04 - Development of Roebel Cable Based 1 MVA Superconducting Transformer (Glasson)R1

7/28/2019 04 - Development of Roebel Cable Based 1 MVA Superconducting Transformer (Glasson)R1

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The development of a Roebel cable based

1 MVA HTS transformer

Neil Glasson

11 October 2011

Mike Staines1, Mohinder Pannu2, N. J. Long1, Rod Badcock1, Nathan Allpress1, Logan Ward1

1 Industrial Research Limited, New Zealand2 Wilson Transformer Pty Ltd, Melbourne


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Outline

Introduction

Design overview

Roebel cable

Short circuit fault

High voltage insulation

Heat transfer

Cryostat design

Summary


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Project Partners

www.hts110.co.nz

www.wtc.com.au

www.eteltransformers.co.nz

www.fabrum.co.nz

www.pbworld.com

www.vectorelectricity.co.nz

www.gcsuperconductors.com

www.weltec.ac.nz

www.aut.ac.nz
http://www.hts110.co.nz/http://www.wtc.com.au/http://www.eteltransformers.co.nz/http://www.fabrum.co.nz/http://www.pbworld.com/http://www.vectorelectricity.co.nz/http://www.gcsuperconductors.com/http://www.weltec.ac.nz/http://www.aut.ac.nz/http://www.aut.ac.nz/http://www.weltec.ac.nz/http://www.gcsuperconductors.com/http://www.vectorelectricity.co.nz/http://www.pbworld.com/http://www.fabrum.co.nz/http://www.eteltransformers.co.nz/http://www.wtc.com.au/http://www.hts110.co.nz/http://www.hts110.co.nz/


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Design parametersParameter Value

Primary Voltage 11,000 V

Secondary Voltage 415 V

Maximum Operating Temperature 70 K, liquid nitrogen cooling

Target Rating 1 MVA

Primary Connection Delta

Secondary Connection Wye

LV Winding20 turns 15/5 Roebel cable per phase

(20 turn single layer solenoid winding)

LV Rated current 1390 A rms

HV Winding918 turns of 4 mm YBCO wire per phase

(24 double pancakes of 38.25 turns each)

HV Rated current 30 A rms


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HV winding

Uses 4 mm Superpower tape I/Ic ~ 25%

Polyimide wrap insulation

24 double pancakes

No encapsulation due toconcerns of

Poorer heat transfer

Voids lowering withstand voltage

Potential Ic degradation


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LV winding

Single layer solenoid on fibre glass composite former

Liquid nitrogen in contact with cable surface

YBCO Roebel Cable

L = 20 m

15/5 (15 strands, 5 mm width)

Self field Ic ~ 1400 A @ 77 K

No strand or cable insulation

Flux deflectors will be added

First transformercable configured forend-to-end Ic test


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Core

Warm core withcruciform, 6-steppedsection of high gradecore steel

No-load loss of about750 W

At 20:1 cooling penalty,cold bore is not feasible


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YBCO Roebel Cable

Roebel cable or Continuously Transposed Cable (CTC) is useful for Forming a high current capacity conductor

100s to 1000s of Amps (even 10,000s at low T)

Reducing AC losses

rule of thumb magnetisation losses scale with strand width

Strands wound together and geometric parameters

Roebel strand

Cables are labelled with the convention

# of strands / strand width

We are making two designs 15/5 and 10/2


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Roebel Cable ManufacturePunch tool and

frame

Tape de-spool

Tape re-spool

Control

systems

Set-up for automated

multi-strand Roebel

strand production.

(a)

(b)

(c)

(d)

Formation of Roebel punched strands in 40 mm and 12

mm wide feedstock material.

(a) 4 x 5 mm strands in 40 mm wide material,(b) 1 x 5 mm wide strand in 12 mm wide material,

(c) 10 x 2 mm strands in 40 mm wide material,

(d) 3 x 2 mm wide strands in 12 mm wide material.

Punching

Winding Automated planetary wind system for15/5 cable

Capable of winding several hundred

continuous metres of cable.


