For arc welding, both alternating and direct welding current are used. Welding transformers are used as a source of alternating welding current, and welding rectifiers and welding converters are used as a source of constant current.

The welding transformer is used to reduce the network voltage from 220 or 380 V to a safe, but sufficient for easy ignition and stable burning of the electric arc (no more than 80 V), as well as to regulate the strength of the welding current.

Transformer (Fig. 10). has a steel core (magnetic core) and two insulated windings. The winding connected to the network is called primary, and the winding connected to the electrode holder and the workpiece being welded is called secondary. For reliable arc ignition, the secondary voltage of welding transformers must be at least 60–65 V; The voltage during manual welding usually does not exceed 20 - 30 V.

Fig. 10 Welding transformer

At the bottom of the core is the primary winding, consisting of two coils located on two rods . The primary winding coils are fixed motionless. The secondary winding, also consisting of two coils, is located at a considerable distance from the primary. The coils of both the primary and secondary windings are connected in parallel. The secondary winding is movable and can move along the core using the screw with which it is connected and the handle located on the cover of the transformer casing.

The welding current is regulated by changing the distance between the primary and secondary windings. When the handle is rotated clockwise, the secondary winding approaches the primary, the leakage magnetic flux and inductive reactance decrease, and the welding current increases. When the handle is rotated counterclockwise, the secondary winding moves away from the primary, the leakage magnetic flux increases (inductive reactance increases) and the welding current decreases. The limits of regulation of the welding current are 65 - 460 A. The serial connection of the coils of the primary and secondary windings makes it possible to obtain low welding currents with control limits of 40 - 180 A. The current ranges are switched with a handle located on the cover.

The properties of the power source are determined by its external characteristic, which represents the curve of the relationship between the current (I) in the circuit and the voltage (U) at the terminals of the power source.

The power source may have an external characteristic:

rising, hard, falling

The power source for manual arc welding has a falling volt-ampere characteristic.

Open circuit voltage of the power source - the voltage at the output terminals when the cooking circuit is open.

Rated welding current and voltage - the current and voltage for which a normally operating source is designed.

The welding arc power source - welding transformer is designated as follows: TDM – 317

T – transformer

D – for arc welding

M – mechanical regulation

31 – rated current 310 A

Welding transformers are divided into single-phase and three-phase according to the phase of the electric current, and into single-station and multi-station according to the number of posts. Single station transformer serves to supply welding current to one workplace and has a corresponding external characteristic.
Multi-station transformer serves for simultaneous power supply of several welding arcs (welding stations) and has a rigid characteristic. To create a stable combustion of the welding arc and ensure a falling external characteristic, a choke is included in the arc welding circuit. For arc welding, welding transformers are divided according to design features into two main groups:
transformers with normal magnetic dispersion, structurally made in the form of two separate devices (transformer and inductor) or in a single common housing;
transformers with developed magnetic dispersion, structurally differing in the method of regulation (with moving coils, with magnetic shunts, with step regulation).
In the USSR, transformers of both groups have found use, and in recent years, mainly transformers in a single-case design with developed magnetic dispersion and with magnetic shunts.
Transformers with normal magnetic leakage.
Transformers with a separate choke. The rigid external characteristic of such a transformer is obtained due to insignificant magnetic scattering and low inductive reactance of the transformer windings. The falling external characteristics are created by a choke having a large inductive reactance.
Technical data of transformers STE-24U and STE-34U with chokes are given in table. 23.

Table 23

Technical characteristics of welding transformers

Continuation of the table. 23

Transformers type STN with built-in choke. Transformers STN-500 and STN-500-1 for manual arc welding and transformers with remote control TSD-500, TSD-2000-2, TSD-1000-3 and TSD-1000-4 for automatic and semi-automatic welding are made according to this design scheme under gumboil. Technical data of these transformers are given in table. 23.
The design diagram of the STN type transformer of the system of Academician V.P. Nikitin and its external static characteristics are shown in Fig. 58. Magnetic scattering and inductive reactance of windings ( 1 And 2 ) transformers are small, the external characteristic is rigid. The falling characteristic is created due to the reactivity of the winding 3 , creating inductive reactance. The upper part of the magnetic circuit is also part of the inductor core.

