Three-Phase Transformer: The Ultimate FAQ Guide

The Three-phase transformers are widely used to generate, transmit and distribute electrical power to industrial and commercial businesses, but are they practical?

When it comes to generating and transmitting electrical power to your business establishment, transformers can furnish sufficient energy to run your business efficiently. Nonetheless, there are many different types of three phase transformer that you can choose from nowadays. Thus, it is best to pick the most suitable transformer based on your needs.

If you are a business owner that owns a manufacturing business or other industrial or commercial establishments, the 3 phase transformer is for you! This transformer is more practical when it comes to supplying large loads and large power distribution.

Although most of the utilization pieces of equipment are connected by single-phase transformers, these are not ideal for large power distribution in the viewpoint of practicality. So, if you are looking for a high-quality transformer for your business, it is best to look for it through trusted transformer manufacturers like Daelim.

DAELIM is one of the most renowned transformers suppliers around the globe. The company is committed to render only the best services and high-quality transformers that meet the client’s expectations and needs. DAELIM also offers reasonable quotes to each of their clients based on their corresponding requirements.

In this article, you will have a better understanding of the functions of a three-phase transformer. This will also give you further information about the 3 phase transformer before making an actual purchase.

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Three-Phase Transformer: The Ultimate FAQ Guide

What is a three-phase transformer?

A three-phase transformer is the type of transformer that operates with a three-phase electrical system. This is a conventional method of alternating current electric energy generation, transmission, and distribution. It is also typically used to increase or decrease the voltage in a three-phase system.

This phase is a kind of polyphase system generally used by electrical grids worldwide to transport energy. It is also widely used to run large motors and other heavy loads. This transformer consists of six windings, consisting of three primary and three secondary windings.

The 3 phase transformer is a transformer that runs with a three-phase electrical system. Basically, this transformer is utilized to step up or step down the high voltages in different stages of the energy transmission system. This transformer has been invented since 3-phase electricity is widely used for power distribution due to its capability to provide a balanced load.

These types of three phase transformer are built by winding three single-phase transformers on a single core. After that, they are put into an enclosure filled with dielectric oil, which executes various functions.

Since dielectric is a nonconductor of electricity, it can render insulation between the voltage windings and the case. It also assists in cooling and preventing the formation of moisture that can dwindle the winding insulation.

The working three-phase transformer working principle is the same as the single-phase, Faraday’s Law of Induction. Single-phase and three-phase transformers only differed in wiring configurations. To further explain this, it is better to take a look at three-phase electrical systems.

Three-Winding Transformer | Three-Phase Transformer | Daelim

Three-Phase Electrical System

Both single-phase and three-phase electrical systems utilize alternating current or better known as AC. AC is an electricity type, which regularly alters direction and amplitude, typically portrayed by a sine wave.

AC signals are composed of three main properties; period, frequency and amplitude. Both period and frequency define the time component of the wave, whereas amplitude determines the strength and magnitude of the electricity.

In the three-phase systems, the current has three peaks and three troughs running on three separate conductors. Alternating currents are out of phase by 120° from each other. In these types of electrical systems, the highest amplitude is reached more frequently for a given period. This helps produce power at a relatively steady rate.

Connection Mode of Working Winding of Three-phase Transformer

What are the parts of three-phase transformer?

The structure of a three-phase transformer constitutes three central parts:

Steel Core

One of the central parts of a threephase transformer is the steel core. The three-phase transformer’s steel core consists of three magnetic pillars and a magnet that closes the magnetic circuit. Furthermore, the steel core of a machine is crafted from electrical steel sheets, covering two sides with an insulating paint and formed collectively into the shape of a cylinder.

What is the Difference Between 1 Phase 2 Phase and 3 Phase Power?

parts of three-phase transformer-steel core
parts of three-phase transformer-steel core

Transformer Enclosures

Another parts of the three phase transformer is the transformer enclosures. This plays a significant part in protecting and maintaining the life cycle of the transformer. The three-phase shell is typically made from steel, iron, contingent on the structure of the equipment and manufacturer.

Part of the use scenario is due to the high temperature and humidity environment, the three-phase transformer factory can also provide anti-corrosion coating steel shell.

Three Winding

Another parts of the three phase transformer is the machine winding. The machine winding consists of six copper windings which are insulated and wrapped around the cylinder. The winding receives the energy and transmits power out throughout machine operation.

What are the types of transformer windings ? What are the types of concentric windings?

Winding of 15 MVA transformer
Winding of 15 MVA transformer

Voltage Regulators

Voltage regulators are used to alter the output voltage. Throughout loaded conditions, the output voltage of the transformer may recede. Thus, there is a need to regulate the voltage ratio by adjusting the tapping turns. The adjustment is done by using a tap changer, depending on the frequency with which it is needed to change the output voltage.


Thermometers are utilized for controlling the oil temperature.

10kv distribution transformer design
10kv distribution transformer design


Breathers are utilized to extract moisture from the air space above the oil level of the conservatoire, sustaining the dryness of the transformer oil.


