Electrical Power Transformer Basic Guide

Electricity is an important energy source in today's human society and the foundation of national development. In the power system, the electrical power transformer is a very basic and important component, which is commonly used in power generation, transmission, substation, distribution, and other systems, and can be called one of the cores of the power system. 


Daelim Belefic is a professional electrical transformer manufacturer, with rich experience in the international electric market, and is familiar with international electrical power transformer standards. Today we will check out this article with you, to learn the basic information about electrical power transformers.

electric-power-transformerpad mounted transformer

Table Of Contents
1. What is an electrical power transformer? 
2. What are the electrical power transformer types? 3. What information should be shown on the electrical power nameplate? 
4. Why should the iron core of the electrical power transformer be grounded?
5. Customize and sell electrical power transformer

What is an electrical power transformer? 

Electrical power transformers are one of the most important items in power plants and substations. Electrical power transformers serve many purposes. The device not only increases the voltage and directs the electric energy to the electricity-consuming areas, but it also reduces the voltage to meet the needs of electricity consumption at all levels. The transformer is required to complete both step-ups and step-downs. Voltage and power losses occur inevitably when electrical energy is transmitted in a power system. Whenever the same amount of power is transmitted, the voltage loss is inversely proportional to the voltage, and the power loss is inversely proportional to the voltage squared. When transmission losses are reduced by increasing the voltage, transformers are used.


Read more: The Ultimate Guide to Electric Transformer


Electrical power transformers are composed of two or more windings wound around the same iron core. An alternating magnetic field connects the windings, which operates on the principle of electromagnetic induction. Transformer installation places should be convenient for operation, maintenance, and transportation, as well as safe and reliable. It is important to select a transformer with a reasonable rated capacity when using it. When the transformer is running at no-load, it requires a larger reactive power. The supply system must supply these reactive powers. A large transformer capacity will not only increase the initial investment, but it will also make the transformer run at no-load or light-load for a long time, thereby increasing no-load loss, reducing the power factor, and increasing network loss. Reasonable. A small transformer capacity will overwork the transformer for a long time, causing the equipment to be easily damaged. It is therefore important to choose the transformer rated capacity according to the electrical load requirements, rather than too large or too small.


What are the electrical power transformer types?

According to different ways of distinguishing, electrical power transformers can be divided into different types:


Learn more: How Much Do You Know For The Different Types Of Transformers?


Oil immersed transformer and dry type transformer

Based on the cooling system, there are oil immersed transformers and dry type transformer. 

Oil immersed transformer
Oil immersed transformers are filled with transformer oil as cooling liquid, also the transformer oil has an insulating effect. Most of the projects will need mineral oil as transformer oil, they can work in the temperature from -45℃ to +45℃. For some projects which have high requirements on safety and environmentally friendly, we will use vegetable oil instead of mineral oil. Vegetable oil has a higher burning point, which comes with higher safety. With higher safety, comes a higher cost than mineral oil, so it will be an optional part for the customer. Oil-immersed transformer with mineral oil, their cooling system will be marketed as ONAN; With vegetable oil, the cooling system will be marked as KNAN. 


Try for free: How much do you know about oil-immersed distribution transformers?

dry type transformer

Dry-type transformers are widely used in local lighting, high-rise buildings, airports, terminal CNC machinery and equipment, etc. Simply speaking, dry-type transformers refer to transformers whose iron cores and windings are not immersed in insulating oil.

Read my article on the Ultimate guide of cast resin dry-type transformer


The cooling methods are classified as natural air cooling (AN) and forced air cooling (AF). If the transformer is cooled by natural air, it can run continuously for a long time below its rated capacity. The output capacity of a transformer can be increased by 50% when forced air cooling is employed. It is suitable for intermittent overload operation or emergency accident overload operation; due to the large increase of load loss and impedance voltage during overload, it is in a non-economic operation state, so it should not be in continuous overload operation for a long time.


Single-phase transformer and three-phase transformer

According to the phase of the transformer, there are single-phase transformers and three-phase transformers. 

single phase transformer
In general, single-phase electrical power is for civil electricity, such as apartments, communities, office buildings, etc... Three-phase electrical power is for industry electricity, such as factories, data centers, renewable projects, bitcoin mining farms, etc... 

Single-phase transformer usually has arelatively small capacity and can be designed as pole-mounted or pad-mounted, depending on the application scenarios. Single-phase pole-mounted transformer is mounted on poles, we can see them on the electricity poles around the street. Single-phase pad-mounted transformers are usually seen in the back yard of the house, or near the office building or apartment. 

Keep reading: Tips for single phase transformer

3 phase transformer
Three-phase transformers can be designed with bigger capacity and higher voltage. Daelim can produce up to 200MVA, and 235kV, which is mainly for substation use. In the power distribution system, Daelim also produces three-phase transformers based on ANSI/IEEE, DOE, CSA, AS/NZS, IEC, and GOST standards, the high voltage from 4.16kV, 12.47kV, 13.8kV to 44kV, 66kV, 69kV, perfectly suitable for any international market's needs. 


