Current Transformers with nanocrystalline cores

Transcription

1 Current Transformers with nanocrystalline cores

2 Power Measurement MeasurementErrors Exact power value P true = U I cos φ Measured power value including errors P meas ( 1 F( I) ) ( φ + ϕ ( I) ) = U I cos P P meas true Error P [% ] = 100 P true Power error DP [%] , Primary current I prim [A rms ] CurrentTransformers withnanocrystalline cores Page 2

3 Power Measurement Functional principlesof currenttransducers Shunt resistor Hall Effect sensor Pickup coil sensor Current transformer with fluxconcentrating pole pieces withgapped laminated core Rogowski-Coil (no core) gapped laminated core withgapped ferrite core with ferrite core with optimised toroidal VAC core D complexjoining technology D no galvanicseparation D lowoutputvoltage D outputdriftsovertime D high offset, high T-drift offset extensive compensation D lowoutputsignals D needsintegrator C securegalvanicseparation C high dynamicrange C insensitive to external magneticfields(closed core) Dominant technology D high susceptabilityto external magneticfieldsforfield-detecting measurementmethods( shielding) differentiation bymaterial CurrentTransformers withnanocrystalline cores Page 3

4 Toroidal Core CTs CT Design Fundamental Formulae I prim I sec Burden resistor R B Toroidal soft magnetic Primary Secondary core current conductorwinding Material: permeabilities core losses d, µ = ' '' µ s + i µ s '' µ s δ = ' µ s tan saturationinduction B sat Current ranges Errors CurrentTransformers withnanocrystalline cores Page 4

5 Toroidal Core CTs CT design Maximum primaryac current I sec I prim N prim =1 N sec R B ω = 2π f R Cu U B Current range : I maxrms ω N 2 2 sec R = R Cu + R B Bˆ sat A R Fe Primary current range increases with highersaturation induction B sat crystalline, amorphous and nanocrystallinecores (B sat > 1T) superiorto ferrites (B sat ~ 0.4T) increased corecross section A Fe drawbacks: highercost, biggercomponent, A Fe R ~ A Fe decreased winding resistance RCu exhaustavailable windingspace Mostly R Cu >> R B, withr Cu ~ N sec ² R ~ N sec ², increasingn sec does notextendprimary currentrange. CurrentTransformers withnanocrystalline cores Page 5

6 I prim ω = 2π Errors improve with f I sec N prim N sec R B R Cu Toroidal Core CTs CT design Errors Phase error: Amplitude error: ϕ( I) F( I) FOM = arctan sinδ R ω L R ω L higherpermeabilityµ µ L, crystalline, amorphous, nanocrystallinecores (µ > ) superiorto ferrites (µ< 15000) R ω L lowercorelosses (amplitudeerror) amorphous and nanocrystallinecores superior to crystallinecores and ferrites U B R = R Cu + R B ρ µ Cu decreased winding resistance R Cu exhaustavailable windingspace CurrentTransformers withnanocrystalline cores Page 6

7 Toroidal Core CTs Materials Non-DC-tolerantCTs 0,60 0,40 0,20 High-perm crystalline(c), amorphous(am) and nanocrystalline (NC) cores Phase error j [ ] crystalline ULTRAPERM 10 nanocrystalline VITROPERM 500 F amorphous VITROVAC 6025 F AM, NC: no load dependence of phase error 0,00 Amplitude error [%] ~ (bigger) ferrite AM, NC: Low amplitude errors Losses! -0,20 I prim [A rms ] 0, Easy error compensation requires independence of L, tan δ on load and temperature + stable production processes with low tolerances for µ and tan δ. CurrentTransformers withnanocrystalline cores Page 7

8 Toroidal Core CTs - Material selection: Non-DC-tolerantCTs accuracy very high high High current range + low errors Amorphous high-µ VITROVAC Nanocrystallinehigh-µVITROPERM 80%NiFe ULTRAPERM medium high-µ ferrite toolow 50%NiFe PERMENORM 3% SiFeTRAFOPERM primarycurrent CurrentTransformers withnanocrystalline cores Page 8

9 Toroidal Core CTs CT design Maximum unipolar current I sec I prim N prim N sec R B U B Current range : Iˆ DC max = π µ 0. Bˆ sat µ l Fe ω = 2π f R Cu Unipolar current rangeincreases with highersaturation induction B sat crystalline, amorphous and nanocrystallinecores (B sat > 1T) superiorto ferrites (B sat ~ 0.4T) lowerpermeability µ lowµ low L generally higheramplitudeand phase errors increased corelength l Fe highercost, biggercomponent CurrentTransformers withnanocrystalline cores Page 9

10 Toroidal Core CTs Materials DC-tolerant CTs 6 Low-permnanocrystalline core basically no loadand temperature dependence easy compensation Phase error j [ ] Phase and amplitudeerrorshave to becompensated; compensation easy, if errorsdo notvarywith temperatureand load Amplitude error [%] , I prim [A rms ] CurrentTransformers withnanocrystalline cores Page 10

11 Toroidal Core CTs - Material selection: DC tolerant CTs accuracy very high high High unipolar current range + low errors Nanocrystalline low-µvitroperm Amorphous low-µ VITROVAC newlow-µ VITROPERM variants medium low-µferrite toolow 50%, 80%NiFe, 3% SiFe primarycurrent~ unipolar current CurrentTransformers withnanocrystalline cores Page 11

12 Furtherdevelopmentof material basis: New low-µnanocrystalline VP alloys Toroidal Core CTs New developments: Low-perm VITROPERM cores, integrated CTs smallercores (OD) nanocrystalline material costsavings Design of application-specific and customer-specific components_ Integration of CT fore.g. 3 phase applicationsinto 1 component easierassembly costsavings Customer-specificdesigns CurrentTransformers withnanocrystalline cores Page 12

13 Integrated seamlessprimary conductor radial through ID of core connection to meterbasethroughblades Toroidal Core CTs New developments: CT with integrated primary conductor Picture to visualizeconcept optimizedcoregeometry (ID smaller) less expensivecopper bar costsavings CurrentTransformers withnanocrystalline cores Page 13