In the power transmission and distribution system, the transformer is an indispensable core equipment, and single-phase transformer by virtue of its simple structure, low loss and other advantages, in the low load density of low-voltage distribution network occupies an important position. Many people have cognitive misconceptions about single-phase transformers, that it has a “loss reduction magic”, and even better than three-phase transformers, but it is not. This article will comprehensively disassemble the working principle of single-phase transformer, detailed explanation of its type, performance factors, advantages and disadvantages and application scenarios, combined with the actual application data and industry experience, presenting the most professional and comprehensive analysis, and at the same time to correct the industry cognitive bias.
what is a single-phase transformer
Single-phase transformer is a transformer whose primary and secondary windings are single-phase, which needs to be distinguished from single-pole switching power supply with only positive and negative outputs (bipolar power supply has three outputs: positive, negative and ground). Its core features are simple structure, small size, low loss (low iron loss is the key), suitable for low load density low-voltage distribution network, both practicality and economy. Suzhou has accumulated more than 1,000 units, saving 45GWh of electricity, and it is also widely used in the United States and Japan for residential power supply, but it is only a supplement to the three-phase power supply system, only applicable to specific scenarios, and cannot reduce losses unconditionally.
Working principle of single-phase transformer
The core working principle of single-phase transformer is based on the phenomenon of mutual inductance in electromagnetic induction, using the iron core as the magnetic conduction medium, connecting two independent circuits of primary and secondary with the help of common magnetic flux, realizing the contactless and low-loss transmission of AC energy.
Applying AC voltage (V1) to the primary winding generates an alternating current, which excites the alternating magnetic flux (Φm) in the iron core and forms a magnetic coupling with the secondary winding through the core conduction; according to the law of corrugator, the secondary will generate an electromotive force (E2) by induction, and the core formula is E2=-N2dϕmdt and E2/E1=N2/N1, which is the core basis for the design of step-up and step-down voltage and winding. This is the core basis for step-up, step-down and winding design.
The turns ratio determines the type of transformer: N1>N2 is a step-down transformer (converts high voltage to low voltage such as 220V, suitable for residential and small commercial scenarios); N2>N1 is a step-up transformer (increases low voltage to high voltage, used for long-distance power transmission).
Secondary access to the load after the formation of current (I2), to complete the transmission of electrical energy, the core characteristics are: primary and secondary without direct electrical connection (by magnetic coupling, security and anti-interference), the transmission of electrical energy in the frequency constant (to ensure the normal operation of equipment).
The core is made of insulated thin silicon steel sheet stacked (to reduce eddy current losses), the stacked sheet adopts the “stacked tile” design to reduce the magnetic flux leakage; primary and secondary windings are wound in the core column, the number of turns, the winding direction is strictly designed to enhance the efficiency of the magnetic coupling and reduce losses.
In summary, the core of its work is three points: efficient transmission of power and adapt to different voltage requirements, transmission of constant frequency, relying on mutual inductance and core magnetic coupling to achieve contactless transmission, which is also the basis for its wide application in low-voltage distribution networks.
The relationship between voltage and current
In-depth understanding of the working principle of single-phase transformers, need to master the core relationship between voltage and current, both are transformers to achieve the basis of stable transmission of electrical energy, but also in the field of electronic circuits, the basic concepts.
Voltage is a measure of electrical potential energy in the circuit, analogous to the water pipe pressure, the higher the voltage, the stronger the driving force of the charge flow; current is a measure of charge flow, analogous to the speed of the water flow, reflecting the number of charges per unit of time through the circuit at a certain point.
The core connection between the two is that the voltage difference is the fundamental driving force for the flow of current, and there is no directional current without the voltage difference. This relationship can be quantified by Ohm’s law, that is, I = U/R, when the resistance is constant, the voltage is proportional to the current; the greater the resistance, the greater the resistance to the flow of current, and vice versa, the smoother.
Flashlight light, computer power supply adaptation, can visualize this relationship. The single-phase transformer, its step-up, step-down function, the essence is to change the number of turns of the winding to adjust the primary and secondary voltage ratio, and then adjust the size of the current, to achieve stable transmission of electric energy, adapt to different power needs.
