Insulation technologies for HTS apparatus - unibo.it · PDF filePartial discharge...

Insulation technologies

for HTS apparatus

Naoki Hayakawa

(Nagoya University, Japan)

ESAS Summer School, June 8-14, 2016, Bologna, Italy

Contents

1. Self-introduction

2. Background

Why is the electrical insulation important?

3. Fundamentals of electrical insulation

Electromagnetism, Electric field

4. Breakdown characteristics

Gas, Vacuum, Liquid, Solid, Composite system

5. Partial discharge characteristics

Precursor of breakdown, Insulation degradation

6. Electrical insulation peculiar to applied superconductivity

Quench-induced dynamic insulation characteristics

7. Conclusion and future works

Naoki Hayakawa

Biography

Date of birth: September 9, 1962

Date of place: Nagoya, Japan

Academic career:

Ph.D. in electrical engineering, Nagoya University, 1991

Work experience:

Assistant professor, Nagoya University, 1990 - 1996

Associate professor, Nagoya University, 1996 - 2008

Professor, Nagoya University, 2008 -

Guest scientist, Forschungszentrum Karｌsruhe,

Germany, 2001-2002


Tokyo

Nagoya

(2.3 million people)

Where is Nagoya?

Osaka

Nagoya University

Nagoya University

Year of foundation: 1871

Number of

Staff Members: 3,606

Undergraduate Students: 9,893

Graduate Students: 5,979

Area of

Ground: 3,276,293 m2

Building: 768,350 m2

(as of May 1, 2015)

Hayakawa Lab.

1. Electric Power Transmission and Distribution

Efficient, reliable and environment-friendly power supply

Intelligent Grid Management

System (IGMS)

Material Equipment System

Functionally Graded

Materials (FGM)

Condition Monitoring

and Diagnosis (CMD)

Spacer for gas insulated

switchgear (GIS)

Alumina-filled epoxy resin with

spatial distribution of permittivity

Integration of smart grid (system)

and asset management (equipment)

Hayakawa Lab. / Nagoya University, Japan

2. High Voltage and Electrical Insulation

Discharge inception, propagation & breakdown mechanism

in vacuum, gas, liquid, solid insulators

Streamer and leader discharge in air

Surface discharge in oil/pressboard composite system

High-voltage laboratory with 800 kV impulse

voltage generator Breakdown in liquid helium


3. Applied Superconductivity

R&D on high-temperature superconducting (HTS) cables,

transformers, SMES and fault current limiters

HTS transmission cable

HTS fault current limiting

transformer (World’s first)

Cryogenic & high-voltage

laboratory

HTS tape (YBCO)


Contents


2. Background











275kV-3kA Cable

(Japan)

10MJ SMES (Japan) 15kV-3kA Cable (USA) 66/6.9kV-2MVA Transformer

(Japan)

10kV SFCL (Germany)

220kV SFCL (China)

Superconducting power apparatus


Power

Electrical insulation is inevitable as one of

the common techniques for power apparatus

- Superconductors carry the current. (LN2 = Cooling medium)

- Dielectrics withstand the voltage. (LN2 = Insulating medium)

Current Voltage x =

What will happen, if electrical insulation fails?

Breakdown of dielectrics

Malfunction of power apparatus

Interruption of power transmission (Blackout!)

Lightning (Breakdown of air)

Electric field strength in the order of 106 V/m

m mm μm

MV kV V Motor LSI Transmission line

Electrical insulation only for power apparatus?

Electrical insulation for all apparatus & devices

(e.g. breakdown in air at 3 kV/mm, i.e 3x106 V/m)

http://cfs9.tistory.com/upload_control/download.blog?fhandle=YmxvZzIxNTk0M0BmczkudGlzdG9yeS5jb206L2F0dGFjaC8yOS8yOTc1LmpwZw==

http://upload.wikimedia.org/wikipedia/commons/d/d7/Wafer_2_Zoll_bis_8_Zoll_2.jpg

Contents


2. Background











Maxwell’s Equations

HV

GND

Uniform field

High voltage

Ground

HV

GND

High voltage

GND Ground

Electric line

of force

Electric field strength and distribution

Equi-potential

line

Non-uniform field

Electric field strength Electrical potential

Dielectrics Dielectrics

Grounded electrode Grounded electrode

strength strength

Rod e

lectr

ode

Rod e

lectr

ode

Electric field analysis

V0

2b

2a

According to Gauss’s law,

Electric field strength

Electrical potential Coaxial cylinder

0

0.5

1

1.5

2

2.5

3

3.5

4

Electric field strength Er

Distance from center axis [mm] Distance from center axis [mm]