Insulations serve as a barrier system, separating the windings from the core and the two windings from each other.

Parts of the three phase Dry-type Transformers
Parts of the three phase Dry-type Transformers

Transformer oil

Transformer oil insulates and cools the generated heat from the core and windings. The oil has a high heat capacity that can carry and expel this heat. Oil flow can be produced either by the thermosiphon effect or by pumping.

4 Methods of Transformer Drying Treatment


The tank shields the cores and the windings from the outside conditions that can affect its functions. It also acts as a vessel for the oil.

Oil Conservator

An oil conservator is a separate container that holds the expansion of the oil as it can expand when heated.


When the oil absorbs the heat found in the system, it then delivers the heat to the cooling cooler. The cooler or cooling system accumulates hot oils and cools them down via air or water-cooled tubes then reverts them to the windings and core.

inside Three phase pad–mounted transformer
inside Three phase pad–mounted transformer

Gas Actuated Rela

The gas actuated relay collects free gas bubbles from the transformer tank. When you notice the presence of free gas, it shows a fault inside the transformer.

Pressure Relief Systems

These systems are safety devices used to reduce overpressure in oil flashing due to short circuits.


Which type of winding is used in 3 phase?

This type of three-phase transformer operates with six windings, three for the primary and another three for the secondary. Each winding can be linked in either star or delta configurations. These windings can be seen as separate single-phase windings.

Therefore, three single-phase transformers can be attached to build a three-phase transformer. There are three fundamental parts of a transformer and these are the following:

Primary Winding

The primary winding takes electrical power and generates magnetic flux when it is attached to an electrical source.

How many windings are there in distribution transformer?

Magnetic Core

This refers to the magnetic flux generated by the primary winding. The flux crosses through a low reluctance path connected with secondary winding forming a closed magnetic circuit.


Secondary Winding

The secondary winding supplies the desired output voltage due to shared induction in the transformer. The construction of a three-phase transformer is quite similar to the single-phase transformer. Its core is also constructed either in core type or shell type. The low voltage (LV) and high voltage (HV) windings of the 3-phases are put on the three limbs of the core.

Core Type

In the core type of 3 phase transformer, the core is split into three limbs. Each limb conducts both high voltage (HV) and low voltage (LV) windings of the three phases. Now, the generated flux made by the primary winding will then be linked to the secondary windings.

The low voltage winding (LV) is placed on top of the core limb and the high voltage winding(HV) is placed on the low voltage (LV) winding. This is because the amount of insulation needed is low to insulate the low voltage winding from the core.

The three-phase winding consists of three core limbs that are 120° apart from one another. In a core type, three-phase transformer, one limb functions as the return route for the magnetic flux of the two limbs. The total of fluxes in two limbs is equal to the flux in one limb that serves as the return track.

Shell Type

The construction of the shell type three-phase transformer is not typically used. This type of three-phase transformer has five limbs where the core encloses the windings built on the three limbs. The other two limbs found between phases keep the three limbs together, forming a unit.

This also provides a return route for the fluxes.

The construction of this type is comparable when three single-phase transformers are placed on each other’s side. In contrast to core type construction, each phase has its individualistic magnetic circuit and return way for flux. Therefore, the three phases are more independent in shell-type form.

What is the Three Phase Transformer Connections?

The three-phase transformer connections have two primary forms, the delta, and star. In order to understand these two better, see the given details below.

Delta Connection

In the Delta or mesh connection, three windings are attached on both ends, creating a closed loop. Both ends are connected to a terminal, having no neutral point and use ground connections instead.

This connection type can also be configured as a high leg system by grounding the focal point of one phase. The voltage in this configuration measured across the line opposite to the center-tapped phase and ground is higher than measured across terminals.

Transformer three-phase dual power supply automatic switching

Delta connection of 10 kV transformer
Delta connection of 10 kV transformer
Star Connection
Star Connection

Star Connection

In a Star connection (wye connection), there are three windings and four terminals. One end of the three windings is fastened to a regular neutral point or terminal, while the others form the three phases of the circuit.
The whole core structure, be it a core type or shell type, is placed inside the transformer tank saturated with oil with their windings. The three-phase winding connections are made inside the transformer tank. The primary and secondary terminals of the three phases are taken out of the tank by bushings for outside connections. The most generally used three-phase transformer winding connections are, Star-to-Star, Delta-to-Delta, Star-to-Delta, and Delta-to-Star.

Star-to-Star Connection

Star-to-star connection type works on both small currents and high voltages, making it cost-effective for transformers. In this type of connection, the primary and secondary terminals of three-phase windings are linked, forming the letter Y.

Star-to-Star Connection
Star-to-Star Connection

Delta-to-Delta Connection

In delta-to-delta connection, one end of a three-phase winding coil is attached to the end of another coil. When connected this way, you will notice that it will take the form of a delta, typically seen as a triangle. The delta-connected windings can produce large currents with low rates of voltages.

Star-to-Delta Connection

Star-to-delta connection is a type of winding connection used when you need to reduce the voltage levels. In this connection, the transformer’s neutral primary winding is earthed.

