Plasma power supply: the power source unit of a mechanized plasma cutting system

01

Read the output rating: current, arc voltage, open-circuit voltage and duty cycle

Hypertherm's specification table for the XPR300 lists a maximum output current of 300 A, maximum output power of 66.5 kW, output voltage of 50–210 VDC, a 100% duty arc voltage of 210 V and a maximum open-circuit voltage (U0) of 360 VDC. Its duty cycle rating is 100% at 66.5 kW and 40 °C (104 °F), over an operating ambient range of −10 °C to 40 °C. The same table lists a power factor of 0.98 at 66.5 kW, forced-air cooling (Class F), Class H insulation, CE EMC emissions Class A and a top lift eye rated 680 kg. [1]

Kjellberg states the cutting current of its HiFocus 280i neo power source as 280 A at 100% duty cycle on 3x 400 V, 50 Hz mains, with other voltages and frequencies available on request, and a separate marking current of 5–50 A. [2] For its Smart Focus 300 it gives a cutting current range of 35–300 A and a marking current of 10–50 A on the same mains. [3]

Editorial note: a current figure without the duty cycle and the ambient temperature at which it was rated does not tell you whether the unit can cut continuously at that current; ask for the duty-cycle statement in the form Hypertherm gives (percentage, power and temperature). The open-circuit voltage matters for the torch leads and for operator safety, so obtain it together with the output voltage range.

Give the supplier the materials and thickness range, cutting and marking currents needed, required duty cycle and shop ambient, mains voltage and frequency, cable run from power supply to torch, gas console and gases, the CNC or robot interface, and the documents needed (rating plate data, conformity declarations).

02

Choose the power circuit: interleaved chopper or high-frequency inverter

A Hypertherm patent application describes a mechanized plasma power supply built around a multi-pulse (six- or twelve-pulse) transformer feeding series-connected three-phase diode bridges, a bank of four DC bus capacitors, and two IGBT choppers each wired to its own output inductor and switched in an interleaved mode. It states that interleaving can reduce arc ripple current to a peak of about 3 A at about 200 A, cites a power factor of 0.98 and input-current THD of about 13% at 33 kW in some embodiments, and gives a load range of about 3 kW to 120 kW. [4]

The same document compares an earlier circuit of four IGBTs, eight DC bus capacitors, six power resistors, four fans, two heat sinks and four circuit-board assemblies with a liquid-cooled design using two IGBTs, four capacitors, three resistors, no circuit fans, one cold plate and one board, and targets an average semiconductor case temperature of about 100 °C during cutting. It notes that the pilot arc between electrode and nozzle can be started by a high-frequency, high-voltage signal coupled to the DC supply or by contact starting. [4]

A South China University of Technology patent application on a SiC inverter plasma cutting power supply states that compact MOSFET or IGBT inverters were in use for low-power cutting sources, while medium and high-power sources were still mainly rectifier or chopper types because of the high voltage and power the process needs. Its design rectifies the mains, switches it with SiC devices into a high-frequency square wave above 200 kHz, which it describes as more than ten times the frequency of existing IGBT inverter cutting supplies, isolates it through a power transformer and rectifies it again; it claims energy efficiency that can exceed 96% and adds a non-contact arc-striking module. [5] Kjellberg describes the HiFocus 280i neo as using soft-switch inverter technology. [2]

Editorial calculation: a ripple peak of about 3 A at about 200 A is 1.5% of the cutting current (3 ÷ 200). [4] Patent figures describe embodiments, not a tested product; ask the supplier which circuit the offered unit uses and for its measured power factor and current ripple.

03

Compare the cutting and piercing capacity makers state for each current

Makers state capacity as a cutting range, a pierce capacity and sometimes a separate severance capacity; the table keeps each figure with its source and current.

Editorial note: severance capacity is the thickness a unit can part, not the thickness it cuts to production quality; Kjellberg's split between an 80 mm maximum and a 1–60 mm recommended range for the Smart Focus 300 shows the same distinction. [3] Ask for the cut chart (current, gas, speed and thickness) for your materials rather than one headline thickness.

04

Inside the cabinet: from mains transformer to pilot-arc circuit

05

Duty cycle, open-circuit voltage and mains data that decide the unit

Editorial calculation: 1.03 m × 0.68 m × 1.45 m is about 1.02 m³ of enclosure volume for the Kjellberg units. [2] A weight-to-power ratio of about 22.4 lb per kilowatt, given in the Hypertherm patent, is about 10.2 kg per kW (22.4 × 0.4536). [4]

06

Send the output, mains and capacity data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Work: [materials; thickness range; cut quality; marking]
Output: [cutting current; duty cycle and ambient; open-circuit voltage]
Mains: [voltage; frequency; supply capacity; power quality limits]
Circuit: [chopper or inverter; arc-start method]
Cooling: [air or liquid; site temperature]
Interface: [CNC, robot or pipe cutter; protocol]
Documents: [cut charts; rating plate; conformity declarations]

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