TYPES OF TRANSFORMER

What is the classification of the transformer?

For the industrial electrical industry and some other fields, a transformer is an indispensable device. The transformer is widely used to solve electrical problems. Today, Vietnamtransformer will join you in learning about the transformer's primary classification to better understand this equipment.

Table of Contents

1. Types of transformer based on the transformer's core

a. Core Type Transformer

b. Shell Type Transformer

c. Berry Type Transformer

2. Types of transformer based on voltage conversion

a. Step Up Transformer

b. Step Down Transformer

3. Types of transformer based on its purpose

a. Power Transformer

b. Distribution Transformer

c. Isolation Transformer

d. Instrument Transformers

e. Current Transformer

f. Potential Transformer

4. Transformer types based on windings

a. Two Winding Transformer

b. Autotransformer

5. Transformer types based on the insulation used

a. Dry Type Transformer

b. Oil Immersed Transformer

6. Transformer types based on the number of phases

a. Single Phase Transformer

b. Three Phase Transformer

 

Like many other electrical devices, there are many ways to classify  types of transformer

  • Based on phase, we will divide into two types of transformer that is single-phase transformers and three-phase transformers
  • According to the function, there are Step-up transformers and Step down transformers
  • According to the usage: power transformers, distribution transformer, isolation transformer
  • Based on windings, we have Two Winding Transformer and Autotransformer.
  • Based on core design, we have Core Type Transformer, Shell Type Transformer, and Berry Type Transformer.

 

1. Types of transformer based on the transformer's core

One of the main differences between a core-type transformer and a shell-type transformer is how the winding surrounds the core. In shell-type transformers, the core surrounds the transformer's windings, while on a core-type transformer, the windings wrap around the core.

a. A core type transformer has two cylinders and two horizontal bars forming the frame. The magnetic core is a square form with a common magnetic circuit. The cylindrical coils (HV and LV) are located on two cylinders.

 

 

b. Shell type transformer has a center cylinder and two outer cylinders. Both the HV and LV coils of it are located on a center column. This transformer has a dual magnetic circuit.

 

 

c. Berry type transformer: Magnetic circuit looks like a wheel. The metal shell is tightly fixed and filled with oil inside.

 


2. Types of transformer based on voltage conversion

a. Step-up transformer

The step-up transformer helps the voltage increase on the output side because the number of turns on the secondary is always more than the number of turns on the primary. A high voltage is developed on the secondary side of the transformer.

 

In countries like India, electricity is generated at 11kv. For economic reasons, AC power is transmitted at very high voltage (220v-440v) over long distances. Hence a step-up transformer is applied at the generating station.

 

b. Step-down transformer

A step-down voltage transformer reduces the output voltage. In other words, it converts high voltage, low current power into low voltage, high current power. For example, the power supply has a voltage of 230-110v, but the doorbell only requires 16v. Therefore, it is recommended to use a step-down transformer to reduce the voltage from 110v or 220v to 16v.


For many regions, the voltage is reduced to 440v / 230v for safety reasons, so the number of turns on the secondary is less than the primary ones; Less voltage is generated at the transformer's output (secondary) end.

 

 

3. Types of transformer based on its purpose

a. Power Transformer

Power transformers are mainly used in the transmission networks of higher voltages. Its ratings are as follows 400kv, 200kv, 110kv, 66kv, 33kv.  Most of the power transformer is rated above 200MVA. They are installed at the generating stations, transmission substations, which need a high capacity transformer. The power transformer is designed for maximum efficiency of 100%  and is larger than the distribution transformer.

 

At a very high voltage, the power cannot be distributed to the consumer directly because they need smaller voltage, so the power is stepped down to the desired level with the help of a step-down power transformer. The transformer is not loaded fully; hence the core loss occurs for the whole day, but the copper loss is based on the load cycle of the distribution network.

 

Suppose the power transformer is connected to the transmission network. In that case, the load fluctuation will be significantly less as it is not connected at the consumer end directly. Still, if connected to the distribution network, there will be fluctuations in the load.

 

The transformer is loaded for 24 hours at the transmission station; thus, the core and copper loss will occur for the whole day. The power transformer is cost-effective when the power is generated at low voltage levels. If the voltage level is raised, then the current of the power transformer is reduced, resulting in I2R losses and the voltage regulation is also increased.

b. Distribution Transformer

A distribution transformer, also known as a consumption transformer, is responsible for switching from a low medium voltage source to the voltage used for home appliances and industrial equipment.