Connection of three-phase Power Load
Connection of three-phase Power Load

Delta-to-Star Connection

The delta-to-star connection is a combination of delta-connected winding on the primary side and star connection. The delta-star connection is utilized when there is a need to increase the voltage levels.

This connection type is most suited for distribution purposes because of its 3-phase and 4-wire system at the secondary side. However, its applications are restricted due to the existence of a phase shift between the primary and secondary winding.

A Complete Guide to Three-Phase Distribution Transformers

What is the Working Principle of Three-phase Transformer?

The basic three-phase transformer working principle is relative to a single-phase transformer like on mutual induction. The alternating supply is given to the primary windings and generates an EMF( electric magnetic field) in the secondary winding. The amount of generated electric-magnetic field will depend on the count of secondary turns, be it a step-up or step-down transformer.

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What are the Advantages of a Three-phase Transformer?

When it comes to transformers, a three-phase transformer has several advantages compared to the single-phase one, such as the following:

Weigh less

A three-phase transformer has lesser weight compared to the single-phase


A three-phase transformer costs less than three single-phase transformers, which are of equal ratings.

Don't take up a huge space

A three-phase transformer utilizes less space than the single-phase transformers as it is smaller than the single-phase transformers.

Easy to assemble and install

You will only have one unit (a 3-phase transformer ) to handle, and it is already pre-wired, making it much easier and smoother to assemble and insta

More economical to use

A three-phase transformer unit is more economical. Three-phase transformers are more practical for providing large loads and large power distribution. This is because the exchange in connection from single-phase to three-phase will not boost energy costs on your electricity bill. Thus, your electricity consumption will remain the same as they depend on the wattage of your machines, not on the electricity connection.

Smoother and more advantageous experience

When the number of phases increases in the system, the DC voltage becomes smoother and more beneficial.

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Requires less conducting materials

A three-phase power only needs lesser conducting materials compared to one-phase to transmit and distribute electrical power. Therefore, when it comes to the cost, this type of phase is more cost-effective.

It will only take less space to install.


  • Affordable compared with three units of single-phase transformers.
  • Transporting is easy and also costs less.
  • Easier to install as it is pre-wired and ready to install.
  • The core material needed is very little as opposed to three single-phase transformers in getting the same kVA.
  • Smaller in size and much lighter

What are the Drawbacks of a Three-phase Transformer?

Higher costs for standby units

In a three-phase transformer, a common core is distributed in all three units. So, when a unit is faulty or damaged, the whole three-phase transformer must be shut down entirely. This is why the cost of defective units is much higher and more difficult to get repaired.

High repair cost

The repair cost for 3-phase transformers is higher compared to the single ones because each component must be changed, which is costly. This is why in service recovery, the cost of the spare unit is more expensive than the single-phase transformers.

Reduced power capacity

Another downside of the 3-phase transformer is that it’s self-cooled. Therefore, the transformer’s power is also reduced at the same time.

Fault repair

Another drawback for this type of transformer is that once one of the three phases is faulty, the entire unit must be replaced. This is because the error can get transported to the other two phases.

One of the disadvantages of a three-phase transformer is the entire unit shuts down when one phase is at fault. This is due to the core that is shared for all three units. In other words, if one unit is broken, the core of the faulty unit would instantly drench due to the absence of an opposing magnetic field.

Without the opposing magnetic field, there will be an immense escape of magnetic flux to the metal’s core enclosures. This can increase the metallic parts’ heat that can cause fires in some cases. Thus, it is critical to remember to shut down the three-phase transformer if you find that one of the phases is faulty.

Other disadvantages of this transformer are the following

  • The repair for a three-phase transformer is much costly compared to a single-phase.
  • The spare unit of three-phase costs more compared to a single transformer spare unit.
  • Self-cooled.
  • This means that the capacity of the transformer is reduced.

What is the Meaning of Three-phase?

Three-phase power is the standard system of AC power generation, transmission, and distribution. It is a polyphase-type system commonly used by electric grids worldwide to transport electrical energy or power.

The three-phase has three alternating currents that are 120 electrical degrees apart from each other. Each leg of ac reaches a maximum voltage, solely separated by 1/3 time of a complete cycle. Simply put, the power output never drops to zero and remains constant. This is why most commercial and industrial businesses always opt for three-phase when it comes to transformers.

In the three-phase power supply, it’s best to remember that you will need three conductor wires and one neutral wire. The three conductor wires should be 120-degree apart from one another.

There are two classes of circuit configurations in a three-phase power supply. These are the Delta and the Star. The Delta configuration doesn’t require any neutral wire, and only the high voltage systems utilize it. On the other hand, the Star requires both ground wire and a neutral wire.


How do you Wire a 3 Phase Transformer?

In connecting transformers, you could be attaching them to single-phase and 3-phase power sources along with single and three-phase loads. Avoid making any wrong connections to prevent the equipment that may also result in damages.

Three-phase power, single voltage connection

In this phase and voltage, you have three conductors. Thus, you must connect all three conductors for three-phase voltage and connect any pair for a single-phase voltage.

