Effective materials used in transformer construction
Almost every modern electronic or electrical device contains a transformer. The main material used in the production of which is transformer steel. Scientists have found a way to improve the properties of electrical steel and optimize its production process by using a laser.
Transformers convert the standard mains voltage into a reduced voltage required for electronic devices (power supplies, rechargers, etc.) Similar, but more powerful transformers are used in substations to convert high voltage high-voltage lines from power generating stations into a standard alternating voltage of 50 Hz 380 or 220 V used in manufacturing or households. All transformers have the same basic structure: a core made of electrical steel, on which windings (2 or more) are wound with aluminum or copper wires of different lengths and cross-sections. One of them generates a magnetic field, and the other converts this field into an electric current and gives it to the consumer. In order to minimize the energy losses associated with this process, special iron-silicon alloys, known as electrical steel, are used from which the core (frame) is made. In the initial state, these alloys have a grain-oriented structure that determines their magnetic properties.
A grain oriented model means that the material has a crystalline structure in which each grain or crystal is arranged in a specific order. By heating selected areas in the material, it is possible to reduce the size of domains with the same magnetic orientation, which in turn changes the magnetic structure of the steel. This means a lower heating process and, as a result, reduced hysteresis losses in the steel, says Dr. Andreas Weizig, Head of Laser Cutting and Beam Technology at the Fraunhofer Institute for Materials Science in Dresden, describing the complex changes within the material. The laser process has been tuned and matched for quite some time as the preferred method for this type of heat treatment. A steel sheet about one meter wide moves forward at a speed of just over 100 meters per minute, and a focused laser beam moves at a high speed, about 200 meters per second, from side to side across the entire surface of the material along paths spaced several millimeters apart ...
Flexible control of the movement of the laser beam
The Dresden Institute team conducted research and optimized this process. Namely, they developed a method of deflecting laser beam, which allows you to flexibly control the distance between the paths of the beam through the sheet of steel and adapt it to different parameters. To do this, scientists used galvanometric scanners. This device consists of a galvanometer, moving mirrors attached to one side, which are used to deflect the laser beam. This increases the flexibility of setting up the machine process and allows it to be adapted to various tasks, such as quality control of raw materials. The main objective of this study is to advance laser processing into the existing manufacturing environment in order to reduce costs and cycle times.
Further efforts of scientists are to reduce losses due to hysteresis in electrical steel. They have recently started using solid state fiber laser. The results are promising. This laser offers better heat absorption performance than traditional CO2 lasers. They reduce hysteresis losses to 15%, compared to 10% that have been achieved so far. This optimized process has already been implemented by the customer in production.
Ability to reduce energy loss by 25%
The institute's team is now working on the next major challenge - expanding the use of laser technology in the production of electrical steel for electric motor components. However, unlike transformer steel, these materials do not have a strictly oriented domain structure and thus have different magnetic properties. “This means we cannot apply a one-to-one transformer steel process to produce steel for electric motors without making changes to the process.” - says the head of the institute's direction Dr. Weizig. The advantages of using a laser on a non-oriented electric steel furnace depend on the specifics of the operation of the electric motor. Namely, it is the duty point or intersection point of the torque curve and the speed curve. For high-end electrical machines, such as high-revving motors, energy losses can be reduced by a few percentage points. In high torque electrical machines such as pump motors, loss reduction can be up to 25%.