Single Phase Transformer: A Full Guide

Transformers play a key role in power distribution and voltage conversion. Among various types of transformers, single-phase transformers are essential components in many electrical systems. Single-phase transformers are a type of distribution transformer that we often see. It is a cylindrical electrical device that is not very large and is usually installed on a pole. When you walk in the suburbs or on the side of the road, you can see single-phase transformers when you look up.

A single-phase transformer transfers electrical energy from one circuit to another through inductively coupled coils. The primary coil (input) is connected to the power source, and the secondary coil (output) supplies power to the load. Transformers can be used to step up or step down voltage, depending on the application. In this ultimate guide, we will discuss the basic construction and operation of a single-phase transformer and look at the different parts that make it up.

1. What is a single-phase transformer?

A single-phase transformer is a type of power transformer designed to transfer electrical energy between two or more circuits through electromagnetic induction. Unlike three-phase transformers commonly used in industrial settings, single-phase transformers are primarily used in residential and small commercial applications.

The single phase transformer is powered by a single phase supply and consists of two parts – the magnetic part and the electrical part. The magnetic transformer part consists of a magnetic iron core while the electrical part consists of a copper transformer.

Only alternating current can operate a transformer as direct current does not create an electromagnetic field. Because a transformer has no moving parts, it does not create mechanical friction while operating. Therefore, there is very little energy loss when using a single phase transformer, making single phase transformers highly efficient.

When the primary winding of a transformer encounters alternating current, an alternating electromagnetic field is generated. Part of the generated magnetic field is connected to the secondary winding through mutual inductance, generating a current. A voltage with the same frequency as the primary winding is induced in the secondary winding. Faraday’s law can determine the magnitude of the induced voltage.

2. Working principle of single-phase transformer

The working principle of a single-phase transformer is based on Faraday’s law of electromagnetic induction. Basically, the mutual inductance between two or more windings is responsible for the voltage transformation action in a power transformer.

Faraday’s law states that an electromotive force (EMF) is generated in any closed circuit when the magnetic flux through the circuit changes. This electromagnetic induction effect is the basis for the operation of a single-phase transformer. When an alternating current passes through the primary winding, it creates an alternating magnetic flux around the core. According to Faraday’s law, this changing magnetic flux induces an EMF in the secondary winding.

The working principle of a single-phase transformer is mutual induction. The primary winding is connected to an alternating current, which powers the coil, thus forming a magnetic field. The process of magnetic field formation is called mutual induction, and current flows through the coil according to Faraday’s law.

The greater the current flowing through the coil, the stronger the magnetic field generated, forming magnetic lines of force, which form magnetic flux, and the secondary winding connects the system with the magnetic flux.

The turn ratio between the primary and secondary windings will determine the strength of the magnetic field produced. An increase in current will result in an increase in magnetic flux – they are directly proportional. The magnetic flux flowing in the core will induce a voltage in the secondary winding. Based on Faraday’s law, the induced voltage can be calculated.

3. Components of a single-phase transformer

The single-phase transformer parts include isolation, core, and windings. Here is a detailed explanation of each:

Isolation: Isolation is necessary to protect the transformer windings from the core. Isolation is achieved by using insulating materials like glass, mica, varnish, etc.
Core: The core of a transformer is made of iron or steel. It provides a path for the magnetic flux.
Winding: Winding is the coil of wire wound around the transformer core. It carries the current flowing through the transformer.
Primary windings are the ones connected to the AC power source on the transformer. An AC voltage applied to the primary winding produces a magnetic field.
The secondary winding is the one connected to the load on the transformer. When an AC voltage is applied to the primary winding, a voltage is induced in the secondary winding.

The components of a single-phase transformer work together to provide a safe and efficient way to transfer electrical energy. When choosing a transformer, it is important to select the right transformer for the application. Transformers come in a variety of sizes and shapes, so it is important to consult an expert to ensure you choose the right transformer.