The amount of welding current is regulated by moving the movable package 4 (screw mechanism using a handle 5 ). The open circuit voltage of these transformers is 60 - 70 V, and the rated operating voltage U nom = 30 V. Despite the combined magnetic circuit, the transformer and inductor operate independently of each other. In electrical terms, transformers of the STN type do not differ from transformers with separate chokes of the STE type.
For automatic and semi-automatic welding, TSD type transformers are used. A general view of the design of the TSD-1000-3 transformer and its electrical circuit are shown in Fig. 59 and 60.

Transformers of the TSD type have an increased no-load voltage (78 - 85 V), necessary for stable excitation and combustion of the welding arc during automatic submerged arc welding.
The falling external characteristic of the transformer is created by the reactive winding 4 . The TSD type transformer has a special electric drive for remote control of the welding current. To turn on the drive synchronous three-phase electric motor DP with a reduction worm gear, two magnetic starters PMB and PMM, controlled by buttons, are used. The movement of the moving part of the magnetic core package is limited by the limit switches VKB and VKM.
Transformers are equipped with filters to suppress radio interference. In addition to being used for automatic and semi-automatic submerged arc welding, transformers TSD-1000-3 and TSD-2000-2 are used as a power source for heat treatment of welded joints made of alloy and low-alloy steels.
Transformers with developed magnetic dissipation. Transformers type TS and TSK They are mobile rod-type step-down transformers with increased leakage inductance. They are designed for manual arc welding and surfacing, and can be used for submerged arc welding with thin wires. In transformers of the TSK type, a capacitor is connected in parallel to the primary winding to increase the power factor.
Transformers such as TS, TSK do not have moving cores prone to vibration, so they operate almost silently. The welding current is regulated by changing the distance between the moving I and motionless II coils (Fig. 61, c). As the moving coil moves away from the stationary coil, the magnetic leakage fluxes and the inductive reactance of the windings increase. Each position of the moving coil has its own external characteristic. The farther the coils are from each other, the greater the number of magnetic lines of force will be closed through the air spaces without capturing the second winding, and the steeper the external characteristic will be. Open circuit voltage in transformers of this type with coils shifted by 1.5 - 2 V more than the nominal value (60 - 65 V).

The design of the TS-500 transformer and external current-voltage characteristics are shown in Fig. 61,a,b. Technical data of transformers TS and TSK are given in table. 23.
Transformers with magnetic shunts such as STAN, OSTA and STS.
Welding transformers of type STSh-500 (A-760) developed by the Institute of Electric Welding named after E. O. Paton have high performance indicators and a long service life compared to transformers of the TS, TSK, TD types.
The STS rod-type transformer, single-phase, is made in a single-case design and is designed to supply an electric welding arc with alternating current with a frequency of 50 Hz for manual arc welding, cutting and surfacing of metals. In Fig. Figure 62 shows a diagram of the STS-500 transformer.

The magnetic core (transformer core) is made of electrical steel E42 with a thickness of 0.5 mm. Steel sheets are connected with insulated studs.
The coils of the primary winding of the transformer are made of insulated aluminum wire of rectangular cross-section, and the secondary winding is made of bare aluminum busbar, between the turns of which asbestos gaskets are laid, designed to insulate the turns from a short circuit.
The current regulator consists of two movable magnetic shunts located in the window of the magnetic circuit. By rotating the screw clockwise, the shunts move apart, and counterclockwise, they move, and the welding current is gradually regulated. The smaller the distance between the shunts, the lower the welding current, and vice versa. Shunts are made from the same electrical steel as the main line.
To reduce interference to radio receivers that occurs during welding, a capacitive filter of two KBG-I type capacitors is used. The capacitors are mounted on the high voltage side.
Currently, a number of new portable AC welding arc power sources have been created - small-sized transformers. Examples of such transformers are, for example, installation transformers TM-300-P, TSP 1 and TSP-2.
The TM-300-P installation transformer is designed to power the welding arc during single-station arc welding during installation, construction and repair work. The transformer provides a steeply falling external characteristic (with a ratio of short circuit current to the current of the rated operating mode of 1.2 - 1.3) and stepwise regulation of the welding current, which allows welding with electrodes with a diameter of 3, 4 and 5 mm. It is single-hull, lightweight and easy to transport. The TM-300-P transformer has separated windings, which makes it possible to obtain significant inductive reactance to create falling external characteristics. The rod-type magnetic core is assembled from cold-rolled textured steel E310, E320, E330 with a thickness of 0.35 - 0.5 mm. The electrical circuit of the transformer is shown in Fig. 63.

