Transformers are widely used in the field of electrical and electronic equipment. Transformers are electromagnetic elements that follow the basic law of electromagnetism, Faraday’s law. In a previous article, we gave a brief overview of the structure of transformers and their performance. In this article, we will examine the different types of transformers and their applications. It should be noted that although all transformers follow the same principles, they have different structures, which we will discuss later.
Different types of transformers depending on the voltage level
Transformers can have different structures. In transformers, there is no electrical connection between the primary and secondary sides. In other words, each transformer has two independent windings that transfer electricity from the primary side to the secondary side by passing a magnetic flux. تر A transformer can have several windings in the primary side and Have a secondary. The primary side windings are usually connected in series, called a central connection transformer. The central connection structure can also be seen on the side of the secondary winding.
The structure of transformers can be such that they change the voltage level from primary to secondary. According to the change in voltage level, transformers are classified into three main categories: increasing, decreasing and isolating. In isolated transformers, the voltage level is the same on both the primary and secondary sides.
1- Reducing transformers
Reducing transformers are used in both electrical and electronic equipment. In this type of transformers, the voltage level decreases by passing from the primary to the secondary side, and the amount of surface reduction is proportional to the ratio of the primary to secondary winding turns. In reducing transformers, the number of turns of the primary winding is more than the secondary winding, so the ratio of the turns of the primary winding to the secondary is always greater than 1.
Electronic equipment sometimes requires 24, 12, 9, 6, 5 and 48 volts, so to reduce the voltage of 230 volts AC to the desired voltage level for electronic applications, reducing transformers are used. This transformer is also used in many other applications such as instrumentation.
Reducing transformers play an important role in electrical equipment such as electrical distribution systems (in which high-voltage voltages are used to reduce losses and cost-effectively transmit power over long distances). In this type of applications, a step-down transformer is used to convert the high level voltage to the low level voltage of the power supply line.
2- Increasing transformer
The performance of step-up transformers is exactly that of step-down transformers. The voltage level passing through the primary to secondary direction is increased in step-up transformers and the rate of increase depends on the ratio of the primary to secondary winding turns. In other words, the ratio of primary to secondary winding turns in incremental transformers is always less than 1.
In electronics, step-up transformers are used in stabilizers, rectifiers and, as mentioned, low voltage levels are converted to high voltage levels.
Incremental transformers are also used in electrical power distribution systems. In power distribution equipment, high voltage levels are required, so before this equipment, step-up transformers are usually used.
3- Isolated transformers
Isolated transformers have no effect on the voltage level and the voltage level in this type of transformers is the same on both the primary and secondary sides. In other words, the ratio of primary and secondary winding speeds in this type of transformers is always equal to 1, and in fact, the number of turns on both sides is equal.
Isolated transformers are used to separate the primary and secondary parts. As mentioned earlier, there is no electrical connection between the primary and secondary sides, meaning that it acts as a barrier and passes only a magnetic flux. Therefore, it is used to increase the security of circuits and eliminate noise from the primary side to the secondary side and vice versa.
Different types of transformers depending on the material of the core
Transformers transfer energy from one side to the other by directing a magnetic flux from their core. The materials used in the nucleus affect the flux density. Depending on the type of core used in the transformers, there are various applications for them, which we will discuss in the following.
1- Transformer with iron core
The iron-core transformer uses several soft iron plates as the core material. Due to the excellent magnetic properties of iron, the flux in this type of transformers is well transferred and therefore the efficiency of transformers with iron cores is very high.
After the primary and secondary coils are wound, they are placed on soft iron plates. The soft iron plates used in the core are available in a variety of sizes and shapes. Depending on the size and shape of the core plates, different types of transformers are produced, the most common of which are I, U, L, E and اشک shapes. Iron plates are thin, so to achieve the final shape, it is necessary to connect several plates to each other. For example, to make an E core, several thin iron plates are joined together to resemble the letter E.
Iron-core transformers have a wide range of applications and are usually larger and heavier than other types of transformers.
2- Transformer with ferrite core
Ferrite materials have high permeability, so in this type of transformers are used as the core. Ferrite core transformers at high frequencies have low losses and therefore have been considered in high frequency equipment such as multimode power supply SMPS , RF equipment and..
The shape and size of transformers with ferrite cores vary according to the type of application and are mostly used in the form of E. It should also be noted that this type of transformer is used in electronic devices more than electrical devices.
3- Transformer with toroidal core
Toroidal core transformers are made of nuclei of different materials such as iron and ferrite in geometrical toroidal shapes. Thyroids are in the form of rings or donuts and are used in applications that require very high efficiency. Due to the ring shape of this type of transformers, the leakage inductance is very low and as a result the Q factor is high. Also, in this type of transformers, the windings are usually shorter than the old models and also weigh less.
4- Transformer with air core
The air-core transformer does not use any physical material as the core. Flux transfer in this type of transformer is done completely through the air.
