Welding transformer with continuously adjustable welding current

Encyclopedia of radio electronics and electrical engineering / welding equipment

 Comments on the article

Having a fairly large archive of technical documentation on welding equipment, both domestic and imported, I began processing it and systematizing technical solutions used in welding equipment. Naturally, I hoped that with the involvement of the Internet this task would be simplified and, perhaps, it would be possible to supplement the existing information. Conducting a constant search not only in the Russian-speaking part of the Internet, but also in the English-speaking one, I was surprised to find that the required information was almost completely absent or very sparsely presented.

We can talk about just a few amateur designs whose authors developed them without being specialists in the field of welding equipment, and therefore were guided mainly by knowledge in the field of electronics, and not the welding properties of specific equipment. That is why amateur “welders” do not provide easy ignition of the arc, “soft” welding without significant splashing of the metal of the electrodes or welding wire.

The basis of all welding machines is the current source. The simplest and, apparently, the most common is the welding transformer. When welding with stick electrodes, the excitation of the welding arc begins with a short circuit of the welding circuit - the contact between the electrode and the workpiece. This generates heat and the contact area quickly heats up. At this stage, increased voltage is required from the source. Subsequently, the resistance of the arc gap decreases, which leads to a decrease in voltage.

During the welding process, drops of electrode metal break off from the electrode and enter the weld pool, leading to frequent short circuits in the welding circuit. With each successive short circuit, the voltage drops to zero, and an avalanche-like increase in the current occurs to the level of the short circuit current, i.e. current that the welding source can provide maximum. This, in turn, leads to spattering of the metal of the electrode, which was intended to fill the seam. Welders say that the welding is “hard”, it spatters, and the seam is poorly formed.

Based on the conditions under which the welding process takes place, it is possible to determine what requirements the welding arc power source must meet:

1. The "no-load" voltage should be sufficient to easily initiate an arc and at the same time should not reach values ​​dangerous to human life. This is especially true for AC sources.
2. The arc voltage must respond quickly to the arc length, i.e. the source must have good dynamic properties. The static characteristic of a source for manual welding, expressing the dependence of the output voltage as a function of the flowing current, must have a clearly defined slope. This type of curve is called a steeply falling dependence U_east=f(l_St.).
3. The magnitude of the short circuit current should be limited due to the properties of the source and not exceed the welding current by more than 40...50%. It must also be ensured that the welding circuit stays in short circuit mode for a long time without overheating or damaging the windings.

The above requirements are only partially met in a number of amateur designs. This is especially true for ensuring the steepness of the U graph_east=f(l_St.) and requirements regarding the safety of output voltages.

The situation is no better with the methods of adjusting the welding current. In the vast majority of amateur designs, it comes down to making additional taps on the primary winding of the transformer. This solution, although obvious from the point of view of simplicity, nevertheless leads to a complication of the design of the most expensive part of the welding machine - its transformer, and an increase in its cost.

The design includes switches with moving contacts, which are one of the most unreliable elements. And the technical level of execution of such a device is primitive. True, there are designs with moving elements (coils or magnetic shunts). But such designs entail the need to manufacture additional mechanical components, which many would not like to do and which significantly increase the complexity of the design as a whole.

Where is the solution to the current regulator problem? One solution to the problem of a single-phase adjustable welding transformer is the use of a so-called thyristor transformer, i.e. a conventional transformer with two windings (primary and secondary), equipped with a thyristor regulator. Almost all circuits of such amateur welding installations have a drawback that their authors transfer from the circuitry of conventional phase regulators designed to control the heating of electric furnaces or change the brightness of incandescent lamps.

With the traditional construction of the power part of thyristor phase regulators, when trying to provide low currents, the pauses between pulses become so significant that no additional measures can stabilize the arc. But the specificity of the circuit designed to work with welding equipment is that it is necessary to ensure continuity of the arc without leading to deionization of the arc gap and extinction of the arc in pauses between pulses. When faced with this problem, it is useful to remember that in welding there is no need to adjust the current from zero to maximum. It is enough to adjust it in the required range of values.

In industrial welding equipment of this type, special circuits are introduced to feed the arc in pauses between pulses. Figure 1 shows the connection diagram of a welding transformer with a thyristor regulator in the circuit of its primary winding.

The primary winding of the transformer is connected through a choke with a fairly large inductance. Two thyristors of the regulator are connected counter-parallel to the inductor. With completely closed thyristors, the transformer current is limited by a choke that has a fairly large inductive reactance. The thyristors, when opening, bypass the inductor, which ultimately leads to an increase in the welding current. At any angle of opening of the thyristors, the current of the primary winding in pauses between pulses does not decrease to zero, thereby ensuring stable arc burning at any welding current. According to a similar scheme, in past years the industry mass-produced the TZR-500 welding transformer.

Choke Dr1 (Fig. 2) can be wound on transformer iron, similar to the core of a welding transformer.

The cross-sectional area of ​​the inductor core for a transformer for a welding current of 120... 160 A should be approximately 40x50 mm. The diameter of the wire is chosen equal to the diameter of the wire of the primary winding. The number of turns is 80-120. The air gap is about 1,5 mm. These figures are very approximate and require some clarification for a specific design.

