A transformer is a device that utilizes the principle of electromagnetic induction to change AC voltage. Its main components include the primary coil, the secondary coil, and the iron core (magnetic core). Its main functions include voltage transformation, current transformation, impedance transformation, isolation, voltage stabilization (magnetic saturation transformer), etc. Transformers can be classified by their purposes into distribution transformers, power transformers, fully enclosed transformers, combined transformers, dry-type transformers, oil-immersed transformers, single-phase transformers, electric furnace transformers, rectifier transformers, reactors, anti-interference transformers, lightning protection transformers, box-type transformer testers, angle transformers, high-current transformers, excitation transformers, etc. Transformers are basic equipment for power transmission and distribution, widely used in industries, agriculture, transportation, urban communities, and other fields. China has approximately 17 million transformers in operation, with a total capacity of about 11 billion kVA. Transformer losses account for about 40% of power transmission and distribution losses, indicating significant potential for energy conservation. A transformer is a device that utilizes the principle of electromagnetic induction to change AC voltage. Its main components include the primary coil, the secondary coil, and the iron core (magnetic core). In electrical equipment and wireless circuits, it is commonly used for voltage boosting and reduction, impedance matching, safety isolation, etc. In generators, whether the coil moves through the magnetic field or the magnetic field moves through the fixed coil, an electromotive force can be induced in the coil. In both cases, the value of the magnetic flux remains unchanged, but the number of magnetic fluxes intersecting the coil varies, which is the principle of mutual induction. A transformer is a device that utilizes electromagnetic mutual induction to transform voltage, current, and impedance. The components of a transformer include the body (iron core, windings, insulation, leads), transformer oil, oil tank and cooling device, voltage regulating device, protective device (moisture absorber, safety airway, gas relay, oil conservator, temperature measuring device, etc.), and outlet bushing. Specific components and functions: (1) Iron core. The iron core is the main magnetic circuit part of the transformer. It usually contains high silicon content and is made of hot-rolled or cold-rolled silicon steel sheets with thicknesses of 0.35mm, 0.3mm, and 0.27mm, coated with insulating paint. The iron core is divided into two parts: the core column and the cross piece. The core column is covered with windings; the cross piece is used for closing the magnetic circuit. [1] (2) Windings. The windings are the electrical circuit part of the transformer, which are wound with double-wire insulated flat wires or enameled round wires. The basic principle of a transformer is electromagnetic induction. Taking a single-phase double-winding transformer as an example, its basic working principle is as follows: When a voltage U1 is applied to the primary winding, a current I1 flows, generating an alternating magnetic flux O1 in the iron core. These magnetic fluxes are called main magnetic fluxes. Under their influence, the two side windings induce electromotive forces respectively, which ultimately drive the transformer regulating device. [1]
1. Classification standards for transformers: 1. According to voltage levels, they can be divided into: 1000KV, 750KV, 500KV, 330KV, 220KV, 110KV, 66KV, 35KV, 20KV, 10KV, 6KV, 0.66KV, 0.38KV, 0.22KV, etc. 2. According to insulation and cooling medium, they can be divided into: dry-type transformers and oil-immersed transformers. Among them, dry-type transformers are further divided into: SCB epoxy resin cast dry-type transformers and SGB10 non-encapsulated H-grade insulation dry-type transformers.
3. Classified by the material of the iron core structure: silicon steel laminated core transformer, silicon steel wound core transformer, and amorphous alloy core transformer.
4. Classified by designed energy-saving sequence: SG, SJ, S7, S9, S11, S13, S15.
5. Classified by the number of phases: single-phase transformer, three-phase transformer.
6. By capacity: The rated capacities of transformers in China are: 3KVA, 5KVA, 10KVA, 15KVA, 20KVA, 25KVA, 30KVA, 40KVA, 50KVA, 80KVA, 100KVA, 125KVA, 160KVA, 200KVA, 250KVA, 315KVA, 400KVA, 500KVA, 630KVA, 800KVA, 1000KVA, 1250KVA, 1600KVA, 2000KVA, 2500KVA, 3150KVA, 4000KVA, 5000KVA, etc.
I have organized this, categorized by purpose, and the accompanying images are as follows:
(1) Power Transformer: Power transformers are commonly used in power systems for voltage boosting or reduction, serving the needs of power transmission, distribution, and industrial and mining enterprises. They are among the most widely used transformers. Power transformers can be categorized into the following types: ① Step-up Transformer: This type of transformer is used to increase the voltage of power from a power plant and transmit it to distant areas for consumption.
② Step-down transformer: It reduces the high voltage received from the source to meet the needs of various power grids.
③ Distribution transformers are installed in various distribution network systems for use in industrial and agricultural production.
④ Interconnection transformer: It serves as the link between the two substation systems.
⑤ Auxiliary or service transformer: It refers to a transformer used for the generator or substation, or a dedicated transformer for factories and mines.
(2) Instrument transformers Instrument transformers are used for measuring instruments and relay protection devices. They can be divided into: ① voltage transformers; ② current transformers.
(3) Special-purpose transformers. Special-purpose transformers can be divided into the following types: ① Electric furnace transformers, used for smelting; ② Rectifier transformers, used for electrolysis and chemical applications.
③ Test transformers: Test transformers include power frequency test transformers, voltage regulators, etc., which are used for testing electrical equipment. Power frequency test transformers can increase the voltage to test high-voltage electrical equipment. Voltage regulators can adjust the voltage level for use during testing.
