A transformer mainly consists of an iron core and windings. The iron core is the magnetic circuit channel of the transformer and is usually made of stacked silicon steel sheets with a thickness of 0.35 to 0.5 mm, coated with oil on both sides and painted to insulate the sheets from each other.
The windings are the electrical components of a transformer, made of a certain number of turns of air-insulated wire. The winding connected to the power source is called the primary winding, or main winding. The winding connected to the load is called the secondary winding, or secondary side winding. The basic forms of transformer core structure are core-type and shell-type. In a core-type transformer, the core is surrounded by the windings. Simply put, the windings surround the core; the structure is relatively simple, and assembly and insulation are easier, so transformers often use a core-type structure.
A transformer works on the principle of mutual inductance between two coils, or Faraday's law of electromagnetic induction. When the current in the primary coil changes, the magnetic flux connected to the secondary coil also changes. Therefore, due to Faraday's law of electromagnetic induction, an electromagnetic flux (EMF) is induced in the secondary coil. Transformers are based on two principles: first, current can generate a magnetic field (electromagnetism); second, the constantly changing magnetic field within the coil induces a voltage across the coil (electromagnetic induction). Changing the current in the primary coil changes the generated magnetic flux. The changing magnetic flux induces a voltage in the secondary coil.
For the load, the induced electromotive force in the secondary winding is equivalent to the power source. The current flowing through the secondary winding causes the light bulb to light up. The transformer converts the alternating voltage and current on the primary side into a voltage and current on the secondary side through electromagnetic induction. The magnitude of this voltage and current may be different from or the same as that on the primary side, thus achieving the purpose of electrical energy transmission. The power frequency remains constant during transmission; this is the basic working principle of a transformer.
The magnetic field generated by an induced current is an induced magnetic field, and its determination method is as follows:
(1) Magnetic field generated by electric current: Determined by the right-hand screw rule
Ampere's law, also known as the right-hand screw law, is a rule that describes the relationship between the direction of a current and the direction of the magnetic field lines it generates. Ampere's law for a current-carrying straight conductor (Ampere's law 1): Grasp the current-carrying straight conductor with your right hand, with your thumb pointing in the direction of the current; the direction your four fingers point is the direction of the magnetic field lines. Ampere's law for a current-carrying solenoid (Ampere's law 2): Grasp the current-carrying solenoid with your right hand, with your four fingers pointing in the direction of the current; the end your thumb points to is the N pole (North pole) of the solenoid.
(2) Magnetic field generated by induced current: determined by Lenz's law.
Lenz's Law: The induced current has such a direction that the magnetic field of the induced current always opposes the change in the magnetic flux that caused the induced current.
When the magnetic flux of the original magnetic field decreases, the magnetic field generated by the induced current is in the same direction as the original magnetic field; the magnetic field generated by the induced current opposes the decrease of the original magnetic field and increases it.
When the magnetic flux of the original magnetic field increases, the magnetic field generated by the induced current is in the opposite direction to the original magnetic field; the magnetic field generated by the induced current opposes the increase of the original magnetic field, causing it to decrease.
3. Graph showing the relationship between magnetic flux and current in electromagnetic induction.
The rate of change of current determines the rate of change of magnetic flux, the rate of change of magnetic flux determines the magnitude of the induced current, and the magnitude of the induced current affects the rate of change of current E=L*(ΔI/Δt) (self-induced electromotive force).
Magnetic flux is represented by the letter Φ, current by I, and magnetic induction intensity by B (distinct from magnetic field strength H, which refers to the strength of the magnetic field source). Magnetic flux is equal to magnetic induction intensity multiplied by the effective cross-section of the magnetic circuit, that is, Φ = B * S. The product of the current I through the coil and the number of turns N of the coil is the magnetomotive force F (which can be compared to the electric potential in a circuit), also called ampere-turns.
4. The relationship between electromagnetic induction and magnetic flux
Electromagnetic induction, also known as magnetoelectric induction, refers to the phenomenon where a conductor in a closed circuit moves through a magnetic field, cutting magnetic field lines, and a current is generated in the conductor. This phenomenon of generating current using a magnetic field is called electromagnetic induction, and the generated current is called induced current.
Electromagnetic induction refers to the phenomenon of induced electromotive force generated by changes in magnetic flux. The discovery of electromagnetic induction is one of the greatest achievements in the field of electromagnetism. It not only revealed the intrinsic connection between electricity and magnetism but also laid the experimental foundation for the interconversion between them, paving the way for humanity to obtain vast and inexpensive electrical energy, and has significant practical implications.
The discovery of electromagnetic induction marked the beginning of a major industrial and technological revolution. As proven by facts, the widespread application of electromagnetic induction in electrical engineering, electronics, electrification, and automation has played a vital role in promoting social productivity and the development of science and technology.
This is how a transformer works. If you find it complicated, just remember this: the primary coil and the secondary coil are magnetically coupled, and from the power source's perspective, it's as if it's directly supplying power to the load.
