applications of high temperature superconductivity in electrical power devices: the southampton...

Applications of Applications of

High Temperature Superconductivity High Temperature Superconductivity

in Electrical Power Devices:in Electrical Power Devices:

the Southampton perspectivethe Southampton perspective

Professor J.K. Sykulski, FIEE, SMIEEE, FInstPProfessor J.K. Sykulski, FIEE, SMIEEE, FInstP

School of Electronics & Computer Science

University of Southampton, UK

University

of Southampton Superconductivity UK, 23 October 2003Superconductivity UK, 23 October 2003

Applications of HTSApplications of HTS (High Temperature Superconductivity)(High Temperature Superconductivity)

•conductivity 106 better than copper

•current density 10 times larger than in copper windings

•cheap technology (often compared to water cooling)

• great potential in electric power applications (generators, motors, fault current limiters, transformers, flywheels, cables, etc.), as losses are significantly reduced

•operate at liquid nitrogen temperature (78K)

•ceramic materials discovered in 1986

• present a modelling challenge because of very highly non-linear characteristics and anisotropic properties of materials, and due to unconventional designs

HTS transformerHTS transformer built and tested at Southampton 1998/99built and tested at Southampton 1998/99


Vac

uum

Spa

ce

Conductionpaths

ThermalInsulation

CoolingCoil

ThermalInsulation

Current Leeds

Vac

uum

Spa

ce

Vapour

Liq

uid


Field plots with and without flux diverters

0

1

2

3

4

5

6

7

8

9

10

11

0 10 20 30 40 50 60

Secondary Current (A)

Lo

ss (

W)

Measured (no Flux Diverters)

Calculated (no Flux Diverters)

Calculated (with Flux Diverters)

Measured (with Flux Diverters)


I

x

y

HTS tape

Flow of transport current through an HTS tape

Field and current Field and current penetration in penetration in HTS tapeHTS tape

Diffusion of current density into HTS tape

AC loss as a function of average current density

Rhyner model:

The critical current density Jc corresponds to an electric field Ec of 100 Vm1, and c = Ec/Jc.

The power law contains the linear and critical state extremes ( = 1 and respectively).

In practice 10 - 20 and thus the system is very non-linear.

HTS tape subjected to an external magnetic fieldHTS tape subjected to an external magnetic field

,1

1

02

2

2

2

EE

ty

E

x

Ec

The governing equation:

The FD scheme:

where

Cij =

and R=x/y



AC loss as a function of Hm (applied peak magnetic field strength)

Current

Field angle

Electric field

0o

45o

90o

Experimental verificationExperimental verification

Superconducting generators and motorsSuperconducting generators and motors

Why ?


Losses in conventional and superconducting designs


LTS (Low Temperature Superconductivity) has not been successful in electric power applications

•low reliability•high cost•difficult technology

Impact of HTS (High Temperature Superconductivity)

•better thermal stability•cheaper cooling•improved reliability


All conceptual HTS designs and small demonstartors use BSCCO tapes at temperatures between 20K and 30K

•at 30K critical fields and currents order of magnitude better than at 78K

•it is possible to have a core-less design

But !!!

•liquid neon or helium gas needed

•increased cost and complexity of refrigeration plant

•reduced thermodynamic efficiency

•worse reliability and higher maintenance requirements


Southampton design

•100 kVA, 2 pole

•cooling at 78 / 81 / 65 / 57 K (liquid nitrogen or air / sub-cooled nitrogen or air)

•magnetic core rotor design

- reduces the ampere-turns required by a factor of ten

- significantly reduces fields in the coils

•rotor made of cryogenic steel (9%)

•10 identical pancake coils made of BSCCO (Ag clad Bi-2223), length of wire approx 10 x 40m

Machine DesignMachine DesignStatorStator

An existing 100kVA stator with 48 slots An existing 100kVA stator with 48 slots and a balanced 2-pole 3-phase winding and a balanced 2-pole 3-phase winding has been usedhas been used

The pitch of the stator coils ensures that The pitch of the stator coils ensures that the winding produces very little 7the winding produces very little 7thth harmonic fieldharmonic field

Higher order fields are reduced Higher order fields are reduced significantly by the distribution of the phase significantly by the distribution of the phase conductors throughout each phase beltconductors throughout each phase belt

The primary concern is the 5The primary concern is the 5thth harmonic harmonic

Rotor and field windingRotor and field winding The rotor is made of 9% The rotor is made of 9% nickel steel nickel steel

The core is formed by The core is formed by thirteen plates of various thirteen plates of various shapes and sizes shapes and sizes

The HTS rotor winding is The HTS rotor winding is made of silver clad made of silver clad BSCCO-2223 tapesBSCCO-2223 tapes

10 identical coils and each 10 identical coils and each coil has 40 turnscoil has 40 turns

Nominal critical current of >100A at 77K self-fieldNominal critical current of >100A at 77K self-field

Each superconducting coil is separated by the flux divertersEach superconducting coil is separated by the flux diverters

