HTS Rotating Machines - Prizztech Oy · HTS Rotating Machines • Motivation ... constant supercurrents Æoperates as synchronous motor • ... Stirling machine

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Corporate Technology

HTS Rotating Machines• Motivation• Concepts• Siemens Model Machine & Results• Development Strategy, Steps• Conclusion

Dr. Wolfgang NickSiemens AG, Corporate Technology, Corporate Research and Technology

GTF: Power Components & Thermodynamic Processes

[email protected]

ESAS Summer School, Turku, Finland, June 2011

Seite 2 June 2011 © Siemens AG, Corporate TechnologyW. Nick, CT T DE HW4

Scenario

Systems for energy transformation, consumption and generation are changing worldwide, due to limited resources and climate consequences of this use.Efficient utilization of electricity has to be part of these solutions superconductivity!

Source:Ludwig-B

ölkow-System

technik Gm

bH, 2008


Power of rotating machines

Electricity is the best form of energy• Versatile• Efficient (esp. with superconductivity)• Generated where the sources are,

used at the application

Industrial power consumption in Germany?(mining, metals, machine building, chemical, ...)• Total 2300 PJ• Electricity 750 PJ• ~60% of that for (large) rotating machines!

valuable, must not be spoiled

(how much is 1kWh?10t truck at 100km/h)

Energy balance for Germany, unit: PJ = 1015J, 2009

Source: Arbeitsgem

einschaft Energiebilanzen, 2010


BasicsBasics

Electrical machines: motors and generators (+ transformers)

electrical power mechanical power

extremely large range: ~ mm to 10m, µW to 1000 MWslow, high force/torque high speed

basic principle: Lorentz force force / length = current I x induction B+ forces on magnetic dipoles, ferromagnetic parts …

different configurations:rotating vs. linear, cylindrical vs. plane, …

I

BF


Utilization of Superconductor

How to use superconductivity for electric machines?

Which properties to utilize?

Machine concepts: ● innovative designs(based on specific sc material behaviour),

or● “improved conventional designs“

(high current density, zero losses)

Meissner effectflux pinningHTS permanent magnet (trapped flux)Coil in permanent modenon-resistive dc currenthigh current density...

Lot of space for brilliant inventions

Ishikawa..., M

T-11, 1989


Survey of Machine Concepts:Hystereses / Reluctance Machine

Hysteresis machine

What about cooling? Rotor is immersed in bath of LN2, so stator windings are also cooled by LN2

reduced resistance, improved performance (but less efficiency !)

Reluctance machine

Source: Sfetsos et al. “Flux Plot Modelling of Superconducting H

ysteresis Machines“

Rotor:superconducting cylinder

in a (conventional) rotating stator field

Rotor:massive cylinder

stacked of bulk superconductor and non-sc metal or insulator


Overview of machine concepts:Synchr. Machine with HTS bulk magnets

Recipe:• Take a conventional PM excited machine• Replace magnets by innovative HTS bulk magnets

Idea:Flux density of conv. NdFeB magnets: ~1Twith magnetized HTS bulk material: 2T ... 5T (... 10T)

so the torque/power will increase accordingly.

Problems:• How to create stable trapped flux of that size?

Must always be kept at suff. low temperature• Magnetize in situ? Or move magnet / rotor?• Needs a very strong magnetizing winding

= another superconducting magnet• ...

NS

SNN

S

SN

NS

SN

Great potential, if these difficulties can be passed !


Overview of Machine Concepts:Induction Machine

“Workhorse“ in todays application, small to medium sizerotor needs no coils, just a conducting layer, at least “squirrel cage“slower (rotor) speed than rotating stator fields

induced currents magnetized rotor interacts with driving stator fields torque

What, if we add HTS bars to the cage? (+ immerse in LN2)

• Acceleration: operates as (good) induction motor with ac losses conductor heating• Close to nom. speed: constant supercurrents operates as synchronous motor

• (Whenever conductor gets too hot normalconducting induction machine)

HTS induction/synchronous machine with increased torque

SIMPLE

B stator

Nakam

ura et al: SuST 24, 2011


Potential Application Field

15 rpm 150 rpm 1500 rpm 15,000 rpm

where efficiency and/or compactness and/or dynamic performanceprovide valuable customer advantages !

high torqueship propulsion (5 -30 MW)

wind power geno's (2 -10 MVA)

industry geno's (20 -50 MVA)

high speed geno's (directly coupled to gas turbine)

utility generators (100 - 900 MVA)

industrial motors (1 -10 MW)


Synchronous Machine

rotor with DC excitation windingrotates synchroneously in AC generated stator field

2 types:a) salient pole machine:b) cylindrical rotor machine

a) is well suited for implementation of (flat) HTS coils !

