Presentation on theme: "High Temperature Superconductivity in Electrical Power Devices:"— Presentation transcript:
1 High Temperature Superconductivity in Electrical Power Devices: Applications ofHigh Temperature Superconductivityin Electrical Power Devices:the Southampton perspectiveProfessor J.K. Sykulski, FIEE, SMIEEE, FInstPSchool of Electronics & Computer ScienceUniversity of Southampton, UKUniversityof SouthamptonSuperconductivity UK, 23 October 2003
2 (High Temperature Superconductivity) Applications of HTS(High Temperature Superconductivity)ceramic materials discovered in 1986conductivity 106 better than copperoperate at liquid nitrogen temperature (78K)cheap technology (often compared to water cooling)current density 10 times larger than in copper windingsgreat potential in electric power applications (generators, motors, fault current limiters, transformers, flywheels, cables, etc.), as losses are significantly reducedpresent a modelling challenge because of very highly non-linear characteristics and anisotropic properties of materials, and due to unconventional designs
3 HTS transformer built and tested at Southampton 1998/99
4 HTS transformer built and tested at Southampton 1998/99
5 HTS transformer built and tested at Southampton 1998/99
6 HTS transformer built and tested at Southampton 1998/99 Field plots with and without flux diverters
7 HTS transformer built and tested at Southampton 1998/99
8 I Field and current penetration in HTS tape Diffusion of current density into HTS tapexyHTS tapeIFlow of transport current through an HTS tapeAC loss as a function of average current density
9 HTS tape subjected to an external magnetic field 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 and thus the system is very non-linear.
10 HTS tape subjected to an external magnetic field The governing equation:The FD scheme:whereCij =and R=x/y
11 HTS tape subjected to an external magnetic field AC loss as a function of Hm (applied peak magnetic field strength)
15 Superconducting generators and motors Losses in conventional and superconducting designs
16 Superconducting generators and motors LTS (Low Temperature Superconductivity) has not been successful in electric power applicationslow reliabilityhigh costdifficult technologyImpact of HTS (High Temperature Superconductivity)better thermal stabilitycheaper coolingimproved reliability
17 Superconducting generators and motors All conceptual HTS designs and small demonstartors use BSCCO tapes at temperatures between 20K and 30Kat 30K critical fields and currents order of magnitude better than at 78Kit is possible to have a core-less designBut !!!liquid neon or helium gas neededincreased cost and complexity of refrigeration plantreduced thermodynamic efficiencyworse reliability and higher maintenance requirements
18 Superconducting generators and motors Southampton design100 kVA, 2 polecooling 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 coilsrotor made of cryogenic steel (9%)10 identical pancake coils made of BSCCO (Ag clad Bi-2223), length of wire approx 10 x 40m
19 Machine DesignStatorAn existing 100kVA stator with 48 slots and a balanced 2-pole 3-phase winding has been usedThe pitch of the stator coils ensures that the winding produces very little 7th harmonic fieldHigher order fields are reduced significantly by the distribution of the phase conductors throughout each phase beltThe primary concern is the 5th harmonic
20 Machine Design Rotor and field winding The rotor is made of 9% nickel steelThe core is formed by thirteen plates of various shapes and sizesThe HTS rotor winding is made of silver clad BSCCO-2223 tapes10 identical coils and each coil has 40 turnsNominal critical current of >100A at 77K self-fieldEach superconducting coil is separated by the flux divertersThe required low temperatures are provided using purpose built closed circuit liquid cryogen cooling system with pipe-network feeding liquid cryogen to the rotor body
24 2D Modelling and Analysis In early designs the rotor was made of Invar, but this was rejected due to large difference in thermal expansion coefficient- Difficult to connect to stainless steel shaftAfter thorough investigation, it was decided to use 9% Nickel steelThe 9% Nickel steel is usually produced in plates- Each plate is 22 mm thick- Various shapes and sizesRotor with Invar designRotor with 9% Nickel steel design
25 2D Modelling and Analysis The latest design changes:The HTS coils was reduced to 10 instead of 12 in previous designEach coil has 40 turnsThe plates were made from different thickness
26 2D Modelling and Analysis The distribution of the normal field in the HTS coils and the flux potential plot. The flux diverters successfully reduced the normal field to only 0.038T with the air-gap flux at 0.66T.