Three-phase power, dual voltage connection (4-wire, 3-phase system)

Three-phase power and dual voltage connection involve three hot conductors and a grounded neutral conductor. In this connection, you have to connect the three hot conductors for 3-phase power. For lower, single-phase voltage, you can connect two or three hot conductors.

Wiring method of Dry-type Transformer

What is the Purpose of a Three-phase Transformer?

A three-phase transformer plays an essential role in transmitting power. This machine is primarily used worldwide for industrial purposes to generate electrical power, transmit and distribute. They are typically used and installed in places that consume a remarkably enormous amount of electricity, such as hospitals, apartments, industrial buildings, transformer stations and more.

3 phase transformers are used in many industries, including manufacturing, health care, electrical contracting and many more. These mentioned industries need a reliable and consistent source of power to keep their operations running smoothly, which can be found in three-phase transformers.

These transformers can carry large loads and large power distributions efficiently that are highly required by many large industries. Most power generating channels are in three-phase nature, and the voltages range from 13.2 kV to 22 kV.

To decrease the power loss to the distribution end, the power is transmitted at much higher voltages like 132 kV to 400 kV. So, if there’s a need for higher voltages, a three-phase step-up transformer is used.

On the other hand, at the end of transmission, a step-down three-phase transformer is used to step down these high voltages to levels 6600, 400, 230 volts, etc. This is why 3 phase-transformers are ideal when it comes to power distribution for large industries as they can balance the power perfectly.

These transformers are highly dependable in converting substantial amounts of energy from the primary source into a form they can utilize for various machines and building utilities.

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What is the Difference Between a Single and Three-phase Transformer?

The difference between a single and three-phase transformer is that a single-phase transformer only needs two wires, namely Phase and Neutral. The phase wire carries electricity from the source to any electrical appliance attached to it. Moreover, the neutral wire sends the circuit back to the original power source.

On the other hand, a three-phase transformer only works through three wires, inclusive of a neutral wire and three-conductor wires. This is created by winding three single-phase on one core. Transformers are placed in an enclosed place, jammed with dielectric oil to reach the specified voltage.

It’s best to remember that 3-phase transformers have six coils, distributed impartially on both the primary and secondary sides.


Single Phase and Three Phase Pad-mounted Transformer From Daelim
Single Phase and Three Phase Pad-mounted Transformer From Daelim

What is the Difference Between a Single-phase System and a Three-phase System?

When it comes to the power supply systems, it has two classifications, namely single phase-system and three-phase system. The single-phase is typically used in a place where there’s less power needed and working for small loads. On the other hand, three phases are widely used in large businesses, such as factories and other industrial enterprises, where immense power is needed.

Another significant difference between the two is that the single-phase has one neutral wire and one conductor compared to the three-phase having one neutral wire and three conductors for circuit completion. A single-phase carries 230V, while a three-phase carry 415V. The single-phase is also less efficient and economical compared to the three-phase.

Electrical Power Transformer for Agricultural

The single-phase is best used for home appliances, while the three-phase is ideal for large industries and running heavy loads. To know more about the difference between the two, see them all below.

  • The single-phase supply necessitates more maintenance and becomes more expensive compared to the three-phase.
  • In the single-phase system, it only has one phase wire, and if the fault transpires on the network, then the power supply entirely fails. However, in the three-phase system, the network has three phases and if an error happens on any one of the phases, the other two will continuously provide power, making it more reliable.
  • The three phases can transfer maximum power compared to the other one.
  • When it comes to efficiency, the three-phase wins this area as it requires less conductor in comparison to the single-phase for the same circuit.

Does Three-phase Transformer Help me save more?

There are several manufacturers of three-phase transformers like Daelim that guarantee energy savings for extensive electricity distribution. In terms of power supply, the three-phase power is more efficient, as it can transmit trifold the power of a single power supply.

Where are the Three-phase Transformers Used?

Three-phase transformers are typically used for generating and distributing power. You can find these transformers in high-power industrial loads like motor drives, rectifiers among other equipment. It can also be used in applications that need a step up or step down of transmission lines and electrical grid station power generation.

What are the Three Types of 3-Phase Transformers?

There are three types of 3-phase transformers, the sealed-type, the open-type and the dry-type.

Sealed-Type Transformer

The sealed type of three-phase transformer cools itself through its expansion blades. The blades will automatically expand when the temperature gets high in the VH, and the air blows directly through the blades that cool the machine down.

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220KV Class Three Phase Two Winding NLTC Power Transformer
220KV Class Three Phase Two Winding NLTC Power Transformer
power transformer solutions for oilfields
power transformer solutions for oilfields

Open-Type Transformer

In this type of three-phase transformer, its cooling cycle is through the extra tank and the fan blade. The only discrepancy between the open-type and sealed-type is the auxiliary oil tank.

