RU2011493C1 - Method and device for producing electric arc - Google Patents

Abstract

FIELD: electrical engineering. SUBSTANCE: method involves applying across the arc gap a voltage from an arc current supply source, as well as triggering pulses. Prior to applying the triggering pulses, the output of the arc supply source is short-circuited for the time sufficient for a short-circuit current to build up to the level pertinent to a stable arc current. The device embodying the method has an arc current supply source, a threshold member, a switch, a triggering pulse generator, output buses of the supply source. EFFECT: more reliable operation, simplified design. 3 cl, 8 dwg

Description

 The invention relates to electrical engineering, in particular to a method and devices for powering an AC welding arc, and can be used in welding machines with low open-circuit voltage.

 A known method of excitation of the welding arc, which consists in applying the voltage of the power source to the arc gap and switching the turns of the transformer winding [1].

 However, this method does not provide an effective start of the welding arc when designing modern small-sized welding machines.

 A device for exciting the welding arc, containing a key, the input of which is connected to the output of the threshold element, the first input of which is connected to the first output bus of the power source of the welding arc [1].

 However, this device does not provide an effective start of the welding arc.

 Closest to the proposed method is the excitation of the welding arc, which consists in applying voltage to the arc gap from the power source of the welding arc and pulse pulses, implemented in a device for exciting the welding arc containing a power source of the welding arc, the first output bus of which is the first output bus of the device, and the second output bus is connected to the first output of the driver of the ignition pulses [2].

 However, the known method and device also does not allow reliable start-up at open-circuit voltages of the power source of the welding arc, since the current through the output inductance of the power source cannot quickly reach the required value, which affects the quality of the transient process of ignition of the welding arc, at open-circuit voltage of the source power of the welding arc, close to the voltage of its burning.

 The aim of the invention is to increase the reliability of starting at open circuit voltages of the power source of the welding arc, close to the voltage of its burning.

 This goal is achieved by the fact that in the method of excitation of the welding arc, which consists in applying voltage to the arc gap from the power source of the welding arc and the excitation pulses, before supplying the excitation pulse, shorten the output of the welding arc power source for the duration of the increase in the short-circuit current to the level of the stable arc current.

 This goal is also achieved by the fact that in the device for exciting the welding arc, containing a power source for the welding arc, the first output bus of which is the first output bus of the device, and the second output bus is connected to the first output of the exciter of the ignition pulses, a threshold element and a key are introduced, and power the key outputs are connected to the output buses of the welding arc power source, to which the input outputs of the threshold element are connected, the output of which is connected to the key control input, and the second output the driver of the ignition pulses is connected to the second bus of the power source of the welding arc.

 The essence of the invention lies in the fact that the shortening of the output of the power source prepares the power source for rapid excitation of the arc, since the current through its inductance increases to the required value, which determines a successful start at low voltage of the power source.

 In FIG. 1 is a functional diagram of a device for exciting a cooking arc that implements the proposed method; in FIG. 2 - a key in a transistor design with a threshold element; in FIG. 3 - driver of ignition pulses for operation with a transistor switch; in FIG. 4 - the proposed device with a key without the use of semiconductor elements and an exciter of ignition pulses; in FIG. 5 - execution of the key and the threshold element, combined in the arrester; in FIG. 6 - phase portrait of the excitation of the arc; in FIG. 7 - time diagrams at the output of the power source of the welding arc; in FIG. 8 is a timing diagram at the output of a welding arc power source with a key without using semiconductor elements.

 A device for exciting the welding arc contains a power source 1 of the welding arc, a threshold element 2, a key 3, a driver 4 of ignition pulses, output buses 5 and 6, to which an electrode and a part are connected, respectively, forming an arc gap. The power source 1 of the welding arc includes a source 7 of excitation, inductor 8, the first and second output buses 9 and 10, respectively. The causative agent of 4 ignition pulses is made in the form of a pulse transformer with primary 11 and secondary 12 windings. The power terminals 13 and 14 of the key 3 are connected to the tires 9 and 10, respectively.

 The key 3 in the transistor embodiment (Fig. 2) contains a bipolar avalanche diode 15, capacitors 16 and 17, a bipolar transistor 18, connected in series to the primary winding circuit of the pulse transformer 19 (transformer blocks), the secondary winding of which 20 is connected with positive feedback in it the base circuit, with saturable magnetic core 21. The primary winding 22 of the pulse blocking transformer with saturable core 23 with a gap, the secondary winding 24 of which is included in the pulse blocking circuit, is included in the same circuit. Positive feedback to the base of bipolar transistor 18 is supplied from the winding 20 through a circuit of parallel-connected direct diode 25, reverse diode 26 and resistor 27. Resistor 28, connected between the collector and the base of bipolar transistor 18, forms a voltage divider from collector to base with resistor 27 . The resistor 29 is connected to the base of the bipolar transistor 18 from the pulse blocking capacitor 30. The diode 31 is connected in the opposite direction with the secondary winding 24 of the pulse blocking transformer. Zener diode 32 is connected in parallel with the primary winding 22 of the pulse blocking transformer. Diodes 33.1. . . 33.4 form a rectifier bridge, the diagonal of which includes a transistor blocking generator and a zener diode 34, shunted by a capacitor 17. The winding 35 of the inductor with saturable magnetic circuit 36 is connected in series with the diode 37, shunting the windings 19 and 20 of the pulse transformer.