27 2D Modelling and Analysis Gap field up to 19th orderFlux density (T)Angle (deg)Harmonic components of air gap flux and phase voltage0.02%190.01%170.19%150.07%130.39%111.29%90.18%70.17%50.49%3100%1% Harmonic voltage contributionActual harmonicWinding factorSine harmonic magnitudeSpace harmonic order3D modelling?2D modelling prevents some important features from being investigated:The effect of the through bolts and their holes.The leakage flux at the ends of the rotor.
28 3D Modelling and Analysis StatorwindingStatorHTS field windingFluxDivertersRotor
30 3D Modelling and Analysis The flux density vectors and its distribution
31 3D Modelling and Analysis 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
32 3D Modelling and Analysis 0.03%190.02%170.11%150.09%130.41%110.59%90.18%71.46%50.47%3100%1% harmonic voltage contributionActual harmonicWinding factorSine Harmonic magnitudeSpace harmonic order5th harmonic voltage causes the most significant problemThe undesirable 5th harmonic voltage is higher than predicted in 2DTotal rms harmonic voltage in the 3D model increases from 1.47% to 1.716%Require further 3D optimisation!Angle (deg)Flux density (T)
33 Field OptimisationTo reduce the 5th harmonic, the gap density is reduced at an angle where the 5th harmonic contribution is positive.Two methods:(1) Sink the bolts deeper into the core.(2) Reduce the width as shown in the diagram.The total rms harmonic voltage improved from 1.46% to 1.35% and the 5th harmonic reduced to 0.55%.However mechanical constraint allowed only slight improvement.
34 Modelling of Eddy-Current Loss Two type of losses:No-load tooth ripple losses due to the distortion of the fundamental flux density wave by the stator slotting.Full transient non-linear rotating machineAssumed fixed value of field current (as the cold copper screen prevents changes in reluctance and changes of stator MMF from affecting the value of field current)Fixed rotation velocity of 3000 rpmFull-load losses that include the effects of the MMF harmonics of the stator winding.Static and steady-state modelsTransient solution too slow due to low resistance of the cold copper the time constants are very long
35 Modelling of Eddy-Current Loss No-load lossesEddy currents occur as 48th time harmonicTransient losses were estimated and subtractedTotal no-load loss found to be W
36 Modelling of Eddy-Current Loss Full-load lossesDominating 5th harmonic (and much smaller 7th)Losses due to 11th and higher harmonics negligibleTotal full-load loss found to be W(a) DC field(b) Additional 6th time harmonic fieldContours of vector potential: (a) Non-linear static model and (b) Linear AC model with new current densities defined in each stator slot and incremental permeability data taken from the static model.Total power loss in the cold region is W.
37 Summary of eddy current losses No-load losses: WFull-load losses: WThese losses are released at liquid nitrogen temperature and have to be removed using the inefficient refrigeration systemEach 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)
38 Fault Condition Simulation Full transient non-linear rotating machine modelLosses due to the transient were estimated using a rotating machine simulationEnd winding leakage inductance was estimated and addedFixed time step equivalent to a period for the rotor to pass one stator slotSimulation was set to run for a period of 2.5 cycles (largest currents occur during this period)External circuit is connected to finite- element model (to simulate 3-phase short circuit fault condition)
39 Fault Condition Simulation Results:Currents in each phase are recorded from each output time-step (curves fitted as shown)High losses in the stator winding (cause large torque)Peaks at approximately 1.7 MWGradually decrease to steady value as the trapped flux decays
40 Fault Condition Simulation Results:Large current also produce large torqueSpeed reduces rapidly to % after 50 ms of simulationTemperature increases to 103K
41 ConclusionsIncreasing activity around the world in HTS applications for power devicesAll existing demonstrators use HTS tapes at temperatures 20 to 30 K (helium or neon gas)Southampton design for 78KParameters of new tapes improved dramaticallyAbility to predict and reduce all ‘cold’ losses of paramount importance to show economic advantages of HTS designs
42 Thank you Superconductivity UK, 23 October 2003 University of SouthamptonSuperconductivity UK, 23 October 2003