Corporate Technology
HTS Rotating Machines Basics Concepts Siemens Demonstrator Possible applications Developments worldwide (+Siemens) Challenges to be overcome Dr. Wolfgang Nick Siemens AG, Corporate Technology, Power & Sensor Systems
[email protected] European Summer School, Pori, Finnland, 2008 Copyright © Siemens AG 2006. Alle Rechte vorbehalten.
Basics
Basics
Electrical machines: motors and generators (+ transformers) electrical power ÅÆ mechanical power extremely large range:
~ mm to 10m, µW to 1000 MW slow, high force/torque ÅÆ high speed almost everywhere !
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, …
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June 2008
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© Siemens AG, Corporate Technology
Utilization of Superconductor How to use superconductivity for electric machines? what machines? Which properties to utilize?
Which create difficulties?
Meissner effect coil = permanent magnet flux pinning dc current capacity high current density ...
low temperature range requiring unefficient cooling ac losses mechanical limits (esp. HTS) costly ...
Machine concepts:
- completely innovative designs (based on specific sc material behaviour),
or - “improved conventional designs“ (high current density, zero losses) Seite 3
June 2008
W. Nick, CT PS 3
© Siemens AG, Corporate Technology
Overview of Machine Concepts
Hysteresis machine Reluctance machine Pictures taken from:
Induction machine
A.Sfetsos et al. “Flux Plot Modelling of Superconducting Hysteresis Machines“
No good superconducting solution! Synchronous machine = standard for efficient, high-power application (more specific: electrically excited, radial flux synchronous machine)
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© Siemens AG, Corporate Technology
Induction Machine “work horse“ for most applications rotor needs no coils, just a conducting layer, at least “squirrel cage“ slower (rotor) speed than rotating stator fields Æ induced currents, rotor magnetization Æ interact with driving stator fields to generate torque
B stator
advantage: very simple rotor
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at first:
seems easy to replace cage by sc structure
but:
ac conditions, losses cryogenic cooling required
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W. Nick, CT PS 3
Æ no longer simple ! © Siemens AG, Corporate Technology
Synchronous Machine
rotor with DC excitation winding rotates synchroneously in AC generated stator field
2 types: a) cylindrical rotor machine b) salient pole machine: b) is well suited for implementation of (flat) HTS coils ! Seite 6
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© Siemens AG, Corporate Technology
Calculation of Torque and Power
torque / length
~ n*Istat * Br * R ~ A1*R * Br * R
Br : radial magnetic induction
of rotor at position of stator
power = torque * speed ~ A1 * Br * R² *L * speed power/volume
A1 [A/m]:
~stator current per circumference
~ A1 * Br * speed
How can we increase this?
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June 2008
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© Siemens AG, Corporate Technology
Comparison: Conventional Design Stator core Stator tooth
Stator winding (Cu) Î Laminated stator core with teeth Î Stator copper winding Î Rotor copper winding
B A1 P
=1T = 1 p.u. = 1 p.u.
(1:stator 2:rotor) Losses:
Rotor iron Seite 8
June 2008
PCu1
= 1 p.u.
PCu2
= 1 p.u.
PFe
= 1 p.u.
Rotor winding (Cu) W. Nick, CT PS 3
© Siemens AG, Corporate Technology
Let‘s switch to HTS Design ! Stator core Stator tooth
Stator winding (Cu) Î Rotor HTS winding Î Laminated stator core without teeth Î Stator copper winding
B A1 P
= 2 T (-x) = 2 p.u. ≈ 4 p.u. (-y)
Losses:
Rotor winding HTS winding (Cu)
Rotor iron Seite 9
June 2008
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PCu1
= 2 p.u.
PCu2
= 0 p.u. + PCooling
PFe
= 0.6 p.u.
© Siemens AG, Corporate Technology
Task of Siemens Model Machine
Goals to be demonstrated: high power density at improved efficiency But is it technically achievable ? Æ Check feasibility: rotating HTS windings robust rotor cooling system air gap stator winding
goals of 400kW HTS model machine
interaction of innovative components test in different configurations…
1999 – 2002 funded by BMBF
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© Siemens AG, Corporate Technology
Mechanical & Cryogenic Concept
drive end
cooling
room temperature
vacuum insulation
• rotor = rotating cryostat • torque transmission (cold Æ warm) with minimum heat influx • cooling via hollow shaft (needs a rotating seal) • stator: without iron teeth, iron yoke, and housing
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magnetic air gap
© Siemens AG, Corporate Technology
Cooling Options
Needed: High current density in large background field Æ HTS < 40K Possible coolants: Neon - Hydrogen - Helium gas or liquid Tliquid at 1bar 27K 20K > 4.2K =4.2K Problem: Transfer of cooling power from (ext.) refrigerator to rotating HTS coils Avail. cooling modes: thermal conduction forced convection heat pipe / thermosiphon Avail. refrigerators: LHe liquefiers GM refrigerators (1-/ 2-stage) Stirling machine Pulse Tube Refrigerator others…
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June 2008
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© Siemens AG, Corporate Technology
Capability of Neon Thermosiphon (Heat Pipe)
20°C Condensation
Thermosiphon
10 cm²
1000 times
L=1 m
more powerful !!!
