KR950001779B1 - Source of electric power of plasma welding torch - Google Patents

Abstract

The power supply device for accurately controlling the pilot arc current and increasing the efficiency of the pilot arc current, comprises a reactor (5) connected with the positive pole of DC output, a current detector (13) and the mother material (12); condenser (18) connected with an end of the cendenser (9) and a common contact between the reactor (5) and the mother material (12); a current detector (19) connected with the relay switch (11) and a rectifying circuit (4) to detect the plasma current; a pilot current setting section (20) for setting the basic pilot current; a pilot current controller (21) for controlling the plasma current after comparing the results between the detector (19) and the section (20); an arc judging section (22) for judging the arc after receiving the current of the detector (13); a switching section (23) for switching the output of the current controllers (15)(21).

Description

Power supply units for plasma arc cutting

1 is a block diagram of a conventional plasma arc cutting power supply.

2 is a block diagram of a plasma arc cutting power supply of the present invention.

* Explanation of symbols for main parts of the drawings

19: current detector 20: pilot current setting unit

21: pilot current controller 22: arc determination unit

23: switching unit

The present invention relates to a power supply for plasma arc cutting, and in particular, to be suitable for the precise control of the pilot arc current and increase the efficiency.

In general, a plasma arc cutting power supply is used when cutting a metal, in particular, it is possible to cut the conductive metal, as well as excellent cutting characteristics are used in various industries.

Transition type is mainly used to generate plasma arc with DC low voltage. It is the process of electrothermal destruction between torch electrode and nozzle, pilot arc generation between electrode and nozzle, and main plasma arc generation between torch electrode and substrate for high voltage and high frequency. Go through

In this transition type, the main plasma arc generation is highly dependent on the pilot arc.

The configuration of a conventional plasma arc cutting power supply is shown in FIG. This includes the primary rectifier circuit 1 for rectifying and smoothing the three-phase AC input, the inverter unit 2 for converting the output of the primary rectifier circuit 1 to high-frequency alternating current, and the output of the inverter unit 2. Transformer part 3 for converting voltage to low pressure high frequency, secondary rectifier 4 for converting low voltage high frequency into direct current, rectifying smoothing reactor 5, torch electrode 6 and nozzle 7 The high voltage high frequency part 8 for initial breakdown of insulation, the capacitor 9 for high voltage high frequency bypass, the resistance 10 for pilot current limiting, the relay switch 11 for opening and closing a pilot circuit, and the base material 12 The output of the current detector 13 for detecting the current of the current, the plasma current setting unit 14 for setting the plasma current, and the outputs of the current detector 13 and the plasma current setting unit 14 are compared with each other. 15) and the inverter to receive the output of the plasma current controller 15 so that the set plasma arc current flows. And an inverter driver 16 for driving the rotor 2 and a relay driver 17 connected to the current detector 13 to drive the relay RY.

The operation of the conventional arc cutting power supply configured as described above is as follows. That is, when the three-phase AC power is input, it is rectified and smoothed through the primary rectifier circuit 1 and then applied to the inverter unit 2.

The AC output of the inverter unit 2 is applied to the transformer unit 3 to be a DC output through the secondary rectifying unit 4. This DC output cannot directly plasma the air or gas, so the following transition steps are performed. Rough

First, when the high voltage high frequency column 8 generates a high voltage high frequency and simultaneously turns on the relay switch 11, the generated high voltage high frequency destroys the insulation between the torch electrode 6 and the nozzle 7 through the condenser 9. .

Therefore, when the insulation is broken, a pilot arc is generated between the electrode 6 and the nozzle 7 by the direct current output applied through the resistor 10. The pilot arc is injected into the base material 12 through the nozzle 7 and detected by the current detector 13.

The current detected by the current detector 13 is fed back and compared with the set value in the plasma current setting unit 14 and then input to the plasma current controller 15. In addition, the output of the plasma current controller 15 is input to the inverter driver 16 and the inverter driver 16 drives the inverter unit 16 so that the set plasma arc current flows. Thus, the relay switch 11 is opened while the plasma arc is insulated.

However, the prior art as described above has the following drawbacks.

First, since the pilot arc current limiting resistor 10 is used, the loss and weight due to the resistance increase and the resistance value is fixed, so that it is difficult to precisely control the pilot arc according to the torch characteristic.

Second, since the reactor 5 is connected to the negative end of the direct current output and is in the pilot arc current path, loss by the reactor 5 occurs when a pilot arc occurs.

