Transformer principle

A transformer is a device that converts AC voltage, current, and impedance. When AC current is passed through the primary coil, AC magnetic flux is generated in the iron core (or magnetic core), inducing voltage (or current) in the secondary coil. A transformer consists of an iron core (or magnetic core) and a coil, which has two or more windings. The winding connected to the power supply is called the primary coil, and the other windings are called the secondary coils. In a generator, whether the coil moves through a magnetic field or the magnetic field moves through a fixed coil, an electric potential can be induced in the coil. In both cases, the value of the magnetic flux remains unchanged, but the number of magnetic fluxes intersecting the coil varies. This is the principle of mutual inductance. A transformer is a device that utilizes the electromagnetic mutual inductance effect to transform voltage, current, and impedance.
There are corresponding technical requirements for different types of transformers, which can be represented by corresponding technical parameters. The main technical parameters of a power transformer include rated power, rated voltage and voltage ratio, rated frequency, operating temperature level, temperature rise, voltage regulation rate, insulation performance, and moisture resistance. The main technical parameters for general low-frequency transformers are: transformation ratio, frequency characteristics, nonlinear distortion, magnetic and electrostatic shielding, efficiency, etc.
Transformer principle
Voltage ratio:
The number of coils in the two sets of transformers is N1 and N2, where N1 is the primary and N2 is the secondary. Applying an AC voltage to the primary coil will generate induced electromotive force at both ends of the secondary coil. When N2>N1, its induced electromotive force is higher than the voltage applied to the primary, and this type of transformer is called a step-up transformer; When N2
n=N1/N2
In the formula, n is called the voltage ratio (number of turns ratio). When n>1, N1>N2, U1>U2 ， This transformer is a step-down transformer. On the contrary, it is a step-up transformer.
Efficiency of Transformer:
At rated power, the ratio of the output power to the input power of a transformer is called the efficiency of the transformer, where η is the efficiency of the transformer; P1 is the input power, P2 is the output power.
When the output power P2 of the transformer is equal to the input power P1, the efficiency η is equal to 100%, and the transformer will not produce any losses. But in reality, this type of transformer does not exist. Transformers always generate losses when transmitting electrical energy, which mainly include copper loss and iron loss. Copper loss refers to the loss caused by the resistance of transformer coils. When current passes through a coil resistor and generates heat, a portion of the electrical energy is converted into heat and lost. Due to the fact that coils are usually wound with insulated copper wire, they are called copper losses.
The iron loss of transformers includes two aspects. One is hysteresis loss. When an AC current passes through a transformer, the direction and magnitude of the magnetic field lines passing through the silicon steel sheet of the transformer change accordingly, causing the molecules inside the silicon steel sheet to rub against each other and release heat energy, thereby losing some electrical energy. This is hysteresis loss. The other is eddy current loss, which occurs when the transformer is in operation. When magnetic lines pass through the iron core, induced currents are generated in a plane perpendicular to the magnetic lines. As this current forms a closed loop and a vortex, it is called eddy current. The presence of eddy currents causes the iron core to heat up and consume energy, which is called eddy current loss.
The efficiency of a transformer is closely related to its power level. Generally, the higher the power, the smaller the ratio of losses to output power, and the higher the efficiency. On the contrary, the smaller the power, the lower the efficiency.