Intelligent power supplies for electron beam welding at 300 kV and 150 kW

Electron beam welding (EBW) is widely used in industry, most notably for the manufacture of aeroengines. The equipment consists of a vacuum chamber, work piece manipulator and electron gun. The guns typically operate at 150 kV and produce a DC beam of 100 mA (i.e. 15 kW of beam power). At TWI high power guns have been developed that operate at up to 300 kV and 500 mA (150 kW of beam power). The TWI HV power supply unit (PSU) differs from other HV PSUs in that it is an HV only supply as the cathode heating and beam current control are provided by an RF amplifier. Therefore there are no auxiliary power supplies (e.g. the filament and bias supplies in other EBWs) in the transformer tank. Also the HV cable uses one core, that carries the beam current. The function of the power supply is to convert the 3 phase mains at 400 V, 50 Hz into a regulated voltage of (for example) 200 kV. The voltage should not vary if either the mains or the beam current varies. The power supply consists of an inverter and a transformer tank. The inverter converts the mains to a 5 kHz output. The width of the current pulses is controlled to regulate the high voltage. The transformer tank consists of a transformer, rectifier, smoothing capacitor, surge arrest resistor and monitoring components for the high voltage and the beam current. To provide insulation, the components are submerged in oil.