UA52839C2 - Method of electric arc excitation, device for its implementation, circuit breaker for device of electric arc excitation (variants) and method of preparation of functioning of circuit breaker for device of electric arc excitation - Google Patents

Abstract

The invention relates to the field of electrical engineering. In order to excite an electric arc in a normal manner and melt contaminated and oxydized aluminium, steel and metal, the circuit breaker is disconnected from the output of a power supply and said output is supplied with an amplification voltage having the same polarity and being of a greater amplitude. A delayed voltage pulse of an opposing polarity to the power supply for said electric arc is transmitted in the arc interval. The rated value of said voltage exceeds the above-mentioned amplification voltage and has a shorter flank. The invention also relates to a device for exiting an electric arc, comprising an internal amplification voltage source, a blocking inductance and a long "cable-type" element The invention further relates to an improved excitation voltage pulse source and magnetic conductors, in addition to a method for the use and control thereof.

Description

The inventions relate to the field of electrical engineering, and more specifically, to the method and devices for powering an alternating current welding arc and an auxiliary plasmatron arc, and can be used in devices capable of welding oxidized and rusted metal, steel, stainless steel, aluminum and other metals, which are welded by alternating current devices previously thought impossible.

The electric arc was discovered by accident by Petrov and then by Devi. However, the essence of the phenomena was not understood correctly by them. Even now, the calculations of electrical circuits with negative resistance are difficult, although they can be considered mastery for high-level engineers. The arc has a 5-type volt-ampere characteristic and is stable only when fed from a current source with inductive or sufficiently large active resistance. Connecting a capacitor with a sufficiently large capacity in parallel with the arc (especially at low currents) inevitably breaks the arc.

The alternating current arc, discovered by Yablochkov, with an inductive current limiter, on which the power is not dissipated, is difficult to perceive. The moment of changing the sign of the current with an arc break has not been sufficiently investigated. The "oscillator", invented by Vologdin in the thirties, remained a purely empirical invention, despite its wide application. The initiation of an arc by a spark from the first pulse on a cold part has not been investigated. Until now, there were simply no devices capable of carrying it out. Some provisions that were considered generally accepted turned out to be simply wrong.

Yes, the recommendations to use pulses with an energy of 1J or more for starting seem strange, if in our devices the pulse energy is measured in millijoules. This position can be understood if we consider that there was no electronic equipment that allows recording single processes in the time range starting with fractions of a nanosecond.

A spark discharge of 1 - Zmm at a voltage of 5 - 15 kV occurs in tenths of a nanosecond in a channel with a width of one micron with a temperature of 100,000 K and higher (characteristic purple color). Pressure 500 atm. The energy capacity of such plasma is 100 times or more higher than the TNT equivalent. The shock wave expands the channel at a speed of about 10 μm per nanosecond (10,000 m/s). The temperature drops to 8-6 thousand K, characteristic of an arc discharge (white color). The heat content of such plasma is ZmJ/mm3. Plasma conductivity is 1500Sym/m. Thermal conductivity of air (nitrogen) X. - 0.0255 for T - 27ZK and - 0.151 for T - 5000K. The thermal conductivity of plasma is 7. - 4 for higher temperatures, that is, it exceeds the thermal conductivity of air by more than two orders of magnitude. These numerical data are important for understanding arc statics and dynamics.

In a stationary (static) state, the heat release from the conduction current is exactly equal to the heat dissipation.

The shape of the arc body can be found by jointly solving the equations of thermal conductivity and electrical conductivity under obvious boundary conditions. Both of them strongly depend on temperature, that is, the equations are non-linear. As mentioned above, the thermal conductivity of plasma is more than two orders of magnitude higher than the thermal conductivity of air, the electrical conductivity of plasma is higher, and air is generally an insulator. A similar (but simpler) problem was solved in 1950 under the leadership of A.D. Sakharov ("Nature" magazine, May 8, 1990, article

Yu.A. Romanov "Father of the Soviet hydrogen bomb!").

Therefore, descriptions of welding arc excitation in the literature do not correspond to reality.

Known electric arc power sources with a saturable transformer and a current-limiting choke in the primary circuit (50) Me 1839648, 21.09.90).

Excitation of the arc in them is carried out by high voltage pulses produced from the voltage front when the magnetic circuit exits saturation. The oscillograms show that the arc is not excited clearly, only from the third-fourth pulse from the train of pulses that occur after 5O0μs, excitation occurs.

A method of electric arc excitation is known, in which, before applying an excitation pulse to the arc gap, the output of the electric arc power source is short-circuited for the time of the rise of the short-circuit current to the level of a stable arc current, and an electric arc excitation device containing a source of excitation pulses, an electrode holder, a terminal grounding, the power source of the electric arc, the blocking capacitor and the key with the threshold element are connected in parallel to the buses (NI Mo 2011493, 07/27/1991).

In known inventions, it is proposed to short-circuit a power source with an equivalent inductive output resistance and keep it closed until the current in the inductor rises to a level sufficient to maintain the arc current, then open it and apply an excitation pulse. Practice shows that such exciters provide excitation of the welding arc from the first pulse remotely, at a distance of 0.5 - 1 mm from the part.

Oscillographic observations show that in the first nanoseconds after the passage of the spark, the voltage on the arc gap decreases from 7-5KV (this is the voltage of the spark) to a voltage of the order of 500-300V, and then decreases to 150-70V in tenths of a microsecond. Then it should decrease to the voltage 208, characteristic of the arc, in a time in units of microseconds. However, it stores 150 - 708 for a time in tenths of a millisecond. If the voltage of the power source at the moment of excitation is 35 - 50V, then the voltage on the arc reduces the current of the inductive source and excitation may not occur. The reasons for this behavior of the arc voltage are unknown.

This has been observed to occur in the case of a contaminated and oxidized part. Although the spark occurs at a distance of 2 mm from the part, the arc does not ignite until contact occurs, because the main voltage drop occurs in a narrow, pierced oxide channel with an energy capacity of the order of 10 J/mm3. The invention is based on the task of developing a method and device capable of ensuring the normal process of arc excitation and welding of contaminated and oxidized metal, steel, aluminum, etc.

This problem is solved by the fact that in the method of excitation of an electric arc, in which, before applying an excitation voltage pulse to the arc gap, the output of the power source of the electric arc is short-circuited during the rise of the short-circuit current to the level of the stable arc current, according to the invention, after the short-circuit current reaches the level of a stable arc current, a forcing voltage of the same polarity, which exceeds the voltage of the power source, is applied to the output of the power source of the electric arc, after which a pulse of the excitation voltage of the reverse polarity with respect to the power source - the electric arc, which exceeds the nominal forcing voltage, is applied to the arc gap with a time delay and has a shortened front duration, while the delay time of the excitation voltage pulse is chosen in the range from З to Зб0Оонsec, and the ratio of the delay time of the excitation voltage pulse to the duration of its front is 1 - 30, in addition, the forcing voltage is formed by transforming the energy of the power source from of the circuit that short-circuits it, and the excitation voltage pulse is formed by transforming the energy of the power source from the circuit that short-circuits it.

The task is also solved by the fact that in the device for exciting the electric arc, which contains a source of excitation voltage pulses, the first and second terminals of the arc gap, a power source of the electric arc, in parallel with which a blocking capacitor and a key with a threshold element are connected, according to the invention, a source is introduced of the internal forcing voltage, the blocking choke and the "long line" element, while the source of the internal forcing voltage is connected according to the power source of the electric arc, the source of excitation voltage pulses is connected to the power source of the electric arc oppositely by one of its outputs - through the blocking choke, and the second - directly, and through the "long line" element, the terminals of the excitation voltage pulse source are connected to the first and second terminals of the arc gap, while the source of the internal forcing voltage can be made in the form of a series-connected key element, elements of resistance and inductance and capacitive voltage sources.