Third, when the torch nozzle 7 is in contact with the base material 12 during the high-frequency high-frequency generation period, it is detected by the high-pressure high-frequency current controller 13 through the secondary rectifier diode path, which makes control difficult. SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned general drawbacks, and to provide a plasma arc cutting power supply device capable of precisely controlling a pilot arc, obtaining an increase in power efficiency, and achieving a compact and light weight. Hereinafter, an embodiment of the present invention for achieving such an object will be described in detail with reference to the accompanying drawings.

2 is a schematic diagram of the present invention using the same reference numerals for the same parts as in the prior art, and description thereof will be omitted.

In the present invention, the reactor 5 connected between the current detector 13 and the base material 12 and connected to the (+) end of the direct current output in the conventional configuration as shown in FIG. 1, and the reactor 5 and the base material 12 A capacitor 18 connected between the common contact of the capacitor and one side of the capacitor 9, a current detector 19 connected between the relay switch 11 and the rectifier circuit 4 to detect plasma current, A pilot current setting unit 20 for setting a pilot current and a result obtained by comparing the current detected by the current detector 19 with the current setting value of the pilot current setting unit 20 are input to receive a pilot current. The pilot current controller 21 for controlling, the arc determination unit 22 that determines the arc by receiving the current detected by the current detector 13, and the current controller 15 by the arc determination unit 22. It is configured to include a switching unit (23) for switching between the output of the (21). When the three-phase alternating current is input, the present invention configured as described above is converted into high-frequency alternating current through the primary rectifier circuit 1. This high-frequency current is converted into low-voltage high-frequency alternating current through the transformer 3, rectified by the secondary rectifier 4 to be a direct current output.

However, this direct current output cannot directly plasmaize the air or gas supplied to the torch, so the initial insulation breakdown between the torch electrode and the nozzle due to the high pressure and high frequency, the torch electrode and the nozzle undergo the pilot arc generation, and the main plasma arc generation. . That is, when a high frequency is generated in the high voltage high frequency circuit part 8, the relay switch 11 of the pilot arc circuit is turned on and the high voltage high frequency breaks the insulation between the torch electrode 6 and the nozzle 7 through the condenser 9. . When the insulation is broken in this way, a pilot arc is generated by the pilot arc current set by the pilot current setting unit 20 between the electrode and the nozzle. In addition, the pilot arc current is detected through the current detector 19 and precisely controlled by the pilot current controller 21. Therefore, a stable pilot arc is generated and injected into the base material 12 through the nozzle. The current of the arc injected into the base material 12 is detected by the current detector 13 and fed back. The feedback current is compared with the value set by the plasma current setting unit 14 and input to the plasma current controller 15. At the same time, the value detected and fed back by the current detector 13 is input to the arc judging unit 22 so that the control command selection switch of the switching unit 23 is switched from the contact point a to the contact point b, so that the inverter driver ( 16 outputs the output of the plasma current controller 15 required for plasma arc generation. Therefore, the inverter driver 16 drives the inverter unit 16 to generate a plasma arc and simultaneously open the relay switch 11.

The present invention as described above has the following effects.

First, by removing the conventional pilot current limiting resistor and installing a current detector 19 to precisely control the pilot arc current using the current controller 21 and the current setting unit 20 according to the torch characteristics Elimination of losses due to resistance and compact and lightweight power supply is possible.

Secondly, by connecting the reactor 15 to the (+) end, it prevents the loss in the reactor 15 due to this in the event of a pilot arc.

Third, the condenser 9 and the separate condenser 18 are installed so that when the torch nozzle 6 and the base material 7 come into contact with each other when the high-frequency high frequency is generated, the current detector 13 does not detect the controller so that the controller operates normally.

Claims (1)

A plasma arc power supply for supplying current to a plasma arc circuit and a pilot arc circuit, comprising: a reactor (5) connected between a current detector (13) and a base material (12) and connected to a positive end of a direct current output; A current connected to the condenser 18 connected between the common contact of the reactor 5 and the base material 12 and one side of the condenser 9 and the relay switch 11 and the rectifier circuit 4 to detect the plasma current. The current setting column 20 of the pilot current setting unit 20, which is a reference to the detector 19, and the current detected by the current detector 19 and the current setting value of the pilot current setting unit 20 are compared. A pilot current controller 21 for receiving a result and controlling a plasma current, an arc determination unit 22 for determining an arc by receiving a current detected by the current detector 13, and the arc determination unit 22 Switching section 23 for switching between the outputs of the current controllers 15 and 21 by Plasma arc cutting power supply, characterized in that for configuring including.