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Dry-Type Transformer

A dry-type transformer is a type of transformer with coils wrapped in epoxy resin. Contrary to the standard transformer, its magnetic cores and windings are pressurized by air. This type of transformer can overcome the drawbacks of oil transformers. This transformer is used in particular circumstances such as dense pollution, higher air humidity, extra cold surroundings temperature.

Three Phase Epoxy-resin Dry Type Distribution Transformer Manufacturer – Daelim

Why Choose Daelim?

Daelim has been dealing with designing, engineering and manufacturing high-quality transformers for more than 15 years. Our company consists of experts and ad professionals in this field. Our team has brilliant researchers and a production team that help form and deliver exceptional and efficient transformers to various businesses and homes.

Our team undergoes intensive and methodical training committed to continuous advancement on the quality guidelines and systems. It is also our mission to meet the expectations and needs of our valued customers to earn their trust and fulfill their needs. This way, we can forge a strong and long-term partnership with our clients.

BEIJING DAELIM GREEN EP TECHNOLOGY CO., LTD. is built by the experience and expertise of the people working passionately for the company. Each staff works incessantly with the thought of giving the best possible products to each of our customers. It’s in our best interest to innovate a product like a three-phase transformer to put our clients at an advantage in running their business without any interruptions when it comes to power.

We also offer product customization based on your company’s needs and demands. With us, you can expect high-level products and quick execution abilities without sacrificing the quality of the products. We also ensure that each of our clients feels special with our top-notch customer service. So, if you’re looking for transformers for your home or business, our company is always open for you.

We always stand by our company’s mission, which is to meet our customer’s needs. This is why if you choose us for your transformer’s needs, you will never go wrong with Daelim!

What is the purpose of a three phase transformer in power distribution?

The three phase transformer is a cornerstone in modern power distribution, bringing efficiency and reliability to electrical systems. Its primary purpose? To step-up or step-down the voltage levels as required, ensuring consistent power delivery.

Essential Role in Power Transmission

Three phase transformers play a vital role in transferring power from generation plants to the end-users. Their design enables them to handle vast amounts of power, making them indispensable in industrial settings.

Stepping Up and Down Voltage

By transforming the voltage levels, these transformers ensure the power transmitted over long distances retains its integrity. This feature safeguards equipment and systems from potential damage due to voltage fluctuations.

Efficiency and Reliability

One of the standout features of the three phase transformer is its efficiency. By distributing power in three simultaneous phases, it optimizes energy use and minimizes power losses.

Connection Configurations

The three phase transformer comes in different configurations, such as star-star, delta-delta, star-delta, and delta-star. Each configuration has its own set of advantages, ensuring flexibility in various applications.

Benefits over Single Phase Transformers

While single-phase transformers are suitable for smaller applications, the three phase variants are better equipped for large-scale operations. They provide a balanced load, which is vital for heavy-duty machinery and large commercial buildings.

Safety Measures

Safety is paramount when dealing with electrical equipment. The three phase transformer boasts built-in safety features that help in protecting both the equipment and the people working around it.

Longevity and Durability

Built with precision and designed to last, these transformers are a testament to Daelim's commitment to quality. Their longevity ensures that industries can function smoothly for years without frequent replacements or downtime.

Integration with Renewable Power Plants

As the world moves towards greener solutions, three phase transformers find their application in renewable power plants. They aid in the efficient transmission of power generated from solar or wind sources.

Compliance with International Standards

Adhering to standards like ANSI, IEC, and IEEE, three phase transformers align with global best practices. This adherence ensures reliability and quality, no matter where they are installed.

Customization Options

Given the varied requirements across industries, Daelim offers customized transformer solutions. These bespoke options ensure that every industry's specific needs are met with precision.

How do the prices of three phase transformers vary based on their specifications?

When it comes to the three phase transformer price, several factors come into play, influencing the final cost. It's essential to understand these determinants to make informed purchasing decisions.

Size and Capacity

Larger transformers designed for heavy-duty operations usually come at a higher price point. The power rating, often measured in kVA (kilo-volt-amperes), directly impacts the cost.

Material Used

High-quality materials ensure better performance and longevity. Transformers crafted with superior materials might be more expensive, but they guarantee a longer operational life.


As industries come with specific needs, customization might be necessary. Custom features or specifications can lead to a change in pricing. Daelim's expertise in providing tailored solutions ensures that the cost remains competitive even with customization.

Manufacturing Standards

Transformers produced according to international standards like ANSI, IEC, and IEEE often come with a premium. Compliance with these standards guarantees quality and safety.

Type of Cooling

Three phase transformers use various cooling methods, such as oil-filled or air-cooled. The choice of cooling method can influence the price, with oil-filled variants generally being more expensive due to their enhanced cooling efficiency.

Ancillary Equipment

Transformers might come with additional equipment, such as tap changers, protective relays, or circuit breakers. The inclusion of this equipment can increase the price.

Brand Reputation

Reputed brands like Daelim, with a track record of delivering quality products, might price their transformers slightly higher. This price often reflects the trust and reliability associated with the brand.

Geographic Location

The location where the transformer is purchased and installed can also impact the cost. Factors like transportation, import duties, and local taxes play a role.