In addition, to enhance the effect in a key for an electric arc excitation device containing a capacitor, a saturable magnetic wire with a working winding, one terminal of which is connected to the input of the magnetic key, and the other terminal is connected through a capacitor with an output, according to the invention, a winding is introduced offset for series connection with the primary winding of a power transformer with a saturable magnetic core of an electric arc power source.

In addition, in one of the turnkey options for an electric arc excitation device containing a capacitor, a discharger, a saturable magnet wire of a transformer with working and high-voltage windings, to the latter of which a capacitor and a discharger are connected, according to the invention, a displacement winding is introduced for a series of connection with the primary winding of a power transformer with a saturable magnetic core of an electric arc power source.

In addition, preferably in the method of preparing the key for activation of the electric arc excitation device, made in the form of a cascade chain of p-magnetic keys, which includes setting the magnetic circuit of the i-th key in the initial state of magnetization, according to the invention, for the activation of the i-th magnetic key supply the bias current from the (i-2) magnetic key and the jamming current from the (i-3) magnetic key.

The essence of the invention is that due to the introduction of the above-described elements and the connections between them, conditions are created for arc excitation, namely, during the passage of a negative pulse along a long line and an arc gap, a current with a polarity that coincides with the polarity of the future current accumulates in the blocking choke arc, and the internal forcing voltage source provides the significant arc current necessary to remove ("vaporize") contaminated or oxidized surfaces.

The essence of the invention for the method of preparing the magnetic key for activation is that the winding of the interference protection of the i-th magnetic key is supplied with a current pulse before the arrival of the interference from the (i-3)-th magnetic key and ends simultaneously with the end of this interference.

Further, the invention is explained by the description of examples of its implementation and the attached drawings.

Fig. 1 shows the functional diagram of the proposed device, Fig. 2 shows the equivalent circuit at the end of the spark passage, Fig. 3 shows the shape of the arc body at the end of the spark, Fig. 4 shows the time diagrams for arc currents and voltages, Fig. 5 - the schematic electrical diagram of the first version of the proposed device, Fig. 6 - a device for exciting the auxiliary arc of the plasmatron, Fig. 7 - oscillograms of the version of the device shown in Fig. 5, and time diagrams of stabilization, Fig. 8, 9 and 10 - schematic electrical diagrams of the second, third and fourth variants of the proposed device, in Fig. 11 - versions of magnetic keys, in Fig. 12 - the fifth variant of the proposed device, in Fig. 13 - a schematic electrical diagram of an electronic key, in fig. 14, 15 and 16 - the sixth, seventh and eighth variants of the proposed device, fig. 17 - the basic electrical diagram of the attachment for reducing the welding current (ballast inductor).

The device (Fig. 1) contains a source 1 of excitation voltage pulses, the first and second terminals 2 and C of the arc gap, a source 4 of electric arc power supply, parallel to the buses 5, 6 of which the blocking capacitor 7 and the key 8 with the threshold element are connected. In addition, the device contains a source 9 of the internal forcing voltage, a blocking choke 10 and an element 11 "long line".

The outputs of the source 9 of the internal forcing voltage are connected according to the buses 5 and b of the source 4 of the electric arc power supply, the first output of the source 1 of the excitation voltage pulses is connected through the blocking choke 10 to the first bus 5 of the source 4 of the electric arc power supply, the second output is connected to the second bus b source 4 of electric arc power supply directly, and the first and second terminals of source 1 of excitation voltage pulses are connected through element 11 "long line" to the electrode holder - the first terminal 2 and the second terminal C (ground), respectively.

Element 11 "long line" is characterized by a wave resistance of 150 - 300 Ohms and a delay of 4 ns per 1 meter of length. Element 11 is made in the form of welding cables.

The key 8 with a threshold element for the electric arc excitation device can be electronic (Fig. 13) or magnetic (Fig. 5) and contain a key element 12 and elements 13, 14, 15 of inductance, resistance and capacity, respectively.

The source 9 of the internal forcing voltage may contain a key element 16 (or be switched by other keys), elements 17 and 18 of resistance and inductance, respectively, and a capacitive voltage source 19.

The source 1 of excitation voltage pulses may contain a key element 20 (or be switched by other keys), an inductance element 21 and a capacitive voltage source 22 of reverse polarity.

The body 23 of the arc (Fig. 3) with a gap of one micron touches the cold electrode (terminal 2) around the circle, where there is a heat sink and a voltage drop of 6 - 108, in the middle part of the body 23 the arc is expanded and the voltage drop is minimal.

The entire voltage drop occurs in a narrow area of oxide 24, which evaporated from the spark discharge along the discharge channel.

The schematic electrical diagram of the first version of the proposed device (Fig. 5) contains a power source 4 of the electric arc, which includes buses 25, 26 of the alternating voltage network, a switch 27, a transformer with a saturating magnetic circuit 28, a primary winding 29, a secondary winding 30, an excitation winding 31 with active resistance 32.

The key 8 is made of a magnet on a saturating magnetic circuit, with a working winding 33, a resistor 34 and a bias winding 35. In addition, the key 8 contains a capacitor 15, a transformer 36 with windings 37 and 38, working and displacement, respectively.

The function of the threshold element of key 8 is performed by a volt-second area that responds to the voltage integral.

The auxiliary winding 39 of the transformer 36 with the capacitive source 19 and the resistance element 17 form the source 9 of the internal forcing voltage.

The source 1 of excitation voltage pulses may contain a high-voltage winding 40 of the transformer 36, a capacitive voltage source 22 of the reverse polarity with respect to the voltage on the buses 5, b, a key element 20 in the form of a discharger and an inductance element 21, the role of which is performed by the inductance of the mounting wire.

A variant of the blocking choke 10 in the form of a secondary winding 41 of a transformer having a primary winding 42 is possible.

The device for exciting the auxiliary arc of the plasmatron (Fig. b6) contains a power source 4 of the electric arc (auxiliary arc) of the plasmatron, which includes buses 25, 26 of the alternating voltage network, a transformer with a magnetic circuit 28 that is saturated, a primary winding 29 and a secondary winding 30 and a power winding 43 for powering the main arc of the plasmatron, as well as choke 44.

In addition, the device contains a source 1 of excitation voltage pulses, a key 8 with a threshold element, a source 9 of the internal shaping voltage, a blocking capacitor 7, a blocking choke 10, an element 11 of the "long line"? the first, second terminals 2 and 3 of the electric arc (auxiliary plasmatron arc) and terminal 45 of the grounding of the main arc.

Another version of the proposed device, shown in Fig. 8, additionally contains a magnetic key that shortens the duration of the pulse, including a magnetic wire 46 that is saturated, with windings 47 and 48, respectively, displacement and working, and a capacitor 49.

In the version of the proposed device, shown in Fig. 9, the key element 12 should be made non-magnetic, preferably transistor, capable of holding the voltage of both polarities and interrupting the direct current. In this case, it is possible to use an inductive accumulator 50, connected through a series circuit from a resistor 51 and a capacitor 49 to the output of the winding 37.

