SU1613263A1 - Method and apparatus for exciting electric arc - Google Patents

Abstract

This invention relates to welding production. The purpose of the invention is to simplify the process of exciting the arc. One powerful impulse with a short leading edge and a voltage amplitude of 5–15 kV, sufficient for the arc gap, is applied to the interelectrode gap. The sloping falling front ensures the overgrowth of a spark into an arc. For carrying out the method, an additional capacitor is connected in series in the discharge circuit of the device for initiating an electric arc. The primary and secondary windings of the pulse transformer are connected by the ends of the same name and, together with an additional capacitor, a current-limiting resistance and a diode, form two circuits with respect to the arc gap — a high-voltage circuit with a small time constant and a low-voltage circuit with a long time constant. The arc excitation time is determined by transients at the welding current source and is several tens of milliseconds. A single pulse is enough to excite the arc, and therefore the level of radio interference is minimal. 2 sec. f-ly, 2 ill.

Description

The invention relates to welding production, in particular to methods for initiating an electric arc.

The purpose of the invention is to simplify the process of exciting the arc.

FIG. 1 is a schematic diagram of an apparatus for implementing an electric arc driving method; in fig. 2 - oscillograms of voltage and current of an electric arc of direct current when it is excited by a single high-voltage powerful pulse,

where Uxx is the no-load voltage of the main power source;

Umaks - the amplitude of the pulse;

Ufl - steady arc voltage;

tH is the rise time of the pulse (the leading edge of the pulse);

tc is the pulse decay time (the leading edge of the pulse);

1imp high voltage current source;

1pc current of welding current source;

1e is the electric arc current.

The secondary winding of the pulse transformer 1 (T1) is connected at one end to the electrode terminal, with the other end connected to the same end of the primary winding of the same transformer. At this point, an additional capacitor 2 (C1) and start-up chain 3 (R1, R2, C2) are included. Storage capacitor 4 (Sz) is connected to the other end of the primary winding

about

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transformer 1 (l 1) v thyroid anode 5 (VI). Accumulative capacitor 4 (Sz) and additional capacitor 2 (C1) are connected through the primary winding of a pulse transformer 1 CT1). The plates of these capacitors, which are connected to the thyristor 5 (VI), include half-wave rectifiers b (V3, V4, R3, R4) and 7 (V5, V6, R5, R6), powered by a network transformer 8 (T2 ) through connector 9 (X1). Diode 10 (V7) connects the negative terminal of the current source and the output of the primary winding of the pulse transformer 1 (T1). A semiconductor diode 1 1 (V2) with a CTOKOpaHH4H- resistor 12 (R7) connects the cathode of the thyristor 5 (VI) to the positive terminal of the welding current source and the product. Relay 13 (K1) is connected by its winding parallel to the terminals of the welding current source, a normally open contact of the relay is connected to the triggering chain 3 (R1, R2, C2) and the control electrode of the thyristor 5 (VI).

The storage capacitor 4 (SOC) and the additional capacitor 2 (C1) are charged to a voltage of 400 V from one full-wave rectifiers 6 and 7 from the step-up transformer 8.

. When welding voltage is applied from a source of welding current, relay 13 (K1) is activated and, with its normally open contact K1.1, triggers thyristor 5 (V1) through triggering chain 3 (R1, R2, C2). In this case, a discharge circuit is formed with a small time constant: additional capacitor 2 (C1), winding pulsed transformer 1 (T1), nak | Itel; capacitor 4 (C3), thyristor 5 (VI), On the secondary winding of the boost Transformer 1 (T 1) induces a high-voltage pulse, thereby supplying the inter-electrode gap with a special-purpose powerful pulse with a short leading front and voltage amplitude of 5-15 kV, which leads to the breakdown of the arc gap of the electrode-product. Capacitor 2 (C1) has a much smaller capacity than capacitor 4 (C3) and recharges the voltage of the sensor 4 (C3) to another polarity (indicated by 3 brackets in Fig. 1).

