Application of new magnetic core structure in electronic transformer

1) Overlap wound core
Overlap wound core was first used in amorphous alloy distribution transformers. It has the advantages of wound core, small excitation current, low no-load loss, and can be opened for loading and unloading, eliminating the disadvantages of general wound cores. It does not need to use a special winding machine to wind the coil, which improves production efficiency and is easy to replace and repair when there is a problem with the coil. The thickness of existing 3% oriented silicon steel has been reduced to 0.23mm and 0.27mm, and it is easier to use them to manufacture overlap wound cores than amorphous alloys. Therefore, overlap wound cores may be used in silicon steel power transformers above 500VA, especially silicon steel power transformers in large-capacity rectifier power supplies and uninterruptible power supplies.

2) Three-dimensional triangular core
The three-dimensional triangular three-phase core is now popular in China. The earliest three-dimensional triangular core can be traced back to the 1930s. However, it has not been widely used because the core needs special shearing and the coil needs to be wound by a special winding machine. Now the core shearing can be controlled by computer, and there are special winding machines for winding. There are 5-6 domestic companies applying for patents for three-dimensional triangular core transformers. Compared with the three-column three-phase core arranged in a plane, the three-dimensional triangular three-phase core has a uniform magnetic flux distribution, no local saturation, and good symmetry of the excitation current and magnetic flux. The problem is that it is quite difficult to form a cross-section of each column close to a circle, the average turn length of the winding increases, and the load loss also increases. It can be used for large transformers above 30kVA.

3) Orthogonal core
Rotate half of the C-shaped core by 90° and join them together to form an orthogonal core. The inductance of the orthogonal core can be controlled by a DC control winding. Sony Corporation of Japan has made this core with soft ferrite, called SX-shaped core, and has been used in the switching power supply of various televisions as a driving transformer to control its inductance, so that the circuit has voltage resonance or current resonance, and achieve soft switching conditions. Tohoku University and Tohoku Electric Power Company of Japan have made this core with silicon steel for power compensators and phase shifters to control the active and reactive power of the power system. Compared with thyristor power compensators and phase shifters, it has the characteristics of less high-order harmonics, less electromagnetic interference, and simple control circuits.

4) Magnetic liquid core
Some people have imagined that using an injection molding machine to process transformer cores can avoid multiple processes such as silicon steel core punching, heat treatment, lamination, and assembly. Now, magnetic liquid cores are being developed to realize this idea. The core shell is made of engineering plastics, magnetic liquid is injected in the middle, and the surface is sealed with magnetic sheets. In this way, the processing efficiency of mass-produced small and medium-sized power transformers can be significantly improved, and the cost can be reduced, which has obvious advantages compared with laminated silicon steel cores.