A transformer is an electrical appliance that transmits electrical energy from one electrically isolated circuit to another through a magnetic field medium without changing the frequency.
Power transformers are one of the main pieces of equipment in power plants and substations. Transformers serve multiple functions: they not only raise voltage to deliver electrical energy to the user area, but also lower voltage to the appropriate levels to meet electricity needs. In short, both voltage step-up and step-down must be accomplished by transformers. During the transmission of electrical energy in a power system, both voltage and power losses inevitably occur. When transmitting the same amount of power, voltage loss is inversely proportional to the voltage itself, while power loss is inversely proportional to the square of the voltage. Using transformers to raise voltage reduces transmission losses.
A transformer consists of two or more coil windings wound on the same iron core. These windings are connected by an alternating magnetic field and operate according to the principle of electromagnetic induction. The installation location of the transformer should facilitate operation, maintenance, and transportation, and should be a safe and reliable location. When using a transformer, its rated capacity must be selected appropriately. When a transformer is running under no-load, it requires a large amount of reactive power. This reactive power must be supplied by the power supply system. If the transformer capacity is too large, it not only increases the initial investment but also causes the transformer to operate under no-load or light-load conditions for extended periods, increasing the proportion of no-load losses, lowering the power factor, and increasing network losses. This operation is neither economical nor efficient. If the transformer capacity is too small, it will cause the transformer to be overloaded for extended periods, easily damaging the equipment. Therefore, the rated capacity of the transformer should be selected according to the needs of the electrical load and should not be too large or too small.
We can classify transformers according to different classification parameters, which are as follows:
Voltage rating: Transformers can be classified according to the voltage they operate at. Transformers can operate at voltages ranging from a few volts to megavolts.
Rated power: The rated power of transformers ranges from a few volt-amperes to megavolt-amperes.
Number of turns in primary and secondary windings: step-down transformer, step-up transformer.
Construction Core: Based on the core structure of transformers, they can be divided into two types: shell type and core type.
Cooling type: Transformers can be classified according to their cooling type. There are several types of transformers - self-cooled, oil-cooled, forced-cooled, etc.
Application types: Based on various applications of transformers, such as energy transmission, power distribution, voltage and current stabilizers, isolation, etc., they can be divided into several categories.
An ideal transformer is one that theoretically has no losses and provides 100% efficiency. An ideal transformer cannot be manufactured in reality; it can only exist in the imagination.
1. Real transformer
2. Step-up transformer
3. Step-down transformer
4. Power Transformer
5. Single-phase transformer
6. Three-phase transformer
7. Center-tapped transformer
8. Instrument Transformer
9. Pulse Transformer
10. Radio Frequency Transformer
11. Audio Transformer
Main components and functions of transformers
The most basic structural components of a transformer consist of an iron core, windings, and insulation. In addition, for safe and reliable operation, it is also equipped with an oil tank, cooling system, and protection devices.
(1) Iron core: The iron core of the transformer is the passage of magnetic lines of force, which plays the role of concentrating and strengthening magnetic flux, and at the same time supports the winding.
(2) Winding: The winding of a transformer is the current path. Current is passed through the winding and an induced electromotive force is generated by electromagnetic induction.
(3) Oil tank: The oil tank is the outer shell of the oil-immersed transformer. The main body of the transformer is placed in the oil tank, which is filled with transformer oil.
(4) Oil Conservator: Also called an auxiliary oil tank, the oil conservator is a cylindrical container made of steel plate, horizontally installed on the transformer tank cover and connected to the tank by a curved connecting pipe. One end of the conservator is equipped with an oil level indicator. The volume of the conservator is generally 8% to 10% of the volume of oil in the transformer tank. Its function is to keep the transformer interior filled with oil. Because the oil level in the conservator is within a certain limit, there is room for the oil to expand and contract at different temperatures. Furthermore, the small amount of empty space in the conservator reduces the contact between the oil and air, decreasing the possibility of moisture absorption and oxidation. Additionally, the oil in the conservator is much cooler than the oil in the upper part of the tank, and there is almost no convection with the oil in the tank. A gas relay is installed on the connecting pipe between the conservator and the tank to detect internal transformer faults.
(5) Breathing apparatus: The breathing apparatus contains a desiccant, namely silica gel, which is used to absorb moisture in the air.
(6) Explosion-proof pipe: The explosion-proof pipe is installed on the transformer tank cover. The top of the explosion-proof pipe is equipped with a glass plate. When a fault occurs inside the transformer and high pressure is generated, the gas in the oil will break through the glass plate and be discharged outside the oil tank, releasing the pressure and thus protecting the transformer tank from damage.
(7) Thermometer: The thermometer is installed in the side temperature cylinder on the oil tank cover and is used to measure the temperature of the upper layer of oil in the oil tank.
(8) Bushing: Bushing is an insulating device that leads the high-voltage and low-voltage windings of a transformer to the outside of the tank. It serves both to insulate the leads from the ground (outer shell) and to fix the leads in place.
(9) Cooling device: The cooling device is a device that dissipates the heat generated by the transformer during operation.
(10) Oil Purifier: Also known as a temperature difference filter. Its main part is a cylindrical oil purification tank welded from steel plates, installed on one side of the transformer oil tank. The tank is filled with adsorbents such as silica gel and activated alumina. During operation, due to the temperature difference between the upper and lower layers of oil, the transformer oil flows from top to bottom through the oil purifier, forming convection. The oil comes into contact with the adsorbent, and the moisture, acids, and oxides are absorbed, thus purifying the oil and extending its service life. The oil purifier of a forced oil circulation transformer relies on the oil pressure difference to make the transformer oil flow through the oil purification pump to achieve the purpose of purification.
