Power transformers can be classified into several categories based on their purpose, structure, and other characteristics:
1. According to purpose:
Step-up transformer: Raises the voltage of electricity from low to high, facilitating transmission over long distances through power lines.
Step-down transformer: Lowers the voltage of electricity from high to low, supplying power to nearby or relatively close loads via distribution lines.
2. According to phase number: Single-phase transformer; Three-phase transformer
3. According to winding arrangement: Single-winding transformer (also known as an autotransformer, providing two voltage levels); Double-winding transformer; Triple-winding transformer
4. According to winding material: Copper wire transformer; Aluminum wire transformer
5. According to voltage regulation: No-load tap changer transformer; On-load tap changer transformer
6. According to cooling medium and method:
Oil-immersed transformer: Cooling methods include natural cooling, forced air cooling (with fans mounted on radiators), and forced-air forced oil cooling (utilizing an oil pump to promote oil circulation). Additionally, large transformers may employ forced oil circulation with either air or water cooling.
Dry-type transformer: Windings are either placed in a gas medium (air or sulfur hexafluoride gas) or encapsulated in epoxy resin insulation. They are commonly used as distribution transformers in part of the distribution network. Currently, dry-type transformers can be manufactured up to 35 kV, with broad application prospects.
Working Principle of Transformers:
Transformers operate based on the principle of electromagnetic induction. Their operation relies on electromagnetic processes similar to those found in electric motors (generators and motors), with the distinction that transformers operate at zero rotational speed (i.e., stationary). The main components of a transformer are windings and a core. During operation, the windings serve as the "electrical" path, while the core acts as the "magnetic" path and provides structural support for the windings. When electrical energy is input to the primary side, an alternating magnetic field is generated within the core (converting electrical energy into magnetic field energy). Due to flux linkage, the magnetic flux lines in the secondary windings continuously alternate, inducing a secondary electromotive force (EMF). When an external circuit is connected, induced current flows, outputting electrical energy (i.e., converting magnetic field energy back into electrical energy). This process of energy conversion, known as "electric-magnetic-electric" conversion, is achieved based on the principle of electromagnetic induction and constitutes the working process of transformers.