The primary winding consists of two coils of the same size, completely placed on one magnetic core. The secondary winding also consists of two coils, one of which - the main one - is placed on the magnetic core along with the primary winding, and the second - the reactive one - has three taps and is placed on the other magnetic core.
The reactive secondary winding is significantly removed from the primary winding and has large leakage fluxes, which determine its increased inductive reactance. The amount of welding current is regulated by switching the number of turns of the reactive winding. This current regulation makes it possible to increase the no-load voltage at low currents, providing conditions for stable burning of the welding arc.
The primary winding is made of copper wire with insulation, and the secondary winding is wound with a busbar. The windings are impregnated with organosilicon varnish FG-9, which makes it possible to increase their heating temperature to 200° C. The magnetic core with the windings is placed on a cart with two wheels. For welding in installation conditions with electrodes with a diameter of 3 and 4 mm A lightweight transformer TSP-1 is used. The transformer is designed for short-term operation with a post load factor of less than 0.5 and electrodes with a diameter of up to 4 mm. The electrical circuit and external characteristics of such a transformer are shown in Fig. 64. Due to the large distance between the primary winding A and secondary winding B Significant magnetic scattering fluxes are formed. The voltage drop due to the inductive resistance of the windings provides steeply falling external characteristics.

The welding current is controlled in steps, just like the welding transformer TM-300-P.
To reduce weight, the transformer design is made of high-quality materials - the magnetic core is made of cold-rolled steel, and the windings are made of aluminum wires with heat-resistant glass insulation.
Technical data of the TSP-1 transformer are given in table. 23.
For welding in installation conditions, small-sized lightweight welding transformers STSh-250 with smooth regulation of welding current, developed by the E. O. Paton Institute of Electric Welding, and TSP-2, developed by the All-Union Scientific Research Institute of Electric Welding Equipment are also produced. The main technical data of these transformers are given in table. 24.

Table 24

Technical characteristics of transformers STS-250 and TSP-2

To perform welding work at various heights in installation conditions, a special welding transformer TD-304 on a skid was created, equipped with remote control of the welding current directly from the electric welder’s workplace. The main technical data of such a transformer in comparison with the TS-300 transformer are given in table. 25.

Table 25

Technical characteristics of transformers TD-304 and TS-300

You can test the welding inverter to see what it is capable of. We take the most affordable TIG welding inverter. I will give an example of a device in the photo there IN 256T/ IN 316T.

If you look at the table, it shows where the idle speed is located in the form of an indication. On such devices, the idle speed is programmed by a computer. When you select the desired mode, the idle current is automatically set. It can be checked with a regular voltmeter at the ends of the power wires in the on state. That is, on the holder and the crocodile. The voltage drop should not deviate by more than five volts when igniting the arc and welding.

For example, if you ate a Chinese state employee, you will not find information about idle speed at all. Plus the Amperes are too high. In fact, some won’t even handle Uoni 13/55 electrodes. And why all? This electrode requires an idle current of 70 volts at 80 amps. And such welding machines are designed in such a way that as the current increases, the voltage also increases. In other words, at the highest current they will give you 90 volts. The voltage even before the secondary winding is controlled by a unit that converts the high voltage into the primary winding. Then, under the influence of electromagnetic force, it is transmitted to the secondary winding. The tension removed from her passes on. If the voltage at the input of the primary winding is low, then the output will be low.