Types of single-phase transformers
According to the different structural design and application scenarios, single-phase transformers are mainly divided into three categories, each type of transformer structure, advantages and application scenarios have their own focus, to meet the needs of different areas of electricity.
Iron core type single-phase transformer
Iron core as the core, primary and secondary winding in the core column, iron core using silicon steel sheet stacked to reduce eddy current loss, improve efficiency; strong magnetic coupling, low loss, compact structure, low cost and easy to maintain, suitable for residential community, small business and other medium power low-voltage power distribution, is the most widely used type.
Shell type single-phase transformer
Iron core completely wrapped winding, can enhance the magnetic flux density, reduce magnetic field leakage and loss, strengthen the winding mechanical protection; short-circuit strength, low noise, durability, suitable for load fluctuations of industrial scenes.
Specialized single-phase transformer
Designed for specific scenes, beyond the traditional boosting and bucking functions: autotransformer compact size, high efficiency, used for motor starting, voltage regulation; isolation transformer can realize electrical isolation, protection of sensitive equipment, suitable for medical, laboratory and other scenes.
Key factors affecting transformer performance
Single-phase transformer performance is affected by five core factors, master these can do a good job of maintenance, extend life: high temperature accelerated insulation aging, degradation of transformer oil; long-term overload prone to failure; voltage stress damage insulation; pollution degradation of insulation (outdoor need to be regularly cleaned); routine maintenance is the key to detect hidden problems.
Single-phase transformer performance directly determines its operational stability, service life and energy efficiency, its operational status is mainly affected by five core factors, master these factors, can effectively do a good job of equipment maintenance, extend the service life, to protect the long-term stable operation of equipment.
Advantages and disadvantages of single-phase transformer
The application of single-phase transformer is so widely used, and its own advantages are inseparable, but at the same time, by the structure and characteristics of the limitations, it also has certain disadvantages, to understand its advantages and disadvantages, can help us more reasonably select the application scenarios, to play its maximum value.
Advantages
Low material loss, the same capacity compared to three-phase transformer to save 20% iron core, 10% copper, winding iron core structure can reduce more than 15% no-load loss, fits the trend of energy saving; less investment in the line, can save 33%-63% conductor materials, reduce transmission construction costs; suitable for mass production, the structure of the simple and easy to large-scale production, fits the energy-saving national policy; flexible investment, light load areas and residential communities can be through multiple small capacity transformers near the power supply, reduce the cost of transmission; the structure and features, can help us choose the application scenario, the biggest value. Flexible investment, light load areas and residential communities can be powered by multiple small-capacity transformers in the vicinity, reducing line losses and improving power quality.
Disadvantages
Easy to overheat, long-term overload or poor ventilation will damage the winding insulation, triggering a short circuit; noise problems, abnormal noise may indicate failure; insulation is easy due to humidity, high-voltage surge aging, outdoor equipment is more affected by the environment; winding is easy due to damage, overheating failures, and failures need to be detected by professional equipment, affecting the transmission of power or even lead to equipment scrapping.
Common applications of single-phase transformers
Combined with the structural characteristics and advantages and disadvantages of single-phase transformers, its application scenarios are concentrated in the field of low load, high requirements for power supply flexibility, specifically divided into four categories:
First, residential power supply, the United States, Japan and other countries are widely used in residential power supply, China is mainly used in residential communities, urban and rural low-voltage distribution network, to protect the family and public electricity;
Second, small commercial and civil scenarios, applicable to street lighting, small stores and other low-load scenarios, which can take advantage of its small size, flexible installation and low cost;
Third, industrial auxiliary scenes, with special single-phase transformers, used for motor starting, voltage regulation and medical, laboratory and other scenes with high requirements for power safety and precision;
Fourth, special scenarios, rural, remote and other light load dispersed areas, can be installed flexibly to shorten the power supply distance, reduce losses, reduce construction investment.
Summarize
In summary, single-phase transformers are based on the principle of mutual inductance to achieve contactless transmission of AC energy, with simple structure, low loss and other characteristics, divided into three categories: core, shell and dedicated, is an important supplement to the three-phase power supply system, only for low load and other specific scenarios. Temperature, overload and other five factors affect its performance and life, the use of good maintenance and troubleshooting. Its advantages such as low material loss and flexible investment are significant, but there are also disadvantages such as easy overheating.