In the version of the proposed device shown in Fig. 10, a magnetic key with a magnetic circuit 52, a working winding 53, a displacement winding 54 and a capacitor 55, a magnetic key with a magnetic circuit 56, a working winding 57, a boosting winding 58, a displacement winding 59 and a capacitor 60 are used. a magnetic key with a magnetic circuit 61, a working winding 62, a boosting winding 63, a biasing winding 64 and a capacitor 65, and a magnetic key with a magnetic circuit 66, a working winding 67, a boosting winding 68, a biasing winding 69 and a capacitor 22.

In addition, a charging magnetic key with a working winding 70 and a bias winding 71 is used, as well as a bias circuit with a resistor 34, a filter choke 72 and bias windings 73 - 77 with their belonging to the corresponding above-mentioned magnetic keys.

In the lower part of Fig. 10, a version of the displacement circuit is presented without including it in the scheme, where the element 78 is not a resistor 34, but the resistance of a closed conductor passing through the choke 72 of the filter, the indicated windings 73 - 77 of the displacement and the turn 79 on the magnetic circuit 46.

Fig. 11 shows various options for connecting magnetic keys and diagrams explaining their operation.

Fig. 12 shows a variant of turning on the proposed device.

The electronic key (Fig. 13) contains a rectifier bridge on diodes 80 - 83, the input diagonal of which is connected to buses 5, 6 of the power source, to which the varistor 84 is connected. The output diagonal of the above-mentioned bridge includes a series circuit with the K-E transition of the transistor 85, resistor 86, emitter winding 87 of the base transformer 88 and emitter winding 89 of the accelerating transformer 90.

The base winding 91 of the base transformer 88, resistor 92 and a series circuit of diodes 93, 94 and the base winding 95 of the accelerating transformer 90 are connected to the emitter-base circuit of the transistor 85.

A reverse diode 96 is connected to the base of the transistor 85, as well as a threshold element on a thyristor 97, a capacitor 98 and a chain of resistors 99 - 102. In addition, a protective capacitor 103 is used in the scheme.

The version of the proposed device shown in Fig. 14 requires the use of an electronic key.

The version of the proposed device shown in Fig. 15 also requires the use of an electronic key with an inductive accumulator 104, separated from a transformer with a magnetic core 36 by a series circuit on a resistor 105 and a capacitor 106.

The version of the proposed device shown in Fig. 1b6 requires the use of an electronic key, an inductive accumulator 104, and shortening magnetic keys, which avoids the use of a discharger.

In Fig. 17. a variant of the proposed device using a low-current welding attachment is shown.

The attachment contains a choke 107 with a winding 108, parallel to which a protective capacitor 109 and a series circuit of a resistor 110 and a capacitor 111, and terminals 112 - 115 are included.

For a correct understanding of the essence of the proposed method, we will present our understanding of the arc excitation process. The passage of the spark creates a channel with a width of one micron, which is stable in the longitudinal direction. Current,

that enters the channel, uniformly ionizes it and expands it, and the conductivity is equal to 1500Sym/m, and the energy capacity is ZmJ/mm3. Then the behavior of the channel is determined by heat conduction to the "cold" electrode and the part (because 1500K is "cold" to 8000K). The channel swells in the middle, the voltage drop and heat release decrease until the heat dissipation exactly equals the heat release. In the literature, this is interpreted as "contraction" (compression) of the arc at the electrodes. Calculations show that a spot is formed at the electrode with a diameter proportional to the current (the flat part of the plasma in Fig. 3 at the top). The voltage drop on the spot is 8 - 108 in the range of currents, and this is a drop on the plasma, not on the contact. The approximate diameter of the spot is 0.1 - 0.2 mm for a current of 1A. Note that the entire volume of plasma in Fig. 3 is less than 1 mm3, that is, there is only 5 mJ of energy. A cube of 1 x 1 x 1mm at - 1500Sym/m has a conductivity of 1.5Sym, or a drop of 5V occurs at a current of 7.5A, in the rest 2 x 88 near the contacts.

Real declines are much larger on contaminated and oxidized parts. Presumably, this is caused by the huge heat capacity of vaporization of the oxide, which is equal to 10J/mm, that is, 3000 times more than the heat capacity of plasma. Then the hole in the oxide shown in Fig. 3, pierced by a spark discharge, 0.1 x 0.1 x 0.1 mm, has a conductivity of 0.15Sym, i.e. 50V at a current of 7.5A and 2008 at a current of ZOA, i.e. it is this that causes the decline voltage on the arc.

Excitation of the arc according to the proposed method (see Fig. 1) begins with closing the key 8 and holding it during the time when the current in the inductance of the power source 4 increases to the calculated arc retention current. Thus, the output of source 4 of electric arc power supply is shorted for the time of short-circuit current growth to the level of stable arc current.

Then, after opening the output short circuit (terminals 5, 6), the 4 electric arc power sources supply it with a forcing voltage of the same polarity, but exceeding its value.

After that, an excitation voltage pulse of reverse polarity is applied to the arc gap (to the holder - electrode terminal 2 and ground terminal 3) with a time delay in relation to the electric arc power supply source 4, which exceeds the nominal forcing voltage indicated above and has a shortened front duration.

The delay time of the above-mentioned excitation voltage pulse should be in the range from 3 to 300 seconds, which is determined experimentally.

Moreover, the ratio of the delay time of the above excitation pulse to the duration of its front should be in the range of 1 - 30.

At the same time, the forcing voltage is formed by transforming the energy of the power source 4 from the circuit that short-circuits it. The excitation voltage pulse is also formed by transforming the energy of the power source 4 from its short-circuit circuit.

The device works as follows.

The power source 4 (Fig. 1) at the moment of arc excitation is a source of EMF "e" with an equivalent output inductance (for example, the secondary winding of a welding transformer), and its output terminals and 6 must be shunted by a blocking capacitor 7, which protects the insulation of the transformer from actions of a high-voltage starting pulse.

When the instantaneous value of the voltage of the power source 4 reaches the threshold level, the switch 8 is closed, the current increases in the inductance of the power source 4. By the time the current reaches a level sufficient to maintain the arc, the key 16 of the source 9 is closed with the source 19 of the voltage of the same polarity as that of the source 4, and the exciting pulse has the voltage of the source 22 of the opposite polarity to the voltage of the source 4, and the pulse choke 10 basically not saturated.

An excitation pulse of reverse polarity (suppose, for clarity - negative) arrives at the output of the device and through element 11 the "long line" spreads to the electrode holder - terminal 2. A negative voltage, for example, 7.5 kV, is applied to the right end of the inductance of the blocking choke 10, suppose its inductance is equal to 5μH. Then the current increases in it from left to right by 1.5A every ns. Having reached the end of element 11 "long line", the pulse is reflected, doubling in voltage. Suppose, in this case, the arc gap is broken by a spark discharge. At the same time, the spark current is negative. The spark discharge is reflected and returned to the beginning of the element 11 "long line", and after several fading circulations in the circuit of the choke 10, element 11 and the arc gap, a current coinciding with the future arc current is established. You can see that the current is 20 - 30A. The arc body shown in Fig. 3 is formed. Next, the process can be illustrated by the equivalent circuit in Fig.2. It shows voltages and current directions.

This scheme is described by a system of differential equations: - 1 - ykom y- Yipom ipom - (Opom t Tsuz)/Apom dO - d/g I go about mIdta- a. I go oi/oi- (e - uz.

O icom/2 Y - (uz - OMkom)/I com o id/yu i - (com - ipom g Nlom - i FL di

O kom/0 Y - Ikom/Skom d Mpom/O Y - - Ipom/Spom, where s is the steady voltage on the arc at "average" currents, for example, 00 - 208; a - coefficient, with an oxide thickness of 0.1 mm, its energy capacity 10 J/mm3 and plasma conductivity 1500Sym/m a - 15;

Y is the conductivity of the plasma in the channel in the oxide, Sim.

