Understand the Working Principle / Function and Loss of Power Transformer

Working principle of power transformer

As for the power transformer, it is a special transformer whose output and input share a set of coils. The step-up and step-down are realized with different taps. The tap voltage of less than the common coil is reduced. The tap voltage of more than the common coil increases. The working principle of power transformer is to use the principle of electromagnetic induction. The alternating current we use generates a magnetic field through coil n, and there is a coil m next to coil n. because the magnetic field generated by coil n is not constant, it changes accordingly according to the change of current. The change of magnetic field causes the corresponding current in coil m, and the frequency of coil m will change according to the different turns ratio of coil N and coil M. Of course, now many power transformers are becoming single coil (called autotransformer), and the principle is basically the same.

Autotransformer is a transformer with only one winding. When it is used as a step-down transformer, some wire turns are extracted from the winding as the secondary winding; When used as a step-up transformer, the applied voltage is only applied to part of the wire turns of the winding. Generally, the part of the winding belonging to both primary and secondary is called common winding, and the rest of the autotransformer is called series winding. Compared with ordinary transformers, autotransformer with the same capacity has not only small size, but also high efficiency, and the larger the transformer capacity, the higher the voltage. This advantage is more prominent. Therefore, with the development of power system, the improvement of voltage level and the increase of transmission capacity, self coupled transformer is widely used because of its large capacity, low loss and low cost.

Function of power transformer

In addition to the small volume of power transformer, there is no clear boundary between power transformer and electronic transformer. Generally, the power supply of 60Hz power network is very large, which may cover as large a capacity as half a continent. The power limitation of electronic devices is usually limited by the ability of rectification, amplification and other components of the system. Some of them belong to the power amplification, but compared with the power generation capacity of the power system, it still belongs to the scope of small power. Various electronic equipment are commonly used in transformers for the following reasons: providing various voltage levels to ensure the normal operation of the system; Provide electrical isolation of parts operating at different potentials in the system; Provide high impedance for AC current, but low impedance for DC; Maintain or modify the waveform and frequency response at different potentials.

Loss of power transformer

In the power supply voltage regulator, when the current passes through the primary coil, a certain amount of heat will be generated. (the magnetic flux generated by the coil flows in the iron core, because the iron core itself is also a conductor, and the potential will be induced on the plane perpendicular to the magnetic line of force. This potential forms a closed loop on the broken surface of the iron core and generates current, like P a vortex, so it is called "eddy current". This "Eddy current" increases the loss of the transformer and heats the iron core of the transformer and increases the temperature rise of the power transformer.) more energy loss is generated in the "eddy current", which is the "iron loss" in the term. In addition, when a large number of copper wires are used in our power transformer, a large amount of heat will be generated when the current passes through, which is what we call "copper loss" The main heat sources of power transformer are "copper loss" and "iron loss" It is also these two phenomena that make the power transformer lose more power. Therefore, the temperature rise of the transformer is mainly caused by iron loss and copper loss. Because the power transformer has iron loss and copper loss, its output power is always less than the input power. Therefore, we introduce an efficiency parameter to describe it, = Output power / input power.