Let's consider the primitive VD-306M U3. At low currents of 70-190 A, the voltage is 95 volts plus or minus 3 volts. At high currents of 135-325 A, the idle current is 65 volts plus or minus 3 volts. Moreover, it is stable in all current ranges. No matter how you twist the crank and change the amps to your heart's content, the idle speed will not decrease.

What am I getting at if the welding inverter does not weld well at low currents, the reason is in the control unit described above. As some say, install an additional choke or a ballast at the output. We turn the current up to full and adjust it at the ballast. The extra amperes will be taken over and the idle speed will remain unchanged.

Just for fun, check your welding machine. Throw the probes from the voltmeter onto the power cables and try cooking. See how the voltage drops. I personally cooked on my home network with an Interskol 250A inverter using 3mm UONI 13/45 electrodes with reverse polarity. As soon as I didn’t twist the amps properly and couldn’t ignite them, but the MP-3s burned, be healthy from the first touch.

When purchasing equipment, read in the passport how much idle current the device produces and at what currents. If this is not professional equipment, you will not be able to adjust the idle speed in any way. If not the method described above. You are unlikely to find such information on the unit body itself. Manufacturers usually hide it with big names and current strength.

What is the open circuit voltage of a welding inverter and what depends on it?

Answer:

Among the characteristics of welding inverters there are several important indicators. This is the supply voltage (220 or 380 Volts), the range of output current (from 10 to 600 Amperes), available functions, weight and dimensions of the device, as well as no-load voltage.

This characteristic shows us at what voltage the current reaches the electrode after it has gone through all the stages of conversion after the power supply. Let us recall that current flows from the electrical network through the power cable to the first converter, from there it comes out constant and goes to the filter, and then to the second converter. As a result, we again get alternating current with a frequency of not 50 Hz, but 20-50 kHz. This is followed by a decrease in input voltage with a simultaneous increase in current. As a result, we get an output voltage of 55-90 Volts and a force that can be adjusted within the range specified for each specific model.

This output voltage is the open circuit voltage. Two things depend on it:
. Tool safety for the owner;
. Easy to ignite the welding arc.

The higher the open circuit voltage, the easier it will be to ignite the inverter's welding arc. It would seem that it would be worthwhile then to buy inverter devices with a high no-load voltage. But high voltage is quite dangerous for a person in case of contact, so it is not always made high. If you still want to light the arc easily, then you should choose a welding inverter with a high voltage, but with an additional installed protection function that automatically reduces the voltage to a level safe for humans if there is a risk to the user, and then returns the level back.

If you have not yet chosen a welding inverter, then among the household models, pay attention to and; among the semi-professional models, we can recommend and

The initial data for this calculation are: P nom - rated short-term power of the transformer, PV nom - rated on-time, U 1 - voltage in the network supplying the machine, E 2 - e. d.s. secondary winding, as well as the limits and number of control stages. P nom and E 2 are usually set for the case when the transformer is turned on at the penultimate stage, which, when turned on at the last, highest stage (E 2 has a maximum value), provides some power reserve.

The calculation of a welding transformer begins with determining the dimensions of the core. The cross section of the core (in cm 2) is determined by the formula

Where E 2- calculated e. d.s. transformer secondary winding in V

f-AC frequency (usually 50 Hz)

w 2- number of turns of the secondary winding (one, less often two);

IN- maximum permissible induction in Gauss (gs)

k- a coefficient that takes into account the presence of insulation and air gaps between the thin steel sheets from which the core is assembled.

The permissible induction B depends on the steel grade. When using alloy transformer steel in transformers for resistance welding, the maximum induction usually lies in the range of 14,000 - 16,000 gf.

With good tightening of the core from sheets 0.5 mm thick insulated with varnish, k - 1.08; with paper insulation k can increase to 1.12.