Read on: Three-phase Transformer Industry Basic Guidelines 2022 | Daelim Belefic


Here we introduce some types of three-phase transformers: 

substation type transformer
Substation type transformer. As the name suggests, substation type transformer is usually used in power substations, as the core of power substations, transfers the voltage from high to low or low to high, depending on the project needs. Substation-type transformers are usually oil-immersed designs, cooling fans can be added to increase the capacity, and the cooling system of an electrical power transformer with cooling fans will be marked as ONAF. 

three phase pad mounted transformerThree-phase Pad-mounted Transformer. Similar to the single-phase pad-mounted transformer we mentioned, three-phase pad-mounted transformers are also widely used in Canada, the USA, Latin America, and the South American markets. Crypto mining, data center, renewable, and construction projects will have a big need for three-phase pad-mounted transformers. 

Three-phase Pole-mounted Transformers. Also mounted on electrical poles, and commonly used in Asia, and African markets. It’s a very common electrical power transformer in our daily life, commonly used in the power distribution system, and usually purchased by local government, by public bidding with big quantity. 

Three-phase dry-type transformer. As we mentioned above, dry-type transformers have better safety than oil-immersed transformers, so they are widely used in office building, substation station, airport, etc... Dry-type transformer has the advantages of easy installation and repair, low noise, and smaller footprint. 


What information should be shown on the nameplate? electrical-power-transformer-nameplate

The rated value of the electrical power transformer is the regulation made by the manufacturer for the normal use of the electrical power transformer. The electrical power transformer operates under the specified rated value to ensure long-term reliable work and good performance. Its ratings include the following:

1) Rated capacity: It is the guaranteed value of the output capacity of the electrical power transformer in the rated state. The unit is expressed in volt-ampere (VA), kilovolt-ampere (kVA) or mega-volt-ampere (MVA). Due to the high operating efficiency of the transformer, usually The design value of the rated capacity of the primary and secondary windings is equal.

2) Rated voltage: refers to the guaranteed value of the terminal voltage of the electrical power transformer when it is no-load, expressed in units of volts (V) and kilovolts (kV). Unless otherwise specified, the rated voltage refers to the line voltage.

3)Rated current: refers to the line current calculated from the rated capacity and rated voltage, expressed in ampere (A).

4)No-load current: the percentage of the magnetizing current to the rated current when the electrical power transformer is running at no-load.

5) Short-circuit loss: The active power loss when one side of the winding is short-circuited and the other side of the winding is applied with voltage so that both sides of the winding reach the rated current, expressed in watts (W) or kilowatts (kW).

6) No-load loss: refers to the active power loss of the electrical power transformer when it is running at no-load, expressed in watts (W) or kilowatts (kW).

7) Short-circuit voltage: also known as impedance voltage, refers to the percentage of the voltage applied when one side of the winding is short-circuited and the other side of the winding reaches the rated current and the rated voltage.

8)Connection group: Indicates the connection method of the primary and secondary windings and the phase difference between the line voltages, expressed in clocks.


Learn more about nameplate: How To Read A Transformer Nameplate - Daelim Belefic?


Why should the iron core of the transformer be grounded?

When the electrical power transformer is in normal operation, the iron core must be grounded reliably at one point. If there is no grounding, the floating voltage of the iron core to the ground will cause intermittent breakdown discharge of the iron core to the ground. After the iron core is grounded at one point, the possibility of forming the floating potential of the iron core is eliminated. However, when the iron core is grounded at more than two points, the uneven potential between the iron cores will form a circulating current between the grounding points and cause a multi-point grounding heating fault of the iron core.


The ground fault of the iron core of the electrical power transformer will cause local overheating of the iron core. In severe cases, the local temperature rise of the iron core will increase, light gas operation, and even a trip due to heavy gas operation. The smelted partial iron core forms a short-circuit fault between the iron chips, which increases the iron loss and seriously affects the performance and normal operation of the electrical power transformer. Therefore, the transformer does not allow multi-point grounding, only one and only point grounding.


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Customize and sell electrical power transformer

Daelim Belefic is a top electrical power transformer brand in China. Has nearly 20 years of experience in overseas transformer design and export. A strong and professional team of transformer engineers can design and customize various types of electrical power transformers.


Advantages of Daelim Belefic:

1. Short production time for transformers: conventional transformers can be produced in 6-8 weeks;
2. The price of transformers is competitive: the factory is located in China, under the premise of ensuring quality, the equal cost of labor and raw materials will be lower;
3. Daelim Belefic has UL/cUL, CSA, CNAS, SGS, and other certification reports, there are many cases in the United States and Canada and other regions, and got qualification on selected transformer supplier list in USA markets;
4. It is an electrical power transformer supplier of well-known brands: cooperating with Eaton, Amazon, and other companies.
5. Electrical power transformer has a long warranty period: usually a 24-month warranty period, if you need a longer warranty period, Dalin can also meet it.
6. Daelim has overseas service centers: locate in Canada, the USA, Australia, and Ecuador.

Click here to check Daelim transformer projects

Daelim's fast delivery, competitive price, and high-quality transformers will be your most suitable supplier. No matter your power company, transformer distributor, or crypto mining can contact the Daelim team to provide you with the best electrical power transformer solution.

Get it now: How to choose a pad-mounted transformer for Crypto Mining?

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