Designations of elements, currents and voltages are shown in Fig.2. For example, let's take: Y - 600. 105Hn, I com - 70.106Hn, I di - 5. 109Hn, Skom - 140. 106F, Som - 2.0. 109F, VAplom - 10Ωm, e - 508.

Initial conditions: id (0) - ZOA, M (0) - 010Sym, i(0) - 7A, icom (0) - 7A, com (0) - 60V, pom (0) x 1208.

In Fig.4. the given solution of the equations with the specified parameters. It can be seen that initially the arc voltage is 3008 and the current is supported by the inductance current I d. It coincides in direction with the future arc current precisely because the polarity of the excitation pulse is opposite to the voltage of the power source. If it were the other way around, the arc current would have to pass through zero, which would slow down the establishment of the desired conductivity and could cause the arc to break, i.e. starting could not occur. It is important that the IC is made non-saturating during excitation (during arc operation, the current is hundreds of amperes and saturation is inevitable), the magnetic conductor 41 must be made with an air gap. Calculations of options according to the given system of equations allow finding the optimal value of I and i. As mentioned above, the "accumulation" of the current depends on the time of maintaining the high voltage until the pulse travels along the line and returns reflected.

Then the arc current from the range of tens of amperes goes to units and is supported by the current of the auxiliary circuit. During this time, the current i is "intercepted", which initially comes entirely through the inductance of the switching key Id. The solution of the system of equations with different parameters of the elements of the equivalent circuit and initial conditions shows the direction of efforts to create the device according to the proposed method.

In Fig.5. shows the schematic electrical diagram of the first variant of the proposed device, designed to work with a transformer with a magnetic core 28, which is saturated. The choke in the primary circuit and the transformer with the primary winding (it is the choke winding) are connected. The magnet wire of the choke and the transformer, i.e. combined, does not saturate. The magnetic wire on which the secondary winding of the transformer is located has a smaller cross-section and is saturated at idle. On the magnetic circuit 28, there are windings 29, 30, 31, respectively, primary, secondary and excitation, wound on the side of the secondary winding 30. As was shown in the example of the excitation calculation, the capacity of the switching capacitor was 140 μF, which is non-constructive. When using the excitation winding, the capacitance is transformed, in this case it decreases to 2 - 5 μF. But an additional inductance appears in the switching key circuit due to the incomplete connection of the windings Z1 and 30. In order to reduce this inductance, the excitation winding 31 is switched on in series according to the secondary winding 30, that is, autotransformer switching takes place.

As a key element 12 (in Fig. 1) in this device, a magnetic key is used, which has windings and 33, offset and working, respectively. The primary winding 37 of the high-voltage transformer 36, which has a displacement winding 38 and a secondary winding 40, is sequentially included in this circuit. A capacitive voltage source 22 in the form of a capacitor is connected in parallel with this winding, and a discharger is used as the key element 20 of excitation. The auxiliary resistor of the resistance element 17 and the auxiliary capacitor of the capacitive source 19 are connected to the auxiliary winding 39 of the high-voltage transformer 36.

For the operation of the exciter with magnetic keys, it is important to synchronize them for accurate inclusion according to the method. This synchronization is achieved by the displacement windings 35, 38 connected in series in the circuit of the primary winding 29. Due to the saturation of the transformer at idle, significant currents (up to half the amplitude of the operating currents) pass through its primary winding 29, which set the magnetic key and the transformer 36 in the induction state of readiness to work

Figure 7 shows experimental oscillograms of the exciter at idle. Synchronization is performed at the beginning of the sinusoidal network voltage. For orientation, a virtual voltage is applied to the oscillogram. The magnetic key current is measured by a current transformer connected in series with resistor 34 (Fig. 5). During the saturation of the power transformer, the bias current calms the oscillations in the circuit of the magnetic key. The voltage tso() is close to zero when the output of the transformer from saturation begins.

The voltage sh() on the primary winding of the transformer is close to zero until now. The current of the magnetic key is also zero. The voltage tso() is applied to the working winding 33 of the magnetic key, and induction movement occurs in its magnetic circuit from -Vx to 4Vz. When saturated, the magnetic key is short-circuited according to the method, through the excitation winding it is transferred to the secondary winding. The current i() charges the switching capacitor 15, as a result of which the voltage tso() increases, and through the winding 40 charges the capacitor of the capacitive source 22. When the voltage of the discharger's activation level is reached, a high-voltage pulse is applied to the output of the device, and with a negative polarity, according to the method. At the same time, the discharge causes a voltage jump on the winding 37, producing a positive auxiliary voltage, according to the method. Excitation of the arc is described earlier. Figure 5 shows a variant of using a pulse transformer with a primary winding 42 instead of a choke.

The arc is excited from idling. If the arc burned, then the current passes through zero and it is necessary to restore the arc again, then there is a stabilization mode, which is generally different from excitation.

The difference is that when the arc is stabilized, the voltage ts(y) comes not from the zero level, but from the negative voltage of the arc burning.

Estimated stabilization time diagrams are shown on the right in Fig.7. It can be seen that the voltage ts() lags behind the voltage y2() on the arrester (or the voltage on the arrester is ahead of it), the discharge occurs at the moment when the voltage tsod(i) has not reached the required level of 40 - 60V, and arc stabilization does not occur . The device again switches to XX mode, and excitation will occur only in the next half-cycle. When welding, this is manifested in "breaks" - dips in the oscillograms of the welding arc current, splattering of the metal.

The diagrams show the stabilization process in the presence of resistor 34 in the switching circuit (the resistance is reduced to the circuit of the secondary winding). At the same time, the rate of voltage rise on the arrester slows down and the discharge occurs at the right moment. There is an optimal value of this resistance. In addition, with zero or too little resistance, transient processes do not have time to end before the transformer exits saturation. Fig. 7 on the right shows the calculation diagrams of voltage (I) at zero resistance and at r - 3 Ohms and current icom() of the key (reduced to the secondary circuit) at r : - 0 and at r - 3 Ohms.

This version of the exciter is quite reliable in operation, although the transformer comes out with the number of turns in the secondary winding 40 of the order of 12000 - 4000. In order to reduce the dimensions of the transformer and slow down the operation of the arrester, a magnetic key with a displacement winding 47 and a working winding 48 and a shortening capacitor 49 is introduced to shorten the pulse duration , shown in Fig. 8. The directions of the windings are shown by generally accepted signs. It should be borne in mind that the shorting key in this switch-on changes the polarity of the pulse, therefore the auxiliary winding 37 and the primary winding 40 have the reverse polarity of the switch-on.

The capacity of the shortening capacitor 49 can be chosen so that the turns of the primary winding 40 and the winding 37 are equal, and since in this case the voltages are in the same phase, it can be one winding, as shown in Fig.8.

In this version of the exciter, despite the introduction of another magnetic key, more acceptable design parameters are obtained. The turns of the transformer are reduced to 3000 - 1500, the volume of steel is quadrupled. The tripping delay of the shorting magnetic key makes stabilization easier, but the 34 resistor is useful. Note that in these two versions of the exciter, after the commutation key current is "intercepted" and becomes zero, the magnetic key automatically opens, which facilitates starting. After some time, its reverse operation occurs, but its current is directed into an arc, that is, it will not prevent the start. It should also be noted that the required mixing currents are generated in the displacement windings when using a transformer that is saturated. Magnetic keys do not respond to the voltage amplitude, like ordinary threshold devices, but to the integral of the voltage at the front of the transformer core, which comes out of saturation.

