Experimental validation of Prototype High Voltage Bushing

5th International Symposium on Negative Ions, Beams and Sources, Oxford, UK

Experimental validation of Prototype High Voltage Bushing

Sejal Shah, H. Tyagi, D. Sharma, D. Parmar, K. Joshi, A.

Yadav, K. Patel, Vishnudev, R. Patel, M. Bandyopadhyay,

C. Rotti, A. Chakraborty

DNB, ITER-INDIA

1. DNB HVB & requirement of prototype

2. Design optimization through FEA

3. Manufacturing of non-standard components

4. Assembly and test set up

5. High voltage withstand test results

- Voltage holding test up to 60 kV

- 1 hour withstand test for 50 kV

6. Preliminary results of neutron irradiation

- Activation assessment

- Microstructure analysis

7. Summary and discussion

8. Next steps

Outline

Sejal Shah 25th NIBS , Oxford, UK 12-16th Sept, 2016

DNB HV Bushing

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DNB HV BushingVacuum boundary

HV feedthroughSIC component

DNB High Voltage Bushing (HVB)

• Beam source requirement like electricalbusbars, hydraulic & gas feed lines, RF supplyetc are provided by HV Power supply throughHV Bushing.

• Purpose of HV bushing is to provide isolatinginterface between this 100 kV feedlines andgrounded Vessel

• HV Bushing also forms primary vacuumboundary with ITER Tokamak.

• SIC requirement have been considered whiledesigning DNB HVB.

5th NIBS , Oxford, UK 12-16th Sept, 2016

• Specific requirements for SIC component

• Manufacturing challenges

- Large diameter insulators

- Insulator to metal transitions

- Precise dimension and shapes of electrostatic shields

• Define electric stress limit on different zones

• Hands-on experience of system operation in high voltage and vacuum

environment

Requirement of prototype


Scale down of DNB HVB_PHVB

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Operating voltage: 50 kVDC• Same electric stress value as DNB• Cost effective solution : To be

used as feedthrough for TS

Integration with TS

Cross sectional PHVB


Configuration finalization - FE

Analysis


g

FE Model data:Number of Elements:220231Number of Nodes: 444678

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Electrostatic analysis

Axis symmetry

V

N

N

A F

V – VacuumA – AluminaN – NitrogenF - FRP

Equivalent FE Mesh


Interspace flange alteration impact on electric field


Ceramic-Kovar brazed joint

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Max. localized stress at triple point: 1.87 kV/mm

Ceramic

Kovar

M/s Kyocera, Japan


Clamp shield configuration

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0.73 kV/mm UPPER CLAMP SHIELD

0.7 KV/mm LOWER CLAMP SHIELD 5th NIBS , Oxford, UK 12-16th Sept, 2016

ES analysis results


Structural analysis results

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Max. stress 21.6 MPa

Components ResultsVon Mises Stress(MPa) Deflection (mm)

Ceramic Ring 3.37 0.007Kovar ring 21.6 0.016FRP Ring 3.71 0.0013Glue material 1.64 0.0016Metal Parts 21.6 0.038

Max. Deflection 0.03 mm

PHVB integration with TS


Manufacturing


Major development

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Assembled ceramic ring

FRP with metal transition

Connecting flange

•Auxiliaries

- Power Supply

- Pumps and gauges

- Data acquisition: DAQS, photodiodes & Oscilloscopes


Ceramic-Kovar joint

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(a) (b)

As fabricated

As designed

Spilling assessment by SEM analysis

Deviation in Kovar radius


FRP ring

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Megger study @ 5 kV

• FAT at Manufacturer site: >80 GΩ

• SAT at ITER-India: 580 MΩ• After Vacuum Impregnation: 5 GΩ

HV withstand test performed for 50 kV

* FRP-Metal leak joint

FRP Metal rings,

glued with

FRP


Metal parts

17

Metal parts manufactured @ M/s Vacuum Techniques, Bangalore, India

• Metallic components like large diameter flanges, stress

shields, rings with desired tolerance are manufactured.

• Due to HV application, precise shape and size control and

surface finish was achieved for triple point shield by hot

spinning method. Surface roughness Ra: 0.1-0.4 µm

• Assembly of all metallic components considering dummy

metal ring (instead of ceramic ring) was performed.