4. Construction of single-phase transformer

A single-phase transformer has a primary winding and a secondary winding. The windings are placed on a core made up of silicon steel laminations. The purpose of the core is to provide a path for the magnetic flux. The silicon steel reduces hysteresis losses, while the laminations reduce losses caused by eddy currents (local currents induced in a conductor due to a changing magnetic field).

Laminations are thin sheets, which are stacked together to form the core. An enamel insulating coating insulates the laminations from each other. Depending on the construction, single-phase transformers can be core type or shell type.

(1). Iron core transformer

The transformer has two vertical pillars (legs) and two horizontal parts (yokes) in the magnetic flow. For minimal leakage flux, half of the windings are placed on each leg. The two windings form a cylindrical winding.

Both windings are wound around the central post of the core. Compared with shell types, it has better magnetic coupling. The main disadvantage of the core-type transformer is the leakage flux generated due to a small part of the magnetic lines of force flowing outside the core.

(2). Shell type transformer

The magnetic circuit of the transformer has three branches. The winding is located in the middle branch, and the other branches complete the low reluctance flux path. The primary and secondary windings have two sub-sections; the low voltage section and the high voltage section.

The primary winding is wound on the center column, and the secondary winding is wound on the outer column. The leakage flux is small and the efficiency is high. The shell-type transformer overcomes the leakage flux, reduces the core loss, and improves efficiency.

5. Application of single-phase transformer

Single-phase transformers are widely used in various applications due to their versatility and efficiency. Here are some common application scenarios:

Power Distribution: One of the most common applications of single-phase transformers is to step down the local distribution voltage in the power distribution system. The high voltage electricity generated by the power plant is stepped down to a lower voltage suitable for residential and commercial use. This ensures safe and efficient delivery of electricity to homes and businesses.
Voltage Regulation: Single-phase transformers are also used for voltage regulation. They can increase or decrease voltage levels to maintain a steady supply of power to sensitive devices and appliances. This is essential to prevent damage to equipment that requires a specific voltage level to operate properly.
Isolation: Electrical isolation is essential to protect sensitive equipment from voltage spikes and other interference. Single-phase transformers create galvanic isolation between circuits, ensuring that a problem in one circuit does not affect another.

6. Selection of single-phase transformer specifications

When considering a single-phase transformer, it is important to understand the corresponding parameters in detail according to the following table for its selection.

Operating frequency range: Transformers that operate at higher frequencies tend to be smaller because fewer windings are required to match impedance.
Primary Voltage Rating: Input voltage range; several nominal voltages represent multiple primary windings.
Secondary voltage rating: Output voltage range
Secondary current rating: Rated output current
Power Rating (VA): The maximum voltage applicable to a transformer, expressed in volt-amperes.
Turns Ratio: The turns ratio of a single-phase transformer is the ratio of the number of primary turns to the number of secondary turns. This ratio determines how much the voltage rises or falls. Selecting a transformer with the correct turns ratio is critical to achieving the desired voltage transformation.
Operating Temperature: The safe temperature range of the transformer during operation; the temperature of the transformer will rise during use.

7. Advantages and disadvantages of single-phase transformers

Single-phase transformers are easy to use and have relatively low losses, so they can be used in scenarios or areas where conditions are limited. Of course, single-phase transformers also have some defects, such as low efficiency. A correct understanding of the advantages and disadvantages of single-phase transformers can help us more accurately determine usage scenarios and actual needs.

(1) Advantages

Single-phase transformers generally adopt new materials. According to analysis, when the urban and rural power grids are transformed to a certain extent, the proportion of line loss in network loss will be greatly reduced, and the no-load loss of distribution transformers will occupy a major position in network loss. Only by significantly reducing the core loss can the power loss of the power grid be further reduced. Therefore, single-phase transformers with wound cores and amorphous cores have great development potential. The application of wound core and amorphous core technology in single-phase transformers can greatly reduce the loss of transformer cores. It is conducive to modern production. The single-phase transformer has a simple structure and is suitable for mass production, which is conducive to improving product quality and efficiency.