heat pipe
40 W ΔT < 0,5 K
ΔT = 10 K
Copper at RT
4W
26,0 K
liquid/gaseous Neon at ~26K
1 cm² L=1m
26K +x x=ΔTcond +ΔTevap
30°C
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June 2008
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or more
Evaporation
© Siemens AG, Corporate Technology
Cooling System for Model Machine
Compressor
• GM Cryocooler 40W @ 25K Cold Head (commercially avail.: up to 100W) • heat transfer by thermosiphon into center of rotor • Cooling medium: Neon Condensor boiling point ~ HTS operation point
Thermosiphon (Heat Pipe) Evaporator Seite 14
June 2008
Rotating Feedthrough W. Nick, CT PS 3
• modular • robust • reliable
© Siemens AG, Corporate Technology
Let‘s design an HTS 4-pole rotor!
This is essentially the design of the Siemens model machine Seite 15
June 2008
W. Nick, CT PS 3
© Siemens AG, Corporate Technology
Cross Section in FE Analysis
stack of HTS pancake coils
prestressed bandage
distribution of |B | in coil cross section Seite 16
June 2008
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resulting deformation (enlarged) due to rotation and EM forces © Siemens AG, Corporate Technology
Winding of Rotor Coils Quality control for HTS: - performance at operating cond. Charge NST 90607(SIE#56) - dimensions - insulation 50
IC in A
45 40 35 30 100
150
200
250
Länge in m
Leiterdicke in mm
0,40 0,35 0,30 0,25 0,20 0,15 100
150
200
250
Leiterbreite in mm
Länge in m 3,5 3,4 3,3 3,2 3,1 3,0 2,9 2,8 2,7 2,6 2,5 100
150
200
250
Länge in m
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© Siemens AG, Corporate Technology
Manufacturing Rotor of HTS Model Machine
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© Siemens AG, Corporate Technology
Manufacturing Stator of HTS Model Machine
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 Seite 19
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© Siemens AG, Corporate Technology
CAD of 400kW Model Machine
HTS rotor winding rotating cryostat torque transmission
hollow shaft for rotor cooling air core stator winding
iron yoke
telemetry
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June 2008
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© Siemens AG, Corporate Technology
Testing 20 kV, 50 Hz
20 kV, 50 Hz
resistor bank
Belastungswiderstand
Master-Drive AC-Umrichter
HTS machine connected to conventional load machine
400 V, 50 Hz • • *)
• •
Q3
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
Q1
• •
• •
Q2
Stromrichter
HTS machine =
HTSL
load machine exciter const. current
Belastungsmaschine
Konstantstromgerät
“short“ experiments: overload, load switching, short circuit “long“ experiments: temperatures, efficiencies, limits Seite 21
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Electrical Characteristics of Conventional Machine
Open Loop / No Load
1,2
U, I
1,0 Short Circuit Characteristic
only small excitation voltage (no load)
0,8 0,6
large addl. excitation to overcome armature response
0,4 0,2 0,0 0
10
with varying power excitation has to be controlled ! Seite 22
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20
30
40
50
60
If (A) © Siemens AG, Corporate Technology
Characteristics of HTS Machine
dashed lines: plot for conv. machine
1,2
U, I
1,0
opposite behaviour, compared to conventional machines !
0,8 0,6
HTS machine
0,4
open loop
0,2
short circuit
0,0 0
10
20
30
40
50
60
If (A) Seite 23
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© Siemens AG, Corporate Technology
Excursion: Phasor Diagrams (schematic)
I1 * Xd
for conventional machine: large Xd
large Xd → large load angle θ
U1 Up I1
phase angle φ
load angle θ
I1 * Xd U1 = Up - I1*Xd Up
I1
small Xd → small reaction → small load angle θ → full stability for any phase φ
for HTS machine with air gap armature: xd
