SU1505701A1 - Apparatus for ignition and power supply of plasma arc - Google Patents

Abstract

The invention relates to mechanical engineering and can be used in installations in which plasma torches are used, in particular, for metal cutting. The purpose of the invention is to improve the dynamic characteristics of the plasma arc, energy and mass and dimensions of the device. The device contains a power transformer connected to the electrodes of the plasma torch current sensor and a smoothing choke. The opposite-connected pairs of transistors are connected between the power supply network and the primary winding of the power transformer. The presence of a phase shift unit, a comparator and the introduction of four analog switches, a phase shift blocking device, and a control unit allow a smooth ignition and power supply of the plasma arc with a stabilized current. 2 hp f-ly, 1 ill., 1 tab.

Description

The invention relates to electrical engineering, in particular to devices with a characteristic arc load, and can find application in all areas of engineering and technology where plasmatrons are used, in particular in installations for plasma metal cutting.

The aim of the invention is to improve the dynamic characteristics of the plasma arc, energy and mass and size parameters of the device.

The drawing shows a block diagram of the proposed device.

The state of analog switches, comparators and start buttons, depending on the device operation mode, is given in the table.

The device contains a power transformer 1, the secondary winding of which is connected through an uncontrolled rectifier 2,

containing in the output circuit a current sensor 3 and a smoothing choke 4, with electrodes of a plasma torch 5, to the cathode 6 and the nozzle 7 of which is connected an oscillator 8. Between the supply network 9 and the primary winding of the power transformer 1 are connected anti-parallel to the thyristor pair 10. The device contains also charged RC circuit consisting of series-connected resistors 11, capacitor 12 and analog switch 13. Parallel to capacitor 12, a second analog switch 14 is connected, and the connection point of resistor 11 and capacitor 12 is connected to one inputs of the comparison unit 15, a second input coupled to an output of the current sensor 3, and an output - with a phase shift unit 16 via the third analog switch 17, the output terminals of the phase shift unit 16 are connected to the control yusl

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common electrodes of on-thyristor pairs 10.

The installation contains a phase shift locking device 18, which is connected via an analog switch 19 to a phase shift unit 16, as well as a unit operation control unit 20, which includes three comparators 21-23, a demultiplexer 24, an encoder 25, and three logic elements 2I 26- 28 The output of current sensor 3 is connected

through it the minimum current of the plasma arc, the second comparator 22 changes its state and the combination of potentials at the output of the encoder 25 of the control unit 20 is changed. In this state, only the analog switch 19 is turned on, which connects the phase shift interlock device 18 to the phase shift block 16.

Thus, the control electrical direct input of the comparator 21, to the inverse of the opposite thyristors, the 10th input of which, as well as the direct input of the comparator 22, are applied to the reference voltage UMHH equal to the voltage drop on the current sensor 3 when a minimum current flows through it, the maximum voltage of the holos-plasma arc is applied. Inventing inputs of the installation stroke. After a sample of air parators 22 and 23 are connected to the point

pulses are applied, synchronized with the moment of voltage crossing the power supply network 9, therefore, to the electrodes of the plasma torch 5

and iici are connected to the connection of the resistor 11 and the capacitor 12 of the RC circuit, and a direct voltage equal to the voltage drop across the current sensor 3 is applied to the forward input of the comparator 23 when the plasma arc current flows through it. The outputs of each of the three comparators 21-23 are connected respectively to the inputs of logic elements 2I 26-28, the second inputs of which are combined and connected to the connection point of the start button 29 and the first current-limiting resistor 30 and the outputs to the address bus X |, X2, Xs of the demultiplexer 24 The inlet of the multiplexon gap by an oscillator 8 between the cathode 6 and the nozzle 7 produces an arc, which is blown out by the plasma-forming gas from the plasma torch and closes the circuit 20 of the main arc of the plasma torch. When the current plasma arc reaches the minimum value at which its burning is stable, the first comparator 21 changes its state, and as a result, the control unit 20 closes the analog switch 19, disconnecting the phase shift interlock device 18, opens the analog switch 13, continuing the charge of the capacitor 12, and opens the analog switch 17, connecting the comparison device 15 to the phase shifter 16.

