superconducting dc transmission lines for electric …. 75 (2004) pp.207. low thermal conductivity...

Center of Applied Superconductivity and Sustainable Energy Research

Superconducting DC transmission lines for electric power as energy saving systems

Toshio KawaharaCenter of Applied Superconductivity and Sustainable Energy Research (CASER),

Chubu University


No. 1Global warming and exhausting energy resources

Warming in the world

Ref: IPCC fourth assessment report (2007)

Oil peak

Ref: M.K. Hubbert; American Petroleum Institute (1956).

CO2 come from fossil energy could cause the global warming.

•Energy saving•Change to sustainable natural energy

Heat

greenhouse effect gas


No. 2

Genesis project

Solar power Wind power Solar power works well only at day time.

Sustainable energy can be transferred to the world by power grids to solve this.normal conducting transmission or superconducting (SC) one

Example of SC AC transmissionY. Kuwano; 4th International Photovoltaic Science and Engineering Conference (1989) .H. Kitazawa; Japan and its economical dreams by a scientist (2002) (in Japanese).

(Albany, USA)

wind Solar SC cable


No. 3

SC DC transmission for Ultra long distance

DC has advantage for the long distance.

Superconducting DC transmission

Low lossLow voltage → Low cost?

Base for the actual use of the sustainable energy

ABB Asea Brown Boveri Ltd.; http://www.abb.com/HVDC/.


No. 4

AC transmission

DC equipments at home

Natural energy

DC distributionInternet data center(iDC)

Server works with DC power

AC-DC conversion

Home

Power plant

Future DC transmission

Energy saving and SC transmission

Ultra long distance transmission for the natural energy

Energy super highway using SC-DC transmission

Steam power


No. 5

20 m DC superconducting transmission line

Ingredients for SC transmission lines1. Superconductors2. Cryogenic systems3. Supporting Circuits

Low heat loss and low cost systems should be developed.

DC superconducting transmission line has been constructed in Chubu University

S. Yamaguchi, et al.: J. Phys.: Conf. Ser., Vol. 97 (2008) 012290.

Terminal A Terminal B

DC power supply

Superconducting cable

Measurements terminal box


No. 6

High Tc superconductor materials

Both tapes are useful for transmission and distribution.

1. Y-123 coated conductors: Potentially cheap tapes.

2. Bi-2223 tapes: It seems to be better for cryogenic systems with higher Tc.

There are many superconductors.

Now two kinds of superconductors can be used as high Tc superconductors.


No. 7

Superconducting Cables

Powder in tube (PIT) methods for Bi tapesRef: H. Kitaguchi and H. Kumakura; MRS Bulletin 26 (2001) 121.

Bi Multifilament tape

coated conductors for Y-123

SEI has developed commercial tapes using controlled over-pressure (CT-OP) method.

Several methods could be selected.ex.) CVD (SuperPower Inc.)

MOD (American Superconductor)PLD or evaporation (LANL)

Stabilization layer: Cu, Au etc.

Superconducting layer: Y-123, Gd-123 etc.

Buffer layer: YSZ, Gd2Zr2O7, MgO, CeO2, LaMnO3 etc.Substrate: Hastelloy,

Stainless steel etc.


No. 8

Superconducting AC transmission line

• Normal-conducting AC grid systems are widely used. – Easy to obtain high voltage by a transformer– Easy to break the circuits– No need of expensive UHV AC-DC converters

• Superconducting AC transmission seems to be fit to conventional grid systems with low loss systems.

• However, – There are small AC loss.– 3 cables are required. Then, it is higher cable cost.– Long distance transmission is difficult because of phase

imbalance.


No. 9

AC grid experiments using AC cables

There are many projects in U.S., Korea, Japan etc.


No. 10

AC losses

• Hysteresis loss– Magnetization curve has

hysteresis energy loss.• Coupling loss (Eddy current

loss)– Shielding current should flow

between filaments.– Then, the current goes

through normal metals.

Twisted multifilament conductors have small AC loss.

