Classification of power transformers

Power transformers are classified according to their usage: step-up (power plant 6.3kV/10.5kV or 10.5kV/110kV, etc.), interconnection (220kV/110kV or 110kV/10.5kV between substations), step-down (35kV/0.4kV or 10.5kV/0.4kV for distribution).
Power transformers are classified by phase number: single-phase, three-phase.
Power transformers are classified by winding: double winding (each phase is installed on the same iron core, and the primary and secondary windings are wound separately and insulated from each other), triple winding (each phase has three windings, and the primary and secondary windings are wound separately and insulated from each other), and autotransformer (a set of windings with a middle tap as the primary or secondary output). A three winding transformer requires the capacity of the primary winding to be greater than or equal to the capacity of the secondary and tertiary windings. The percentage of the capacity of the three windings is in the order of high voltage, medium voltage, and low voltage: 100/100/100, 100/50/100, 100/100/50. It is required that both the second and third windings cannot operate at full load. Generally, the voltage of the tertiary winding is relatively low and is mostly used for nearby power supply or compensation equipment, used to connect three voltage levels. Autotransformer: There are two types of transformers: step-up or step-down. Due to its small loss, light weight, and economical use, it is widely used in ultra-high voltage power grids. The commonly used model for small autotransformers is 400V/36V (24V), used for power supply of safety lighting and other equipment.
Power transformers are classified according to insulation media: oil immersed transformers (flame retardant, non flame retardant), dry-type transformers, and 110kVSF6 gas insulated transformers.
The iron cores of power transformers are all core type structures.
The three-phase power transformer configured in general communication engineering is a double winding transformer.