25

35

Pa 24 through the current limiting resistor 31

thyristors 10 is reduced to a value at which the plasma arc current is minimal. In the future, there is a gradual increase in the opening angle of the thyristors 10 with a given RC time constant. Simultaneously with the increase in the current of the plasma arc, its stabilization is carried out. When the current of the plasma arc reaches its nominal value, the comparator 23 changes its state compared to the previous one. As a result, only the analog switch 17 is turned on and the device feeds the plasma arc with a stable current. Switching off the installation is carried out by closing the start button 29. At the same time, a potential of zero level is applied to one of the inputs of each logic element 2I. D 26-28, which closes them. Logic zeros are fed to the address busses of the demultiplexer 24, regardless of the state of the comparators 21-23. As a result, the control unit 20 turns off all analog switches, is connected to the positive potential point of the power supply of the control unit and the resistor 30, and the outputs are connected to inputs of a terminal 25, four outputs of which are connected respectively to the control electrodes of four analog switches 13, 14, 17 and nineteen.

The device works as follows.

When pressing the start button 29 to one of the inputs of each logic element 2I 26-28, a positive level signal is applied through the current-limiting resistor 30. A positive potential is also applied to the input of the demultiplexer 24 through the current-limiting resistor 31, and its address buses Xi, X2, Xs through the elements 26-28 from the outputs of the comparators 21-23 receive a combination of high and low levels, which is determined by the magnitude of the charging voltage the bottom of the capacitor 12, as well as the magnitude of the current plasma arc. In the initial 40

Startup Voltage on the capacitor 12 50 - Р which discharges the condensate and the plasma arc current is zero. Match 12.

Corresponding information at the outputs is commensurately, the installation is practically

Parameters are converted by the demultiplexer 24 and encoder 25 into a combination of control signals, through which the first analog switch 13 is opened and the capacitor 12 starts charging. When the capacitor 12 reaches a voltage equal to the voltage drop on the current sensor 3

it will instantly be ready for subsequent launch, which is possible when the start-up button 29 is opened. In the event of a sudden extinction of the plasma arc during operation of the device due to significant fluctuations of the plasma-forming gas or for other reasons, the output of all three comparators through it is the minimum plasma arc current, The second comparator 22 changes its state and the combination of potentials at the output of the encoder 25 of the control unit 20 is changed. In this state, only the analog switch 19 is turned on, which connects the phase shift interlock device 18 to the phase shift block 16.

Thus, the maximum control voltage of the installation is applied to the control electrodes of the on-connected thyristors 10. After the air breakdown

 I will give counter-switched thyristors 10 the maximum voltage of the idle stroke of the installation is applied. After the air breakdown

pulses are applied, synchronized with the moment of voltage crossing the power supply network 9, therefore, to the electrodes of the plasma torch 5

I will give counter-switched thyristors 10 the maximum voltage of the idle stroke of the installation is applied. After the air breakdown

between the cathode 6 and the nozzle 7, an arc arises, which is blown out by the plasma-forming gas from the plasma torch and closes the circuit of the main arc of the plasma torch. When the current plasma arc reaches the minimum value at which its burning is stable, the first comparator 21 changes its state, and as a result, the control unit 20 closes the analog switch 19, disconnecting the phase shift interlock device 18, opens the analog switch 13, continuing the charge of the capacitor 12, and opens the analog switch 17, connecting the comparison device 15 to the phase shifter 16.

