With the development of the electricity industry and some other sectors, the transformer is vital equipment. They use it widely to solve electricity matters. To know more about this product, let us show you its meaning, structure, and types.







Some types of transformer

Oil-immersed transformer

Dry-type transformer



Purpose of using transformer: The transformer converses alternating voltage. It can raise or reduce initial voltage according to its turns. Today, the electricity transformer device has a shorter name, which is the transformer. The transformer is an electromagnetic device. According to the electromagnetic induction principle, it works to converse an alternating current in this voltage to another voltage with a constant frequency.


Transformer definition: The transformer is an electric device using electromagnetic induction to pass, transfer energy, or alternating current signals between electronic circuits with a particular principle. Some people have a wrong thought with the transformer function. Practically, the transformer has the task of transferring or distributing energy, not changing them.


You can think that way: "Transformer is an electric device using electromagnetic induction to transfer energy or alternating current signal between electric circuits depending on a particular principle."


To know more about transformer definition, you should understand about its components. The transformer has four parts: The Input Connection, the Output Connection, the Windings or Coils, and the Core.

a. Input Connections

It's also called that the primary side because electricity goes into the transformer, it has to be connected to this site.

b. Output Connections

The output side have another name that is the secondary side of the transformer.  On that side, electrical power is sent to the electric device in your house or factories. Depending on some equipment requirements, the incoming electric power (which transfers into the primary side) increases or decreases their power.

c. Winding

All Transformers have two windings, divided into the primary and the secondary winding. The primary winding has a function of drawing power from the source. The secondary winding is the transformer's coil, transferring the energy at the transformed or changed voltage to a load of equipment. Typically, these two coils are subdivided into several coils to decrease the form of flux.

d. Core

The transformer core provides a path that controls the magnetic flux created in the transformer. Typically, the core is not a solid bar of steel. It is a design of so many laminated steel sheets, or layers folded neatly. This design is applied to eliminate or decrease heating.

The transformer's cores have two types, used following your demand: Core Type and Shell Type. The way to distinguish the types is how the primary and secondary coils folded around the steel core.

  • Core type -With this type, the windings are wrapped in the laminated core.
  • Shell type -With this type, the laminated core wraps the windings

When the input voltage gets into the primary winding, alternating current starts to flow in that one. As the current goes through it, a continuously changing and alternating flux is created in the transformer's core. As this magnetic field runs across the secondary winding, an alternating voltage is formed in the secondary winding.


The key to determining the transformer types and the output voltage is the ratio of actual turns of wire in each coil. Say the number of turns of the primary and secondary winding is N1 and N2, the voltage in the two windings call U1 and U2; we have a formula: N1/N2 = U1/U2


According to this formula, if the output winding voltage is higher than the input coil's voltage, then the secondary winding has more wire turns than the primary one. So, the output voltage increased higher, also called "a step-up transformer." Whereas, if the output voltage is less than the input voltage, it's called "a step-down transformer."


Types of transformer


To understand what transformer is, we should know some typical types of them. Like any other electric equipment, we have many ways to distinguish the transformer. Anyways, the differences of these transformers are not change transformer definition.

  • According to the design, we have a single-phase transformer and a three-phase transformer.
  • According to function, we have a step-down transformer and step-up transformer.
  • According to the manners of insulation, we have oil-immersed transformers and dry-type transformers.
  • According to the relationship of windings, we have an auto-transformer and induction transformer.
  • According to their tasks: power transformers, civil transformers, welding transformers, pulse transformers.

In this article's limitation, we will show you the feature of 2 type-transformers: oil-immersed transformer and dry-type transformer to help you know more about transformer definition.

a. Oil-immersed transformer

Oil-immersed transformer definition: We have another name that is an oil-filled transformer. It’s a kind of voltage transformation device using an oil cooling method to reduce the transformer temperature.


The oil-immersed transformer was one of the first transformers to be used. Using this transformer will cool the inner core of the wire while increasing its durability and electrical conductivity. When you want a stable grid, this is one of the first products people use.


The oil-immersed transformer is one of the critical components of electrical systems and is highly economical. For each KW of power source capacity in the world electrical system, there should be about 5 - 6KVA transformer capacity. This principle suggests that transformers' power losses account for nearly 30% of all electrical losses in the grids.


The transformer is one of the most crucial electrical equipment used. Besides these significant advantages, oil-immersed transformers also have limitations.


Types of oil-immersed transformer: 


The oil-immersed transformer has 2 types: Sealed type and open type. 

Sealed type transformers don't have a sub oil tank when open type transformer is vice versa.

  • Advantages of Oil-Immersed Transformer

The oil-immersed transformer has a reasonably large capacity, which saves energy and reduces costs for the user.


The transformer uses oil to cool the system; power lines have higher load capacity and prolong other electrical equipment's life cycle.

