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Answer: There are many different types of transformers, but in terms of their working principle, they are all designed based on the principle of electromagnetic induction. The common classifications of transformers can be summarized as follows: (1) By purpose: ① Power transformers are used for stepping up or stepping down voltage in power transmission and distribution systems, and they are the most common type of transformer. ②A test transformer generates high voltage to conduct high-voltage tests on electrical equipment. ③Instrument transformers such as voltage transformers and current transformers are used in measuring instruments and relay protection devices. ④ Special-purpose transformers: electric furnace transformers for smelting, rectifier transformers for electrolysis, and welding transformers for welding. Voltage-regulating transformers for testing. (2) Classified by the number of phases: ① Single-phase transformers: used for single-phase loads; ② Three-phase transformers: used for stepping up or stepping down voltage in three-phase systems. (3) Classified by winding configuration: ① Autotransformers are used to connect power systems with ultra-high voltage, large capacity, and modest transformation ratio requirements. ② Two-winding transformers are used to connect power systems of two different voltage levels. ③ Three-winding transformers are used to connect three voltage levels, and are generally employed in regional substations within power systems. (4) Classified by core type: ① Core-type transformers are used for high-voltage power transformers. ②Shell-type transformers: Special transformers used for high currents, such as furnace transformers and welding transformers; or power transformers for electronic devices as well as televisions and radios. (5) Classified by cooling method: ① Oil-immersed transformers such as oil-immersed self-cooling, oil-immersed air cooling, oil-immersed water cooling, forced oil circulation, and water cooling. ②Dry-type transformers: They rely on air convection for cooling and are generally used for small-capacity applications such as local lighting and electronic circuits.

Transformers have different operating conditions and installation locations, as well as various voltage levels and capacity ranges; they also come in different structural forms and cooling methods, so they should be classified according to different principles. I. Classification by purpose: Transformers are divided into power transformers (which can be further categorized into step-up transformers, step-down transformers, distribution transformers, and station service transformers, etc.), special-purpose transformers (electric furnace transformers, rectifier transformers, welding transformers, etc.), instrument transformers (voltage transformers, current transformers), as well as high-voltage transformers and voltage regulators for testing purposes. II. Based on the configuration of their windings, transformers are classified into two-winding, three-winding, multi-winding transformers, and autotransformers. III. Based on different core structures, transformers are divided into core-type transformers and shell-type transformers. IV. According to the number of phases V. Transformers are classified into single-phase transformers, three-phase transformers, and multi-phase transformers. VI. Based on different cooling methods, transformers are classified into dry-type transformers, oil-immersed self-cooling transformers, oil-immersed air-cooled transformers, forced oil circulation transformers, forced circulation guided cooling transformers, gas-insulated transformers, etc. VII. According to different coil structures. Transformers are divided into single-coil transformers, double-coil transformers, three-coil transformers, and multi-coil transformers. VIII. Based on the difference in insulation at the center point, transformers are divided into fully insulated transformers and semi-insulated transformers. Although transformers come in different types and structural forms, their basic working principle is the same – they all operate based on the principle of electromagnetic induction, namely the generation of electricity from magnetic movement and the generation of magnetic field from electrical movement

Operating principle: UI remains constant; it is neither dry-type nor oil-immersed

The working principle of a transformer is based on the principle of electromagnetic induction. The transformer has two sets of coils. Primary coil and secondary coil. The secondary coil is outside the primary coil. When alternating current is passed through the primary coil, an alternating magnetic field is generated in the transformer core, which in turn induces an electromotive force in the secondary coil. The turn ratio of the transformer’s coils is equal to the voltage ratio.

The working principle of a transformer is based on the principle of electromagnetic induction. The transformer has two sets of coils. Primary coil and secondary coil. The secondary coil is outside the primary coil. When alternating current is passed through the primary coil, an alternating magnetic field is generated in the transformer core, which in turn induces an electromotive force in the secondary coil. The turn ratio of the transformer’s coils is equal to the voltage ratio. Classified by cooling method: dry (self-cooling) transformers, oil-immersed (self-cooling) transformers, and fluoride (evaporative cooling) transformers. Classified by moisture protection method: open-type transformers, potting-type transformers, and sealed-type transformers. Classified by core or coil structure: core-type transformers (slotted core, C-core, ferrite core), shell-type transformers (slotted core, C-core, ferrite core), toroidal transformers, and metal foil transformers. Classified by the number of power phases: single-phase transformers, three-phase transformers, multi-phase transformers. Classified by application: power transformers, voltage-regulating transformers, audio transformers, intermediate-frequency transformers, high-frequency transformers, pulse transformers.

