Introduction to Transformers

A transformer is a device that uses the principle of electromagnetic induction to change the AC voltage. The main components are the primary coil, the secondary coil, and the iron core (magnetic core). The main functions are voltage transformation, current transformation, impedance transformation, isolation, voltage regulation (magnetic saturation transformer), etc. According to the purpose, it can be divided into power transformers and special transformers (electric furnace transformers, rectifier transformers, power frequency test transformers, voltage regulators, mining transformers, audio transformers, intermediate frequency transformers, high-frequency transformers, impact transformers, instrument transformers, electronic transformers, reactors, transformers, etc.).

The working principle of 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 coil, and the rest of the windings are called secondary coils. It can transform AC voltage, current, and impedance. The simplest core transformer consists of a core made of soft magnetic material and two coils with different turns on the core.

working principle

The role 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 by lacquered silicon steel sheets; there is no electrical connection between the two coils, and the coils are wound by insulated copper wire (or aluminum wire). One coil connected to the AC power supply 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 is inevitably copper loss (coil resistance heating), iron loss (iron core heating) and magnetic leakage (magnetic induction line 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 iron core, and ignoring the no-load current (current in the secondary coil open circuit primary coil). For example, when the power transformer is running at full load (the secondary coil outputs rated power), it is close to the ideal transformer condition.

Transformers are static electrical appliances made of electromagnetic induction. When the primary coil of the transformer is connected to the AC power supply, an alternating magnetic flux is generated in the iron core, and the alternating magnetic flux is represented by φ. The φ in the primary and secondary coils is the same, and φ is also a simple harmonic function, and the table is 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 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 the subscript 1, and the physical quantity of the secondary coil is represented by the subscript 2), and its complex effective value is U1=-E1=jN1ωΦ, U2=E2=-jN2ωΦ, Let k=N1/N2, which is called the transformation ratio of the transformer. U1/U2=-N1/N2=-k can be obtained from the above formula, that is, the ratio of the rms value of the transformer primary and secondary coil voltages is equal to its turns ratio and the phase difference between the primary and secondary coil voltages is π.

which leads to:

U1/U2=N1/N2

Under the condition that the no-load current can be ignored, there is I1/I2=-N2/N1, that is, the effective value of the primary and secondary coil currents is inversely proportional to the number of turns, and the phase difference is π.

and then obtain

I1/I2=N2/N1

In an ideal transformer, the power of the primary and secondary coils is equal to P1=P2. It shows that the ideal transformer itself has no power loss. The actual transformer always has losses, and its efficiency is η=P2/P1. The efficiency of power transformers is very high, reaching more than 90%.

as the beginning of the number. Example: T01, T201, etc.