Hysteresis loss Coupling loss

Current flows in the whole conductorsOptimum region

fc1: inverse of coupling current time constantHp: center reachable magnetic field

F. Sumiyoshi et al.; J. Appl. Phys. 50 (1979) 7044.

Suppose time varying magnetic field is applied to multifilament SC conductors

AC losses


No. 11

AC cables design

Sumitomo 3-in-One HTS Cable for Albany(http://www.sei.co.jp/super/cable_e/index.html)

Three American Superconductor’s HTSC cables were used for AC transmission lines on LIPA.

For AC, 3 cables or 3-in one type cable are standard designs.

LIPA1


No. 12

DC cable design

図2-2-4 三相一括交流ケーブルと直流ケーブルの断面模式図

Three phase AC cable and DC cable

Advantage of DC as a cryogenic system

1. Simple structure is effective for low cost system.

2. Low heat loss cable with small diameter is high performance in cryogenics.

20 m cables used for superconducting transmission line in Chubu University

40φ

insulation30kVDC

earth layer

formercopper wires

HTS Tape x 39

Simple and small cables are for low cost and high performance systems


No. 13

Cryogenic system

• Heat loss in the cryogenic systems.– Double pipes are most important for large systems.– Terminals are important for small systems. – Cryo-cooler and pumps – small circulation loss of LN2 are required

for actual systems.

Cooler and

pumpLN2

Terminal B

Terminal ACurrent

Double pipes

SC cables

LN2

Schematic pictures for DC transmission lines


No. 14

Emissivity of metals

MaterialsFulk, Reynolds,

Park(1955) T = 300 K and 78K

McAdams(1954)T = 300K

Amano, Ohara(1990, 1991)

T = 300 K and 78 KAl（Polished） 0.02 0.04 0.036~0.04

Al（Oxide） 0.31Brass（Plished） 0.029 0.03Brass（Oxide） 0.6Cu（Polished） 0.015~0.019 0.02 0.06

Cu（Oxide） 0.6 0.30~0.50Cr plate 0.08 0.08Au foil 0.010~0.023 0.02~0.03

Au plate 0.026Ag plate 0.008 0.02~0.03

SUS 0.048 0.074 0.11~0.13

Stainless steel exhibits high Emissivity.


No. 15

Outer； Electro polishing (φ 165)

Iner； Electro polishing (φ 89)

Outer；Electro polishing (φ 140)

Iner； Electro polishing (φ 76)

Inner； Zn plating (φ 89)

Inner；Zn plating (φ 89)+ 3 layers MLI

2)

Ref.) Nasu et al.; Abstracts of CSJ Conference 79 (2008) p.97.

Our pipes are low heat loss compared with Corrugate pipes

Corrugate pipes (Nexans)

0.5W/m

Heat loss reduction in double cryo pipes

Diameter of inner pipe

Hea

t los

s [W

/m]

Small pipes with high reflectivity


No. 16

Low loss systems

• Low loss systems come from cryogenic improvements.Suppose heat leak is 0.5 W/m and 0.3 m/sec, for low pump power condition.

Distance between cooling station 4 km 20 km 100 km

Temperature rise with initial LN2

of 78 K.80 K 88 K 128 K

SC tapes Y tapes are better.

Bi tapes are better. X

Cheap Y tapes can be used. Bi tapes are sufficient or

cryo cooler with COP 0.1@70 K is required for Y tapes.

Larger flow rate or the followings, for example, with slow circulation.1. Slash nitrogen (63 K)2. Heat leak < 0.4 W/m3. Tc ~ 115 K

⊿T ~ 0.5 K/ km


No. 17

Principles of Peltier current lead (PCL)

S. Yamaguchi, et al.: Rev. Sci. Instrum., Vol. 75 (2004) pp.207.

low thermal conductivity and heat pump effects of thermoelectric materials are useful.


No. 18

PCL in the 20 m transmission lines

0

20

40

60

80

100

0 10 20 30 40 50 60 70 80

N-type PCLP-type PCL

Temperature dif

fere

nce

TH-T L[K

]

Current[A]

BiTe alloy(10 x 10x t8 mm)Cu Block

Cu Block

Picture of PCL

TH

TL

Ref.) Fujii et al.; Abstracts of CSJ Conference 79 (2008) p.98.


No. 19

Gas cooled Peltier current lead

• PCL + Gas cooled current lead = Gas cooled Peltier current lead (GC-PCL)

Cu CuThermoelectric material

Heat Current lead Terminal

Cold gas is useful to cool the Joule heat.