Installation Costs

Beyond the transformer's price, installation costs, especially for larger units, can be significant. It's essential to factor in these costs when budgeting.

Warranty and After-sales Service

A robust after-sales service and warranty can influence the transformer's price. Brands that offer comprehensive warranties and global support might have a slightly higher price point, reflecting the value they provide post-purchase.

In conclusion, while the three phase transformer price is an essential factor, it's vital to consider the overall value offered. Quality, reliability, and post-sales support are just as crucial as the initial investment.

Can you explain the basic wiring diagram of a three phase transformer?

Understanding the wiring of a three phase transformer is essential for its efficient operation and safety. Let's delve into its fundamental wiring diagram and the components involved.

Primary and Secondary Windings

Three phase transformers consist of three sets of primary and secondary windings. These windings can be configured in various ways, such as star (Y) or delta (Δ), depending on the application.

Star (Y) Configuration

In a star configuration, one end of each winding is connected to a common point, called the neutral. The other ends are connected to the respective phases. This configuration is common in systems where a neutral is necessary for connecting single-phase loads.

Delta (Δ) Configuration

In a delta setup, the windings are connected end-to-end, forming a closed loop. There's no neutral point in this configuration, making it common for transmission systems.

Input and Output Connections

Three phase transformers can step-up or step-down voltages. The input side (primary winding) receives the incoming voltage, and the output side (secondary winding) delivers the transformed voltage.


For safety reasons, the transformer's neutral in the star configuration is often grounded. Grounding helps protect the system from voltage surges and provides a path for fault currents.

Tap Changer

Some three phase transformers come equipped with a tap changer. This device allows for adjusting the output voltage level without shutting down the transformer.

Cooling System

Depending on whether it's an oil-filled or air-cooled transformer, there will be associated components like radiators or fans depicted in the wiring diagram.

Protective Devices

Wiring diagrams also display protective devices like circuit breakers and relays. These components safeguard the transformer against overloads and faults.

Additional Notes

  • Always refer to the manufacturer's specific wiring diagram when working on a transformer.
  • Ensure the system is powered off before working on any electrical connections.
  • Regularly inspect the wiring for signs of wear or damage.

It's crucial to remember that while the above provides a general overview, the exact wiring can vary based on the transformer's design and purpose.

How does a three phase transformer function and what's its working principle?

Delving into the workings of a three phase transformer, one can marvel at its ingenuity and efficiency. At its core, the transformer operates on the principle of electromagnetic induction.

Electromagnetic Induction

When an alternating current (AC) flows through the primary winding, it creates a magnetic field. This magnetic field, in turn, induces a voltage in the secondary winding.

Role of the Core

The transformer's core, usually made of iron or ferrite, plays a pivotal role. It provides a path for the magnetic flux, enhancing the efficiency of energy transfer between the windings.

Voltage Transformation

The ratio of turns in the primary and secondary windings determines whether the transformer steps up or steps down the voltage. For example, if the primary winding has fewer turns than the secondary, the transformer will step-up the voltage and vice-versa.

Balanced Power Distribution

Three phase transformers distribute power in three simultaneous phases. This design ensures a balanced load, optimizing energy consumption and minimizing losses.


By operating in three phases, these transformers can transmit higher amounts of power with less wire, saving on infrastructure costs and reducing power losses.

Safety Measures

Built-in safety mechanisms, such as circuit breakers and protective relays, ensure that the transformer remains protected against overloads, short circuits, or any other electrical faults.

Integration with Modern Systems

Given the digital age we're in, modern three-phase transformers often integrate with monitoring systems and smart grids. These integrations allow for real-time tracking of transformer health, performance, and efficiency.

Customization for Various Applications

Three phase transformers are versatile and can be customized based on the application. For industries with specific needs, transformers are tailored to meet precise voltage requirements, ensuring optimal performance. Daelim, with its vast experience, excels in crafting these bespoke solutions.

Energy Savings

Due to their efficient design, three phase transformers minimize energy losses. This efficiency translates to significant energy savings, especially in large-scale industrial operations and power distribution networks.

Environmental Considerations

Modern transformers are also designed with the environment in mind. Whether it's using biodegradable cooling oils or ensuring minimal electromagnetic emissions, environmental sustainability is a key consideration.

In essence, the working principle of a three phase transformer is rooted in the fundamentals of electromagnetic induction. However, the versatility, efficiency, and integration with modern technologies make it an indispensable asset in contemporary power systems. Always ensuring safety and reliability, these transformers play a pivotal role in driving industries and energizing cities.

What are the main types of three-phase transformers available?

Three-phase transformers, pivotal in power distribution and industrial applications, come in various types tailored to specific needs. Let's explore the primary kinds available in the market.

Core Type Transformers

These transformers have their windings encircle the core. They are generally used for lower voltage applications and can be further classified into:

  • Shell Type: The windings surround the core, which provides better insulation and protection.
  • Tube or Column Type: The core surrounds the windings, offering a compact design suitable for certain applications.