In air-core transformers, the primary winding is connected to a variable current, which generates a magnetic field around it. When the secondary winding is exposed to the magnetic field , according to Faraday’s law, the magnetic field is also induced in the secondary winding and the power reaches the load on the secondary side.
Air-core transformers have less cross-inductance than physical-core transformers such as iron and ferrite.
These types of transformers are used in equipment related to radio frequencies. It should be noted that these transformers are lighter than other transformers due to the lack of a physical core. Air-core transformers are also used in the construction of wireless chargers, so that the primary coil is installed on the side of the charger and the secondary coil is placed in the device to be charged.
Types of transformers depending on the type of winding of the wires in the winding
Transformers are also classified based on how complex their wires are. .One of the most popular types of these transformers is the automatic winding transformer.
Automatic winding transformer
Until now, the primary and secondary windings have been fixed, but in transformers with automatic windings, the primary and secondary windings can be connected in series and their central connection point can be varied. The secondary voltage will vary according to the location of the central connection point.
This coil consists of two parts, primary and secondary. The rate of the primary and secondary circuits is determined by the location of the central connection point, and in fact the output voltage depends on it.
This transformer is mostly used in generating AC voltage from an AC input (in VARIAC application). They also use this transformer in power transmission and distribution systems when high voltage lines need to be changed frequently.
Types of transformers according to application
Different transformers are designed and built for use in specific areas. In electrical and electronic equipment, there are various step-up and step-down transformers that are designed to suit a specific type of application. Therefore, there is another classification related to the type of user as follows.
- Power field equipment
- Power transformer
- Measuring transformer
- Distribution transformer
- Electronic equipment
- Pulse transformer
- Audio output transformer
1- Transformers used in power field equipment
In electrical systems, the power domain means the generation, measurement and distribution of power. In fact, transformers are an essential component in ensuring the security of power conversion and its successful delivery to small stations and end users.
Transformers used in the field of power are more in the open air and less in the living space.
Power transformers are usually large in size and are used to transfer power to small stations and public power sources. These transformers act as a bridge between the generators and the primary distribution network. According to the power transfer rate and its specifications, power transformers are divided into three general categories. Low power transformers, medium power transformers and high power transformers.
Power transmission rates can vary from 30KVA to 700-500 KVA. In some applications this value can reach 7000KVA or more. In medium transformers, the power transfer rate can reach above 100-50 MVA, while in large transformers, the power transfer rate is more than 100 MVA.
Due to the significant amount of power generated by power transformers, the structure of this type of transformers is very important. Insulation accessories and cooling system are used in the construction of this type of transformers. Conventional power transformers are usually filled with oil.
An important point in power transformers is the conversion of low voltage and high current to high voltage and low current. For this purpose, it is necessary to reduce power loss in the power distribution system.
The next important criterion for a power transformer is the phase access level. Power transformers usually work in three-phase systems, but in some cases low-power single-phase transformers are used. Three-phase power transformers are more expensive and more efficient than single-phase power transformers.
Measuring transformers are also known as precision instrument transformers. These transformers are used to isolate the main power as well as convert current and voltage at a low rate and send it to the secondary. By measuring the output, phase, current and voltage of the main power line can be calculated.
The image above shows the structure of a current transformer.
This type of transformer is used in the last phase of the power distribution system. Distribution transformers are step-down transformers that convert high-level voltage to the voltage required by the consumer, ie 110 volts or 230 volts, which can be single-phase or three-phase.
Distribution transformers can be small or large depending on the capacity and conversion rate.
Distribution transformers are divided into different types according to the type of insulation used. Which may be dry or immersed in liquid. For the core of this transformer, usually C-shaped steel plates are used.
Distribution transformers are also divided into several categories based on the location used. The transformer can be placed in a single polarity, in which case it is called a distribution transformer mounted on a pole. This transformer can also be placed in an underground chamber and installed in a concrete layer or inside an enclosed steel box.
In general, distribution transformers have a rate of less than 200KVA.
2- Transformers used in the field of electronic equipment
Ultra-small transformers use a variety of miniatures that can be mounted on a PCB or housed inside a small enclosure.
Pulse transformers are PCB-type transformers that generate electrical pulses at a constant amplitude. These transformers are used in various digital circuits that require a pulse generator in an isolated environment. Therefore, pulse transformers isolate the primary and secondary side and transmit the pulse from the primary side to the secondary circuit, which is usually the logic gate or driver.
Transformers built for proper operation require galvanic coating to insulate and reduce leakage and jamming capacitors.
Audio output transformers
Audio transformers are another common transformer used in the field of electronics. These transformers are used in audio equipment that requires impedance matching. The sound transformer modulates the amplifier circuit and loads similar to the process that occurs in the sound speaker. Audio transformers can have several primary and secondary windings that are centrally or centrally connected.
Different types of transformers are designed and built for general and special use, some of which were discussed in this article.
- Source: Translation from circuitdigest.com
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