④ Electric welding transformers (also known as arc welding transformers) are used for welding.
II. Specification and model of transformer
The specifications and models of transformers, as well as their meanings, are quite diverse. Different types of specifications have varying meanings.
Common: dry-type transformer
The meaning of “SCB10-1000KVA/10KV/0.4KV” dry-type transformer:
The symbol S indicates that this transformer is a three-phase transformer, while replacing S with D indicates that this transformer is a single-phase one.
The meaning of C indicates that the winding (of a dry-type transformer) is a solid formed by resin casting.
B represents foil winding, R represents wound winding, L represents aluminum winding, and Z represents on-load tap changer (copper is not indicated).
The representation of 10 is the design number, also known as the technical number.
1000KVA indicates the rated capacity of this transformer (1000 kVA).
10KV refers to the primary rated voltage, while 0.4KV refers to the secondary rated voltage.
The meaning of common specifications and models of “power transformers”
The model of a power transformer typically consists of symbols indicating the number of phases, cooling method, voltage regulation method, winding core material, as well as the transformer capacity, rated voltage, and winding connection method.
For example, the meaning of transformer model “SFSZ9-31500/110”
S: Three-phase, F: Air-cooled, S: Three-winding, Z: On-load tap changer, 9: Design serial number type 9.
31500: The rated capacity is 31500kVA
110: Primary side rated voltage 110kV
Specifications and models of box-type transformers: Box-type transformers (often referred to as “box-type substations”) integrate traditional transformers into a box-type enclosure, featuring small size, light weight, low noise, low loss, and high reliability. They are widely used in residential areas, commercial centers, light rail stations, airports, factories, mines, enterprises, hospitals, schools, and other places.
Box-type substations are generally categorized by capacity (in KVA) as follows: 315, 400, 500, 630, 800, 1000, 1250, 1600, and 2000. This is the national standard capacity sequence.
III. Specification and model of transformer, as well as explanation of transformer classification standards and commonly used specification and models
Specifications are divided into 36V, 110V, 0.4kV, 10kV, 22kV, 6kV, 35kV, 110kV, 220kV, 350kV, 200kV, 500kV, 250kV, and 600kV based on voltage
In terms of capacity, the rated capacity of transformers in China is currently calculated based on the R10 priority factor, which is a multiple of 10 raised to the power of 10. Examples include 50KVA, 80KVA, 100KVA, etc
There are numerous models of transformers, and the model number of a transformer consists of the following elements: the number of transformer windings, the number of phases, the cooling method, whether it is forced oil-circulating or not, whether it has on-load or off-load voltage regulation, the design serial number, a dash (-), the capacity, and the rated voltage on the high-voltage side.
For example: SFPZ9-120000/110
It refers to a transformer with three phases (omitting the number of windings for a two-winding transformer; if it has three windings, there will be an S before it), two windings, forced oil-circulating air cooling, on-load tap-changer, design number 9, capacity of 120000KVA, and rated voltage of 110KV on the high-voltage side.
The transformer capacities, according to national standards, are: 30KVA, 50KVA, 63KVA, 80KVA, 100KVA, 125KVA, 160KVA, 200KVA, 250KVA, 315KVA, 400KVA, 500KVA, 630KVA, 800KVA, 1000KVA, 1250KVA, 1600KVA, and 2000KVA
1. Classification of transformers
Classified by cooling method: dry-type (self-cooled) transformers, oil-immersed (self-cooled) transformers, and fluoride (evaporative cooling) transformers.
Classified by moisture-proof methods: open-type transformer, potted transformer, sealed transformer.
Classified by core or coil structure: core-type transformers (laminated core, C-type core, ferrite core), shell-type transformers (laminated core, C-type core, ferrite core), toroidal transformers, and metal foil transformers.
Classified by the number of power phases: single-phase transformer, three-phase transformer, and multi-phase transformer.
Classified by purpose: power transformer, voltage regulating transformer, audio transformer, medium frequency transformer, high frequency transformer, pulse transformer.
II. Characteristic parameters of power transformers
1. Operating frequency
The loss of transformer core is closely related to frequency, so it should be designed and used according to the operating frequency. This frequency is called the working frequency.
2. Rated power
Under the specified frequency and voltage, the transformer can operate for a long time without exceeding the output power that results in the specified temperature rise.
3. Rated voltage
It refers to the voltage allowed to be applied on the coil of the transformer, which must not exceed the specified value during operation.
4. Voltage ratio
It refers to the ratio of the primary voltage to the secondary voltage of a transformer, which distinguishes between the no-load voltage ratio and the load voltage ratio.
5. No-load current
When the secondary of a transformer is open-circuited, there is still a certain current in the primary, which is called the no-load current. The no-load current consists of the magnetizing current (which generates magnetic flux) and the iron loss current (caused by core loss). For a 50Hz power transformer, the no-load current is essentially equal to the magnetizing current.
6. No-load loss
When the secondary side of the transformer is open-circuited, power loss is measured at the primary side. The main loss is core loss, followed by the loss (copper loss) generated by the no-load current on the copper resistance of the primary coil, which is relatively small.
7. Efficiency
It refers to the percentage of the ratio between the secondary power P2 and the primary power P1. Generally, the larger the rated power of the transformer, the higher its efficiency.
8. Insulation resistance
It indicates the insulation performance between coils and between coils and the iron core of the transformer. The insulation resistance is related to the performance of the insulation materials used, temperature, and humidity level.