 

Distribution transformers are intended to reduce the voltage for distribution for users or commercial use. This machine has good voltage regulation and can operate 24 hours a day with maximum efficiency at 50% load.

c. Isolation Transformer

Isolation transformers are transformers with the primary and secondary winding independently of each other, and there is only a magnetic flux relationship between them. Unlike autotransformers, isolating transformers are composed of the primary and secondary windings linked only through a magnetic field. The windings are separated so that they are electrically independent and form the distinct points of the isolation transformer:

  • Any point on the secondary coil has a voltage of zero relative to the ground. So when we touch any point on the secondary winding, there will be no shock. The voltage is different in the 2 points of the secondary winding, which is the most significant advantage of the isolation transformer. It helps to reduce the risk of electrical leakage in the device housing and provides safety during use.
  • Each primary or secondary winding has a different volt-ampere characteristic according to the ratio of turns on the primary and secondary districts.

d. Instrument Transformers

The instrument Transformer is generally called an isolation transformer. It is an electrical device used to transform current as well as a voltage level. The most common use of instrument transformer is to safely isolate the secondary winding when the primary has high voltage and high current supply. The measuring instrument, energy meters, or relays connected to the transformer's secondary side will not get damaged. The instrument transformer is further divided into two types:

  • Current Transformer (CT)
  • Potential Transformer (PT)

e. Current Transformer

The current transformer is used for measuring electricity and also for protection. When the current is high to apply directly to the measuring instrument, the current transformer is used to transform the high current into the current required value in the circuit.

 

The transformer's primary winding is connected in series to the main supply and the various measuring instruments like ammeter, voltmeter, wattmeter or protective relay coil to measure and control electricity. They have accurate current ratio and phase relation to enable the meter accurately on the secondary side. The term ratio is significant in CT.

f. Potential Transformer

The potential transformer is an instrument transformer used to transform voltage from a higher value in the primary windings to the lower value in the secondary windings. This transformer steps down the voltage to a safe limit value that the ordinary low voltage instrument like wattmeter, voltmeter, and watt-hour meters can easily measure.

4. Transformer types based on windings

a. A two-winding transformer (conventional winding transformer) has a fixed number of turns. They are separate; It is a static machine that transfers electrical energy from one end to another without changing frequency. A two-winding transformer has two separate winding, which is the primary and secondary winding.

b. Auto-transformer shares the same turns (of wire) between the input and the output connections. The primary and secondary winding are not electrically insulated.

5. Transformer types based on the insulation used

a. Dry Type Transformer

The dry-type transformer is a type of transformer not using any insulating liquid where its winding or core is immersed in liquid. Instead, the windings and core are kept within a sealed tank that is pressurized with air. They are still very safe without liquid.

We have two types of the dry-type transformer, that is Cast Resin Dry Type Transformer (CRT) and Vacuum pressure Impregnated Transformer (VPI)

b. Oil Immersed Transformer

Its also called an oil-filled transformer. The oil-immersed transformer is a kind of voltage transformation device using an oil cooling method to reduce the transformer temperature. Unlike the dry-type transformer, the body of an oil-immersed transformer is installed in the welded steel oil tank filled with insulation oil. When operating, the heat of the coil and iron core is first transformed into the insulation oil and then to the cooling medium. And according to the capacity sizes, it can be divided into an immersed natural cooling transformer and an immersed forced air cooling transformer.

6. Transformer types based on the number of phases

a. Single Phase Transformer

A single-phase transformer is an electrical device that accepts single-phase AC power and outputs single-phase AC. A single-phase transformer is used in non-urban areas as the overall demand and costs are lower than the 3-phase distribution transformer. They decrease the home voltage to a suitable value without a change in frequency, so it's used as a step-down transformer. For this reason, it is commonly used in electronic appliances at residences.

 

b. Three Phase Transformer

A three-phase transformer is made of three sets of primary and secondary windings. Each set of windings wound around one leg of an iron core assembly. It looks like three single-phase transformers sharing one joined core as in the image below. 

 

Three-phase oil-immersed transformer

 

We hope the above information will answer your question about the types of transformer.

 

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