Shell Type Transformers

In these, windings are sandwiched between layers of the core. This design offers better magnetic coupling and protection against short circuits.

Power Transformers

Ideal for power transmission, these transformers handle high voltages, typically above 33 kV. They are crucial for electrical grids, stepping up or down voltages for efficient power transfer.

Distribution Transformers

These serve residential and commercial areas, converting high grid voltages to the standard levels suitable for homes and businesses. Their capacity usually ranges between 50 and 2500 kVA.

Rectifier Transformers

Specially designed for industrial processes and electrochemical applications, these transformers convert alternating current (AC) to direct current (DC).


Unlike conventional transformers, autotransformers have a single winding that serves as both the primary and secondary. They are compact and cost-effective but offer less electrical isolation.

Zig-Zag Transformers

Used primarily for grounding purposes, these transformers provide a neutral point in systems that don't inherently have one.

Cast Resin Transformers

The windings in these transformers are encased in epoxy resin, offering excellent insulation. They are flame-retardant, reducing fire risks, and are often used in sensitive areas like hospitals or schools.

For anyone seeking transformers tailored to specific needs, companies like Daelim provide professional solutions, ensuring the best match for diverse applications.

Where can I find a detailed three phase transformers diagram?

Finding a detailed diagram for three-phase transformers is instrumental for understanding their design and workings. Here's where you can get them:

Manufacturer's Manual

The most reliable source would be the manual provided by the transformer manufacturer. Brands like Daelim include comprehensive diagrams, detailing every component and connection, tailored to the specific model you've purchased.

Online Forums and Communities

Platforms like IEEE forums or electrical engineering websites often host discussions where professionals share diagrams and insights. These can be great resources for students or technicians.

Technical Books

Electrical engineering textbooks or specialized transformer manuals dive deep into the topic, often including detailed diagrams and explanations. Libraries or online bookstores are excellent places to seek these out.

Manufacturer's Website

Companies often provide digital versions of their manuals or dedicated sections on their websites with technical resources, including diagrams.

Educational Platforms

Online learning platforms like Coursera, Udemy, or Khan Academy might offer courses on electrical engineering. These courses often come with resource materials, including detailed diagrams.

Consultation with Experts

If you're working in an industrial setting, consulting with experienced electrical engineers or technicians could provide you with the exact diagram you need. They might have accumulated a range of resources over their careers and could share diagrams or direct you to reliable sources.

Industry Workshops and Seminars

Attending industry-specific workshops or seminars can be an enriching experience. Not only do you get to learn from experts, but these events often distribute resource materials, which might include the detailed diagrams you're seeking.

Engineering Universities and Colleges

Academic institutions with engineering faculties often maintain a repository of technical resources for their students. You might be able to access their libraries or digital platforms to find detailed transformer diagrams.

Dedicated Electrical Apps

There are mobile and desktop applications dedicated to electrical engineering and design. Apps like "Electrical Technology" or "Electrical Calculations" might feature diagrams or direct you to resources where you can find them.

YouTube Channels

Many electrical engineering enthusiasts and professionals share their knowledge on YouTube. Channels dedicated to electrical engineering might have video breakdowns of three-phase transformers, accompanied by detailed diagrams.

Daelim's Support Channels

Being a leading transformer manufacturer, Daelim offers unparalleled support to its customers. If you've purchased or are considering a Daelim transformer, their customer support or technical team can provide detailed diagrams specific to their product range.

In conclusion, while the search for a detailed three-phase transformer diagram might seem daunting, numerous resources are available. From manufacturers like Daelim to online communities and educational platforms, the right diagram is just a few clicks or a phone call away. Always remember to use these diagrams responsibly, ensuring safety and adherence to guidelines when working with electrical equipment.

Are there specific places to look for three phase transformers for sale?

For those in the market for three-phase transformers, identifying the right sales points is crucial. Here's a guide to finding these essential power devices:

Manufacturer Direct Sales

Daelim Transformer and other top manufacturers often have direct sales channels. Buying directly ensures you receive genuine, high-quality products.

Local Electrical Distributors

Local dealers often stock transformers catering to regional demands. They can guide on specifications suited to local grid conditions and industry requirements.

Online Marketplaces

Platforms like Alibaba, Amazon, and eBay host multiple sellers offering three-phase transformers. Always check seller reviews and product specifications.

Trade Shows & Exhibitions

Electrical and industrial trade fairs are excellent places to explore. Not only can you find products for sale, but also gain insights into the latest transformer technologies.

Auctions & Liquidation Sales

For budget-conscious buyers, auctions or liquidation sales from industries upgrading their infrastructure might offer great deals.

Industry-Specific Suppliers

Certain industries have dedicated suppliers for their equipment. For instance, renewable energy sectors might have suppliers specializing in transformers optimized for such applications.

Refurbished Equipment Dealers

Some dealers specialize in refurbished or reconditioned transformers. They offer tested and certified products, ensuring reliability at a reduced cost.

Classified Advertisements

Platforms like Craigslist or local newspapers might have listings of used transformers for sale by industries or individuals.

