JPH06320284A - Plasma arc power unit - Google Patents

Abstract

PURPOSE:To make sure of transfer to a plasma arc of a pilot arc by connecting a capacitor between a secondary side midpoint of a transformer and the cathode side of a secondary side rectifier and increasing the no-load voltage between an electrode and a work. CONSTITUTION:The capacitor 10 is connected via an electromagnetic switch between the secondary side midpoint of the transformer 3 and the cathode side of diodes D2 and D3. A commercial AC power source is converted into DC by a primary side rectifier 1, which is converted into high-frequency AC of about 10-20kHz by an inverter 2 for output control and sent to the transformer 3. This is converted into the voltage suitable for welding and cutting by the transformer 3 and DC electric power converted into DC by the secondary side rectifier 5 is supplied to a plasma torch. At this time, the surge voltage generated at the secondary side of the transformer 3 is peak-charged to the capacitor 10. Accordingly, the peak voltage is held as it is for the output voltage of the rectifier 5 and the no-load voltage between the electrode 8 and the work 7 can be held in a high state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transfer type plasma arc power supply device used in a plasma welding machine and a plasma cutting machine.

[0002]

2. Description of the Related Art An inverter control type power supply device is known as a plasma arc power supply device for a plasma welding machine and a plasma cutting machine (for example, Japanese Patent Laid-Open No. 62-2790).
No. 84). This inverter type plasma arc power supply device converts a commercial AC power supply into a direct current by a primary side rectifier, then converts it into a high frequency alternating current of about 10 kHz to about 50 kHz by an output control inverter having a switching transistor, and then transforms it. After being converted into a voltage suitable for welding and cutting by a converter, the secondary side rectifier converts it again into direct current, and the direct current power is supplied to the plasma torch via the direct current reactor.

[0003]

By the way, in this type of plasma arc power supply device, at the time of starting, first, a small-current pilot arc is ignited between the nozzle and the electrode of the plasma torch, and the pilot arc and the work are connected to each other. A plasma arc is generated between the electrode and the work by moving the space between them.

At the time of shifting from such a pilot arc to a plasma arc, generally, a high voltage of several hundreds of volts is applied between the electrode and the work so that the arc is favorably transferred and the plasma arc is surely generated. I have to. However, in order to apply such a high voltage, it is necessary to increase the size of the transformer and increase the capacity of the inverter on the primary side, which causes a problem of increasing the size of the device and increasing the manufacturing cost.

The present invention has been made in view of the above points, and provides a plasma arc power supply device capable of improving arc transferability and ensuring plasma arc generation without increasing the size of a transformer or the like. The purpose is to provide.

[0006]

In order to achieve the above object, a plasma arc power supply device of the present invention comprises a primary side rectifier connected to an AC power source and a high frequency AC connected to the output side of the primary side rectifier. The output side of the secondary side rectifier is provided with an output control inverter for converting to, a transformer connected to the output side of the output control inverter, and a secondary side rectifier connected to the secondary side of the transformer. In a plasma arc power supply device connected to a plasma torch and a work, a capacitor is connected between the secondary side midpoint of the transformer connected to the electrode of the plasma torch and the cathode side of the secondary side rectifier connected to the work. Is configured.

[0007]

[Operations and effects] In the plasma arc power supply device configured as described above, the AC power supply is converted to DC by the primary side rectifier, then converted to high frequency AC by the output control inverter, and then welded by the transformer. -After converting to a voltage suitable for disconnection, it is converted to DC again by the secondary side rectifier, and the DC power is supplied to the plasma torch via the DC reactor.

In such an operation, high-frequency alternating current is sent from the output control inverter to the transformer, but since the collector current of the switching transistor of the inverter rises sharply, a surge voltage is generated on the secondary side of the transformer. .
However, the surge voltage generated on the secondary side of this transformer is
The capacitor connected between the midpoint of the secondary side of the transformer connected to the electrode of the plasma torch and the cathode side of the secondary side rectifier connected to the work is peak-charged, and the no-load voltage between the electrode and the work becomes This is higher than the conventional device that does not connect a capacitor.

Therefore, at the time of starting the plasma arc, when a small current pilot arc ignited between the nozzle of the plasma torch and the electrode is transferred to the plasma arc between the electrode and the work, no load is applied between the electrode and the work. As the voltage rises, the transition to the plasma arc is ensured, and the same effect as when the secondary voltage of the transformer is increased can be obtained.Therefore, without increasing the size of the transformer or the inverter circuit on the primary side, The transferability to the arc can be improved.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a schematic configuration diagram of an inverter type plasma arc power supply device for a plasma cutting machine. 1
Is a primary side rectifier connected to a commercial AC power supply, and has, for example, a bridge-connected diode and a smoothing capacitor C, and converts the commercial AC power supply into DC.