Synchronous machine = standard for efficient, high-power applicationmore specific: electrically excited, radial flux synchronous machine)


Calculation of Torque and Power

force / length ~ n*Istat * Br

torque / length ~ n*Istat * Br * R ~ A1*R * Br * R

power = torque * speed~ A1 * Br * R² *L * speed

power/volume ~ A1 * Br * speed

How can we increase this?

• Increase exciter induction Br by using sc coils

• Increase total stator currentby taking out the iron teeth(possible due to capability of sc coils)

Br : radial magnetic inductionof rotor at position of stator

A1 [A/m]: ~stator current per circumference

Flux lines Br intersecting stator currents torque generation

Iron yoke,to reduce magnetic resistance


Comparison: Conventional Design

Stator core Stator winding (Cu)

Rotor iron Rotor winding (Cu)

Stator toothLaminated stator core with teeth

Stator copper winding

Rotor copper winding

B = 1 TA1 = 1 p.u.P = 1 p.u.(1:stator 2:rotor)Losses:

PCu1 = 1 p.u.

PCu2 = 1 p.u.

PFe = 1 p.u.


Let‘s switch to HTS Design !

Stator core Stator winding (Cu)

Rotor iron Rotor winding (Cu)

Stator tooth

HTS winding

Laminated stator core without teeth

Stator copper winding

Rotor HTS winding

B = 2 T (-x)A1 = 2 p.u.P ≈ 4 p.u. (-y)Losses:

PCu1 = 2 p.u.

PCu2 = 0 p.u. + PCooling

PFe = 0.6 p.u.


Task of Siemens Model Machine

Goals to be demonstrated:high power density at improved efficiency

But is it technically achievable ?

Check feasibility:

rotating HTS windings

robust rotor cooling system

air gap stator winding

interaction of innovative componentstest in different configurations…

} goals of 400kW HTS model machine

1999 – 2002funded by BMBF


Mechanical & Cryogenic Concept

• rotor = rotating cryostat

• torque transmission (cold warm) with minimum heat influx

• stator: without iron teeth, iron yoke, and housing

• cooling via hollow shaft (needs a rotating seal)

drive end

vacuum insulation

room temperature cooling

magnetic air gap


Cooling Options

Needed:High current density in large background field HTS < 40K

Cooling modes: thermal conductionforced convectionheat pipe / thermosiphon

Possible coolants: Nitrogen - Neon - Hydrogen - Helium gas or liquidTboil at 1bar: 77K 27K 20K > 4.2K =4.2K

How transfer of cooling power to rotating HTS coils?

Avail. refrigerators: (classical) LHe liquefiers GM refrigerators (1-/ 2-stage)Stirling machinePulse Tube Refrigeratorothers…


Capability of Thermosiphon (Heat Pipe)

Heat Pipeliquid/gaseous Neon

Evaporation Condensation

Thermosiphonis

10 x 20 x 10x = 2000 times

more powerful !!!

40 W

1 cm²L=1m or more

ΔT < 0,5 K26K +x 26,0 K

x=ΔTcond+ΔTevap

10 cm²

L=1 m

20°C

30°C

ΔT

= 10

K4

W

Copperat RT


Let‘s design an HTS 4-pole rotor!