0

20

40

60

80

100

120

140

a b b a

Electrical potential Vr

Electric field analysis V

r [k

V]

V0

Er [

kV/m

m]

Contents


2. Background











How will the breakdown occur?

Discharge inception High electric field

Generation of Initial electron

Electron avalanche

Breakdown (Flashover) Bridge of discharge channel

between HV and GND electrodes

Discharge development Progressive extension of

discharge channel

Townsend theory

1st generation

3rd generation

2nd generation

Number of

electrons

Cathode Anode initial electron

positive ion

(electron avalanche)

(secondary electron

emission)

Σ If , I （Breakdown) ∞

Paschen curves of gases

Breakdown voltage of cryogenic liquids

Bath cooling

Vacuum insulation

Solid insulation (Tape, FRP, etc.)

↓

Composite insulation system

超電導コイル

LHeタンク／冷凍機

伝熱板

電流リード

真空

超電導コイル


伝熱板

電流リード

真空

4KGM-JT冷凍機（３台）

シールド用GM冷凍機(１台）

電流リード用GM冷凍機（２台）

HTS電流リード1kA級Y系４並列

断熱真空容器（φ 2.8×2.8H）

輻射シールド

He容器

4重極配置超電導コイル






輻射シールド

He容器


Liquid insulation (LN2, LHe, etc.)

Gas insulation (GN2, GHe, etc.)

Solid insulation (Tape, FRP, etc.)

↓

Composite insulation system

Conduction cooling

Electrical insulation structure (SMES)

Current lead

Vacuum

Heat conduction plate

Superconduc-

ting coil

Refrigerator

Bath cooling

超電導コイル


伝熱板

電流リード

真空

超電導コイル


伝熱板

電流リード

真空






輻射シールド

He容器







輻射シールド

He容器


Conduction cooling

Electrical insulation structure (SMES)

Current lead

Vacuum

Heat conduction plate

Superconduc-

ting coil

Refrigerator

Cryostat

Cryostat in shield room

(Nagoya University)

Cross-section of cryostat

Electrode configurations

Coaxial cable models

Rod-plane and sphere-plane electrodes

Measurement of BD/PD strength

100

80

60

40

20

0

Bre

akdow

n s

trength

[kV

pea

k/m

m]

50403020100

Experimental number

ac, LN2

Sphere-to-plane

(d=50mm, g=1.0mm)

Coaxial cylinder

(g=2.3mm, L=100mm)

100

80

60

40

20

0

Bre

akdow

n s

trength

[kV

pea

k/m

m]

50403020100

Experimental number

ac, LN2

Sphere-to-plane

(d=50mm, g=1.0mm)

Coaxial cylinder

(g=2.3mm, L=100mm)

Breakdown (BD) strength of LN2

BD based on physical mechanism

(Weakest-link theory, Size effect)

× Weakest-link theory & Size effect

N

i

i

N

i

i ppp11

)1ln()1(ln)1ln(

ip ：Local BD probability p ：Total BD probability N：Number of chain

Stress increase Local breakdown Total breakdown

Large size Many weak points BD probability increase

Stress Electric field strength

Weak point Protrusion on surface, Impurity in liquid, etc.

Size Stressed electrode area, liquid volume, etc.