The data of transformer T1 are determined based on such initial data as the mains supply voltage, the maximum welding current and the voltage on the secondary winding at no-load.

The advantages of the scheme indicated below are smooth regulation and the possibility of using a ready-made transformer with only two windings without taps. The disadvantage is the need to install a fairly powerful throttle. As a control circuit for a phase regulator, a circuit of almost any regulator can be used, providing binding of the opening angle of the thyristors to the transition through “0” of the network pulses and control of two thyristors connected back-to-back. This can be a regulator with a pulse transformer at the output, and with optocoupler thyristors. An interesting, modern solution could be to implement a controller thyristor control circuit based on a microcontroller with a digital display unit. If you supplement the phase regulator circuit with feedback circuits, it will be possible to form a dependence of the voltage on the welding current.

Author: A.M. Semernev

See other articles Section welding equipment.

Read and write useful comments on this article.

<< Back

Latest news of science and technology, new electronics:

Air trap for insects 01.05.2024

Agriculture is one of the key sectors of the economy, and pest control is an integral part of this process. A team of scientists from the Indian Council of Agricultural Research-Central Potato Research Institute (ICAR-CPRI), Shimla, has come up with an innovative solution to this problem - a wind-powered insect air trap. This device addresses the shortcomings of traditional pest control methods by providing real-time insect population data. The trap is powered entirely by wind energy, making it an environmentally friendly solution that requires no power. Its unique design allows monitoring of both harmful and beneficial insects, providing a complete overview of the population in any agricultural area. “By assessing target pests at the right time, we can take necessary measures to control both pests and diseases,” says Kapil ... >>

The threat of space debris to the Earth's magnetic field 01.05.2024

More and more often we hear about an increase in the amount of space debris surrounding our planet. However, it is not only active satellites and spacecraft that contribute to this problem, but also debris from old missions. The growing number of satellites launched by companies like SpaceX creates not only opportunities for the development of the Internet, but also serious threats to space security. Experts are now turning their attention to the potential implications for the Earth's magnetic field. Dr. Jonathan McDowell of the Harvard-Smithsonian Center for Astrophysics emphasizes that companies are rapidly deploying satellite constellations, and the number of satellites could grow to 100 in the next decade. The rapid development of these cosmic armadas of satellites can lead to contamination of the Earth's plasma environment with dangerous debris and a threat to the stability of the magnetosphere. Metal debris from used rockets can disrupt the ionosphere and magnetosphere. Both of these systems play a key role in protecting the atmosphere and maintaining ... >>

Solidification of bulk substances 30.04.2024

There are quite a few mysteries in the world of science, and one of them is the strange behavior of bulk materials. They may behave like a solid but suddenly turn into a flowing liquid. This phenomenon has attracted the attention of many researchers, and we may finally be getting closer to solving this mystery. Imagine sand in an hourglass. It usually flows freely, but in some cases its particles begin to get stuck, turning from a liquid to a solid. This transition has important implications for many areas, from drug production to construction. Researchers from the USA have attempted to describe this phenomenon and come closer to understanding it. In the study, the scientists conducted simulations in the laboratory using data from bags of polystyrene beads. They found that the vibrations within these sets had specific frequencies, meaning that only certain types of vibrations could travel through the material. Received ... >>

Random news from the Archive The new face of Nokia 29.01.2012 Smartphones based on Windows Phone 7 began to appear on the Russian market. One of the first devices with the new OS was introduced by Nokia. The Lumia 800 is the flagship model. Outwardly, it practically does not differ from the Nokia N9: it has the same one-piece polycarbonate body and full touch control. The smartphone is presented in three colors: turquoise, purple and black. The novelty is notable for its integration with social networks Facebook, Twitter and VKontakte, the pre-installed navigation service Nokia Navigator with detailed maps of more than 100 countries, support for the SkyDrive cloud service, as well as a separate catalog of applications in the Microsoft Marketplace. The cost of Lumia 800 is 670 USD. The second model - Lumia 710 - is more youthful both in its catchy form and bright design, and in its affordable price of 420 USD.

Other interesting news:

▪ NASA and General Motors will create a robotic glove

▪ Wi-Fi for pregnant women

▪ Tunnel project under the Alps

▪ Biometric flight check-in

▪ Ion-sound waves for finding space debris

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ section of the Garland website. Article selection

▪ Article Movement on frozen rivers and lakes. Fundamentals of safe life

▪ article What invention do the British consider the greatest in history? Detailed answer

▪ article Vodyanik black. Legends, cultivation, methods of application

▪ article Compositions for blackening the skin. Simple recipes and tips

▪ article The Secret of the Sliding Pencil. physical experiment

Leave your comment on this article:

All languages ​​of this page

Arabic	Hebrew	Polish
Bengali	Hindi	Portuguese
Chinese	Italian	Spanish
English	Japanese	Turkish
French	Korean	Ukrainian
German	Malay	Vietnamese

Home page | Library | Articles | Website map | Site Reviews

www.diagram.com.ua
2000-2024