This is essentially the design of the Siemens model machine


Winding of (MoMa) Rotor Coils

100 150 200 25030

35

40

45

50

Charge NST 90607(SIE#56)

I C in

A

Länge in m

100 150 200 2500,15

0,20

0,25

0,30

0,35

0,40

Leite

rdic

ke in

mm

Länge in m

100 150 200 2502,52,62,72,82,93,03,13,23,33,43,5

Leite

rbre

ite in

mm

Länge in m

Quality control for HTS:- performance at operating cond.- dimensions- insulation


Manufacturing (MoMa) Rotor


Manufacturing (MoMa) Stator

Air Gap Stator Winding• placed into a G10-structure

to take the forces/moments• winding of coils using

Litz wire to reduce eddy losses• passages for air cooling• to be inserted into yoke • torque transmission

by G-10 support structure


CAD of 400kW Model Machine

HTS rotor winding

torque transmission

telemetry

air core stator winding

hollow shaft for rotor cooling

iron yoke

rotating cryostat


Testing Setup

HTS machine connected to conventional load machine

Operation: as motor or as generator• as generator: connected to grid or to ohmic load

• as motor: driven by grid directly, or by variable frequency inverter

“Short“ experiments: overload, load switching, short circuit“Long“ experiments: temperatures, efficiencies, limits

excitercurrent

load machine

HTS mach.

resistor bank


Electrical Characteristics of a Conventional Machine

0,0

0,2

0,4

0,60,8

1,0

1,2

0 10 20 30 40 50 60If (A)

U, I

only small excitation voltage (no load)

large addl. excitation to overcome armature response

Open Loop / No Load

Short Circuit Characteristic

With varying powerexcitation has to be controlled !

(15 >50 A)

driven at nom. speed


Characteristics of the HTS Machine

opposite behaviour!

compared to conventional machines !

Interpretation: weak coupling rotor–stator, small xd = synchroneous reactance

0,0

0,2

0,4

0,6

0,8

1,0

1,2

0 10 20 30 40 50 60If (A)

U, I

open loop

short circuit

HTS machine

dashed lines: plot for conv. machine


Excursion: Phasor Diagrams (schematic)

U1 = Up - I1*Xd

for conventional machine: large Xd

for HTS machine with air gap armature: xd << 1

I1

I1

U1

Up

Up

I1 * Xd

I1 * Xd

phase angle φload angle θ

large Xd→ large load angle θ

small Xd→ small reaction → small load angle θ→ full stability

for any phase φ


Measured Electrical Data

Siemens HTS demo machine

• nominal rating: 380 kW, 1500 rpmmeasured: 450kW (short term: 600kW)

• field winding current: 49 A (HTS)• armature: 400 V, 560 A• total harmonic distortion: < 0.15%

(conventional: ≤ 3%)• low noise• synchronous reactance: xd = 0.15

(conventional ~ 2.3)however: • large excitation time constant !

(high inductance / low resistance of HTS winding)

• sensitive to grid harmonics

0,0

100,0

200,0

300,0

400,0

500,0

600,0

0 10 20 30 40 50 60 70

If (A)

U (V

)

open loop

measured

calculated

-400

-300

-200

-100

0

100

200

300

400

0 20 40 60 80

time (ms)

open loop voltage

very smooth


Losses and Efficiency

0

4

8

12

16

20

Asynchronmaschine400 kW, cos = 0,87

Synchronmaschine400 kVA, cos =1,0(leistungsoptimiert, hohe Stromdichte)

HTS-Modellmaschine380 kW

Verlu

ste

[kW

]

Kryokühler

Läufer-Cu+ ErregungStänder-Cu

Zusatzverluste,WirbelströmeEisen

Lager+Lüfter

99 %

98 %

97 %

96 %

Efficiency

Stator

Rotor

Compressorfor Cryocooler

Induction machine400 kW, cosϕ = 0,87

conventional Synchronous machine

400 kW, cosϕ = 1,0(power optimized)

400 kW HTSModel Machine(not optimized)


Dynamic Behaviour

small load angle: 8° measured at 400 kW

0

1

2

3

0 10 20 30 40 50 60 70 80 90Load Angle (degrees)

Torq

ue (r

el. u

nits

)

conventional machine

HTS machine

extremely large pull-out torque ( ≈ 700%!)

very stable behaviourno problems with underexcited operation→ well suited for reactive power compensation

stable voltage (ΔU ≈ 0) subject to full (ohmic) load switching without any excitation control

