Air Core Reactors - ccaps.umn.edu · PDF fileNote : eddy loss calculations are normally done ... Electrodynamic Forces ... managing air core reactor magnetic

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Air Core Reactors:Magnetic Clearances, Electrical Connection,

and Grounding of their Supports

David CaverlyKlaus PointnerRoss Presta

Minnesota Power Systems ConferenceNovember 2017

Peter GrieblerHelmut ReisingerOtto Haslehner

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Voltages:600 V to 1000 kV (Series)600 V to 500 kV (Shunt)

Power:5 kVAr to 600 MVAr(60 Hz Equivalent)

Inductance:0.01 mH to 10 H

Current:6000 -8000 Amp for“normal” applications

up to 320 kApeak

Dry Type Air Core ReactorsApplications

for TransmissionSystems

up to765 kV

Current Limiting & PowerFlow Control Reactors

up to500 kV,and150 MVAr/3 phase

Shunt Reactors

Filter Reactors

Current LimitingReactors

Capacitor (Damping)Reactors

HVDC Reactors

Electric Arc FurnaceReactors

Test Reactors

up to100 MVAr /Phase

HVDC SmoothingReactorsup to 800 kV,600 MVAr(incl. seismicdesign)

Note:

Modern Dry Type Air CoreReactors are Custom Designed tothe application. There are no“standard” ratings.

up to4000 A

forDistributionSystems

built according to specificcustomer’srequirements

Thyristor ControlledShunt Reactors

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Dry Type Air Core Reactor Construction:

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Magnetic Field of Air Core Reactors:Plot of Magnetic Flux Density B

ƒ Air Core >>stray field

ƒ Axial & radial components

ƒ Interacts with metallicparts, connections, andthe winding itself

axial

axial

radial

axial

axial

axial

axial

radial

radial

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Magnetic Field of Air Core Reactors:Magnitude Contours of Flux Density B

ƒAt the reactormid-plane:

ƒ field strengthdrops off as theinverse of thecube of thedistance r

Reactormid-plane

418A, 114.23 ohm @ 60Hz, 20 Mvar

50 mT5 mT

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Magnetic Field of Air Core Reactors:Implications of Stray Magnetic Field

Implications of Stray Field:

ƒ eddy currents & lossesin conducting parts

ƒ Induced currents, lossesand forces in closedloops

ƒ forces on current carryingconductors

axial

axial

radial

axial

axial

axial

axial

radial

radial

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Implications of Stray Magnetic FieldEddy Currents

B

I eddy

Radial FieldEddy Currents

B

I eddy

Axial FieldEddy Currents

Connectors

Insulator Caps

Eddy currents are in inducedin all conducting parts in thereactor stray magnetic field

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Implications of Stray Magnetic FieldEddy Current Losses

Eddy Current Loss estimation

ƒ

ƒ

ƒ which can be re-arranged as:

,

Loss dependenceapproaches the cube

of the thickness(depending on )φ

W/m

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Implications of Stray Magnetic FieldEddy Current Losses

Key take Aways:ƒ eddy losses (P) are strongly

dependent on the thicknessof the profile normal to thefield (d)

… and also …ƒ 2BP×

Note : eddy loss calculations are normally doneusing FE methods

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Implications of Stray Magnetic FieldInduced Currents in Closed Loops

Key Take Awaysƒ The strength and direction of the field

AND the orientation of the loop ALLmatter; it is ALL about flux linkage

ƒ If the Xloop >> Rloop (typical) then higher Rjust means higher losses and heating(current does not change much)

Horizontal planeloop linking axial flux

component

Horiz. plane loop linking axial flux component

Vertical plane looplinking radial flux

component


Implications of Stray Magnetic FieldElectrodynamic Forces

ƒ Lorentz Force Lawƒ “Right Hand Rule”ƒ = ƒ = ∅ƒ (t) is oscillatoryƒ direction is lateral to

spider/terminalƒ to minimize force :

minimize ∅

∅


Practical Implications of the Theory:Magnetic Clearance Guidelines

ƒ MC1: Clearance to smallmetallic parts not formingclosed loops

ƒ MC2: Clearance to largemetallic parts or partsforming closed loops

ƒ Clearances are shown ondrawings (based on fieldstrengths)

ƒ OD/2 & OD: roughapproximations


Practical Implications of the Theory:Terminal Losses and Terminal Heating

Terminal temperature rises are a function of :ƒ Terminal contact resistanceƒ I2R of through current

ƒ Eddy Losses – can be the biggest proportion of terminal heating

Admissible Limits for Reactor Terminal Temperature Rise


Practical Implications of the Theory:Eddy Losses in Terminals and Connectors

60mT30mT


Eddy Losses in Terminals and ConnectorsConnector Loss as a function of Connector Thickness

Reactor Data:• 3160A• 19mH• Mvar50 = 59.6• OD : 128 in.• Length : 47 in.