The energy for the excitation pulse in these exciters is generated from part of the energy of the switching capacitor. In principle, the magnetic key cannot switch the constant component of the voltage, in these schemes the circuits of the magnetic keys are separated by capacitors.

The variant of the device according to Fig. 9 uses an inductive energy accumulator. In this case, the key element 12 must have the ability to hold a constant voltage component, that is, it must be an electronic key. Such an exciter is able to work both with a saturating transformer and with a conventional welding transformer. Therefore, all necessary displacements must be produced inside the circuit.

The key element 12 with a threshold device is activated when the voltage of the source 4 reaches a given level, its inductance is closed through the inductive accumulator 50.

After the current of the key element 12 reaches a given level, it is opened (this will be described in detail later), the inductance current of the accumulator 50 through the separation capacitor 49 and the current limiting resistor 51 enters the primary winding 37 of the transformer. The presence of the source capacity 22 limits the growth of the voltage applied to the key element (for clarity, it is chosen 400 - 6008 - depending on the quality of the transistors).

The arrester is triggered when the specified voltage level is reached, the excitation pulse is applied to the blocking choke 10 with negative polarity, according to the method.

The inductor current cannot stop with a jump. But he can jump from one chain to another. In this case, the ICOM stops in tenths of a microsecond and the inductance current of the accumulator 50 jumps to the primary winding 37 of the transformer. But the current 6 of the inductance of the source 4 remains. It jumps from the key element 12 to the circuit of the source 9. This is how the forcing voltage is produced. It can be seen that in this scheme there is no commutation key inductance in the circuit of the increasing arc current. This makes it easier to start.

Pulses with nanosecond fronts are used to excite the spark and arc. So that the high voltage cannot penetrate the welding transformer, it is blocked by the inductance of the blocking choke and the capacity of the blocking capacitor 7. These pulses are produced by the arrester. Experimentally, "breakthroughs" (missing) of pulses were observed, several arresters connected in parallel are used in the devices.

In principle, the required shortening of pulses can be obtained with the help of magnetic switches (Km), but the theory of Km is still insufficient for their practical use in exciters. Therefore, we present the obtained results. Fig. 11a shows two types of magnetic keys Km: "P"-type, or Km type "A", and Km "T"-type, or Km type "B", in generally accepted terminology. Due to the fact that they are shown in the figure, they can be switched on in cascade (according to the accepted custom in electronics, we believe that energy spreads from left to right).

Figures 11g and 11g show real hysteresis cycles of magnetic materials used in Km. Recall that at zero voltage H (zero sum of currents in all turns), induction B(0) can be at any point inside the hysteresis loop. This is fundamentally different from the state of an ordinary electrical circuit, where before the start of the process, if the pause lasted long enough, then the voltage on the capacitors is zero, the currents in the inductors are zero, and the power dissipated on the resistors is zero. This follows from the law of conservation of energy, because non-zero power means a continuous flow of energy. But non-zero induction in a magnetic circuit can be at zero energy, and therefore it is possible.

In addition, phenomena similar to those studied in a new branch of mathematics known as "catastrophe theory" are observed in Km chains. At the same time, unequal consequences follow from equal initial conditions (causes), i.e. "causeless phenomena". An example can be an object called an "attractor" or the movement of a fluid in a turbulent regime. That is why the weather, in principle, cannot be predicted for a long period, and it is not a matter of imperfection of computers. In Km chains, this is expressed in non-periodic transient processes in each half-cycle of the supply voltage of the network, in a jump-like "change of oscillation modes", in changes in the time of appearance of excitation pulses and even in its sign. This makes the exciter operation unstable, and therefore the displacement issue must be given the closest attention.

The work of Km can be understood on the example of the Km chain of type "A" in Fig. 11b. Suppose, initially, all the magnetic conductors are shifted to the position -Vh: by an external source. A voltage stepper is applied to the first capacitor on the left. The first Km on the left moves from -B5 to "Vo. When its volt-second area is exhausted, the magnetic permeability of the magnetic conductor decreases (in ferrite from 1.2 to 2.0 of the vacuum permeability - it is more than one, because the cross-sectional area of the winding coil is greater than the area of the magnetic conductor, in permanent and amorphous steel - similarly, in electrical engineering steel permeability remains from 20 to 3, depending on the depth of saturation and quality of steel annealing). The saturated inductance of the first Km turns out to be connected in series in the circuit with the first and second capacitors, and at this moment the voltage of the first capacitor is maximum, and the second capacitor is zero. A current flows in the circuit in the form of half a sine wave, the voltage shi drops to zero, the voltage c2 increases to the maximum, the current "tends to become" negative, but this means that a reverse voltage is applied to the first Km, which it can hold to the extent of its volt-second area.

In Fig. 11c, it can be seen that a voltage appears on the second Km, then the same process takes place, each Km shortens the duration of the pulse, leaving the voltage amplitude and, therefore, increasing the current.

Fig. 11g shows the Km type "B" chain. When the voltage is applied and through the capacitor of the previous one

Km, the current is transformed into capacitor Si, and the current through Km 2 saturates it and maintains it in a saturated state for the entire time of charging current Si. At this time, Km 1 works as a transformer, the induction moves from -Va to 4"Vz. When saturation is reached, Km 1 is transformed into a small inductance, the charged Si is recharged by the reverse current to the reverse voltage, that is, there is a double drop in the voltage amplitude. At the same time, Km 2 comes out of saturation, capacitors Si and Co become connected in series, half of a double voltage drop is formed on Cg, i.e. a single drop of the opposite sign (for a better idea of the operation of Km type "B", it is useful to imagine the windings turned on according to how it is shown in Fig. .11g, and the turns are equal, then these windings can be connected and the transformer turns into a choke, all capacitors become equal and connected in a series circuit). It can be seen that Km type "B" allows you to change the polarity and carry out transformation, that is, to go from relatively low voltages to high ones, which will be used later.

Note that the voltage si on Km 1 is a series of cosines with decreasing half-periods from the activation of each subsequent Km with a change in the voltage sign (it can be shown that the difference of the transformation coefficients in the Km chain from unity does not change the voltage si). Note that the voltage at the output Km type "A" does not change sign and there is no "dribbling" there.

This is important for arcing, as will be shown later. It is believed that at the end of the Km chain there is a load in the form of a resistor or a spark gap, where the pulse energy is absorbed. In this case, in the "A" type Km chain, all capacitors become discharged, and all magnetoconductors are in the 4V5 state. In the "B" type Km chain, the last "dribble" pulse has zero voltage. This is followed by a new half-cycle of the mains voltage with an offset setting.

However, it may be that there is no load at the end of the Km chain (there was no spark), or there is a short circuit or XX. In this case, there is a pulse reflection to the left according to the scheme, and there are different options. For example, in the Km chain of type "A" (Fig. 116), the last Km 4 "dribbles" between the last capacitor Ca, in Km Z there is zero voltage on the left, zero and full positive amplitude on the right, until this positive voltage exceeds the area volt-second area Km 3, which is activated (and all remarks about the "attractor" are valid), the impulse spreads to the left.

The process is easier in the Km chain of type "A" if there is a short circuit at the output. In this case, the positive voltage on the last capacitor "turns over", that is, it becomes negative, and the entire chain of Km type "A", which are in the -Vz state, transmits this pulse to the left, and the time does not correspond to the time of holding Km, but to the time of their switching. This manifests itself in the fact that during oscillography of the current, for example, Km 1, a second current pulse of slightly smaller amplitude immediately appears after the current pulse (due to losses).