The required low temperatures are provided using purpose built The required low temperatures are provided using purpose built closed circuit liquid cryogen cooling system with pipe-network closed circuit liquid cryogen cooling system with pipe-network feeding liquid cryogen to the rotor bodyfeeding liquid cryogen to the rotor body

Machine DesignMachine Design

Machine DesignMachine Design

In early designs the rotor was made of Invar, but this was rejected due to large difference in thermal In early designs the rotor was made of Invar, but this was rejected due to large difference in thermal expansion coefficientexpansion coefficient

- Difficult to connect to stainless steel shaft- Difficult to connect to stainless steel shaft

After thorough investigation, it was decided to use 9% Nickel steelAfter thorough investigation, it was decided to use 9% Nickel steel

The 9% Nickel steel is usually produced in platesThe 9% Nickel steel is usually produced in plates

- Each plate is 22 mm thick- Each plate is 22 mm thick

- Various shapes and sizes - Various shapes and sizes

Rotor with Invar designRotor with Invar design Rotor with 9% Nickel steel designRotor with 9% Nickel steel design

2D Modelling and Analysis2D Modelling and Analysis

The latest design changes:The latest design changes:

The HTS coils was reduced to 10 instead of 12 in previous designThe HTS coils was reduced to 10 instead of 12 in previous design

Each coil has 40 turns Each coil has 40 turns

The plates were made from different thicknessThe plates were made from different thickness


The distribution of the normal field The distribution of the normal field in the HTS coils and the flux in the HTS coils and the flux potential plot. The potential plot. The flux divertersflux diverters successfully reduced the normal successfully reduced the normal field to only field to only 0.038T0.038T with the with the air-air-gap fluxgap flux at at 0.66T0.66T..



Harmonic components of air gap flux and phase voltage Harmonic components of air gap flux and phase voltage

0.02%0.0000870.003444-0.00133219

0.01%0.0000500.000535-0.00555017

0.19%0.0008510.0092600.00612715

0.07%0.000322-0.003893-0.00635813

0.39%0.0017370.0052460.03010011

1.29%0.005714-0.023096-0.0274899

0.18%0.000776-0.002635-0.0420907

0.17%0.000771-0.038555-0.0040005

0.49%0.0021800.081732-0.0088903

100%0.4418580.7581380.5828201

% Harmonic voltage

contribution

Actual harmonic

Winding factor

Sine harmonic magnitude

Space harmonic

order

2D modelling prevents some important features from being investigated:2D modelling prevents some important features from being investigated:

The effect of the through bolts and their holes.The effect of the through bolts and their holes.

The leakage flux at the ends of the rotor.The leakage flux at the ends of the rotor.

3D modelling?3D modelling?

-0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 30 60 90 120 150 180

1

3

5

7

9

1-19

2D

Gap field up to 19Gap field up to 19thth order order

Flux density (T)

Angle (deg)

Rotor

Flux Diverters

HTS field winding

Stator

Stator winding


The flux density vectors and its distributionThe flux density vectors and its distribution


The field over a patch of 180 degree arc and 200mm length at 160mm The field over a patch of 180 degree arc and 200mm length at 160mm radius is analysed to extract the harmonics of the air gap flux density radius is analysed to extract the harmonics of the air gap flux density



0.03%0.0001420.003444-0.00217519

0.02%0.0000770.000535-0.00844617

0.11%0.0005280.0092600.00380115

0.09%0.000400-0.003893-0.00790813

0.41%0.0018950.0052460.03284411

0.59%0.002736-0.023096-0.0131649

0.18%0.000823-0.002635-0.0446287

1.46%0.006747-0.038555-0.0349995

0.47%0.0021810.081732-0.0088973

100%0.4606890.7581380.6076581

% harmonic voltage

contribution

Actual harmonic

Winding factor

Sine Harmonic magnitude

Space harmonic

order

-0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 30 60 90 120 150 180

1

3

5

7

9

1-19

2D

Angle (deg)

Flux density (T)

55thth harmonic voltage causes harmonic voltage causes the most significant problemthe most significant problemThe undesirable 5The undesirable 5thth harmonic voltage is higher harmonic voltage is higher than predicted in 2Dthan predicted in 2DTotal rms harmonic voltage Total rms harmonic voltage in the 3D model increases in the 3D model increases from 1.47% to 1.716%from 1.47% to 1.716%Require further 3D Require further 3D optimisation!optimisation!

Field OptimisationField Optimisation

However mechanical constraint allowed only slight However mechanical constraint allowed only slight improvement.improvement.

To reduce the 5To reduce the 5thth harmonic, the gap density is reduced at an angle where the 5 harmonic, the gap density is reduced at an angle where the 5thth harmonic contribution is positive. harmonic contribution is positive.

(1) Sink the bolts deeper into the core.(1) Sink the bolts deeper into the core.Two methods:Two methods:(2) Reduce the width as shown in the diagram.(2) Reduce the width as shown in the diagram.

