Cross Transformer Technology (CTT) High Voltage Power Supplies

1. Cross Transformer Technology(CTT)High Voltage Power Supplies PESP 2008 Jefferson Lab October 2, 2008 Uwe Uhmeyer Kaiser Systems, Inc. Beverly, MA This Document Contains Confidential Information Proprietary To Kaiser Systems Inc.

2. Cross Transformer Technology • Dr. James Cross Transformer Technology for HV generation based on Insulated Core Transformer (ICT) techniques • Incorporates several significant innovations • US Patents #5,631,851 & 6,026,004 • Implementations shown from 25kV to 1MV at power levels to 200kW • Kaiser Systems is exclusive worldwide licensee for the Cross Transformer Technology (CTT) patents • Technology suitable for SF6, oil or solid insulation This Document Contains Confidential Information Proprietary To Kaiser Systems Inc.

3. Conventional HV Transformers • A design issue for HV transformers is the insulation system between the HV secondaries and the transformer core • Ferrites are conductive (~ 106Ω/cm) and will draw corona • A 500 kV HV xfmr with a conventional core would require several inches of clearance between secondary and the core in addition to the size of the windings and core itself • Greater size, weight and cost • Increases leakage inductance and decreases efficiency This Document Contains Confidential Information Proprietary To Kaiser Systems Inc.

4. ICT/CTT Principles of Operation • HV DC output of the overall system produced by multiple sections wired in series • Each section has its own secondary winding(s) and rectifiers, usually configured as output doublers • Vdc = 2 x Vpp • Each section is associated with its own piece of magnetic core material, electrically connected to its rectified output, but insulated from its neighbors • Core to Winding insulation requirement for each section is never more than the localized Vdc output of that section This Document Contains Confidential Information Proprietary To Kaiser Systems Inc.

5. Typical ICT Implementations • Conventional ICT designs useline frequency excitation • Higher power units are 3 phase • Each 20kV (typ) disk contains: • 3 Series output arc limiting resistors • 6 Rectifiers/Capacitors • 3 magnetic core pieces & secondary windings • Disk sections are not all the same as higher turns ratio needed on higher disks to keep similar Vout • Most common regulation technique is motor driven variable transformer to vary primary voltage • Control BW limited to 10s of Hz 1st section of 3 Ø Line Freq Design. Disk mounted to base plate This Document Contains Confidential Information Proprietary To Kaiser Systems Inc.

6. Insulated Core HV TransformersICT • In use for many years • Secondary windings in close proximity to secondary core sections • Multiple Gap design • Flux leakage occurs at fringes of gaps. Conceptual Diagram (Middle phase ckts not shown) This Document Contains Confidential Information Proprietary To Kaiser Systems Inc.

7. 25 stage nominal 500kV HVPS ICT If 1st stage is limited to 20kV, the HV output will only go to 420kV If the loop is closed and 500kV is set, then the 1st stage needs to go to about 24000V To minimize flux leakage, ICT design trade off is to decrease # stages at expense of higher stage to stage voltage Often the turns ratio increased with each stage to keep stage to stage voltage the same Effect of Flux Leakage This Document Contains Confidential Information Proprietary To Kaiser Systems Inc.

8. Advantages of CTT over ICT • Uniform Voltage Per Stage • Due To Compensation Of Flux Leakage • Extremely Low Stored Energy • Fast Transient Response Time • Greater Efficiency • Straightforward Manufacturability • Lower Cost To Produce • Compact Size • Higher Reliability • Corona Free Design • Efficient Operation This Document Contains Confidential Information Proprietary To Kaiser Systems Inc.

9. Cross Section of CTT Stack 500kV Stack Shown Dome (corona shield) Ferrite top bar Grading rings Section ferrite tiles 12.5kV stack cards (green) Insulating film (yellow) Primary winding Ferrite bottom bar This Document Contains Confidential Information Proprietary To Kaiser Systems Inc.

10. CTT Stack Card Building Block 17” 12.5kV 12.5kV, 100mA 16” 0 V This Document Contains Confidential Information Proprietary To Kaiser Systems Inc.

11. CTT Stack Card Building Block • 32 Identical Circuits • Each produces up to 400 Vdc • All in series • 12,500V per stack card typical This Document Contains Confidential Information Proprietary To Kaiser Systems Inc.

12. CTT Stack Card Building Block • Zoom in on 4 elements This Document Contains Confidential Information Proprietary To Kaiser Systems Inc.

13. 1 Element of CTT Stack Card • Output series limiting resistor • Flux Compensation Capacitor • Planar secondary xfmr windingsNtyp = 2/5 • Per element fuse • Voltage Doubler This Document Contains Confidential Information Proprietary To Kaiser Systems Inc.

14. CTT Advantages • Low Stored Energy: 50nF/element 0.98J / 100kV 4.88J / 500kV 7.32J / 750kV • Minimal Voltage Stress across stack board • < 200Vpp from xfmr; Components see <400V • Local E field is no more than 1kV/inch! • Compare to 10kV/inch in air widely used clearance guideline! • Corona inception voltage never exceeded. • No gradual degradation of Insulating materials by corona. This is about ½ to ⅛ the stored energy of a Cockcroft-Walton multiplier equivalent This Document Contains Confidential Information Proprietary To Kaiser Systems Inc.

15. CTT Advantages (cont) • Lower implementation cost • Simple 2 layer PCB technology • Planar transformer design • No secondary windings to be individually wound • Stack cards are identical to build large stacks • e.g. 40 stack cards for 500kV or 60 stack cards for 750kV • Only 1 type spare needed • Surface mount technology components. • Relatively low cost, especially in volume purchase • Automated assembly on SMT equipment This Document Contains Confidential Information Proprietary To Kaiser Systems Inc.

