Power losses in the transformer
The main characteristics of a transformer are primarily the winding voltage and the power transmitted by the transformer. The transfer of power from one winding to another is done electromagnetically, while some of the power supplied to the transformer from the mains supply is lost in the transformer. The lost part of the power is called losses.
When power is transmitted through a transformer, the voltage across the secondary windings changes with a change in load due to the voltage drop across the transformer, which is determined by the short-circuit resistance. Power loss in the transformer and short-circuit voltage are also important characteristics. They determine the efficiency of the transformer and the mode of operation of the electrical network.
The power loss in the transformer is one of the main characteristics of the economy of the transformer design. Total normalized losses consist of no-load losses (XX) and short-circuit losses (SC).At no-load (no load connected), when the current flows only through the coil connected to the power source, and there is no current in the other coils, the power consumed by the network is spent to create a magnetic flux at no-load, i.e. for magnetizing a magnetic circuit consisting of sheets of transformer steel. To the extent that alternating current changes direction, then the direction of the magnetic flux also changes. This means that the steel is alternately magnetized and demagnetized. When the current changes from a maximum to zero, the steel is demagnetized, the magnetic induction decreases, but with some delay, i.e. demagnetization slows down (when the current reaches zero, the inductance is not zero point n). The retardation of magnetization reversal is a consequence of steel's resistance to reorientation of elementary magnets.
The magnetization curve when reversing the direction of the current forms the so-called hysteresis loop, which is different for each grade of steel and depends on the maximum magnetic induction Wmax. The area covered by the loop corresponds to the power expended for magnetization. As the steel heats up during magnetization reversal, the electrical energy supplied to the transformer is converted into heat and dissipated into the surrounding space, i.e. is irretrievably lost. This is physically the loss of power to reverse the magnetization.
In addition to the hysteresis losses when the magnetic flux flows through the magnetic circuit, eddy current losses… As you know, the magnetic flux induces an electromotive force (EMF), which creates a current not only in the coil located on the core of the magnetic circuit, but also in the metal itself. Eddy currents flow in a closed loop (eddy motion) at the site of the steel in a direction perpendicular to the direction of the magnetic flux. To reduce eddy currents, the magnetic circuit is assembled from separate insulated steel sheets. In this case, the thinner the sheet, the smaller the elementary EMF, the smaller the eddy current created by it, i.e. less power loss from eddy currents. These losses also heat up the magnetic circuit. To reduce eddy currents, losses and heating, increase electrical resistance steel by introducing additives into the metal.
For each transformer, the consumption of materials must be optimal. For a given induction in the magnetic circuit, its size determines the power of the transformer. So they try to have as much steel as possible in the core section of the magnetic circuit, ie. with the selected outer dimension fill factor kz must be the largest. This is achieved by applying the thinnest layer of insulation between the steel sheets. Currently, steel is used with a thin heat-resistant coating applied in the steel production process and making it possible to obtain kz = 0.950.96.
In the production of a transformer, due to various technological operations with steel, its quality in the finished structure deteriorates to a certain extent, and the losses in the structure are obtained by about 2550% more than in the original steel before its processing (when using coiled steel and pressing the magnetic chain without studs).