Reference numeral 2 is an output control inverter having four switching transistors Tr connected in a bridge, and the switching transistor Tr is switched in a controlled width by the operation of a switching control circuit (not shown), and a direct current of about 10 kHz to about 10 kHz. Convert to high frequency AC of about 20 kHz. The output side of the output control inverter 2 is connected to a transformer 3 for converting a high frequency alternating current into a voltage suitable for disconnection.

A secondary side rectifier 5 is connected to the secondary side of the transformer 3. The secondary side rectifier 5 comprises two pairs of diodes D1 to D4 connected to each pair of secondary side winding terminals of the transformer 3, and the anode side of the diodes D1 and D4 is connected to the plasma via the electromagnetic switch MC1. It is connected to the nozzle 9 of the torch, and the anode sides of the diodes D2 and D3 are connected to the work 7 for processing.

On the other hand, the cathode side of the secondary side rectifier 5, that is, the midpoint of the secondary side of the transformer 3, is connected to the electrode 8 of the plasma torch via the DC reactor 6. Further, the capacitor 10 is connected between the midpoint of the secondary side of the transformer 3 and the cathode sides of the diodes D2 and D3 via the electromagnetic switch MC2.

In the plasma arc power supply device configured as described above, the commercial AC power supply is converted into the direct current by the primary side rectifier 1, and then the direct current is converted into the high frequency alternating current of about 10 kHz to about 20 kHz by the output control inverter 2. To be converted. Then, this high-frequency alternating current is sent to the transformer 3,
The DC power converted into a voltage suitable for welding and cutting by the transformer 3 and converted into DC by the secondary side rectifier 5 is supplied to the plasma torch via the DC reactor.

During such an operation, high-frequency AC is sent from the output control inverter 2 to the transformer 3, but the collector current of the switching transistor Tr of the inverter 2 rises steeply, so that the secondary side of the transformer 3 is provided. , A of FIG.
A surge voltage as shown in is generated. However, the surge voltage generated on the secondary side of the transformer 3 is due to the midpoint of the secondary side of the transformer 3 connected to the electrode 8 of the plasma torch and the workpiece 7.
The capacitor 10 connected between the secondary side rectifier 5 and the cathode side of the secondary side rectifier 5 is peak-charged. Therefore, as shown in FIG. 2B, the peak voltage Vp of the output voltage of the rectifier 5 is maintained as it is, and the output voltage between the electrode 8 and the workpiece 7 is higher than that of the conventional rectifier output voltage (C in FIG. 2) in which no capacitor is connected. The no-load voltage can be kept high.

Therefore, at the time of starting the plasma arc, when the small-current pilot arc ignited between the nozzle 9 of the plasma torch and the electrode 8 is transferred to the plasma arc between the electrode 8 and the work 7, The increase in the no-load voltage between the works 7 ensures the transition to the plasma arc. Then, after the plasma arc is generated, the electromagnetic switch MC
1 is turned off to extinguish the pilot arc, and the work 7 is cut by the plasma arc generated between the electrode 8 and the work 7.

As described above, by connecting the capacitor 10, the same effect as in the case where the secondary voltage of the transformer 3 is increased can be obtained, so that the transformer 3 and the output control inverter 2 are not enlarged. The transferability to the plasma arc can be improved.

It is of course possible to apply the present invention to a power source device for a plasma welding machine.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a power supply device of a plasma cutting machine showing an embodiment of the present invention.

FIG. 2 is a waveform diagram of the secondary side voltage of the transformer 3 and the output voltage of the secondary rectifier 5.

[Explanation of symbols]

 1-primary side rectifier, 2-output control inverter, 3-transformer, 5-secondary side rectifier, 7-work, 8-electrode, 9-nozzle, 10-capacitor.

Claims (1)

[Claims] 1. A primary side rectifier connected to an AC power supply,
An output control inverter connected to the output side of the primary side rectifier to convert direct current to high frequency alternating current; a transformer connected to the output side of the output control inverter; and a secondary side of the transformer. A secondary side rectifier, wherein the output side of the secondary side rectifier is connected to the plasma torch and the work, and a secondary side midpoint of the transformer connected to the electrode of the plasma torch. A plasma arc power supply device comprising a capacitor connected to the cathode side of the secondary side rectifier connected to the work.