Faraday invented an "inductance loop" on August 29, 1831, called a "Faraday induction coil", which was actually the world's first prototype of a transformer. But Faraday only used it to demonstrate the principle of electromagnetic induction, and did not consider its practical use.
In 1881, Lucien Gaulard and John Dixon Gibbs demonstrated a device called "secondary hand generator" in London, and then used this technology Sold to Westinghouse in the United States, this may be the first practical power transformer, but it is not the earliest transformer.
In 1884, Lusson Golar and John Dixon Gibbs demonstrated their equipment in Turin, Italy, which uses electric lighting. Early transformers used linear cores, which were later replaced by more effective toroidal cores.
Westinghouse engineer William Steinley built the first practical transformer in 1885 after buying the patent for the transformer from George Westinghouse, Lucent Golar, and John Dixon Gibbs. transformer. Later, the core of the transformer was made by stacking E-shaped iron sheets, and commercial use began in 1886.
The principle of transformer transformation was first discovered by Faraday, but it was not put into practical use until the 1880s. In the competition that power plants should output DC and AC power, the ability to use transformers for AC power is one of its advantages. The transformer can convert electrical energy into a high-voltage and low-current form, and then convert it back, thus greatly reducing the loss of electrical energy in the transmission process, making the economic transmission distance of electrical energy reach farther. In this way, power plants can be built far away from electricity consumption. Most of the world's electricity reaches the user after a series of transformations.
The transformer is composed of an iron core (or magnetic core) and a coil. The coil has two or more windings. The winding connected to the power supply is called the primary winding, and the remaining windings are called the secondary winding. It can transform AC voltage, current and impedance. The simplest iron core transformer consists of an iron core made of soft magnetic material and two coils with unequal turns sleeved on the iron core, as shown in the figure.
The function of the iron core is to strengthen the magnetic coupling between the two coils. In order to reduce the eddy current and hysteresis loss in the iron, the iron core is laminated with painted silicon steel sheets; there is no electrical connection between the two coils, and the coils are wound by insulated copper wires (or aluminum wires). One coil connected to AC power is called the primary coil (or primary coil), and the other coil connected to the electrical appliance is called the secondary coil (or secondary coil). The actual transformer is very complicated, and there are inevitably copper loss (coil resistance heating), iron loss (iron core heating) and magnetic leakage (magnetic induction wire closed by air), etc. In order to simplify the discussion, only the ideal transformer is introduced here. The conditions for the establishment of an ideal transformer are: ignoring the leakage flux, ignoring the resistance of the primary and secondary coils, ignoring the loss of the core, and ignoring the no-load current (the current in the primary coil when the secondary coil is open). For example, when a power transformer is operating at full load (the rated output power of the secondary coil), it is close to the ideal transformer situation.
Transformers are static electrical appliances made by the principle of electromagnetic induction. When the primary coil of the transformer is connected to the AC power supply, alternating magnetic flux is generated in the core, and the alternating magnetic is represented by φ. The φ in the primary and secondary coils is the same, and φ is also a simple harmonic function, expressed as φ=φmsinωt. According to Faraday's law of electromagnetic induction, the induced electromotive force in the primary and secondary coils is e1=-N1dφ/dt, e2=-N2dφ/dt. In the formula, N1 and N2 are the number of turns of the primary and secondary coils. It can be seen from the figure that U1=-e1, U2=e2 (the physical quantity of the primary coil is represented by subscript 1 and the physical quantity of the secondary coil is represented by subscript 2), the complex effective value is U1=-E1=jN1ωΦ, U2=E2=-jN2ωΦ, Let k=N1/N2, which is the transformation ratio of the transformer. From the above formula, U1/U2=-N1/N2=-k, that is, the ratio of the effective value of the transformer's primary and secondary winding voltage is equal to its turns ratio and the phase difference between the primary and secondary winding voltage is π.