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Wire qualification

0 10 20 30 40 500.90

0.92

0.94

0.96

0.98

1.00

Correlation

Position (m)

Wire 2

22 )()(

))((),(

yyxx

yyxxYXCorrel

For Roebel we require 2D uniformity

- Scan wire magnetically (penetratedor remnant field)

- Quantify uniformity using statisticalcorrelation with an ideal magneticprofile

Correlation along a

length of YBCO wire, a

minimum Correlcan be

specified for input wire

Where |Correl| 1Xis a dataset representing calculated field

Y{y1yj} is magnetic data across tape

0.000 T

200mm

(a)(a)

0.023 T

(b)

We use continuous scanning of the Remnant

magnetic field to assess tape quality (a) tapewith a known defect, and (b) tape with only

small scale variability.

0 2 4 6 8 10 120.010

0.015

0.020

0.025

0.030

0.035

0.040 cor_0.99

cor_0.90

cor_0.75

Field(T)

Position (mm)

Example Profiles

Some wire is extremely good !


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Roebel cable performance

Measured end-to-end Ic ofcable is 1400 A DC @ 77 K.

Design calls for 1390 A rms= 1970 A peak.

Ic tests on strand samples at70 K and subsequentanalysis predicts 2500 Acable Ic. Ipeak/Ic = 0.79

This is yet to be confirmedby experiment on a cable at70 K.

Use of load line method to predict cable critical current

Described by Staines et al, The development of a Roebel cable

based 1 MVA HTS transformer, to be published in Supercond. Sci.Technol. 24 (2011)


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Short circuit fault handling

2 second short circuit withstand is a common requirement ofconventional transformer standards.

What is a realistic target for HTS? HTS lacks the resistive conductor cross sectional area to carry a

short circuit for 2 seconds. What is a realistic short circuit duration

for an HTS transformer?

Determine fault current limiting performance. HTS under short circuit exhibits highly non-linear response how will

this limit fault current?

Cable strand has exposed cut edges. Roebel strand is punched exposing edges of conductor. Does this

pose a risk of conductor damage due to ingress of LN2 and thensubsequent heating in a short circuit?


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Short circuit simulation

Adiabatic model assumes no heat transfer from theconductor into liquid nitrogen.

Assuming instantaneous shift of current into 40 micronthickness of copper (20 micron each side,= 12.5 x 10-3/ m per strand @ 77 K).

Simulation incorporates temperature dependence ofboth resistance and thermal capacity of the conductor.


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Simulation output

LV winding will reach350 K at t = 200 ms

Impedance doublesfrom 0.05 pu to 0.1 puinitially then up to 0.5 puover 200ms (due to changein resistance astemperature increases).

-0.05 0 0.05 0.1 0.15 0.2 0.25 0.350

100

150

200

250

300

350

400

450Tp, Ts vs. Time

Time (s)

Tp,T

s

(K)

TP

Ts

Tp=Temperature of primary windingTs= Temperature of secondary winding


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Simulation output

Fault limited peakcurrent = 14 kA(about 35% of the peakthat would occur iflimited only by the 0.05pu leakage reactance).

pu = per unit, actual value divided by basevalue.

Cable will offer significantcurrent limiting during ashort circuit fault.


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V2F

V2E

V2D

V2C

V2B

V2A

+ve Terminal

-ve Terminal

Current Shunt

V1

Short circuit strand testing

200 ms DC pulse, peaking

at >15 V/m in strand(transformer short circuitvoltage = 12 V/m).

T increased to 300 K

in 60 ms There was no damage

(no change in Ic). Repeat test after 3 week

soak in LN2.Conclusion 200 ms duration short circuit is OK andthere is no evidence of damage due to nitrogen ingressinto the exposed cut edge of the cable strands.


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Impulse response in HV winding

From VOLNAProprietary modelling software modelling response to standard 95 kV impulse

21 kV peak voltage


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High voltage insulation

* Guide for the statistical analysis of

electrical insulation breakdown data

95 kV impulse response modelling HV winding must withstand 550 V from turn-to-turn.

(21 kV / 38 turns per double pancake)

Commercial 25 micron polyimide wrapped insulation wastested to confirm suitability.

Two wrapped strands heldtogether and stresseduntil breakdown @ 77 K.