The total rms harmonic voltage improved from 1.46% The total rms harmonic voltage improved from 1.46% to 1.35% and the 5to 1.35% and the 5thth harmonic reduced to 0.55%. harmonic reduced to 0.55%.

No-loadNo-load tooth ripple losses due to the distortion of the tooth ripple losses due to the distortion of the fundamental flux density wave by the stator slotting.fundamental flux density wave by the stator slotting.

Full transient non-linear rotating machineFull transient non-linear rotating machine Assumed fixed value of field currentAssumed fixed value of field current (as the cold copper (as the cold copper screen prevents screen prevents changes in reluctance and changes of stator changes in reluctance and changes of stator MMF from affecting the value of field current)MMF from affecting the value of field current) Fixed rotation velocity of 3000 rpmFixed rotation velocity of 3000 rpm

Two type of losses:Two type of losses:

Full-load Full-load losses that include the effects of the MMF harmonics losses that include the effects of the MMF harmonics of the stator winding.of the stator winding.

Static and steady-state modelsStatic and steady-state models Transient solution too slowTransient solution too slow due to low resistance of the due to low resistance of the cold cold copper the time constants are very longcopper the time constants are very long

Modelling of Eddy-Current LossModelling of Eddy-Current Loss

Eddy currents occur as 48th time harmonicEddy currents occur as 48th time harmonic Transient losses were estimated and subtracted Transient losses were estimated and subtracted Total no-load loss found to be Total no-load loss found to be 0.264 W0.264 W

No-load lossesNo-load losses


Dominating 5th harmonic (and much smaller 7th)Dominating 5th harmonic (and much smaller 7th) Losses due to 11th and higher harmonics negligibleLosses due to 11th and higher harmonics negligible Total full-load loss found to be Total full-load loss found to be 2.319 W2.319 W

Full-load lossesFull-load losses

Contours of vector potential: Contours of vector potential: (a)(a) Non-linear static model and Non-linear static model and (b)(b) Linear AC model Linear AC model with new current densities defined in each stator slot and incremental permeability with new current densities defined in each stator slot and incremental permeability data taken from the static model. data taken from the static model.

(a)(a) DC field DC field (b)(b) Additional 6th time harmonic field Additional 6th time harmonic field

Total power loss in the cold region is Total power loss in the cold region is 2.583 W2.583 W..


Summary of eddy current lossesSummary of eddy current losses

•No-load losses: 0.264 W

•Full-load losses: 2.319 W

•These losses are released at liquid nitrogen temperature and have to be removed using the inefficient refrigeration system

•Each 1W of loss to be removed requires between 15 – 25 W of installed refrigeration power at 78K (a similar figure at 4K would be about 1000 W)

Losses due to the transient were estimated using a rotating Losses due to the transient were estimated using a rotating machine simulationmachine simulation End winding leakage inductance was estimated and added End winding leakage inductance was estimated and added Fixed time step equivalent to a period for the rotor to pass Fixed time step equivalent to a period for the rotor to pass one stator slotone stator slot Simulation was set to run for a period of 2.5 cyclesSimulation was set to run for a period of 2.5 cycles (largest (largest currents occur during this periodcurrents occur during this period))

Fault Condition SimulationFault Condition Simulation

Full transient non-linear rotating machine modelFull transient non-linear rotating machine model

External circuit is External circuit is connected to finite-connected to finite- element element model (to model (to simulate 3-phase simulate 3-phase short short circuit fault circuit fault condition)condition)

R

R

Ric

ib

ia

L

L

L

ea

ec eb

External circuitHTS Generator

Circuit data:Power supply = 0Phase angle = 0Resistance = 0.029 ohmInductance = 0.125 mHCapacitance = 0Circuit length = 325 mmCircuit type = Filament

Conductor data:Turns = 3Resistance/mm=0

Terminal shortcircuit

Currents in each phase are recorded from each output Currents in each phase are recorded from each output time-step (curves fitted as shown)time-step (curves fitted as shown)High losses in the stator winding (cause large torque)High losses in the stator winding (cause large torque)

Peaks at approximately 1.7 MW Peaks at approximately 1.7 MW Gradually decrease to steady value as the trapped flux Gradually decrease to steady value as the trapped flux decaysdecays


Results:Results:

Large current also Large current also produce large produce large torquetorque

Speed reduces rapidly to Speed reduces rapidly to 19.45% after 19.45% after 50 ms of 50 ms of simulationsimulation Temperature increases to Temperature increases to 103K 103K

Results:Results:


ConclusionsConclusions • Increasing activity around the world in HTS

applications for power devices

• All existing demonstrators use HTS tapes at temperatures 20 to 30 K (helium or neon gas)

• Southampton design for 78K

• Parameters of new tapes improved dramatically

• Ability to predict and reduce all ‘cold’ losses of paramount importance to show economic advantages of HTS designs

Thank Thank youyou

University

of SouthamptonSuperconductivity UK, 23 October 2003Superconductivity UK, 23 October 2003

applications of high temperature superconductivity in electrical power devices: the southampton...

Documents

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o slide

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