50.0

70.0

90.0

99.0

99.99

30.0

10.0

5.0

3.0

1.0

Bre

akd

ow

n p

roba

bili

ty [%

]

10 100

Breakdown strength EBac [kVpeak/mm]

ac

Electrode length : 100mm

Gap length : 2.3mm

LHe

m=12.7

E0=19.7kV/mm

20 50

LN2

m=10.3

E0=23.1kV/mm

50.0

70.0

90.0

99.0

99.99

30.0

10.0

5.0

3.0

1.0

Bre

akd

ow

n p

roba

bili

ty [%

]

10 100

Breakdown strength EBac [kVpeak/mm]

ac

Electrode length : 100mm

Gap length : 2.3mm

LHe

m=12.7

E0=19.7kV/mm

20 50

LN2

m=10.3

E0=23.1kV/mm

0

0 lnlnln1

1lnln

v

vIIm

p

Input (Vertical axis)

Input (Horizontal axis)

Output

Sorting of scattered data

Linear in Weibull plot

Breakdown based on

Weakest-link theory

m

I

I

v

vp

00

exp1

Weibull plot

I ：Stress

v ：Highly stressed area/volume

0v ：Reference area/volume

m：Shape parameter (scattering)

0I ：Scale parameter (intrinsic strength)

Breakdown (BD) characteristics of LN2

(a) Breakdown voltage

f=50 mm

(b) Breakdown strength

f=50 mm

Size (Volume) effect

10

20

30

50

70

100

200

300

Bre

akd

ow

n s

tren

gth

EB [

kV

pea

k/m

m]

10-2

10-1

100

101

102

103

104

105

106

% SLV [mm3]

Nishimachi Goshima Hara Mathes Kaneko Kawashima Fink Blaz Frayssiness Sauers

Saturated condition

Sub-cooled condition

Nishimachi

Volume effect on BD strength of LN2

10

2

3

4

56

100

2

3

Bre

akdow

n s

tren

gth

EB [

kV

pea

k/m

m]

10-2

10-1

100

101

102

103

104

105

106

%SLV [mm3]

Confidence interval (95 %) Prediction interval (95 %)

Prediction interval (3) Prediction interval (0.1 %)


Saturated condition


Nishimachi

Goshima

Hara

Mathes

Kaneko

Kawashima

Fink

Blaz

Frayssiness

Sauers

10

2

3

4

56

100

2

3

Bre

akd

ow

n s

tren

gth

EB [

kV

pea

k/m

m]

10-2

10-1

100

101

102

103

104

105

106

%SLV [mm3]



Saturated condition


Nishimachi

Goshima

Hara

Mathes

Kaneko

Kawashima

Fink

Blaz

Frayssiness

Sauers

10

20

30

50

70

100

200

300

Bre

akd

ow

n s

tren

gth

EB [

kV

pea

k/m

m]

10-2

10-1

100

101

102

103

104

105

106

% SLV [mm3]



Saturated condition


Nishimachi

Goshima

Hara

Mathes

Kaneko

Kawashima

Fink

Blaz

Frayssiness

Sauers

15.8/1)%(4.78 SLVEB 　

( % SLV: Stressed liquid volume with electric field strength higher than % of Emax)

Volume effect is practical BD characteristics for LN2

as well as for conventional transformer oil and SF6 gas.

Increase of diameter f

and/or gap length g

Increase of highly-stressed

volume (weak points)

Decrease of breakdown

strength (Volume effect)

Increase of breakdown

probability


Electric field factor

: Harmful bubble to cause BD

: Harmless bubble not to cause BD

Pressure

Temperature

100 95 90 85

80 75

Electric field stress level [%]

]%[ 100 max

E

Ei　

= ?? % in LN2

Increase at the higher pressure

and the lower temperature

= 90 % in transformer oil and SF6 gas

100

95

90

85

80

75

70

Dec

isiv

e el

ectr

ic f

ield

fac

tor

[

%]

777165

Temperature T [K]

P=0.3MPa

P=0.2MPa

P=0.1MPa

100

95

90

85

80

75

70

Dec

isiv

e el

ectr

ic f

ield

fac

tor

[

%]

0.300.200.10

Pressure P [MPa]

T=65K

T=71K

T=77K

(a) Pressure dependence (b) Temperature dependence

140

120

100

80

60

40Bre

akdow

n s

tren

gth

EB [

kV

pea

k/m

m]

