength, wind loadingand seismic withstand can be accommodated with the reactor.See Fig. 29 for details on construction.

This unique design can be installedin all types of climates and environments and still offer optimum performance.

Trench air core dry type reactors are installed in pollutedand corrosive areas supplyingtrouble free operation. In additionto the standard fixed reactancetype of coil, units can be suppliedwith taps for variable inductance.A number of methods are availableto vary inductance for fine tuningor to provide a range of larger inductance steps.

Trench utilizes various otherdesigns for reactors (eg. iron core,water cooled, etc.) which aredescribed in other sections of thiscatalogue.

Construction

Fig. 29Typical Trench air core dry type

reactor construction

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It is the customer's responsibilityto consider these minimum clearances, especially if steel reinforcing in concrete foundationsor floors, or structural steel is involved in the building or stationdesign. It is important, even outsidethese minimum magnetic clearan-ces, to avoid closed electrical loopswith metallic parts.

Terminals/Magnetic Clearance

D

If required, non-magnetic extensionbrackets can be supplied by Trench to maintain the necessary magnetic clearancebelow the reactor. Trench canprovide additional details on spacerequirements and recommended reinforcing steel(rebar) design, if requested.

Magnetic Clearence

Minimum clearances to metallicparts, and between coils, must bemaintained as indicated by Figs. 32and 33. The values shown are onlyguidelines. Each specific reactordesign will specify magnetic clearance requirements.

Fig. 30Terminal orientation

Fig. 31Terminal details

Fig. 32Minimum magnetic clearance to other reactors and metallic parts

not forming closed loops (approximate values only)

Terminals

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Generally, air core, dry type reactors can be installed in eitherside by side or vertically stackedconfigurations and are oftenadded to existing substations orlocations where space limitationsexist. With its highly developedcomputer design expertise,Trench can design reactors withoptimized dimensions, to suit limited space requirements. Themulti-spider construction allowsflexibility in terminal location,which minimizes connection problems (see Fig. 35).

Number of spider arms to be obtained from the actual quotationdesign.

Installation assembly is minimaland typically requires only thatbrackets and insulators be boltedto the main coil. Installation instructions are provided witheach reactor order.

Trench takes into consideration all aspects of the reactor installation. These includerequirements of ventilation, reactor supports, connections andbusbar arrangements.

Trench can also provide detailedinformation regarding:

• magnetic field distribution analysis for mounting pads andfoundations, grounding grids,fences and adjacent structures

• Force calculations on adjacentcoil installations, bus and cableconnections

Installation

• Seismic analysis on entire reactorassemblies, including support insulators and mounting pedestals,when furnished.

Fig. 33Three-phase

stacked arrangement

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Testing

At Trench each reactormanufactured is subjected to a rigorous test and inspection program. In addition to the routinetesting required by ANSI/IEEE orIEC a number of in-process testsare performed on each unit duringproduction to ensure maximum in-service reliability. Each reactor issupplied with a certified test reportwith the results from all tests performed.

In addition to routine testing wehave the capability in our HighVoltage and Power labs to performmost of the design tests describedin the applicable standards. Designtests can be performed at an additional cost or test reports onsimilar units can be supplied uponrequest.

The materials used in the manufacture of the reactor arealso subject to a strict test program.Cooling duct spacers and the fibreglass epoxy resin compositeencapsulation are subject to routinemechanical strength and trackingresistance testing. Acceleratedthermal and multifactor aging studies are carried out which helpto verify performance of the reactor components over their fullservice life.

This testing coupled with our Quality Assurance program enablesus to ensure the continuous perfor-mance of our reactors throughoutthe design service life.

Losses

The custom design approach usedby Trench allows optimum use ofmaterials to control reactor losses.If a loss evaluation is not indicated in the specification, thereactor will be designed to meetthe applicable standards at a mosteconomical initial cost.

All customers are aware of the advantages in minimizing systemlosses and are applying loss evaluation techniques for reactorpurchases. In the cases where lossevaluations are included in the reactor specifications, Trenchoptimizes the initial cost of thereactor plus the cost of operating losses, to ensure themost economical balance. Generally, a loss optimized reactorwill operate at a lower temperaturerise and will thus extend the reactoroverload capability.

Trench's ability to design andmanufacture low loss reactorsallow many electric power utilitiesto economically justify the replacement of older, inefficientreactor installations. The low lossreactors can usually be installed onexisting mounting pads.

Losses can also be influenced forother purposes. In some applicationsit is important to control the Q factor(X/R ratio) of the reactor. This maybe important at the fundamentalfrequency or at specific harmonicfrequencies where additional lossesare advantageous, for example capacitor switching reactors andcertain filter applications.

Testing/Losses

Fig. 34High voltage test laboratory

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Trench designs and manufactures enclosures and support pedestals specifically forair core, dry type reactors.

Enclosures, depending on the requirement, are made of steel orfibreglass and can be designed forindoor or outdoor installations.Trench enclosure design minimizescirculating current loops and opti-mizes the size by defining ventila-tion area and acceptable tempe-rature rise. Enclosures have beenqualified as complete assemblies by short circuit testingof the enclosed reactor.

Trench can supply support pede-stals to elevate reactor live parts toa height commensurate with per-sonnel safety standards. Pedestalsalso provide proper magnetic clearance below the reactor. Various pedestal designs are available and include fibreglass,braced aluminum and non-magneticsteel designs.

Trench can recommend the mostpractical pedestal for each reactorapplication. Additional informationon enclosures and pedestals isavailable on request.

Sound shields can be provided toreduce the reactor noise level forspecial applications (HVDC).

Enclosures and Pedestals

Fig. 35Filter reactor with sound shield

Fig. 36Filter reactor with top-hat

and pedestal

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Data required with order

• Reactor application

• Indoor or outdoor installation

• System voltage,impulse insulation level (BIL)

• Rated and maximumcontinuous current(fundamental and harmonics)

• Short circuit current leveland duration

• Rated inductance/impedance

• Mounting arrangement(side by side or vertical stack)

• Detailed accessoryrequirements (connectors,buswork, etc.)

• Location of installation andsite conditions

• Ambient temperature range

Änderungen vorbehalten04.09

E 600

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