If a process takes place in the chain of type "B" and a short circuit occurs at the output, then a pulse of reverse polarity spreads from right to left, i.e. a double current Km occurs.

If the output is ХХ, then first there is a problem of how the capacitor will be charged at ХХ. If measures are taken for this, then, when the last Km is activated, the process seems to end and the impulse does not propagate back at all.

Current offset for proper operation of Km, taking into account that the characteristics of magnetic materials can be as shown in Fig. 11, that is, possible PPGs (with a rectangular hysteresis loop) or closer to linear (ferrites) are shown in Fig. 11. It is convenient to start consideration of Km's work with the latest stage in time, then progressing in time to earlier stages. At the same time, the duration of each previous stage increases in proportion to the shortening of each Km.

Stage "1" - switching. Saturated Km is an inductance included between two equal capacities, one of which is charged, the other at zero voltage, i.e. the circuit capacity is equal to half the capacity of the capacitor (in Km type "B" is meant "summed capacity").

Stage "2" - integration or exposure. For Km type "B" it can be called "charge" or "transformation".

If the Km of type "B" has equal windings connected according to it, or if it is Km of type "A", then they behave as a choke, the current of which is the magnetizing current according to its magnetization curve. If Km is type "B" with split windings, then transformed currents flow in them in opposite directions. At this stage, the induction goes from -B to "B, then - stage "1".

Stage "3" takes place only for km type "B". It can be called "preset" or "displacement". At this stage, the capacitor of the previous Km is charged through this Km by the switching current of the previous one

Km This is favorable for this Km, because this current shifts it to the state of readiness for stage "2", that is, in -V. IN

Type "A" km does not have this stage, so it is necessary to take measures for the required displacement.

Stage "4" can be called the stage of "interference sensitivity". Suppose there is a chain Km of type "B" with single transformation coefficients. Then the capacitors are connected in series and they have "dribbling" with decreasing periods. If the current of this Km at stage "3" is favorable for it, then the current at the previous stage gives a reverse bias (although the amplitudes of the previous currents decrease in proportion to the increase in their periods). It is necessary to take measures to prevent obstacles.

Although at stage "3" this Km will be shifted in the desired direction, we are not dealing with a passive VS-chain, but with nonlinear inductances, connected capacities. The displacement of the magnetic wire in this direction is proportional to the volt-second area of the voltage applied to the winding. A non-zero voltage is required to obtain a finite area at a finite displacement time. But this voltage ends up on the capacitors.

This is energy, and it is lost. In itself, this is permissible, because the energy depends on the square of the voltage and can be insignificant, but these insignificant voltages for a long time move other Km in various unpredictable directions, the system of connected Km turns into a typical "attractor" with unpredictable behavior. Therefore, bias currents with the minimum possible rate of increase should be organized. We will give a numerical example for a typical Km chain. Suppose the last three KM are ferrite, shortened five times each, the previous ones are steel, shortened by "10" and "20". The current of the last Km is 200A at 70008 for a time of 23Sns, the voltage is 35000A/m (it is useful to compare the Km parameters with the known parameters of transistor or thyristor switches). In the previous stage, the voltage is 7000A/m, in stage "3" - 1400A/m, in stage "4" - 140A/m. Turning to the characteristics of the magnetic materials in Fig. 11, you can see the scale of the troubles at stage "4" and the amount of displacements necessary to prevent them.

In the variant of the excitation device with magnetic keys, the following biasing order is organized: a bias current from the preceding KM is induced on this KM, which prepares it for stage "2" (integration), and an interference protection current with the appropriate polarity is induced from the preceding KM, which prepares it for the stage "3" (displacement) and protects it at stage "4" (interference sensitivity). This is shown in Fig. 11b for the Km chain of type "A", in Fig. 11d for the Km chain of type "B" and in Fig. 11e for the Km chain of types "B", "B", "A", "B". If the previous Km is of the "B" type, then it itself gives the "displacement" current, so there is no need to specially start the displacement, although it will not hurt. The correct decision can be made when calculating the bias currents numerically.

The last Km in the chain, which has access to the output terminals of the welding machine and welding cables, has a special mode of operation. If it is Km type "B", then the "charge" current in its stage "2" and the "displacement" current in its stage "3" must pass through it and the load. But the output has welding cables with negligible capacitance and a pulse choke inductance with a relatively large inductance. It is necessary to provide paths for the passage of these currents. For this, it is necessary to use an additional Kmzar (charging key) with the appropriate offset. It will be described in more detail on the example of a specific implementation of the exciter.

According to the proposed method, an auxiliary voltage should be applied to the NlomSpom chain using an auxiliary key.

In the Km exciter, for this purpose, it is proposed to use the voltage on one of the Km of the type "B" chain, in which the integration time (stage "2") is greater, and the switching time (stage "1"7) is less than the time constant of the auxiliary circuit. The polarity of the auxiliary pulse must be appropriate for the method, and its amplitude can be calculated by known methods. An additional auxiliary voltage winding can be made on the selected Km type "B". As indicated above, after the end of stage "1" ("switching"), on Km type "B" there is a sign-changing "dribbling" (Fig. 11d), which ends with zero voltage in the case of complete energy output of the Km chain to the load. Then the auxiliary capacitor remains the auxiliary voltage to which it was charged in stage "2" of its Km. It will promote excitement.

Fig. 1 shows a variant of obtaining auxiliary voltage from Km type "A" with the times of stages "1" and "2", as indicated above. A certain advantage in this case is the absence of "dribbling" on Km type "A".

As can be seen from the description of the operation of Km type "A" or Km type "B" with equal windings connected according to (choke), a significant current flows only in stage "1". This allows you to charge C and store the charge on it until the end of all processes in Km until the start of a new cycle. Figure 1 shows the connection of an auxiliary capacitor with one grounded end (which is necessary for the correct operation of the auxiliary circuit), included in a series circuit with Km type "A" and its load - Km type "B". In Km type "A" at stage "2" there is no charge current, so only the charge current of the previous Km type "B" will pass through it, which is much smaller, because it is more stretched in time. It passes through the capacitors and A and enters the circuit of the welding current source.

Fig. 1 shows the option of including the auxiliary circuit in the Km type "B" throttle type circuit.

Often this option turns out to be convenient due to the required polarity of pulses per Km. The operation time of Km 4 in this particular case is about 0.dms, that is, the auxiliary current is maintained for a sufficient time after starting, and zeroing occurs only after hundreds of microseconds in the next bias cycle.

As described above, the currents in these phases of the operation of Km are sign-changing and, therefore, pass through the zero value. But when the currents are zero, the shape of the hysteresis loop becomes significant, because the ferrite "slips" to -V. In order to prevent the appearance of an "attractor", it is necessary to have a displacement of at least a certain value (fig. g, c).

Fig. 10 shows the scheme of the exciter according to the proposed method, made entirely on Km, without an arrester. The exciter is designed to work with a saturating power transformer that has a significant XX current and a sufficiently steep saturation exit front. The first three Km are made of steel and have a synchronizing bias current, like the exciter in Fig. 8, but instead of a high-voltage impulse transformer, the excitation Km C type "A" is included.

Its parameters are chosen such that it saturates at a level that corresponds to the trigger level of the arrester in Fig. 7 (see oscillograms).

