A Complete Guide to Single Phase Distribution Transformer

A Single phase distribution transformer is used to change the voltage of single-phase AC power. Also, the input and output circuits in a transformer must be connected together as they use electromagnetic induction when transferring energy from one circuit to another.

Now, single-phase distribution transformers are necessary components in ensuring an efficient electric distribution. They are the end gateway that allows consumers to use the electricity for different industries. As you read on, you’ll discover every facet of single-phase distribution transformers.

Daelim is a company specialized in designing, engineering, and manufacturing top-tier electrical products and solutions. With over 15 of excellent reputation, our company is versed with different facets of the electrical industry. The brand works with competent experts and professionals that handle the operation, production, and installation of products.

Single Phase Overhead Conventional Transformer
Single Phase Completely Self Protected Transformer
Single Phase Pad Mounted Distribution Transformer

Single Phase Distribution Transformer: The Ultimate FAQ Guide

What’s a single phase transformer?

This is an electrical device that receives single-phase AC power as well as outputs single-phase AC. A single-phase transformer is utilized as a step-down transformer to reduce the home voltage to an acceptable value without frequency change. It consists of a magnetic iron core, functioning as a magnetic component, and a copper winding, which serves as an electrical part.

A single-phase transformer is a kind of power transformer that uses a single-phase alternating current. It indicates that the transformer banks on a voltage cycle that works in a phase of a unified process. They are usually utilized to decelerate long distances along with localized transmission currents within power levels. These are more appropriate for residential as well as light-commercial applications.

How does a single-phase transformer work?

A single-phase transformer works according to Faraday’s principle of electromagnetic induction. Fundamentally, the mutual induction of two or more windings enables an electrical transformer to create transformation action. Based on Faraday’s law, the extent flux change of connection when it comes to time is correspondent to the established EMF in a coil. 

Once the primary winding has been linked to a single-phase supply, an AC will begin passing through it. The primary AC current then generates an alternating flux in the core, joining the secondary winding. The varying flux will start triggering electricity into the secondary winding. 

Both the primary winding and secondary winding is generally made up of insulated copper wire. Iron core needs to be separated, because of its substantial receptiveness. Industrial regulations and utility firms regulate the maximum voltage that applies to a single-phase transformer. 

How to connect a single-phase transformer?

A single-phase transformer can connect into either series or parallel arrangements. A good example is the distribution transformer. It is generally coiled with secondary or windings with a low voltage that can be connected in parallel or series. The obtainability of primary voltages, including the fundamentals of the load, decides how a single-phase transformer gets wired. 

Essentially, transformers are considered AC devices with no fixed polarity, contrary to a DC source. However, they have comparative polarity markings that should be observed when joining them together in various arrangements. 

Normally, single-phase transformer leads are built from the transformer’s steel casing straight from insulating bushings. All kinds of transformers have H and X terminals. H terminals usually have high voltage while X terminals have low voltage.   

What Are Single Phase Distribution Transformers?

Single Phase Distribution Transformers are commonly used on residential and commercial circuits. It is the most common type of AC electrical power that provides energy to buildings, industries, and other facilities. 


Again, single-phase systems aren’t as efficient or powerful as 3-phase systems. Still, it is easier to require only a transformer and a service panel with a disconnect switch. 


In the same way, single-phase distributors have excellent high current capabilities, making them ideal for lighting loads such as chandeliers and fluorescent light bulbs. Manufacturers specify the input capacity of these in kVA (kilovolt amp) or MVA (Mega Volt-Amp).transformers

Single Phase Pad Mounted Distribution Transformer (3)

How Does A Single Phase Distribution Transformer Work?

Electromagnetic induction handles the power of a transformer. This transformation uses mutual induction between primary and secondary windings to create energy from an alternating current source. The Single Phase Transformer has many advantages over 3-phase transformers:


  • Single-phase systems have fewer wires than 3-phase systems because there are only 2 phases instead of three. 
  • Single-phase wiring can be installed with fewer support structures that are easier to install in new construction or retrofitting. 
  • Single-phase systems are also much easier to troubleshoot than 3-phase systems. But, a correct design is necessary for this advantage.
  • Single Phase Transformers – Static Control – Single Phase transformers have several applications, including surge.