0.30.20.1Pressure P [MPa]

g = 0.5 mm

g = 2.0 mm

T = 65 K

T = 71 K

T = 77 K

140

120

100

80

60

40Bre

akdow

n s

tren

gth

EB [

kV

pea

k/m

m]

777165

Temperature T [K]

P = 0.3 MPa

P = 0.2 MPa

P = 0.1 MPa

　),( TPf 15.8/1)%(4.78 SLVEB 　

Electric field factor

10

20

30

50

70

100

200

300

Bre

akd

ow

n s

tren

gth

EB [

kV

pea

k/m

m]

10-2

10-1

100

101

102

103

104

105

106

% SLV [mm3]


Saturated condition


Nishimachi


10

2

3

4

56

100

2

3

Bre

akdow

n s

tren

gth

EB [

kV

pea

k/m

m]

10-2

10-1

100

101

102

103

104

105

106

%SLV [mm3]


Prediction interval (3) Prediction interval (0.1 %)


Saturated condition


Nishimachi

Goshima

Hara

Mathes

Kaneko

Kawashima

Fink

Blaz

Frayssiness

Sauers

10

2

3

4

56

100

2

3

Bre

akd

ow

n s

tren

gth

EB [

kV

pea

k/m

m]

10-2

10-1

100

101

102

103

104

105

106

%SLV [mm3]



Saturated condition


Nishimachi

Goshima

Hara

Mathes

Kaneko

Kawashima

Fink

Blaz

Frayssiness

Sauers

10

20

30

50

70

100

200

300

Bre

akd

ow

n s

tren

gth

EB [

kV

pea

k/m

m]

10-2

10-1

100

101

102

103

104

105

106

% SLV [mm3]



Saturated condition


Nishimachi

Goshima

Hara

Mathes

Kaneko

Kawashima

Fink

Blaz

Frayssiness

Sauers

15.8/1)%(4.78 SLVEB 　

Universal line for sub-cooled LN2 with volume effect

( % SLV: Stressed liquid volume with electric field strength higher than % of Emax)

Contents


2. Background











Electrical insulation of HTS cable

HTS layer

HTS shielding layer

PP laminated paper

PP laminated paper Butt gap

→ LN2/PP laminated paper composite insulation system

Butt gap

(f=5mm)

Partial discharge (PD) in butt gap

Volume effect on PD inception strength 70

60

50

40

30

20

10

PD

IE [kV

rms /m

m]

5 6

10 2 3 4 5 6

100 2 3 4 5 6

1000

Statistical stressed liquid volume SSLV [mm3]

P=0.1MPa

BD strength

PD & BD traces

Coaxial cable models

Contents


2. Background











Quench of superconducting coil in LHe

Superconducting coil (NbTi)

LHe

High-voltage electrode

LHe: Pressure = 0.1 MPa, gap length = 9 mm

Applied voltage = 0 kV

-100

-50

0

50

100

Ap

pli

ed v

olt

age

Va

[kV

]

1.51.00.50.0time [s]

Bubble generated

BD

-100

-50

0

50

100

Appli

ed v

olt

age

Va

[kV

]

1.51.00.50.0

Energizing time th [s]

Applied voltage Heater current

Nichrome sheet electrode

H.V.

(ϕ = 6 mm)

Quench-induced dynamic BD of LN2

P = 0.1 MPa

1.51.00.50.0time [s]

-100

-50

0

50

100

Ap

pli

ed v

olt

age

Va

[kV

]

Bubble generated

BD

-100

-50

0

50

100

Appli

ed v

olt

age

Va

[kV

]

1.51.00.50.0

Energizing time th [s]

Applied voltage Heater current

Nichrome sheet electrode

H.V.