 Resistors 27 and 28 and the emitter - the base transition of the transistor 18 act as a threshold element 2.

 The driver 4 ignition pulses for operation with a transistor switch (Fig. 3) contains a bipolar avalanche diode 15, a combined capacitor in the form of capacitors 38 and 93, zener diodes 40 and 41, a magnetic key 42 in the form of a choke with one winding, a double-winding transformer 43 and magnetic keys 44 and 45 in the form of double-wound chokes with capacitors 46-48.

 The key without the use of semiconductor elements (Fig. 4) contains a step-up transformer with a primary winding 49, a secondary winding 50 and a saturable core 51, a magnetic key 52 in the form of a choke with one winding shunted by a resistor 53, capacitors 54-56, a magnetic key 57 in the form double winding inductor, magnetic key 58 in the form of an inductor with one winding, transformer 59 with a saturable core, magnetic keys 60-62 in the form of double winding inductors with capacitors 63-67.

 The key and the threshold element, combined in the arrester 68 (Fig. 5), contain a capacitor 69, a resistor 70 and a capacitor 71.

=

, (1) где t₁, t₂ - длительность входного и выходного импульсов соответственно:
ΔВ - перепад индукции в сердечнике от нулевого состояния до насыщения, обычно меньше В_s;
μ_нас - магнитная проницаемость насыщенного магнитопровода;
Э_c - энергия, запасаемая в конденсаторе;
V - объем магнитопровода.Magnetic keys 42, 44, 45, 57, 58, 60, 61 and 62 are made with a saturable magnetic circuit. The number of magnetic keys is determined by the need to obtain at the output of the pathogen 4 pulses of a high-voltage powerful pulse of short duration. The construction of a magnetic key in the form of a double-winding inductor with a capacitor allows you to apply a reverse sign voltage to the subsequent magnetic key for pre-setting the magnetic induction of the magnetic circuit of the next cascade, which gives an almost double range of magnetic induction and approximately double the shortening (compression, compression) of the output pulse from the next magnetic the key. This is confirmed by the following formula

=

, (1) where t ₁ , t ₂ - the duration of the input and output pulses, respectively:
ΔВ is the induction difference in the core from the zero state to saturation, usually less than B _s ;
μ _us is the magnetic permeability of the saturated magnetic circuit;
E _c is the energy stored in the capacitor;
V is the volume of the magnetic circuit.

=

(E-i/ϒ),

=

(ai²ϒ^-1/2-ϒ), (2)
i(0) = 0, γ(0) = γ_o где i - ток дуги; t - текущее время;
L - индуктивность дросселя 8, равная, например, 10^-3 Гн;
Е - мгновенное напряжение, равное, например, 45 В;
γ - проводимость дугового промежутка;
γ_o - проводимость дугового промежутка после действия импульса возбуждения, равное, например 0,0935 Сим;
τ - постоянная времени дуги;
а - коэффициент = 0,003.The arc power source 1 is a voltage source with inductive output resistance, described by the following system of equations

=

(Ei / ϒ),

=

(ai ² ϒ ^-1/2 -ϒ), (2)
i (0) = 0, γ (0) = γ _o where i is the arc current; t is the current time;
L is the inductance of the inductor 8, equal, for example, 10 ^-3 GN;
E is the instantaneous voltage equal to, for example, 45 V;
γ is the conductivity of the arc gap;
γ _o - the conductivity of the arc gap after the action of the excitation pulse, equal, for example, 0.0935 Sim;
τ is the arc time constant;
and - coefficient = 0.003.

To excite the welding arc before applying the excitation pulse from the pathogen, 4 ignition pulses are short-circuited using the key 3, the output of the welding arc power source 1. This occurs after the triggering of the threshold element 2 when the voltage of the source 1 reaches a certain value and the output from the output of the threshold element 2 of the switching pulse to the control input of the key 3. In this case, the voltage on the output buses 9 and 10 is 0, and the current of the source 1 increases from 0 to ≈ 5.5 A (see Fig. 6, view along arrow 72, time stamps after 10 μm). Assuming that this current corresponds to the level of the stable arc current, an excitation pulse is supplied from the pathogen 4, causing in the arc gap between the output buses 5 and 6, to which the electrode and the part are connected, conductivity γ _o = 0.0935 Sim. In the phase portrait (Fig. 6), γ _{o is} shown by a straight line 73. The key 3 is opened, as a result of which the point in the phase space moves along the path 74 over a time of the order of 0.1 - 0.2 μs. During this time, the current does not have time to change. The conductivity γ of the arc gap at τ = 10 - 300 μs also does not change. Therefore, the voltage - arc current - point 75 is set within tenths of a microsecond.