Current

RT77 K

SC system

For further heat leak reduction, we will apply the GC-PCL and estimate its efficiency.

Cold gas

Gas cooled current leadR.C. Richardson et al.; “Experimental Techniques in Condensed Matter Physics at Low Temperatures” (1988) p.31.


No. 20

Simulation method

• Temperature distribution on the lead was calculated by the thermal equation.

• Gas cooled conditions－Heat exchange ratio f: 0 ~ 3– f = 0: no gas cooling – Only thermal conductance cools the lead.– f = 1: self cooled – Cold gas and current lead are in thermal equilibrium.– f > 1: over-gas – Cold gas from the total systems comes into the lead.

• The length of the current lead was optimized by the minimum heat leak. Both heat leak and temperature distribution on the lead was calculated.

M. N. Wilson; “Superconducting Magnets” (1983) p.257

0)()(2

=+−

AI

dxdCmf

dxdAk

dxd

pθρθθθ

k: Thermal conductivity, θ: Temperature,Cp: Specific heat, A: Cross section,I: Current, ρ: Resistivity

Seebeck effect (αIθ) is added in the first term (heat flow) for PCL.


No. 21

Heat leak with over-gas conditions

PCL+gas coolingf = 1→17.9 W/kA(37% reduction)

PCL+gas cooling with over gasf = 2→13.5 W/kA(52% reduction)f = 3→11.4 W/kA(60% reduction)

28.5 W/kA

Reduction of heat leak

Heat leak of 15 W/kA

For 30 MW systems with the current of 2 kA,heat leak at terminal could become 0.4 W/m for 200 m.

I = 100 A

Ref.) Kawahara et al.; Abstracts of CSJ Conference 79 (2008) p.138.

10

15

20

25

30

0 0.5 1 1.5 2 2.5 3 3.5

p typen type

Hea

t lea

k (W

/kA

)

Heat exchange ratio f

For p-type,


No. 22

Cost reduction by GC-PCL for iDC

Heat leak in cryo double pipe (0.5 W/m) : 200 W

Heat leak estimation for 400 m, 10 MW (400 V, 25 kA) systems

CCL: 42.5 W/kA ⇒ 1063 W@1 terminal

GC-PCL: 13.5 W/ kA (f = 2) ⇒ 338 W@1 terminalPower loss:

System loss (COP 0.15) is 67 kW@4 terminals

System loss (COP 0.15) is 23 kW@4 terminals

Loss is changed from 0.67 % to 0.23 % by GC-PCL.The cost reduction of electric power is $ 58 k/year ($ 0.15/kW)

This corresponds to $1.1 M at the 5% interest.


No. 23

Summery and future developments

• Heat leak of 0.5 W/m is promising for 4 km transmission by Y tapes and 20 km by Bi tapes.

• Potentially low cost Y coated conductors can be used for short length applications.

• Higher Tc Bi tapes are better for long distance transmission such as under water transmission.

Improvements of terminals such as PCL are highly required for higher performance applications.

Total improvements of cryo double pipes, high performance cryo cooler, and stable high Tc cables are required.


No. 24Load map for the DC SC applications

Distance

Year

DC 20 m

DC 200 m

iDC, Power plans in factories

Local grid system

World wide super grid

1 GW

2 TW

SC DC transmission lines

2010 2012 2015 20202006 Now

1 km

1000 km

20 m

Sustainable energy networks.

Long interval for cold stations.

Connection to grid.

Low heat leak at double pipes, and

terminals.

30~100 MW

1 GWParallel connection with UHV DC lines


Applied Superconducting group in Chubu University

Chancellor and Prof. A. Iiyoshi (Chancellor)Director and Prof. S. Yamaguchi (CASER) Prof. M. Takahashi (Business Administration and Information Science)Prof. A. Hattori (The Chubu Institute for Advanced Studies) Prof. M. Hamabe, Prof. H. Watanabe (CASER)Post Doctor: Dr. T. Sugimoto, Dr. J. Sun, Dr. Y. V. Ivanov

superconducting dc transmission lines for electric …. 75 (2004) pp.207. low thermal conductivity...

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