Remember, wherever you choose to buy, always ensure the transformer meets the necessary safety and operational standards. Having a professional on board for consultation is a prudent choice.

In which industries or applications is a three-phase transformer primarily used?

Three-phase transformers, with their efficiency and power-handling capabilities, are the backbone of many industries. Let's delve into where they're most commonly applied:

Power Distribution & Transmission

These transformers step up or down voltages, facilitating efficient power transfer over long distances across electrical grids.

Industrial Manufacturing

From automobile production to textile factories, three-phase transformers provide the necessary power for heavy machinery and equipment.

Data Centers & Encryption Mines

Powering servers and ensuring uninterrupted operations, these transformers are pivotal in data centers and cryptocurrency mining setups.

Oil & Gas Plants

In refineries and processing plants, transformers ensure the smooth operation of pumps, compressors, and other critical equipment.

Renewable Energy Plants

Whether it's solar farms, wind turbines, or hydroelectric dams, transformers play a crucial role in channeling generated power.

Commercial Buildings

Shopping malls, office complexes, and large residential buildings often require three-phase transformers for their expansive electrical needs.

Railway & Metro Systems

Electric trains and metro systems rely on transformers for their power requirements, ensuring safe and efficient transportation.

Healthcare Facilities

Hospitals, with their critical equipment like MRI machines and surgical tools, depend on reliable power from transformers.

Marine & Offshore Platforms

For ships and offshore drilling rigs, transformers ensure power distribution in these isolated environments.

Water Treatment Plants

Transformers power pumps and filtration systems, ensuring clean water supply in treatment plants.

In essence, any industry requiring steady, large-scale power distribution turns to three-phase transformers. Their reliability and efficiency make them indispensable across various sectors.

What is the difference between a 3-phase shell type transformer and other three-phase transformers?

Three-phase transformers come in different configurations, each with its unique design and function. The 3-phase shell type transformer is one such design. Let's delve into its distinctions:

Design & Construction

3-phase shell type transformer: This design encapsulates the three magnetic circuits within a common core. The windings surround the core, ensuring the magnetic flux remains confined.

Other three-phase transformers: In core-type designs, each phase has its own magnetic circuit, distinct from the shell type's unified core.

Magnetic Flux Distribution

In shell type transformers, the magnetic flux distribution is more uniform. This results in reduced noise levels and better efficiency.

Cooling Efficiency

Shell type transformers generally exhibit better cooling properties due to the larger surface area exposed to the cooling medium.

Mechanical Strength

The shell design offers superior mechanical strength, making it more resistant to short circuits and external mechanical forces.

Space Requirement

Shell type transformers, due to their compact design, usually require less space compared to their core-type counterparts.


The complex construction of shell type transformers might lead to slightly higher costs compared to simpler core-type designs.

In essence, while both designs serve the primary function of voltage transformation, the choice between them hinges on specific application needs, space considerations, and budget.

How does a three-phase transformer differ from a single-phase transformer?

Transformers are pivotal in electrical systems. The distinction between three-phase and single-phase transformers is rooted in their design, application, and operational principles.

Number of Phases

The most fundamental difference: three-phase transformers handle three alternating currents, while single-phase transformers deal with just one.

Design & Complexity

Three-phase transformer: Typically more complex, handling three simultaneous AC cycles. This requires a more intricate winding and core design.

Single-phase transformer: Simpler in construction, with windings for only one AC cycle.

Power Distribution

Three-phase transformers are primarily used for large-scale power distribution and industrial applications due to their efficiency.

Efficiency & Load

Three-phase transformers can handle heavier loads and are generally more efficient as they distribute power in three alternating cycles.

Size & Weight

For the same power rating, three-phase transformers are often smaller and lighter than single-phase transformers.


Three-phase transformers: Widely used in industries, power distribution networks, and large commercial setups.

Single-phase transformers: Common in residential areas, small businesses, and locations with lesser power requirements.


Three-phase systems, due to their efficiency and load-handling capabilities, might have a higher upfront cost compared to single-phase systems.

In summary, while both transformers serve the purpose of altering voltage levels, their applications, design, and efficiencies set them apart. The choice between them depends on the specific power requirements of a project or facility.


Three-phase transformers have similarities with other transformers. They both have advantages and disadvantages. Nonetheless, when it comes to practicality in terms of industrial and commercial use, the 3 phase transformer is much more efficient.

If you are currently looking for a reliable transformer for your establishment, it is time to contact DAELIM professionals. This way, you can get the answers to your questions and concerns right away.

About Bin Dong

Hello, I am Bin, General manager of Daelim which is a leading transformer manufacturer. As a expert, I am glad to share my experience in transformer to you. I believe our professional team can always provide you with high quality service and we are ready to provide you with one stop solution. If you have problems when you are looking for the equipment, what you need to do is tell us.

Custom Three Phase Transformer

When you need to find more than just existing transformers, Daelim’s Transformer Service Center can help you design and produce distribution transformers that meet your unique needs.

We have our own factory and a professional team of engineers, which can design and modify application requirements that meet all your conditions.

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