(ϕ = 6 mm)

Quench-induced dynamic BD of LN2

P = 0.15 MPa

80

70

60

50

40

30

20

10

0

BD

E [

kV

pea

k/m

m]

6050403020100

Electrode diameter f [mm]

P = 0.10 MPa

Static

Dynamic

Stable heating

80

70

60

50

40

30

20

10

0

BD

E [

kV

pea

k/m

m]

6050403020100

Electrode diameter f [mm]

P = 0.12 MPa

Static

Dynamic

Stable heating

Static BD strength

Static BD strength

P = 0.1 MPa P = 0.15 MPa

Dynamic BD strength Dynamic BD strength

Static and dynamic BD strength of LN2

1.0

0.8

0.6

0.4

0.2

0.0

Ele

ctri

cal

loss

[W

/m]

PPLP-C Tyvek/PE

Total loss

Dielectric loss

AC loss

1.0

0.8

0.6

0.4

0.2

0.0E

lect

rica

l lo

ss [

W/m

]

PPLP-C Tyvek/PE

Total loss

Dielectric loss

AC loss

275 kV – 3 kA HTS cable

(M-PACC project, Japan)

Dielectric loss 20 %

Total loss 41 %

Dielectric loss reduction for HTS cable

Contents


2. Background











CIGRE WG D1.38 (Conseil International des Grands Reseaux Electriques

or International Council on Large Electric Systems)

Title of the group： Emerging Test Techniques Common to

HTS Power Applications

Convenor：Mathias Noe

(Karlsruhe Institute of

Technology, Germany)

Secretary: Naoki Hayakawa


Members: 24 persons (14 countries)

Period: 2010-2015

Contents:

1. Introduction

2. Electrical insulation

3. HTS material

4. Cooling systems

5. General and specific requirements

for electrical insulation, HTS materials,

and cooling

6. Summary

7. References

8. Annexes

Technical Brochure: No.644 (153 pages)

(published in December 2015)



Title of the group： Electrical Insulation Systems at Cryogenic

Temperatures

Convenor：Naoki Hayakawa


Secretary: Christof Humpert

(Technische Hochschule Köln,

Germany)

Members: 22 persons (12 countries)

Period: 2016-2019



Member of WG D1.64 (22 persons, 12 countries) NAME GIVEN NAME Affiliation Country

Nielsen Shawn Dennis Queensland University of Technology Australia

Polasek Alexander CEPEL Brazil

Du Boxue Tianjin University China

Zong Xihua Shanghai electric cable research institute China

Filipan Veljko University of Zagreb Croatia

Willén Dag nkｔ cables Denmark

Humpert Christof Technische Hochschule Köln Germany

Kurrat Michael Technische Universität Braunschweig Germany

Noe Mathias Karlsruhe Institute of Technology Germany

Martini Luciano Ricerca sul Sistema Energetico Italy

Hayakawa Naoki Nagoya University Japan

Nagao Masayuki Toyohashi University of Technology Japan

Okubo Hitoshi Aichi Institute of Technology Japan

Yagi Masashi Furukawa Electric Japan

Cho Jeonwook Korea Electrotechnology Research Institute Korea

Lee Bang Wook Hanyang University Korea

Ross Robert TenneT TSO + HAN University of Applied Science Netherlands

Smit Johan Delft University of Technology Netherlands

Samoilenlov Sergey SuperOx Russia

Graber Lukas Georgia Institute of Technology USA

Pamidi Sastry The Florida State University USA

Tuncer Enis Texas Instruments USA

Scope of CIGRE WG D1.64

The scope of WG D1.64 is to study the fundamentals and

applications on electrical insulation techniques for supercon-

ducting power apparatus and other applications to be operated

at cryogenic temperatures.

1. Insulating materials

(solids, liquids, gases, vacuum, composite insulation system)

2. Principles & mechanisms

(partial discharge, surface discharge, ageing, breakdown)

3. Design & test issues

(power apparatus, magnets, components)

4. Others

Kick-off meeting (2016.4.27-28, Yokohama)

Summary

1. Cryogenic electrical insulation is inevitable as one of

the common techniques for HTS power apparatus.

2. Fundamental insulation data at cryogenic temperatures

should be systematized with their physical mechanisms.

3. Practical insulation data peculiar to HTS power apparatus

should be obtained for their design and operation.

4. World-wide collaboration is expected for the realization of

HTS power apparatus.

Thank you very much

for your kind attention

Naoki Hayakawa E-mail: [email protected]

http://www.hayakawalab.nuee.nagoya-u.ac.jp/

Insulation technologies for HTS apparatus - unibo.it · PDF filePartial discharge...

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