(2) Disadvantages

First, there is only one winding on the core of a single-phase transformer, which can only transform the voltage of one phase of the power supply to the secondary output side. Due to the single voltage and small capacity, it can only be used for lighting or small power stations, rural side lines, workshops, and other places, and cannot be widely promoted, resulting in a limited scope of application. It can only be used as a supplement to the three-phase power supply system. The use of single-phase transformers, first, in mountainous areas, where residents are scattered, the power load is small, and there is basically no power application, can greatly reduce line investment.

Secondly, it applies to the street lamp power supply system. The power department charges households and line losses are the power department’s business. Owners and developers are not obliged to provide convenience to the power department.

8. Differences between single-phase transformer and three-phase transformer

It’s not a bad idea to take a closer look at the differences between single-phase and three-phase transformers.

Single-phase transformer: Single-phase transformer works on the principle of electromagnetic induction. It is a device that can change AC voltage. Its main components are primary coil, secondary coil, and magnetic core. In electrical equipment and wireless circuits, it is often used for voltage increase and decrease, impedance matching, safety isolation, etc. Single-phase transformer is suitable for low-voltage distribution networks with low load density.
Three-phase transformer: In order to input different voltages, multiple input windings can be used to adapt to different input voltages. Multiple windings can also be used to output different voltages. Three independent windings are connected in different ways (such as star and triangle) to input three-phase AC power, and their outputs are the same. This is a three-phase transformer. The three-phase transformer is suitable for circuits with frequencies of 50Hz to 60Hz and voltages below 660V. It can be used for imported important equipment, precision machine tools, electromechanical equipment, medical equipment, rectification, lighting, etc.

It is important to note that single-phase transformers are designed for single-phase AC systems. They cannot be used directly in three-phase systems. To work in a three-phase system, multiple single-phase transformers can be connected in various configurations such as delta-star or star-delta to achieve the required conversion.

9. Single-phase transformer maintenance and safety precautions

While single-phase transformers are critical to a variety of applications, they also require proper maintenance and safety precautions to ensure long-term reliability and safe operation. Here are some important considerations:

(1). Regular inspection

To detect wear, damage, or overheating of single-phase transformers, regular inspections are essential. Visual inspections can reveal loose connections, corroded components or oil leaks in oil-filled transformers. Routine thermal inspections using infrared thermography can help detect hot spots that may indicate problems with the transformer windings or connections.

(2). Oil quality testing

Testing the insulating oil is essential for oil-immersed transformers to monitor its condition and the transformer’s insulation. Regular oil sampling and analysis can detect contaminants, moisture, and deterioration so that maintenance and oil changes can be performed promptly when necessary.

(3). Load Monitoring

Monitoring the load on single-phase transformers is important to prevent overloading, which can lead to overheating and shortened service life. Current transformers (CTs) and voltage transformers (VTs) measure the load and provide data to load management and protection systems.

(4). Safety measures

Safety should always be your top priority when working with or around single-phase transformers. Here are some safety measures to follow:

Before performing any maintenance or inspection, ensure the transformer is de-energized and properly locked and tagged.
When working near energized equipment, use appropriate personal protective equipment (PPE), including insulating gloves and safety glasses.
Follow safe protocols for handling and disposing of transformer oil as it may contain hazardous materials.
Maintain clear access to the transformer and, if the transformer is located indoors, provide adequate ventilation to prevent overheating.

10. Conclusion

Single-phase transformers are widely used and essential equipment in many industries, helping with voltage conversion, distribution and voltage regulation. Understanding their functions, applications and key specifications is essential to ensure safe and efficient electrical operation. Mastering the electrical components and understanding its maintenance knowledge can also maximize the efficiency of single-phase transformers.