16. CTT Advantages (cont) • High Reliability • Corona free design • Simple construction • Fault Tolerance • Individual failed elements will not take out the entire system • Typical fault is shorted element as a result of a severe arc. • Fuse for secondary will blow • Shorted element maintains series connectivity • System continues to operate with n-1 output voltage elements This Document Contains Confidential Information Proprietary To Kaiser Systems Inc.

17. Problem Statement from Patent “The segmentation of the magnetic core in the transformer introduces gaps in the magnetic structure with a permeability essentially that of air. This greatly increases the reluctance of the magnetic structure and produces leakage of magnetic flux. As a result, the upper sections of the magnetic core carry less flux than the lower sections of the core, which results in lower generated voltage per turn on the secondary windings.” Page 6, beginning w/ line 63, US Patent 6,026,004 Benefits of flux compensation Flux compensation restores the lost MMF per gap. Resultant Observations The energy associated with the ‘leaking’ fields may be associated with the value of the ‘leakage inductance” property of transformers. Compensating for the leakage flux in effect cancels out the leakage inductance. Ideally, this should help the control system by reducing the second order effect of voltage droop. Overcoming Flux Leakage Inherent in ICT This Document Contains Confidential Information Proprietary To Kaiser Systems Inc.

18. The problem: MMF lost across each gap Reconstructing Lost Flux: Current induced in the secondary will be equal to the voltage in the secondary over the impedance. Voltage from a transformer is # of turns times the first derivative of the time varying flux.: Impedance created by a capacitance across the secondary: …algebra MMF resulting from the reactive current in the secondary: Set MMF induced in the secondary to MMF lost in Reluctance: Solve for the cap value: This is the total cap value associated with 1 gap Derivation of the Cap Value Dr. Cross’ Final equation This Document Contains Confidential Information Proprietary To Kaiser Systems Inc.

19. Further algebraic reduction:Where l = length of insulated core gap A = Area of insulated core gap Substitution: Simplification: This is the useful design equation Derivation (cont) • The value of the Flux compensation Capacitor C is a function of only the transformer physical properties and the operating frequency! • It is independent of the output voltage or output current! This Document Contains Confidential Information Proprietary To Kaiser Systems Inc.

20. Control Topology • Ideal drive topology should produce a fixed frequency sinusoidal voltage waveform at primary of transformer. • Practical Implementations effectively done with Phase Shift Modulation (PSM) • Allows for Zero Voltage Switching (ZVS) • Practical systems built by KSI operate at 80 to 90 kHz This Document Contains Confidential Information Proprietary To Kaiser Systems Inc.

21. PSM / ZVS Efficiency Duty Cycle drives this effect This Document Contains Confidential Information Proprietary To Kaiser Systems Inc.

22. Building a CTT stack Section ferrite tiles 2x insulating films 12.5kV stack cards (green) Grading rings Primary winding Ferrite bottom bar This Document Contains Confidential Information Proprietary To Kaiser Systems Inc.

23. Building a CTT stack HV Divider Resistors This Document Contains Confidential Information Proprietary To Kaiser Systems Inc.

24. Building a CTT stack Clamping bars at top of stack This Document Contains Confidential Information Proprietary To Kaiser Systems Inc.

25. Building a CTT stack Dome (corona shield) Ferrite top bar This Document Contains Confidential Information Proprietary To Kaiser Systems Inc.

26. A 750kV CTT Stack This Document Contains Confidential Information Proprietary To Kaiser Systems Inc.

27. KaiserSF6 Vessel This Document Contains Confidential Information Proprietary To Kaiser Systems Inc.

28. General Specs 750kV, 100mA • Output Voltage and Operating Range • Continuously variable between 50 kV and 750 kV. • Meets all the efficiency, stability and regulation specifications over its normal operating voltage range of 100 kV to 750 kV. • High Voltage Section Insulation. • Pressurized SF6 gas, maximum pressure of 5 atm. absolute (59 psig). • HV Driver • Separate Cabinet with Control module and Inverter module system. • Inverters require water cooling. This Document Contains Confidential Information Proprietary To Kaiser Systems Inc.

29. General Specs 750kV, 100mA • Power Supply Input Voltages. • Inverter supply: 480V ±10%, 3-phase, 50-60 Hz AC. • Controls and interlocks power: 120 Vac • Efficiency • > 80% overall. Typically 92% at full voltage • Line Regulation: < ±0.5% for a change of ±10% • Load Regulation: < ±0.5% for a change of ±10% • Stability & Ripple: < ±0.5% total variation for fixed output voltage, current and temperature • Temp Coefficient: < 200ppm/°C • Reproducibility: < 0.5% after 1 hour warmup • Operating Temp: 15°C to 40°C This Document Contains Confidential Information Proprietary To Kaiser Systems Inc.

30. Conclusions KSI CTT HVPS designs provide many advantages over conventional line frequency ICT designs: • Fault Tolerance • High Reliability due to Corona Free Stage Design • Compact Design • Easily Integrated Into E-beam Vessel • Low Stored Energy • Excellent Transient Response • High Efficiency • Scalable Design This Document Contains Confidential Information Proprietary To Kaiser Systems Inc.

31. CTT Supply Thanks to: • Matt Poelker for inviting KSI to this conference. • Jefferson Laboratory • David Johns, Yuri Botnar, Ken Kaiser and Steve Swech for their contributions to this program and presentation This Document Contains Confidential Information Proprietary To Kaiser Systems Inc.