20 tests analysed accordingto IEC 62539*

Insulation will survive 2 kV.


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Heat transfer experiment

Fix power dissipation in strand and measuredtemperature rise of cable winding in LN2

Used conductor with Tc < 65 K. Copper layer used asboth resistive heater and temperature sensor.

Tested at 68 K and 77 K, both at atmospheric pressure.


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Typical heat transfer regimes

Van Sciver

Helium Cryogenics

Note: hysteresis in

transitions from oneregime to the otherand the shape oftransition fromconvection to nucleate.


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Heat transfer resultsHeat Transfer - Dependence on Bath Temperature

0.001

0.01

0.1

1

10

0.01 0.1 1 10

Conductor Temperature Rise, dT [K]

PowerDissip

ated[W/m]

77K Outer

77K Middle

77K Inner

Subcooled Outer

Subcooled Middle

Subcooled Inner

Assume 1 W/m of strandheating due to AC loss.

Sub cooling necessary toavoid nucleate boiling.

Convective coolingkeeps T < 3 K.

Location of strand hasminimal impact.

3

Convectiveheat transfer

Nucleateboiling

Sub cooled results are at 68 K and atmospheric pressure.Inner, middle and outer refer to position in Roebel cable strand stackinner being against the winding former, outer being directly exposed to liquidnitrogen.


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Desired conditions

inside the transformer cryostat

The windings must be held in the temperature range65K to 70K in order to achieve the requiredperformance of the superconducting cable.

It is desirable to ensure that the evolution of gas in thewindings is minimized. Gas bubbles degrade thedielectric performance of the LN2 as well as risking anaccumulation of gas that might thermally insulate

regions of the windings and give rise to hot spots.

S.M.Baek et al, Electrical Breakdown Properties of Liquid Nitrogen for Electrical InsulationDesign of Pancake Coil Type HTS Transformer. IEEE Trans. Appl. Supercond. Vol 13, No.2,June 2003


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Nitrogen phase diagram

Temperaturerange

Max. pressure

Vapour and liquid onlyco-exist on thesaturation line

Operation at elevatedpressure allows

significant temperatureincrease before phasechange.

Atmospheric pressure

Operation heremakes pressurevessel designeasier


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Cryostat layout Common cryostat for

all three phases is best Smaller footprint and reduced heat load due to

fewer electrical bushings and reduced shell area.

Simplified nitrogen circulation system only oneinlet and one outlet required.

Three individual cryostats - easiest tomanufacture

Cryostat pressure design is easier

Less risk with a simple cylindrical structure

Compromise with three individualeccentric cryostats

Simple cylindrical shells

Reduced transformer length and nitrogen volume

X

1.3 X

1.5 X


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Cryostat lid arrangement

Gas in equilibrium dueto temperature profilethrough foam

Liquid return

Electrical bushing

Bulk liquid at 65K 70K

Foam insulationplug


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Cryostat work in progress

Cryostat cold shell test vessel

Single phase cryostat basecold shell and mould

www.fabrum.co.nz
http://www.fabrum.co.nz/http://www.fabrum.co.nz/


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Summary

Roebel cable described high current capacity/low AC loss.Tests and analysis predict cable Ic of 2500 A at 70 K.

Short circuit fault across the Roebel cable winding can betolerated if disconnected within 200 ms.

Standard copper stabilizer provides significant fault current

limiting - Simulation predicts short circuit fault limited to 35%of the prospective fault current

Standard 25 micron spiral wrapped polyimide insulation willwithstand 2 kV turn-to-turn.

1 W/m continuous dissipation in sub-cooled LN2 will bebelow nucleate boiling regime.

Cable temperature will be up to 3 K warmer than bulk LN2.


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Summary cont...

Cryostat design discussed. The target normal operatingtemperature in the cryostat is in the range 65 K to 70 K.

There is benefit in operating cryostats at elevated pressure.

A foam plug beneath the lid will allow operation at elevatedpressure while maintaining a gas/liquid transition at somepoint between the lid and the bulk liquid region.


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04 - Development of Roebel Cable Based 1 MVA Superconducting Transformer (Glasson)R1

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