  • Disadvantages of Oil- Immersed Transformers

The transformer uses oil to operate, so its quality will determine the transformer's reliability and life circle. It is essential to find out carefully when choosing oil transformer suppliers, expressly whether local and international standards are guaranteed.


Moreover, during the using period, if the oil status is not monitored to unusual changes that may cause unavoidable dangers.


Using oil transformers with a high risk of fire and explosion, you must be very careful to ensure your factory's safety or house.


It is required to have professional technical staff and modern facilities.


When you want to maintain the machine, you must switch off electricity, impacting the user's other activities.


Oil waste needs to be disposed of properly. Otherwise, it will pollute the environment and affect the quality of life of the surrounding people.


When the oil transformer is put into use, it can only be placed indoors, not outdoors. If the area is large, then the transformer size may not be a problem, but it is a problem if the factory is small. The transformer will take up part of the area.


MBT confidently supplies high-quality oil-immersed transformers which help you prevent all dangers as well as provide you long-time guarantee.


With the advantages and disadvantages mentioned above, MBT hopes to help you choose the right transformer appropriate to your needs and minimize the machine's weaknesses.

b. Dry-type transformer

Dry-type transformer definition: It is an electric device that is entirely stationary, and when operating, it needs less maintenance to prevent dangers. Different from oil-immersed transformers, dry-type transformer just applies high-temperature insulation systems that are incredibly safe. Not need fire-resistant vaults and not realize toxic gasses, the device gives a secure and consistent electric power to emit harmful gasses otherwise catch basins. Because of these safety factors, the dry-type transformer is installed in many places, such as hospitals, schools, buildings, and chemical factories. 

This transformer does not use liquids such as silicon or oil to cool its core nor winding. It has ventilation covers and allows outside air to cool the winding.

Types of dry-type transformer

There are two types of dry- types transformers, which are Cast Resin Dry Type Transformer (CRT) and vacuum pressure Impregnated Transformer (VPI)

  • Cast Resin Dry Type transformer (CRT)

Cast Resin Dry Type transformer definition: Used mainly in areas with high humidity, CRT has primary and secondary windings coated by epoxy resin. CRT helps to prevent the ingress of moisture from affecting the quality and longevity of the windings. CRT keeps running without being interrupted by weather conditions. Due to this property, this type of transformer is not hygroscopic. CRT has a range in capacity from 25 KVA to 12,500 KVA, with insulation class F (90oC Temp. Rise).

Some outstanding advantages of Cast Resin Dry Type Transformer:

• Good overload capacity.

• Partial discharge with low losses. Hence the performance is excellent.

• The inner coil is not flammable due to the insulating material outside, so if you install it indoors or in the factory, it is quite suitable.

• Can be placed outdoors in a chassis that has an IP 45 rating.

• Being prevented from humidifying.

  • Vacuum Pressure Impregnated transformer (VPI)

Vacuum Pressure Impregnated transformer definition: This type of transformer also uses a non-combustible material (usually H-grade Polyester) as the coil's insulation and to avoid contamination. Metal foil is arranged in continuous layers to form a winding core. For high voltage machines, the winding is made in the form of a disc and connected in series or parallel according to the power level corresponding to the voltage level. The primary, secondary windings and the core are securely fastened in a vacuum shielding box. This box prevents the transformers from being affected by moisture. This transformer has capacities of 5KVA to 30MVA with insulation classes F (155oC) and H (180oC). With protection up to IP56.

Some outstanding advantages of VPI:

• High mechanical strength, used for a long time.

• No defects in insulation.

• No temperature fluctuations.

• Easy maintenance.

• Less risk of fire.

If you choose a dry-type transformer, you can consider the following advantages and disadvantages of that one.


• Safety for people and equipment.

• Long maintenance and no pollution.

• Easy to install.

• Less space-consuming.

• Environmental friendliness.

• Perfect power to assist if overloaded.

• Reduce investment costs in fire protection systems in inhabitant infrastructures as well as factories.

• Less risk of fire.

• Good ability to withstand short-circuit currents.

• Longer lifespan.

• If installed in a contaminated and humid area, a dry transformer will be suitable.


• Dry transformers have a long lifespan and less winding failure. But once it is damaged, the entire structure will be changed. In other words, it completely changes the voltages sides and the magnetic windings.

• For the same voltage capacity, the dry-type transformer is more expensive than oil-immersed transformers.



MBT is the leading enterprise in Vietnam in the field of electrical equipment manufacturing. With the business motto "Get the quality to nurture trust," MBT focuses on investing in a system of modern advanced technology lines for four factories with ​​nearly 20,000 square meters in area. Most of the input materials are imported from the Group of Seven nations (G7).


With the severe working spirit, professional methods, constant and continuous creativity of a high qualified experts and engineers team as well as many years of working experience for major electrical equipment manufacturers in Vietnam and abroad and the quality management system ISO 9001-2015; ISO 14001..., lean and scientific management model, strict quality control process, MBT's products always meet the requirements of quality, technique, art and on the schedule of customers around the world.


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