Standard Features And Capabilities Of A Single Phase Distribution Transformers

A variety of transformer designs exist, which makes them ideal in different applications. You must get an idea as soon as possible about what your requirements will be. Doing so will enable you to find one suitable enough without wasting time or money. Here are a few of the features to check in selecting your single-phase distribution transformers:


In a transformer, the ratio between primary and secondary coils determines voltage increase or decrease after routing through it. Some transformers have an adjustable turn ratio while others maintain 1:1 (or near-to) to isolate circuits simply. Other transformers use a single coil with power being transmitted by tapping at an intermediate point on that coil.

What’s more, transformers use single windings to increase voltage, and dual-winding transformers can decrease or raise the voltage. Multiple winding configurations come in two variations. A 2+2 decreases output current but increases potential power. While 4+4 and 8+8 outputs maintain a 1% ratio of input secondary voltages with increased output currents.


There are plenty of cooling methods employed to ensure a transformer’s efficiency. Below are the popular methods dated in manufacturing.

Oil-Cooled Systems

Oil-filled transformers that power your homes and businesses rely on a strong dielectric liquid to keep the transformer from overheating. Mineral oils, synthetic esters, or silicone fluids have replaced PCBs in applications over the last few decades.

Because they are better suited for this task than traditional petroleum distillates. It depends on their application; these materials may use radiators, filters, fans pumps, and heat exchangers.

PCB- Filled Designs

The coolant fluid of PCB-filled transformers expires after a certain period, so other cooling methods replace the aging equipment. In addition, the chemical has been identified as carcinogenic for more than 50 years, and many are no longer used today. Yet, some users may seek out less regulated markets where regulations are not enforced or followed.

Water Supplemented Designs

Transformers that use water to cool components are submerged in oil. Afterward, cooling water runs through copper pipes below the surface of the oil, improving circulation and heat exchange. Another method is to pump heated oil out of the transformer with tubes doused with cold-water sprinklers sprinkled on them for additional cooling power.

Dry or Air-Cooled Systems

The principle of convection cools the windings of an air-cooled transformer. Ventilated enclosures and blowers or fans supplement some of these designs. However, unlike other transformers, this one does not have a core that can regulate its temperature.

Encapsulated Designs

Encapsulated transformers are a great solution for tight spaces. They use an extra special dielectric that seals out contaminants.


The magnetic core in transformers increases the magnetic flux. It also concentrates it to connect both coils, which makes a more efficient process. Below are the typical core type available in the market:


Transformers use induction, and manufacturers make them from various materials, such as steel or plastic laminated sheets. The material used will affect how much magnetic flux enters the core during operation. To add to it, this can then cause current leakage due to eddy currents if not properly designed with alternating layers. Thus, this design minimizes magnetizing current.


Manufacturers construct this core with a hinge and lock to make it easy for installers and engineers. The cores can be installed on the conductor in situ, making them more efficient at monitoring currents.


This design helps to reduce the chance of electromagnetic interference by minimizing leakage flux from a transformer.


You should choose a transformer installation based on size and weight. Some smaller transformers can weigh as little as 50 pounds. However, they may not provide enough power for larger homes or apartments. Thus, a bigger one will be ideal instead.

Single Phase Pad Mounted Distribution Transformer (7)

How many tests were performed for testing a single phase transformer?

A single-phase transformer undergoes two important tests to ensure it will work properly to avoid disruption on the entire distribution system. These are the open-circuit test and the close circuit test. The test aims to ensure the proper distribution of electrical energy is made. The tests also determine the transformer’s equivalent circuit, voltage regulations, and efficiency. 

Open-Circuit Test

The open-circuit test’s main goal is to convey a considerable massive no load current for suitable reading. The value of the power factor in a single-phase transformer is insufficient. As a result, the wattmeter used must be able to display precise readings on simple power factors while conducting the open-circuit test on a single-phase transformer.

Moreover, it necessitates only a low voltage supply that is readily accessible and secure to conduct the test. It’s important not to touch the high voltage winding while doing the open-circuit test. Touching it may result in a severe electric shock. 

Short or Closed-Circuit Test

The short circuit or closed-circuit test determines copper losses in a single-phase Distribution Transformer at full load. Likewise, it is used to acquire the range to maximize the transformer’s corresponding circuit. It indicates impedance, equivalent resistance, and leakage reactance.

The test on the single-phase transformer is conducted on the secondary or high voltage winding. The wattmeter, ammeter, and voltmeter are measuring instruments joined to the high voltage winding of the transformer. The primary winding is short-circuited using a thick strip or ammeter connected to its terminal. 

The low voltage source is connected throughout the transformer’s secondary winding. It’s because the full load current surges from the single-phase transformer’s primary and secondary winding. The connected ammeter measures the full load current.