The current i in Fig. 10 is the current i() in Fig. 7. You can see that the current reaches a maximum, then decreases, and the excitation occurs at a current 2/3 - 3/4 of the maximum (this is chosen when setting the number of turns Km 2). The time of this current is 700 μs for this example, the time of activation of the Km chain until the moment of arc excitation is 50 - ZOms, that is, during this time, this current can be considered constant.

A chain of two parallel branches is sequentially included in the circuit of this current, in one of which there is a choke inductance of 721 f, which does not saturate, with series bias windings on all Km, starting with Km 3, and also Kmzar, and in the second - a filter resistor 78 Af, so that the time constant I f/Af is proportional to the duration of the current ii. Then the current in the inductance of the choke 72 until the moment of excitation will be close to the current ii, and then it will remain for the time of operation of the remaining Km and excitation of the arc. VS-circuit from resistor 17 and capacitor 19 is connected to input Km 3, as described earlier. The polarities of the pulses at the inputs of Km are also given.

When the Km is triggered, pulses occur on the displacement coils, which each time increase the bias current of the next Km. It can be seen that at Km 6 the voltage on the displacement turns is half of the full voltage of Km, i.e. 4KV or more. This is inconvenient with regard to winding insulation.

Below, Fig. 10 shows the variant of the offset from the voltage on Km 2. This voltage Шщ(О) (Fig. 7) becomes zero and even changes its sign at the moment of operation of Km 2, that is, it is not suitable for creating a bias current. But due to the inclusion of the inductance of the choke 72, the time constant becomes sufficient to preserve the accumulated current. In this version, one displacement coil is sufficient, penetrating Km 2 and further, the problem with high voltages disappears. Resistance element 78 is the resistance of the wire itself, chosen accordingly.

Fig. 12 shows the fifth version of the proposed device, intended for the operation of a transformer with saturation. The general displacement circuit from Km 2 to Km 3, 4, 5, 6, and Km is made in the form of one turn, as in the previous exciter. The displacement from the currents ii, i", iz, ii compensates for the actions of these currents at the interference sensitivity stages of each of Km. The auxiliary voltage is produced on the capacitor 19, connected in series to the Km 4 type "B" circuit. The rise time of the auxiliary voltage is about one microsecond, during which time the auxiliary circuit will not discharge. There will also be no outflow of auxiliary current into the inductance of the switching circuit (see Fig. 2). At the same time, the charge current of the capacity of the third key Km Z when activated by Km 2, which passes through Km 4 and resistor 17, turns out to be insignificant, i.e. the time constant of the auxiliary circuit should be located between the activation time of Km 4 and the accumulation time of Km 3, i.e. in much more a wide interval than in the previous schemes, which facilitates the implementation of the auxiliary circuit.

Using this example of an exciter, it is convenient to consider the operation of the charging magnetic key Kmgzar. It is made of ferrite of much smaller sizes than the blocking choke 10. This is due to the fact that at nanosecond times the effect of magnetic viscosity is already significantly felt, and the smaller the volume of the magnetic circuit, the smaller the losses. It can be seen that for Km, the "interfering" current is ich, and the "mixing" current is i5.

Although Kmzar is shifted by the total current of the turn in the right direction, the numerical calculation shows that the interference current needs at least 2 - Z turns from the current i" for its compensation. It is kept in the state "-

B" at the stage of "interference sensitivity" by the total bias current and the current Ich, then continues to be held in this state by the more significant current of the "bias" stage from the current i5, the capacitor 22 is charged at the same time, and then during the "switching" stage for Km 6, a negative pulse is supplied on throttle 10 and line output.

As follows from the description of the operation of Km magnetic keys, the threshold for their inclusion is determined not by the voltage level, but by its integral, and by its nature Km cannot maintain a constant voltage. Therefore, there must be a series capacitor in the Km circuit that blocks the constant voltage. All the Km exciters proposed above are designed to work with saturable transformers. In addition, due to the fact that transformers for different welding currents have different inductances, different process times are obtained, and therefore for each type of transformers for different welding currents, there must be an exciter with different Km parameters.

For work with transformers of various types, an electronic key is more convenient, capable of opening and blocking constant voltage.

Fig. 13 shows a diagram of the key element 12, which meets the requirements noted in the description of the device in Fig. 9.

Key element 12 works as follows. When a voltage of any polarity is applied to buses 5 - 6 in the output diagonal of the bridge, the polarity is positive. First, transistor 85 and thyristor 97 are closed. As the voltage from the power source 4 increases, the voltage on the reference resistor 102 increases and reaches the threshold of the thyristor 97 (0.5 - 0.68). The current of this circuit is of the order of milliamperes, it is not enough to open the transistor 85 closed by the resistor 92. But through the capacitor 98, the current of the thyristor 97 will be much larger and is limited by the resistor 100. This current opens the transistor 85, a regenerative process takes place in the base transformer 88, and then the current from of the power circuit will be transformed into the base circuit of the transistor 85, keeping it in the open state. If the source has an inductive resistance (welding transformer), then the current in it increases gradually over a period of hundreds of microseconds. The voltage at the base of the transistor 85 in relation to the collection point is fixed by a chain of limiting diodes 93 - 94. As the current increases, the voltage drop across the current-limiting resistor 86 increases, which causes the transistor 85 to close. Transistor 85 comes out of saturation, a regenerative process takes place. A step-up transformer 90 with very small turns and minimal leakage inductance is used to accelerate the circuit. The current in the inductor cannot stop with a jump, it increases the voltage on the external capacitor beyond the circuit of the key element 12 (see Fig. 9), an oscillating process occurs in the external circuit. Protective capacitor 103 partially limits overvoltages on transistor 85, as well as varistor 84, but its role is not limited to this. It does not allow the voltage and current of the thyristor 97 to drop, so that the current of the thyristor 97 is maintained, although quite small, because the entire chain of resistors limits it, and the capacitor 98 is discharged.

During the action of the direct current of the key element 12, an inductive current accumulates on the base transformer 88 with a cut magnetic conductor 85, and due to the fact that the emitter of the transistor 85 is closed, this current of negative polarity (that is, the closing current for a p-p-p type transistor) goes through the reverse circuit diode 96. For example, if the emitter current was 5A, the base current was 2.5A, then the inductive current can be chosen 14, and 1.5A remains in the base, which is quite enough. With such a closing current, the current of the thyristor 97 cannot open the transistor 85 a second time. The thyristor 97 remains open milliampere current until the end of the half-cycle, until the current drops below the holding current of the thyristor 97 with a chain of resistors 99 - 102 (can be made of the order of 0.5m). Thyristor 97 then closes and remains closed for the rest of the remaining half-cycle, and the next opening will be in a new half-cycle when the voltage source 4 rises again to the threshold. Note that the closing current of the transistor 85 lasts approximately twice as long as its opening, because the reverse voltage on the reverse diode 96 is approximately half the forward voltage on the two diodes 93, 94.

Thus, the requirements relating to the key element 12 are met: activation at the voltage level set by resistor 102, release at maximum current set by resistor 86, blocking of the second activation per half-cycle. If for some reason the current of the transistor 85 does not increase quickly enough (with a large inductance of the external circuit), then the base transformer 88 exhausts its volt-second area, saturates and opens the key element 12. This one-sided saturation is conventionally shown in the diagram in conventional notations. Of course, this transformer is designed for the entire range of operation of the exciter from transformers with different operating currents and, therefore, with different inductances. For example, it is possible to operate the exciter in the range of welding currents of 300 - 30A without reconfiguration.