 the result of switching the opening angle

instantly ready for subsequent launch, which is possible when the trigger button 29 is opened. In the event of a sudden extinction of the plasma arc during operation of the device due to significant fluctuations of the plasma-forming gas or for other reasons, the output of all three comparators 21-23 is zero level, i.e. a situation arises, similar to the off state of the device, in which zeros arrive at the address buses of the demultiplexer 24. In this case, the capacitor 12 is instantaneously discharged through the analog switch 14, the comparators 22 and 23 change their state and the smooth ignition of the plasma arc resumes automatically.

parallel to the primary circuit of the power transformer, the output of the phase shift blocking device is connected via the first analog switch to the first input of the phase shift unit, the second input of which is connected via a second analog switch to the output of the comparator, the third analog switch is connected to the voltage supply pole of the control unit, the first input of which the device provides for the improvement of the circuit is connected to the common point of the / C-circuit, and

parallel to the primary circuit of the power transformer, the output of the phase shift blocking device is connected via the first analog switch to the first input of the phase shift unit, the second input of which is connected via a second analog switch to the output of the comparator, the third analog switch is connected to the voltage supply pole of the control unit, the first input of which is connected to the common point / C-circuit, and

The dynamic characteristics of the plasma arc due to the introduction between the mains supply and the primary winding of the power transformer of on-line thyristors, which reduces the likelihood of sudden extinction of the arc during installation and increases the durability of the plasma torch elements 1.1-1.15 times. The introduction of four analog switches, a phase shift interlock device and a control unit allows smooth ignition and supply of the plasma arc with a stabilized current and improves the device’s weight and size by 1.2 times, reducing power losses by 10%.

Claims (3)

1. A device for igniting and supplying a plasma arc containing a power transformer, the secondary winding of which is connected via a rectifier, a smoothing choke and a current sensor to the electrodes of the plasma torch, thyristors, a comparator, whose inputs are connected to the output of the current sensor and midpoint A C-circuit and a phase shift unit. The outputs of which are connected to the control electrodes of the thyristors, characterized in that, in order to improve the dynamic characteristics, energy and mass-dimensional indices, Eden four anal 35 2. The device according to claim 1, wherein the control unit is made in the form of three comparators, a demultiplexer, an encoder, three AND elements, a resistor and a disconnecting start button, the combined inverse inputs of the first and second comparators being the first input of the control unit, My input of the first comparator and the combined direct input of the second and inverse input of the third comparators are connected to the corresponding voltage levels, and the direct input of the third comparator is the second input of the control unit, the outputs of each through the first inputs of the corresponding elements And are connected to the inputs of the demultiplexer, the outputs of which are thus connected to the inputs of the encoder, that the corresponding outputs of the last are the outputs of the control unit, while the second inputs of the elements And are combined and through a resistor connected to the supply voltage pole of the control unit through the disconnecting start button with the common voltage point of the control unit power supply. 3. The device according to claim 1, wherein key, a phase lock device that a phase shift lock device shear and control unit, with the thyristors being included in pairs in opposite directions in the form of a null network voltage organ. five 0 five about five the second is connected to the current sensor output, the fourth analog switch is connected in parallel to the RC circuit capacitor, the output of which is connected to the common supply voltage point, and the outputs of the control unit are connected to the control inputs of the corresponding analog switches. 2. The device according to claim 1, wherein the control unit is made in the form of three comparators, a demultiplexer, an encoder, three AND elements, a resistor and a disconnecting start button, the combined inverse inputs of the first and second comparators being the first input of the control unit, My input of the first comparator and the combined direct input of the second and inverse input of the third comparators are connected to the corresponding voltage levels, and the direct input of the third comparator is the second input of the control unit, the outputs of each through the first inputs of the corresponding elements And are connected to the inputs of the demultiplexer, the outputs of which are thus connected to the inputs of the encoder, that the corresponding outputs of the last are the outputs of the control unit, while the second inputs of the elements And are combined and through a resistor connected to the supply voltage pole of the control unit through the disconnecting start button with the common voltage point of the control unit power supply. 3. The device according to claim 1, wherein  that the phase shift lock device made in the form of a null-organ network voltage.