 Further movement of the point in the phase space is described by the system of equations (1), in which there are two inertial objects: an arc with a time constant τ and inductance L.

The phase trajectories of the further point motion are shown for two arc time constants: 20 and 100 μs - lines 76 and 77, respectively. They quickly reach the static characteristic of the arc — line 78. To compare the effectiveness of the proposed excitation method in FIG. 6 shows the phase trajectories 79 and 80 for an arc with τ ₁ = 100 and τ ₂ = 20 μs, respectively, with the known method of excitation. It can be seen that trajectory 79 characterizes slow excitation, and trajectory 80 represents interruption of the arc.

 To implement the device of FIG. 2, the voltage from the output buses 9 and 10 of source 1 through the rectifier bridge on diodes 33.1-33.4 is supplied to a blocking generator, the threshold of which is determined by the ratio of resistors 27 and 28 and the base-emitter voltage of transistor 18. The pulse width of the blocking generator is determined by the saturation time of the magnetic circuit 21 transformers. The core 23 of the pulse blocking transformer is made with an air gap for accumulating energy from the current of the blocking generator, which at the end of the pulse enters through the diode 31 into the capacitor 30 and through the resistor 29 increases the threshold of element 2, preventing the generation of the second pulse. Zener diode 34 with capacitor 17 serves to protect the transformer from overvoltage, and a bipolar avalanche diode 15 with capacitor 16 serves to protect the output of power supply 1. At the end of the pulse of the blocking generator, the current of the switch 3 flowing along the primary winding 11 breaks, which causes the appearance of a high-voltage pulse in the secondary winding 12, igniting the arc. Thus, the termination of the short circuit of the output of the power supply 1 is automatically synchronized with the excitation pulse.

 In FIG. 7 a, b, c show voltages on buses 9 and 10 at various time scales; in FIG. 7g - key current 3.

 An example implementation of the proposed device with a specific implementation of the pathogen 4 ignition pulses for the case of operation with the transistor switch 3 is shown in FIG. 3.

 When the key 3 is opened, the current of the inductor 8 breaks through the avalanche diode 15 and charges the capacitors 38 and 39. The magnetic key 42 is saturated (tripped) and transfers energy to the capacitor 46 through the transformer 43. Then the magnetic keys 44 and 45 sequentially transfer energy to the capacitors 47 and 48, shortening pulse duration and increasing current. A pulse with a front of 0.05 μs enters the primary winding 11 of the pathogen 4 and through the secondary winding 12 to the discharge gap. Almost at a current of transistor 5 A, the current of magnetic key 45 is 200 A.

 In the device of FIG. 4, the key 3 and the threshold element 2 are combined, the role of which is played by the magnetic switch 52 and the capacitors 54 and 55. When the voltage pulse front area reaches the threshold, the magnetic switch 52 closes, at the first moment of time, the output of source 1 is a short circuit. Then, the voltage rises across the capacitors 54 and 55. The magnetic key 57 is triggered and similarly to the pathogen 4 of FIG. 3 generates the required high-voltage shortened excitation pulse to the arc gap.

 The great advantage of the device of FIG. 4 is the lack of unreliable semiconductor elements.

Timing diagrams of the device of FIG. 4 are presented in FIG. 8:
a) the voltage on the tires 9 and 10;
b) the voltage at the output of the switch 52;
c) key current 52;
g) the current source 1 power arc;
e) voltage across the arc gap;
g) the voltage at the input of the key 61 without pre-installation of magnetic induction (single-wound inductor);
h) the same with a preset (the increasing effect is visible);
i) the amplitude of the voltage on one turn of the windings of the transformer of the exciter 4 pulses with and without preset.

 In FIG. 5, the threshold element 2 and the key 3 are combined and made on the spark gap 68.

 When working when the leading edge of the voltage pulse arrives through the capacitor 71, the spark gap 68 gives a series of short circuits through the transformer winding 49, and the excitation pulses supplied to the arc gap also contribute to the short circuit of the source 1 output and the increase in current through the inductor 8.

 Thus, the proposed method and device allows to develop small-sized safe welding machines.

Claims (2)

 1. The method of excitation of the welding arc, in which a voltage is supplied to the arc gap from the welding arc power source and excitation pulses are supplied, characterized in that, in order to increase the reliability of starting at a no-load voltage of the welding arc power source close to its burning voltage, by supplying an excitation pulse, the output of the welding arc power source is short-circuited for the duration of the rise of the short-circuit current to the level of a stable arc current.  2. A device for exciting a welding arc, containing an exciter of ignition pulses and a power source for the welding arc, the first output bus of which is connected to the first output bus of the device, the second output bus of the device is connected to the first output of the exciter of ignition pulses, and the second output of the exciter of ignition pulses is connected to the second output bus of the power source of the welding arc, characterized in that, in order to increase the reliability of starting at open-circuit voltage of the power source of the welding arc, close to the voltage of its burning, it is equipped with a threshold element and a key, and the power leads of the key are connected to the output buses of the power source of the welding arc, to which the input leads of the threshold element are connected, the output of which is connected to the control input of the key.

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