Assembly of PHVB

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I: Support structure+Lower

connecting flange+ceramic ring II: I+lower compression ring+Triple

point shield anode+FRP ring

III: II+lower clamp ring

IV: III+upper connecting

flange+Upper compression ring

V: IV+triple point shield

cathode+Upper clamp ring VI: V+Bottom cover plate & its

port flanges


Assembly of PHVB..conti

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VII: VI+Top cover plate+Lower clamp

shields

IX: VIII+corona shields, upper clamp shieldsVIII: VII+PS, pump ang gauge

connections at bottom cover plate


RP: Rotory pump

G: Gauge

TMP: Turbo molecule pump

MV: Manual Valve

HV Power Supply

HV connection

~ 2000 mm

RP2

TMP+RP1

G2

470 mm

700 mm

Photo diode O/P

MV1

G1MV1

500 mm

Manual gate valve Pearson CT

Signal monitoring

DAQ: HVPS current/voltage Oscilloscope:

Photodiode signals, Breakdown event, Pulse CT

Ground connection

20

Experimental Integration

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Photodiodes and

gauge connections

HV Power

supply

TMP pumping station

DAQS approx. 5 m

away from PHVB

Photodiode BNC

connection with

Oscilloscope

Rubber pads for seismic

isolation


60 kV withstand test


1 hr withstand test

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Pressure: 6x10-6 mbar

• No photodiode signals recorded during the shots.

• Radiation impact have not been considered so far for this experiment and in results


Preliminary results of neutron

irradiation


Neutron irradiation

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0

2000

4000

6000

8000

10000

0 2 4 6 8 10 12

Flu

x (n

/cm

2/s

)

Energy (MeV)

Objective of study is to:

• Estimate activation & possible transmutation particularly for Ag

• Estimate microstructural changes in ceramic-Kovar geometry

due to neutron irradiation (as it is forming primary boundary)

Parameters:

• Sample: Ceramic-Kovar production proof sample

• Neutron Source : Am-Be

• Irradiation Time : 45 Days

• Total Neutron Flux at sample Location : ~ 4.6x104 n/cm2/s

Analysis & Experiment:

• Activation estimation using FISPACT-2007

• Neutron irradiation of sample and post irradiation gamma

spectrum analysis

Irradiation facility layout

Test sample


26

• After neutron irradiation for 45 days, HPGE detector is used to detect the counts to

determine activation in sample.

• Max. activity for Ag (analytically: 6.4x103 Bq/kg & experimentally: 8.3x103 Bq/kg).

Activity calculation

Where ε is detection efficiency, λ is decay constant, tcool is cooling time and tcount is counting time.

HPGE detector

C. Takada, T. Nakagawa, N. Tsujimura, Nucl. Sci. and Tech. 1, 122 (2011).


SEM of pristine and irradiated samples

27

• Microstructure analysis of ceramic

sample was carried out using SEM in

different areas of ceramic.

• Defect clusters were observed after

irradiation.

• Further study yet to be done

Unirradiated

Kovar

Ceramic

Brazing

zone

Ceramic

Kovar

Brazing

zone

Irradiated

Post irradiation

EDX analysis


• Scaled down configuration of DNB HV Bushing is designed and manufactured

to ensure operational validation for 50 kVDC

• Large size insulators are fabricated, tested individually and also in assembled

condition

• Insulator to metal transitions are designed, developed and tested from

electrostatic point of view

• HV test performed on PHVB up to 60 kV with different ramp rate

• HV withstand test performed up to 50 kV for one hour

• Electrical stresses of DNB HVB is validated

• Preliminary study of neutron irradiation is performed, analytical calculations

have been compared with experiment.

• Microstructural assessment reveals defect cluster formation on ceramic after

irradiation and is being investigated further.

Summary


• Detection of precise amount of Cd produced by transmutation from Ag

• Study the impact of high energy neutron irradiation

• RIC and its impact on HV withstand test (on test sample)

• FRP ring fabrication using filament winding method

• Provide permanent vacuum sealing by welding

• HV withstand test with interspace evacuation

• Integration of PHVB with TS

Next steps


Thank you for your kind attention…!!


Experimental validation of Prototype High Voltage Bushing

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