Design, manufacturing, and testing of 0.35/25 kV, 20 kHz transformers for particle accelerators

A high voltage, high frequency transformer unit has been designed and built for powering the Cockcroft-Walton voltage multiplier to be used as part of a particle accelerator power supply at the Institute For Plasma Research, India, for the nuclear fusion research facility. A novel combination of high voltage (25 kV), high frequency (20 kHz), and high power (70 kV A) specifications makes its design distinctive and more challenging. The complete unit is composed of two 0.350/25 kV amorphous core transformers connected in center-tap configuration and immersed in an oil-filled tank. To facilitate an iterative design procedure, a spreadsheet method was utilized. The design involved a methodical approach for the core and winding selection, followed by the magnetic analysis and high voltage insulation layout through the finite element method. All the magnetic, electrical, and thermal parameters have been evaluated in detail, assuring a continuous stable operation having an efficiency of greater than 95%. Finally, the transformers were made, and preliminary experiments, including turns ratio, short-circuit, and dielectric tests, were carried out to verify the accuracy of the proposed design. The unit was also field tested under actual load conditions, and the test results were presented and corroborated with the design calculations.