The power necessary for both open and short-circuit tests on a single-phase transformer is equivalent to the power loss resulting in the transformer. If the single-phase transformer doesn’t work correspondingly, the whole distribution system might get damaged and no electrical energy will be transferred. The electrical circuit may also get busted because of electrical damage, winding deformity, thermal change, and mechanical failures.

Other types of tests include:

Routine Tests

This test verifies and confirms the transformer’s functional performance and is conducted in a production lot. It doesn’t include all tests but not the vacuum and temperature rise tests

Type Tests

Type tests verify if the transformer is developed according to the customer’s expectations as well as design specifications. It includes testing the measurement of the transformer’s different specifications. 

Special Tests

This test helps provide applicable information to the user and is performed during the operation and maintenance of the electrical device. It includes dielectric tests and measuring harmonics of the no-load current.

Pre-Commissioning Tests

Pre-commissioning tests are conducted prior to the order or clearance of the transformers at the site. It checks the installation process and analyzes the results.

Periodic/Condition Monitoring Tests

This test enhances the performance and checks the transformer’s condition periodically if it satisfies customer requirements. Moreover, it helps determine the defects during the early stages through monitoring the transformer’s periodical performance.

Emergency Tests

Emergency tests are generally made at the site to check any issues or damages on the transformer during the operation. For instance, high-temperature measurement even if the ventilators are working efficiently. This also involves windings resistance measurement and oil analysis used in cooling the transformer. 

What Are The Applications Of A Single Phase Distribution Transformer?

For Single Phase Distribution Transformer, linear and bushing types operate on the same principle but have different designs.

Single-phase Distribution Transformer can convert voltage from a utility source for distribution or transmission systems. They provide an efficient way of transforming voltage levels while minimizing losses in the form of heat. 

More so, power line systems also use single-phase transformers designed for 3/0 KV voltage service. These large utility-sized single-phase transformers are usually mounted directly beneath the lines due to their high conductor weight. This type may utilize smaller capacity models ranging from 1 kVA through several megawatts depending on load requirements.

What Are The Types Of Transformers?

The professionals categorized transformers on their conversion function. There are two distinct types of transformers which are the following:

Step-Up Transformer

When the secondary voltage is stepped up, it creates a larger output than that of the primary. You can do this by increasing the coils in each group to provide an increased magnitude for power transmission. Likewise, a step-up transformer is a connection device from generators and grids to increase the ratio between input and output voltages.

Step-Down Transformer

Power suppliers use single-phase transformers to step down voltage levels of single-phase AC electrical energy. They use a standard power connector configuration.

Why Do You Need Transformers?

Transformers are essential in power systems to raise and lower voltage levels as needed. This helps improve the safety of a system, which is important for businesses that use large amounts of electricity daily or even those who simply fear outages due to storms. Also, they are important for residential and industrial applications in utilizing electricity. 

Transformers are primarily and significant in distributing and regulating power across long distances. More so, reduce or increase voltages that may be too powerful for use, preventing damage to household appliances.

Single-phase distribution transformers also allow greater electrical flexibility among users who can utilize varying voltages with single-phase devices.

How to wire a single phase transformer?

A single-phase transformer is considered a step-down transformer wherein the primary voltage is greater than its secondary voltage. It’s intended to decrease the voltage from the primary winding to the secondary wiring. 

Below are the steps on how to wire a single phase transformer:

Step 1. Know the single-phase transformer’s schematic and rating to be fixed. Pull out the terminal connection box cover if the transformer has high amperage. Additionally, remove the circuit’s electrical power and make sure that both sides of its protection are switched off.

Step 2. Identify which termination the single-phase transformer goes with. Terminations involve H1, H2, H3, and H4, indicating the high voltage side. At the same time, X1, X2, X3, and X4 signifies the transformer’s low voltage side. Even if the interconnection of the transformer differs according to the manufacturer and input voltage, the termination stays precise despite the transformer’s size. 

Step 3. Connect the input wires and cut them based on the lug. It is also dependent on the amount of wire that slots in the crimping area. 


Step 4. Join the outer insulating cover. This will allow the current to pass through the wire. Afterward, instill the wire lug across the stripped copper wire. Crimp the connection gadget to the wire permanently. 

Step 5. Terminate the single-phase transformer’s high voltage side cautiously. Follow any procedures the manufacturer might have listed. 