Note that the closing time of the transistor key is several hundreds of microseconds, depending on the inductance of the welding transformer. At this time, the voltage on the collector is close to zero, the voltage on the resistor chain and on the capacitor 98 is zero, and the thyristor 97 inevitably closes. Then there is a voltage jump to several hundreds of volts, thyristor 97 opens, but transistor 85 is closed by an ampere current at this time and opening thyristor 97 does not open it. When the amperage closing currents end, the high-voltage transients have long ended and the thyristor 97 remains open in the mode of milliampere currents that cannot cause transistor 85 to re-trigger.

Fig. 14 shows the scheme of the exciter, in which the displacement is provided by the use of a high-voltage pulse transformer with a split magnetic core, which is itself an inductive accumulator. This halves the inductance drop, i.e. requires twice the number of turns, but allows the use of an unbiased exciter, i.e. it can be used for any transformer that does not necessarily saturate. The work of the exciter is similar to the one described.

Fig. 15 shows the scheme of the exciter, in which the bias is provided from the current of the inductive accumulator 104. The current from the bias winding is transformed into the primary winding and charges the separation capacitor 106 so that saturation is ensured at any initial value of induction. For this, 1/10 of the number of turns of the offset winding from the turns of the winding 37 is usually enough.

Fig. 16 shows the scheme of the exciter with an electronic key element 12 with magnetic keys without the use of a discharger. The electronic key element 12 gives such a shortening of the duration of the front that Km 2 is not needed, the Km chain starts immediately with Km 3. The displacement of Km Z is provided by the current i, as described above for the displacement of the transformer. In addition, their current is used for protection at the Km 5 interference sensitivity stage, as described earlier. Km 6 has a bias from current iz, and Kmzar - from current ich, as described earlier. There is a common bias circuit from the current ii of the filter choke 72 and the resistance of the filter resistor 34, as described earlier for the magnetic keys.

Let's pay attention to Km 4 with split windings. They are used to change polarity (sign), but due to the fact that they can be galvanically isolated, part of the circuit can be placed in relation to the zero bus, and part - in relation to the upper bus, as is more convenient. The excitation pulse with Km 6 is applied in relation to the upper busbar. This slightly changes the ratio at start-up, but slightly, because the voltage on the blocking capacitor 7 is changed by the charge current of the inductance of the source 4. Recall that the charge time is the time for the passage of the negative excitation pulse through the element 11 "long line" of the welding cables and return, that is, it is tens nanoseconds When a spark and an arc are excited, the time for the inductance current to fall from tens of amperes is tenths of a microsecond, and during this time capacitor 7 is charged to hundreds of volts. Therefore, it can be assumed that the connection of the excitation pulse circuit in relation to the ground bus or the upper bus is the same and can be chosen for reasons of design convenience.

Devices with an exciter according to the proposed method have such easy excitation of the arc and such stabilization that the problem of choosing the welding current appears in a completely different light. The welder does not feel a change in the welding current, for example, by one and a half times. Moreover, it is possible to weld 0.8 mm metal with an arc current of 200 A, if the welder interrupts this current very quickly. However, for welding especially thin parts, it is advisable to have currents of the order of 50 - 20A. In principle, such adjustment is possible when using a movable magnetic shunt. At the same time, the inductance changes inversely proportional to the current. This creates problems for magnetic keys (for Km 1 and Km 2). Exciters with an electronic key operate in a wider range of inductances. However, the exciter with additional ballast inductance, shown in Fig. 17, is useful. A ballast choke 107 with a winding 108 on steel with an air gap of the usual type is shunted by a capacitor 109 of the transfer of the excitation pulse and a supporting circuit VAS of a resistor 110 and a capacitor 114 can be in the range from fractions of a nanofarad to units of microfarads, the supporting circuit is, for example, 10.0μF and 20Ω . It maintains the arc current until the choke 107 draws a current of several amperes sufficient to ignite the arc. Then the current reaches 50 - 20A, for which the ballast is intended. Choke 107 can be for one current, or have taps, or have smooth adjustment by moving the coils or changing the magnetic gap. To reduce the dimensions and weight of the choke, it is suggested to make it saturated. For example, if the welding transformer itself is designed for a current of 200A, and the volt-second area of the choke is taken as 0.65 of the applied voltage, then the current after its saturation (effective value) is only 0.2 of the source current, i.e. 40A for the given example. A current pulse with an effective value of 40A appears against the background of a "smooth current" of 20A. Such impulses even help to improve the quality of welding, as is known, and the choke with saturation turns out to be 3595 easier. Practice shows that it is possible to have a stable arc at currents in fractions of an ampere.

As you can see from the description of the exciters above, the ballast choke does not affect their operation both with electronic and magnetic keys.

The stated advantages of the proposed method and devices for its implementation provide them with the possibility of wide use in devices capable of welding oxidized and rusted metal, steel, stainless steel and other metals.

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Fig. 17

Claims (10)

1. The method of excitation of an electric arc, in which, before applying an excitation voltage pulse to the arc gap, the output of the electric arc power source is short-circuited during the rise of the short-circuit current to the level of the stable arc current, which is distinguished by the fact that after the short-circuit current reaches the level of the stable arc current to at the output of the power source of the electric arc, a forcing voltage of the same polarity is applied, which exceeds the voltage of the power source, after which a pulse of excitation voltage of the reverse polarity with respect to the power source of the electric arc, which exceeds the nominal forcing voltage and has a shortened front duration, is applied to the arc gap with a time delay . 2. The method according to claim 1, which differs in that the excitation voltage pulse delay time is chosen in the range from 3 to 300 nsec. 3. The method according to claim 1, which differs in that the ratio of the delay time of the excitation voltage pulse to the duration of its front is 1-30. 4. The method according to claim 1, which differs in that the forcing voltage is formed by transforming the energy of the power source from the circuit that short-circuits it. 5. The method according to claim 1, which differs in that the excitation voltage pulse is formed by transforming the energy of the power source from the circuit that short-circuits it. 6. A device for exciting an electric arc, containing a source of pulses of the excitation voltage, the first and second terminals of the arc gap, a power source of the electric arc, in parallel with which a blocking capacitor and a key with a threshold element are connected, which is distinguished by the fact that a source of internal forcing voltage is introduced into it , a blocking choke and a "long line" element, while the source of the internal forcing voltage is connected according to the power source of the electric arc, the source of excitation voltage pulses is connected to the power source of the electric arc oppositely with one of its outputs - through the blocking choke, and the other - directly, and through the "long line" element, the terminals of the excitation voltage pulse source are connected to the first and second terminals of the arc gap. 7. The device according to point b, which differs in that the source of the internal forcing voltage is made in the form of a series-connected key element, elements of resistance and inductance, and a capacitive voltage source. 8. A key for an electric arc excitation device containing a capacitor, a saturable magnet wire, with a working winding, one terminal of which is connected to the input of the magnetic key, and the other terminal is connected through a capacitor with an output, which differs in that a bias winding is introduced for series connection with the primary winding of a power transformer with a saturating magnetic circuit, the power source of the electric arc. 9. A key for an electric arc excitation device containing a capacitor, a discharger, a saturating magnet wire, a transformer with working and high-voltage windings, to the latter of which a capacitor and a discharger are connected, which is distinguished by the fact that a displacement winding is introduced for series connection with the primary winding of a power transformer with a saturating magnetic core, the power source of the electric arc. 10. The method of preparation for the activation of the key of the electric arc excitation device, made in the form of a cascade chain of n magnetic keys, which includes setting the magnetic circuit of the i-th key to the initial state of magnetization, which is distinguished by the fact that a bias current is supplied to activate the i-th magnetic key from the (I-2)th magnetic key and the interference protection current from the (i-3)th magnetic key.