Experimental validation of Prototype High Voltage Bushing

Transcription

1 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 5 th International Symposium on Negative Ions, Beams and Sources, Oxford, UK

2 Outline 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 Sejal Shah 2

3 DNB HV Bushing DNB HV Bushing Vacuum boundary HV feedthrough SIC component DNB High Voltage Bushing (HVB) Beam source requirement like electrical busbars, hydraulic & gas feed lines, RF supply etc are provided by HV Power supply through HV Bushing. Purpose of HV bushing is to provide isolating interface between this 100 kv feedlines and grounded Vessel HV Bushing also forms primary vacuum boundary with ITER Tokamak. SIC requirement have been considered while designing DNB HVB. Sejal Shah 3

4 Requirement of prototype 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 Sejal Shah 4

5 Scale down of DNB HVB_PHVB Cross sectional PHVB Operating voltage: 50 kvdc Same electric stress value as DNB Cost effective solution : To be used as feedthrough for TS Integration with TS Sejal Shah 5

6 Configuration finalization - FE Analysis Sejal Shah 6

7 Electrostatic analysis V Vacuum A Alumina N Nitrogen F - FRP g Equivalent FE Mesh Axis symmetry N FE Model data: Number of Elements: Number of Nodes: V N A F Sejal Shah 7

8 Interspace flange alteration impact on electric field Sejal Shah 8

9 Ceramic-Kovar brazed joint M/s Kyocera, Japan Kovar Ceramic Max. localized stress at triple point: 1.87 kv/mm Sejal Shah 9

10 Clamp shield configuration 0.73 kv/mm UPPER CLAMP SHIELD 0.7 KV/mm LOWER CLAMP SHIELD Sejal Shah 10

11 ES analysis results Sejal Shah 11

12 Structural analysis results Components Results Von Mises Stress(MPa) Deflection (mm) Ceramic Ring Kovar ring FRP Ring Glue material Metal Parts PHVB integration with TS Max. stress 21.6 MPa Max. Deflection 0.03 mm Sejal Shah 12

13 Manufacturing Sejal Shah 13

14 Major development Assembled ceramic ring FRP with metal transition Connecting flange Auxiliaries - Power Supply - Pumps and gauges - Data acquisition: DAQS, photodiodes & Oscilloscopes Sejal Shah 14

15 Ceramic-Kovar joint Spilling assessment by SEM analysis (a) (b) As designed Deviation in Kovar radius As fabricated Sejal Shah 15

16 FRP ring FRP Metal rings, glued with FRP Megger 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 Sejal Shah 16

17 Metal parts 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: µm Assembly of all metallic components considering dummy metal ring (instead of ceramic ring) was performed. Metal parts M/s Vacuum Techniques, Bangalore, India Sejal Shah 17

18 Assembly of PHVB I: Support structure+lower connecting flange+ceramic ring II: I+lower compression ring+triple point shield anode+frp ring III: II+lower clamp ring VI: V+Bottom cover plate & its port flanges V: IV+triple point shield cathode+upper clamp ring IV: III+upper connecting flange+upper compression ring Sejal Shah 18

19 Assembly of PHVB..conti VII: VI+Top cover plate+lower clamp shields VIII: VII+PS, pump ang gauge connections at bottom cover plate IX: VIII+corona shields, upper clamp shields Sejal Shah 19

20 RP: Rotory pump G: Gauge TMP: Turbo molecule pump MV: Manual Valve Signal monitoring DAQ: HVPS current/voltage Oscilloscope: Photodiode signals, Breakdown event, Pulse CT HV connection ~ 2000 mm Photo diode O/P Manual gate valve MV1 G1 G2 Pearson CT Ground connection HV Power Supply 500 mm TMP+RP1 MV1 700 mm RP2 470 mm 20

21 Experimental Integration HV Power supply DAQS approx. 5 m away from PHVB Photodiodes and gauge connections Photodiode BNC connection with Oscilloscope TMP pumping station Rubber pads for seismic isolation Sejal Shah 21

22 60 kv withstand test Sejal Shah 22

23 1 hr withstand test 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 Sejal Shah 23

24 Preliminary results of neutron irradiation Sejal Shah 24

25 Flux (n/cm2/s) Neutron irradiation Irradiation facility layout 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 : ~ 4.6x10 4 n/cm 2 /s Analysis & Experiment: Activation estimation using FISPACT-2007 Neutron irradiation of sample and post irradiation gamma spectrum analysis Energy (MeV) Test sample Sejal Shah 25

26 Activity calculation HPGE detector Where ε is detection efficiency, λ is decay constant, t cool is cooling time and t count is counting time. After neutron irradiation for 45 days, HPGE detector is used to detect the counts to determine activation in sample. Max. activity for Ag (analytically: 6.4x10 3 Bq/kg & experimentally: 8.3x10 3 Bq/kg). C. Takada, T. Nakagawa, N. Tsujimura, Nucl. Sci. and Tech. 1, 122 (2011). Sejal Shah 26

27 SEM of pristine and irradiated samples Unirradiated Irradiated Kovar Brazing zone Kovar Brazing zone Ceramic Ceramic 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 Post irradiation EDX analysis Sejal Shah 27

28 Summary 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. Sejal Shah 28

29 Next steps 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 Sejal Shah 29

30 Thank you for your kind attention!! Sejal Shah 30