Step 6. Connect the low-voltage side of the single-phase transformer according to the manufacturer’s instructions. This includes the configuration that needs to be precisely followed. In small control transformers, there are only two terminals – X1 and X2. The X1 terminal is the line side, while the X2 terminal is the grounding side and low voltage. 


Step 7. Terminate the control transformer for both X1 and X2. The X1 terminal goes directly to the control circuit after passing through a fuse, which is oftentimes developed for the circuit. The X2 terminal is joined to the control circuit’s neutral side and likewise utilized for grounding protection. Accordingly, the X2 terminal needs to be connected to the circuit’s grounding structure. 

Step 8. Modify the single-phase transformer’s shield and any sections that impede current flow. Initialize the feeder power circuit to exert the high voltage to the transformer. Afterward, switch on the safety circuit on the low side. 

Step 9. Check for voltage on the single-phase transformer. The objective is to make certain that the voltage is what’s exactly on the manufacturer’s list.  

Single Phase Self Protected (CSP) Transformer packaging

What are single-phase transformers used for?

Single-phase transformers are traditionally used in low voltage applications. This electrical device is largely adapted to minimize the voltage of a 220 volts supply. It can also be used in television sets for voltage regulation, stepping down localized power distribution, lowering the voltage on electronic devices, and more. 

What is the difference between a single and a three-phase transformer?


A single-phase transformer treats power lines as an input source. It uses two windings (primary and secondary) for changing the voltage. A three-phase transformer, on the other hand,  uses three windings (wye, mesh, and zigzag). These are coils joined in the precise sequence to match the incoming voltage and maintain accepted polarity and phasing. 


A single-phase Distribution Transformer produces a lesser amount of electricity for supporting homes and non-industrial businesses. A three-phase transformer higher amount of energy sufficient enough that can support power grids and aircraft to name a few. It can also support other electronic loads higher than 1,000 watts. 


The stability in power delivery is another noticeable difference between a single and a three-phase transformer. A single-phase transformer can’t offer the same stability, unlike the three-phase transformer, which can deliver power at a stable and constant rate.


When it comes to efficiency, a three-phase transformer is better than a single-phase transformer. It can supply three-fold of power using less conductor material to deliver a sufficient amount of electrical power. 

Additionally, a single-phase transformer can’t start on its own and needs external devices. A three-phase transformer can start by itself without the need for external devices. At the same time, it can transpose the paths of two conductors.  


A single-phase transformer can only serve up to 230 volts. Contrastingly, it’s possible to maximize a three-phase transformer up to 415 volts.

Place of Utility

Residential homes generally require a lower power supply, making the single-phase transformer suitable to use. Less amount of power is needed to power mobile devices and small appliances. However, commercial and industrial firms necessitate heavier electronic load in which a three-phase transformer can provide.  

Electric single phase transformer

What are the advantages of a single-phase transformer?

Most home appliances need only a little amount of energy to function. This is why a majority of residential homes prefer a single-phase transformer to accomplish it. A single-phase transformer can supply power to heaters, refrigerators, lights, televisions, and fans to function efficiently.

A single-phase transformer’s design and operation are simple and ordinary. Its unit is compact and lightweight, producing a lower current when voltage transmission is high.

Because of the reduction in I2R, the current becomes low. This means that a single-phase transformer makes sure that the unit operates at an absolute degree with the increased efficient transmission.

A single-phase transformer can be optimized with fractional or lower horsepower units up to 5 horsepower. It can be utilized to provide low voltages and high currents. Additionally, it can provide the desired output with up to 99% effectiveness without too much power loss.

A single-phase transformer can transmit electrical energy from one circuit to another circuit through mutual induction between the windings. It operates on the concept of electromagnetic induction. This electrical device contains both primary and secondary winding used to surge or subside the circuit’s voltage levels.
Testing a single-phase transformer has a key role in the excellent performance of the electrical device. It’s significant to conduct tests to avoid failures as it verifies specifications and proper functioning

How Do You Choose the Best Single Phase Transformer?

Choosing a single-phase distribution transformer is a challenging task. It’s important to ensure that you’re selecting the right one for your needs and done with just basic knowledge and understanding of what these transformers are all about!

You believe that cost should not compromise the quality of the product. That’s why an excellent one is just as crucial as picking the correct product itself.

Daelim ensures buyers get the best of both worlds: a high-quality product at an affordable price. The transformer brand is excellent in performance and cost-efficient to satisfy consumers’ needs. What’s more, this performance has earned the reputation as one of the most trusted electric companies globally. Therefore, you can’t go wrong with choosing the Daelim brand for all your electrical products or solutions!