The arc gap is a sub-key; others are parallel to the connected capacitors 2 (C1) and 4 (C3), when the thyristor 5 (VI) is open due to the flow of current through the circuit, the diode 11 (V2), resistor 12 (R7), which provides a gently dipping the back front of a high voltage pulse. This causes the transition of a spark from a high-voltage pulse to an arc.

The value of resistor 12 (R7) determines the current at the initial stage of the arc process. The value of the parallel-connected capacitors 2 (C1) m 4 (Sz) together with the resistor 12 (R7) determines the time of maintaining the arc process from the stored energy by the capacitor 4 (Sz).

When the arc process voltage decreases in the initial stage below the no-load voltage of the welding current source, the welding current source is switched on to the arc power supply circuit through the diode 10 (V7). Power diode 10 (V7) protects the source of welding current from impulse overvoltages

5 (DM Uci + Uc2). If the source is protected from welding overvoltages, the diode 10 (V7) may be absent.

When the voltage rises in the interelectrode gap (above the piercing gap), electric arc breakdown of gas occurs, an avalanche-like process is formed leading to ionization of the gas and the formation of a conductive channel, and the electrode-to-conductivity sharply increases. Due to the fact that the electrical circuit of the source of welding current has a significant inductance (L 20 - 200 mH), the current in the circuit of the source increases with a certain speed and cannot reach the required

0 is instantaneous, therefore, the arc is maintained at the expense of the pulse energy (the leading edge of the pulse, Fig. 2). The duration of the trailing edge of the pulse must be longer than the time required for the current to rise from the source of the welding current to the value at which the arc is stable, while a single pulse is enough to initiate the arc. The arc excitation time is determined by the transition processes in the welding current source and is several tens of milliard seconds. The level of radio interference when the arc is excited is minimal.

Device turns out to be enough

5 is safe to handle, since before the arc is excited on the electrode there is no idle voltage of the welding current source, the 3 charged capacitors are disconnected from the main circuits by a closed thyristor 5 (VI) and diode 11 (V2). When the welding arc is energized, the voltage at the electrode is determined by arc transients, which are very short-lived. With this device scheme

5, these voltages are minimal, since ao transient over voltage is quenched at resistor 12 (R7). If the welder accidentally touches the electrode under conditions of a significant arc gap and activates the welding current, a single high-voltage pulse of short duration acts on it (transition process recharging capacitor 2 (C1) from storage capacitor 4 (SOC) through the inductance of the primary winding of the transformer 1 (T1 The capacitor 4 (SOC) turns out to be disconnected from the electrode, since the current through the welder is insufficient to keep the thyristors 5 (VI) in an open state. The welding time in this case is provides: a high voltage component of less than 25 µs, a low voltage component of a few milliseconds.

In comparison with a known object, the process of exciting the arc is simplified and its implementation does not require the use of a timing circuit for switching on two pulsed sources and does not require the use of a low inertia (300-500 V) high-power source

Claims (2)

Claim 1. An electric arc excitation method, which consists in initiating an arc with a high-voltage pulse with a voltage amplitude of 5-15 kV, characterized in that, in order to simplify the arc initiation process, a short circuit is formed. middle front and gently sloping falling edge of the pulse. 2. Device for initiating an electric arc, holding a charge circuit and a discharge circuit formed by a storage capacitor, a thyristor and the primary winding of a pulse transformer, the secondary winding of which is included in the welding circuit, characterized in that, in order to improve the conditions for initiating the arc by increasing time of the current pulse on the arc gap, it is equipped with an additional capacitor, current-limiting resistance and a diode, and the first output terminal of the device is connected to the beginning of the secondary winding of the pulse transformer, the end of which is connected to the end of the primary winding of the pulse transformer, the beginning of which is connected via a storage capacitor to the anode of the thyristor, the cathode of which is connected to the diode anode, the cathode of which is connected to the second output terminal of the device, Thereby, the connection point of the ends of the windings of the pulse transformer is connected via an additional capacitor to the diode anode. a i  w U1b Y : Shde.ie 0V5 7 5 Bh Af 0 + ig.1 The cop IG