-500

-400-300

-200-100

0

100200

300400

500

1120 1140 1160 1180 1200 1220 1240 1260 1280

Zeit in ms

U in

V-2000

-1600-1200

-800-400

0

400800

12001600

2000

I in

A

Strom

Spannung


Pro‘s and Con‘s of HTS Machines

Advantages

increased efficiencymore compact, reduced weightbetter stability, high overload capabilityvoltage qualityreactive power capabilityless noise and vibration(no armature teeth)

Challenges

HTS conductor materialcryogenic cooling + vacuum technologyremove losses from high-power-density stator windingget end-users accustomedto operational procedureshas to compete with well-optimized “cheaper“conventional products


Development Strategy

A “revolutionary innovative technology“ as HTS technology requires a structured longterm development effort

Proof-of-principle for technology solutionsScale-up for tests in realistic dimensions (for different applications)Development of the application case(s) + product development

and continuously stable funding support

1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

HTS I HTS IIHTS III

Longterm Test

Model Machine400 kW 1500 rpmBasic Technology

4 MVA Generator60 Hz, 3600r rpmHigh speed test

4 MW Motor300 kNm, 120 rpmHigh torque test

Generatorconnected to MV Long term test


HTS II: 4MVA 3600rpm Generator

Main goals: develop technologies for 3600rpmscale-up and verify size/efficiency goals

Results• size / weight comparison

~ 70% space of conv. solutionmass 7t instead of 11tshaft height 500mm inst. 800mm

• efficiency

2005: Nuremberg System Test Facility

0%

20%

40%

60%

80%

100%

Conventional HTS

Loss

es

CryoRotor field ohmicStray loadArmature ohmicCoreFriction & Windage

0%

20%

40%

60%

80%

100%

Conventional HTS

Loss

es

CryoRotor field ohmicStray loadArmature ohmicCoreFriction & Windage

HTS

η = 97.0 %

η = 98.7 % approx. ½ of losses of standardconventional machines !

Cryocoolingfor HTS rotor


HTS III: 4MW 120rpm Motor parameters & design

Main goals: develop technologies for high torquescale-up, handle large sizes, check inverter operation

Requirements• robustness & efficiency• variable speed 30-190 rpm• nom: 120 rpm, 4 MW• >120 rpm: field attenuation• weight <40 t• efficiency 96%

Design• verify design procedures

Challenges

• torque 320 kNm• logistics, size of

components, tools,...• ~50km HTS• inverter harmonics


• HTS procurement & QS• coil winding & cold test• rotor assembly (no photo)• final rotor test• stator & machine housing• final assembly (no photo)

HTS III: 4MW Motor manufacturing & assembly


HTS III: 4 MW Motor testing

Results

• weight goal achieved !

• open-loop & short-circuit characteristic:as expected, xd ~ 0.3

• acceptable rotor losses ≤ 120Win all operational states

~10kW compressor power

• unexpected stator losses,over-saturation of stator iron?

conv. component, not critical in this project

• no difficulty with standard SM-150 inverter

• short circuit tests up to 30% excitation robust

0

1000

2000

3000

4000

0 20 40 60 80 100I f / A

U /

V

U_stator_3dMessung


Conclusion

What is achieved?Feasibility has been demonstrated also in realistic scale.Technical advantages can be realized.

However – remember slide “Development strategy“This is not yet a qualified Siemens product!Next steps: product development & qualification

test of prototypes in pilot applications at the customer

Hurdles to this:Cost of unusual components, special manufacturing processes...(superconductors, cryogenics & vacuum technology...)Proof of long-term reliability of components and conceptsLimited commercial advantage for customer, presentation of integrated system performance is required

But, my personal view, in the long run: the technology of superconductivitywill be an essential ingredient of a future, efficient electric power technology !

Competing with a proven conventional technology that has been continuously

optimized for a century !

Main task for CT = central development

Task for BU, with CT support

Documents

HTS Rotating Machines - Prizztech Oy · HTS Rotating Machines • Motivation ... constant supercurrents Æoperates as synchronous motor • ... Stirling machine