Working principle of the transformer: The number of turns in the primary winding is N1, and the number of turns in the secondary winding is N2. When an alternating current flows through the primary winding of a transformer, an alternating magnetic flux is generated in the iron core. According to the principle of electromagnetic induction, induced electromotive forces are generated in both the primary and secondary windings. The induced electromotive force in the secondary winding acts as a new power source; this is the basic working principle of a transformer. Classification of transformers: 1. Classification by purpose: They are divided into power transformers (which can be further categorized into step-up transformers, step-down transformers, distribution transformers, station service transformers, etc.); special-purpose transformers (furnace transformers, rectifier transformers, welding transformers, etc.); instrument transformers (voltage transformers, current transformers); and high-voltage transformers and voltage regulators used for testing purposes. 2. Based on the winding structure: they are divided into two-winding, three-winding, multi-winding transformers, and autotransformers. 3. Based on different core structures: they are divided into core-type transformers and shell-type transformers. 4. Based on the number of phases: They are divided into single-phase, three-phase, and multi-phase transformers (such as six-phase transformers used for rectification). 5. Based on the voltage regulation method: they are divided into excitation-free voltage regulation transformers and on-load voltage regulation transformers. 6. Based on the cooling method: they are classified into dry-type transformers, oil-immersed self-cooling transformers, oil-immersed air-cooled transformers, forced oil circulation cooling transformers, forced oil circulation guided cooling transformers, gas-insulated transformers, etc. 7. Classified by capacity: Small transformers have a capacity of 630 kVA or less; medium-sized transformers have a capacity of 800 kVA to 6,300 kVA; large transformers have a capacity of 8,000 kVA to 63,000 kVA; and extra-large transformers have a capacity of 900,000 kVA or more.

This post was last edited by chuanhengmpq on 2016-2-2 at 11:15. Answer: When the current in the primary coil (the coil that already has an electric current flowing through it) increases, the magnetic field generated by this coil within the iron core also increases (the direction of the magnetic field can be determined using the right-hand rule). At this point, an induced current is generated in the secondary coil (the coil that does not have an electric current flowing through it). The direction of this induced current is opposite to the direction of the current in the primary coil (as a result, the direction of the magnetic field generated by the current in the secondary coil is also opposite to that of the magnetic field generated by the current in the primary coil). As the current in the primary coil decreases, the magnetic field generated by this current in the core also weakens. At this point, a current is induced in the secondary coil in the same direction as the current in the primary coil; the magnetic field produced by this current in the core has the same direction as the magnetic field produced by the primary coil in the core. With this change, due to the variation in current in the primary coil, a current is generated in the secondary coil. This is how transformers work. Classification: By cooling method – dry (self-cooling) transformers, oil-immersed (self-cooling) transformers, fluoride (evaporative cooling) transformers. By moisture protection method – open-type transformers, potting-type transformers, sealed transformers. Classified by core or coil structure: core-type transformers (slotted core, C-core, ferrite core), shell-type transformers (slotted core, C-core, ferrite core), toroidal transformers, and metal foil transformers. Classified by the number of power phases: single-phase transformers, three-phase transformers, multi-phase transformers. Classified by application: power transformers, voltage-regulating transformers, audio transformers, intermediate-frequency transformers, high-frequency transformers, pulse transformers

Electromagnetic mutual inductance, voltage and current transformation, impedance. Step-up and step-down, as well as special transformers

1. Working principle of the transformer: When the current in the primary coil (the coil that is already supplied with electricity) increases, the magnetic field generated by this coil within the iron core also increases (the direction of the magnetic field can be determined using the right-hand rule). At this point, an induced current is generated in the secondary coil (the coil that is not currently supplied with electricity). The direction of this induced current is opposite to the direction of the current in the primary coil (as a result, the direction of the magnetic field generated by the current in the secondary coil is also opposite to that of the magnetic field generated by the current in the primary coil). As the current in the primary coil decreases, the magnetic field generated by this current in the core also weakens. At this point, a current is induced in the secondary coil in the same direction as the current in the primary coil; the magnetic field produced by this current in the core has the same direction as the magnetic field produced by the primary coil in the core. As this change continues, a current is generated in the secondary coil due to the change in current in the primary coil. 2. The classification of commonly used transformers can be summarized as follows: 1. By the number of phases: 1) Single-phase transformers: Used for single-phase loads and three-phase transformer banks. 2) Three-phase transformer: Used for stepping up or stepping down voltage in three-phase systems. 2. Classified by cooling method: 1) Dry-type transformers: They rely on air convection for natural cooling or use fans to enhance cooling; they are commonly used in high-rise buildings, for power supply at highway toll stations, as well as for low-capacity applications such as local lighting and electronic circuits. 2) Oil-immersed transformers: Rely on oil as a cooling medium, such as oil-immersed self-cooling, oil-immersed air cooling, oil-immersed water cooling, forced oil circulation, etc. 3. By purpose: 1) Power transformers: Used for stepping up and stepping down voltage in power transmission and distribution systems. 2) Instrument transformers: such as voltage transformers and current transformers, used in measuring instruments and relay protection devices. 3) Test transformer: capable of generating high voltage for conducting high-voltage tests on electrical equipment. 4) Special transformers: such as furnace transformers, rectifier transformers, regulating transformers, capacitive transformers, phase-shifting transformers, etc. 4. Classified by winding type: 1) Double-winding transformer: Used to connect two voltage levels in a power system. 2) Three-winding transformer: Generally used in regional substations of power systems to connect three voltage levels. 3) Autotransformer: Used to connect power systems with different voltages. It can also be used as a regular step-up or step-down transformer. 5. Classified by core type: 1) Core-type transformers: Used for high-voltage power transformers. 2) Amorphous alloy transformers: Transformers with amorphous alloy cores utilize a new type of magnetic conductive material, which reduces the no-load current by about 80%. They represent an excellent choice for energy-saving distribution transformers, especially suitable for areas with low load levels such as rural power grids and developing regions. 3) Shell-type transformers: Special transformers used for high currents, such as furnace transformers and welding transformers; or power transformers for electronic devices as well as televisions and radios.