Power supply, drives and control systems for industrial processes are most often implemented using electrical technology. The adjustment of electrical parameters for the needs of machines and technological processes is achieved by using transformers of various designs and non-standard execution.
The article presents selected transformers from the TRAFECO Sp.J. company’s offer designed for industrial applications. In addition to standard products, the company designs and supplies transformers with parameters and designs tailored to individual customer requirements.
Transformers in power electronics.
Power electronics is present in all industries. The wide range of converter solutions allows you to freely shape the power supply parameters according to the requirements of industrial processes. Key elements of many power electronic systems are transformers in a special converter, low-loss design (photo 1.). The specificity of power electronics systems, including high frequencies and distortion of the voltage and current waveforms, cause intensive hysteresis and eddy current losses in transformers. The design of converter transformers must take these impacts into account and minimise their effects. Converter transformers form a very wide group of devices ranging from small single-phase transformers to multi-pulse high-power transformers.
Structures and materials in transformer manufacture
In the low frequency range, the design of the transformers is based on cores bundled from classic anisotropic transformer sheets. Depending on the power, the windings are made with copper or aluminium profile wires or sheet metal. Medium operating frequencies of tens or even hundreds of kHz eliminate classic packaged transformer cores. Hence the need for modern low-loss cores of amorphous and nanocrystalline materials. The high saturation inductions of these materials (1.2-1.5 T) allow the weight of the transformers to be reduced.
Mid frequencies favour the use of ferrites, which despite their low saturation inductances (0.4-0.5 T) are used in many transformer and choke applications. The modular form of ferrite blocks and fittings allows the core dimensions to be tailored to the needs of the application. Windings of magnetic elements designed for medium frequency applications are made with face-type conductors, limiting the additional losses in the winding. The common problem of excessive magnetostrictive noise is no longer relevant for frequencies above the threshold of hearing.
Furnace transformers are often found in combinations of several high-power, single- phase or three-phase transformers working in a common housing (photo 2.). This solution allows the supply parameters to be adjusted to the designed or existing sets of heating elements. For very high-power single-phase circuits, the so-called Scott-T transformer is dedicated, which is created by coupling two single-phase transformers in the appropriate configuration. The use of the Scott-T transformer makes it possible to achieve a symmetrical mains load when supplying resistive heaters. In electrothermal engineering there are also power transformers supplying e.g. welding machines, whose secondary windings conduct currents of the order of kiloamperes.
Transformers for galvanic power supplies
The power transformer in the special design is an important part of the galvanic rectifier circuit. The primary winding of the delta- or star-connected transformer is supplied from the three-phase industrial mains or from a thyristor controller that allows the output parameters of the rectifier to be varied. The two secondary windings, which are arranged in stars with their respective connection groups, are permanently connected by directly short-circuiting the star points. This creates a symmetrical six-phase system from the phase voltages of the secondary windings (photo. 5.). The transformer supplied by the thyristor controller must correctly withstand the transients resulting from the operation of the thyristors.
3TTH Scott-T transformer type supplying a set of resistive heaters