225 kV Oil-Cooled High-Voltage Solution for Rotating-Anode Industrial CT Systems

High-throughput industrial CT of automotive castings and aerospace composites requires rotating-anode X-ray tubes at 225 kV / 1200 W continuous with anode rotation up to 9000 rpm, demanding oil-cooled high-voltage generators that maintain focal spot stability <0.18 mm while the entire tank rotates at 120 rpm inside the gantry.

The generator uses a compact 38 kHz resonant inverter feeding a six-stage oil-immersed Cockcroft-Walton multiplier integrated into a cylindrical tank that serves simultaneously as high-voltage insulator and primary coolant container. Total weight including oil is 84 kg, enabling gantry acceleration >2.8 m/s².

Voltage regulation is performed by primary-side phase-shift control with 160 kHz bandwidth, maintaining ±42 V at 225 kV despite load variation from tube aging and anode heat storage. Ripple is <180 V p-p through distributed filtering and active cancellation derived from a capacitive pickup at the anode receptacle.

Oil cooling uses a closed-loop dielectric oil circuit with redundant magnetically driven pumps and plate heat exchangers mounted on the rotating frame. Oil flow is actively varied from 11 to 28 L/min based on anode input power measured via calibrated current monitoring, maintaining tank-to-oil ΔT <7.2 °C even at maximum continuous rating.

Rotation-compatible high-voltage connection to the spinning anode employs a liquid-metal contact system using gallium-indium-tin alloy in a ceramic channel, providing <1.8 mΩ contact resistance and >280 kV breakdown strength at 9000 rpm. Contact wear is <0.6 µm per million revolutions through optimized channel geometry and oil lubrication.

Filament power is supplied via a separate 18 kHz resonant converter with rotating transformer achieving >96 % coupling efficiency, maintaining focal spot position within ±38 µm despite thermal expansion of the 220 mm diameter anode disc.

Thermal runaway prevention during emergency stops uses an active oil bypass valve that instantly diverts flow through an auxiliary heat exchanger when rotation drops below 1200 rpm, preventing oil temperature rise >38 °C/s.

These oil-cooled rotating systems routinely deliver 225 kV continuous with focal spot drift <0.11 mm over 8-hour scans and tube life >4200 hours at 80 % duty, enabling voxel resolution <42 µm on 680 mm aluminum castings at inspection speeds >180 parts/hour.