Optimum connector thickness approx. 10 – 12mm (3/8 to 1/2 in.)


Eddy Losses in Terminals and ConnectorsConnector Loss as a function of Thickness and Orientation

Over 50%increase inconnectorlosses bychangingconnectororientation


Practical Implications of the Theory:Axial versus Opposite Sides Arranged Cables

Axial Cables Opposite Sides Cables


Practical Implications of the Theory:Inappropriate Connection Case Study : Tangential Cables

TCR1: 8 ohm, 3283 Amp85.7 Mvar/phase


Practical Implications of the Theory:Inappropriate Connection Case Study : Tangential Cables

Radial FieldLinking CableLoops

Test Setup

35mT


Practical Implications of the Theory:Recommended Connection

ƒ radial connection(minimizes forces andflux linkages)ƒ perpendicular to coil

vertical axisƒ bus support or axially

arranged cablesƒ sufficient cable sag –

mechanical isolation


Practical Implications of the Theory:Recommended Connector Design

ƒ axially arranged cablesƒ minimize profile to radial fieldƒ connected on one side of terminal

onlyƒ minimize connector thickness (1/2

inch or less)ƒ Stainless bolts & bellville washers


Practical Implications of the Theory:Circulating Currents in Horizontal Plane Loops - Foundations

Problem:ƒ I2R heating of rebar,

foundation cracking,short circuit forces

Solutions(alternatives):ƒ Use fiberglass rebarƒ Isolate rebar

crossovers with hoseƒ Maintain at least MC2

clearance

Horizontalplane rebar

loopslinking axial

fluxcomponent


Practical Implications of the Theory:Circulating Currents in Fences and Ground Grid

I

I

Problem:

ƒ Induced currents inloops formed by fenceencircling complete setof reactors

ƒ Involvement of highresistance contact atgate latch and lock



Problem:ƒ Induced currents in vertical plane loops and ground

grid formed by the fence and multiple fence groundswhich are typically provided to satisfy NESCgrounding/step and touch requirements

I



Solutions:ƒ Sectionalize fence to allow

multiple groundsƒ ground each section of the

fence in only one locationƒ provide a parallel (to latch and

lock) low resistance copperpath for current to flow fromthe gate to the adjacent postground connectionƒ avoid vertical plane loops by

using insulated stringer wires

Solutions:Safety first – satisfy NESC &IEEE 80 grounding guidelines



Problem:ƒ Loops created by

connecting fences tometal buildingsƒ High resistance contact

>> severe local heatingSolution:ƒ do not connect fences to

metal buildings – use anadjacent post & separateground for the building


Practical Implications of the Theory:Circulating Currents in Reactor Supports

Problem:

ƒ closed loops formed by lattice structure (oftensteel) >> loop current (I) >> heating, forces

Solution (alternatives):ƒ maintain at least MC2 clearance

ƒ isolate joints to avoid closed loops(not easy)

ƒ utilize a radial arm structure

ƒ purchase purpose built structures from thereactor supplier

I


Single point star or daisy chaingrounding of base pedestals

Practical Implications of the Theory:Recommended Grounding of Reactor Base Pedestals


Conclusions & Summary

General:ƒ Stray fields: eddy currents, closed loop currents,

losses, forcesƒ for “small” reactors, all of this is less criticalConnections:ƒ radial connection (minimizes forces and flux linkages)ƒ axially arranged cables are the bestConnectors:ƒ minimize the profile to the stray field; more metal

does not necessarily mean cooler terminals


Conclusions & Summary (continued)

Fences:ƒ Safety > satisfy NESC & IEEE 80ƒ segmentation, single point grounding of fence

segmentsƒ grounding: avoid loops involving the ground gridCoil Support Structures:ƒ radial cross arms are better than steel lattice

structuresƒ single point connection to the ground grid (daisy

chain or star)


Conclusions & Summary (continued)

managing air core reactor magneticclearances, connections and grounding is

fairly straightforward,

… once the principles are understood


Thank youfor your attention!


Questions ?


David CaverlyVP Business DevelopmentCoil Products

71 Maybrook DriveScarborough, Ontario, M1V4B6Canada

Phone: +1 416 298-8108 ext 231Fax: +1 416 298-2209Mobile: +1 416 953-3796

E-mail: [email protected]

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Air Core Reactors - ccaps.umn.edu · PDF fileNote : eddy loss calculations are normally done ... Electrodynamic Forces ... managing air core reactor magnetic