In an armored transformer having a branched magnetic circuit, the calculated cross-section obtained from the formula refers to the central rod transmitting the full magnetic flux. The cross-section of the remaining sections of the magnetic circuit that transmit half the flux is reduced by 2 times.

The cross-section of each transformer rod is usually a rectangle with an aspect ratio of 1:1 to 1:3.

The number of turns of the primary winding depends on the limits of regulation of the secondary voltage of the transformer. This regulation is in most cases achieved by changing the transformation ratio by turning on more or fewer turns of the primary winding. For example, with a primary voltage of 220 V and a maximum value of E 2 = 5 V, the transformation coefficient is 44 and with one turn of the secondary winding, the primary winding must have 44 turns; if it is necessary to reduce E 2 (in the process of regulating the power of the transformer) to 4, the transformation coefficient increases to 55, which requires 55 turns of the primary winding. Typically, the control limits of contact machines (the ratio E 2 max / E 2 min) vary from 1.5 to 2 (in some cases these limits are even wider). The wider the control limits of the transformer (the smaller the E 2 min with a constant value of E 2 max), the more turns its primary winding should have and the correspondingly greater the copper consumption for the manufacture of the transformer. In this regard, wider control limits are used in universal type machines (this expands the possibility of their use in production) and narrower ones - in specialized machines designed to perform a specific welding operation.

Knowing the value of E 2 for the nominal stage and the control limits, it is easy to calculate the total number of turns of the primary winding using the formula

With two turns of the secondary winding, the resulting value of w l doubles.

The number of power control stages of a transformer for contact welding usually ranges from 6-8 (sometimes it increases to 16 or even 64). The number of turns included at each control stage is selected in such a way that the ratio between e. d.s. for any two adjacent steps was approximately the same.

The cross-section of the primary winding wire is calculated based on the continuous current at the rated stage I l pr. The short-term rated current is preliminarily determined using the formula

Continuous current is calculated from the nominal value of PV%, using the formula or graph in Fig. 128. The wire cross-section is calculated using the formula

where j lnp is the permissible continuous current density in the primary winding. For copper wires of the primary winding with natural (air) cooling j lnp = 1.4 - 1.8 a/mm 2. When the primary winding is tightly adjacent to the elements of the secondary turn, which have intensive water cooling, the current density in the primary winding can be significantly increased (up to 2.5 - 3.5 A/mm 2) due to better cooling. As mentioned above, the cross-section of the turns of the primary winding, switched on only at low stages of regulation (at a relatively low current), can be reduced compared to the cross-section of the turns that carry the maximum current when switched on at the last stage. The required cross-section of the secondary turn is determined by the continuous current I 2pr in the secondary circuit of the machine. Approximately I 2pr = n * I 1pr,

where n is the transformation ratio at the rated switching stage of the transformer. The cross section of the secondary turn is equal to

Depending on the design and method of cooling in the copper secondary coil, the following current densities can be allowed: in an uncooled flexible coil made of copper foil - 2.2 a/mm 2; in a coil with water cooling - 3.5 a/mm 2; in an uncooled rigid coil - 1.4-1.8 a/mm 2. With increasing current density, the weight of copper decreases, but losses in it increase and the efficiency of the transformer decreases.

The number of turns of the primary and secondary windings of the transformer and their cross-section (taking into account the placement of insulation) determine the size and shape of the window in the transformer core in which the winding elements should be placed. This window is usually designed with an aspect ratio of 1:1.5 to 1:3. The elongated shape of the window allows the windings to be placed without resorting to a large height of the coils, which leads to an increase in copper consumption due to a noticeable lengthening of the outer turns of the winding. The dimensions of the window and the previously found cross-sections of the core rods completely determine the shape of the latter.

The next step in calculating a transformer is to determine its no-load current. To do this, the weight of the core is preliminarily calculated and the active energy losses in it P l are determined. Next, the active component of the no-load current is calculated using the formula

And its reactive component (magnetizing current) is according to the formula . The total no-load current is determined as the length of the hypotenuse in a right triangle