Step-Up Transformer: All You Need to Know

This article takes an in-depth look at the step-up transformer.

Read further and learn more about topics such as:

• Step-up transformer overview

• Step-up transformer classification

• How does a step-up transformer work?

• Step-up transformer fabrication

• Differences between step-up transformers and step-down transformers

Step-Up Transformer Overview

A step-up transformer is a type of transformer, which has the function of voltage compensation and boosting, and it is also called a step-up compensator. In fact, most transformers are divided into two categories: step-up transformers and step-down transformers according to different voltages. The two transformers are diametrically opposite in terms of voltage. A step-up transformer has more secondary turns than the primary, and a step-down transformer has fewer secondary turns than the primary.

The role of the transformer in the power system is to transform the voltage in order to facilitate the transmission of power. After the voltage is boosted by the step-up transformer, the line loss can be reduced, the economy of power transmission can be improved, and the purpose of long-distance power transmission can be achieved. The step-down transformer can change the high voltage into the voltage required by the user at all levels to meet the needs of the user.

Step-Up Transformer Classification

In the following part, Easybom will elaborate on the types of step-up transformers.

High-frequency step-up transformer

The high-frequency step-up transformer adopts a high-frequency voltage-doubling rectifier circuit, applies the latest PWM pulse width modulation technology and power IGBT devices, and adopts a special process according to the electromagnetic compatibility theory to make the DC generator high-quality and portable. It is composed of two parts: the control box and the voltage multiplier. It is equipped with a protective resistor and has the functions of voltage zero-position gate protection, overcurrent, and overvoltage protection. It is small in size, light in weight, easy to carry, convenient, safe, and reliable, it is suitable for on-site DC high voltage tests in the power sector, DC characteristic tests of arresters, and other occasions requiring DC high voltage.

DC step-up transformer

The DC step-up transformer has the characteristics of small size, light weight, compact structure, complete functions, strong versatility, and convenient use. It is especially suitable for power systems, industrial and mining enterprises, scientific research departments, etc. to conduct dielectric strength tests on various high-voltage electrical equipment, electrical components, and insulating materials under frequency or DC high voltage. It is essential and important equipment in high-pressure tests.

AC step-up transformer

The AC step-up transformer is a device that converts AC voltage, current, and impedance. When there is an AC current in the primary coil, an AC magnetic flux is generated in the iron core (or magnetic core), so that a voltage (or current) is induced in the secondary coil. The transformer consists of an iron core (or magnetic core) and a coil. The coil has two or more windings. The winding connected to the power supply is called the primary coil, and the rest of the windings are called secondary coils. The AC step-up transformer has the characteristics of small size, light weight, compact structure, complete functions, strong versatility, and convenient use. It is especially suitable for power systems, industrial and mining enterprises, scientific research departments, etc. to conduct dielectric strength tests on various high-voltage electrical equipment, electrical components, and insulating materials under frequency or AC high voltage. It is essential and important equipment in high-pressure tests.

Dry-type step-up transformer

Compared with oil-type transformers, dry-type step-up transformers have no oil, so there are no problems such as fire, explosion, and pollution. Therefore, electrical codes and regulations do not require dry-type transformers to be placed in a separate room. Especially in the new series, the loss and noise have been reduced to a new level, creating conditions for the transformer and the low-voltage screen to be placed in the same power distribution room. The safe operation and service life of dry-type booster transformers largely depend on the safety and reliability of the transformer winding insulation. It is one of the main reasons that the transformer cannot work normally because the winding temperature exceeds the insulation withstand temperature and the insulation is damaged. Therefore, it is very important to monitor the operating temperature of the transformer and its alarm control. According to the characteristics of the use environment and protection requirements, dry Step-up transformers are available in different housings. IP23 protective casing is usually used, which can prevent solid foreign objects larger than 12mm in diameter and small animals such as mice, snakes, cats, and sparrows from entering, causing vicious failures such as short-circuit and power failure, and providing a safety barrier for live parts. If the transformer must be installed outdoors, the IP23 protective enclosure can be selected. In addition to the above IP20 protection function, it can also prevent water droplets within an angle of 60° from the vertical line. However, the IP23 enclosure will reduce the cooling capacity of the transformer, so pay attention to the reduction of its operating capacity when selecting it.

Low-frequency step-up transformer

The low-frequency step-up transformer core flux is related to the applied voltage. In the current field, the excitation current does not increase with the increase of the load. Although the iron core will not saturate when the load increases, the resistance loss of the coil will increase. If the heat generated by the coil cannot be dissipated in time beyond the rated capacity, the coil will be damaged. If the coil you use is composed of superconducting materials, the current will increase. It will not cause heat, but there is impedance caused by magnetic leakage inside the transformer, but as the current increases, the output voltage will drop. The greater the current, the lower the output voltage, so the output power of the transformer cannot be infinite. If you said again that the transformer has no impedance, then when the transformer flows through the current, it will generate a particularly large electric force, which will easily damage the transformer coil. Although you have a transformer with unlimited power, it cannot be used. It can only be said that with the development of superconducting materials and iron core materials, the output power of transformers with the same volume or weight will increase, but not infinite!

How does a Step-Up Transformer Work?

Next, let's talk about the topic that how does a step-up transformer work.

Step-up transformer principle: A step-up transformer is a device that converts low AC voltage, high current, and small impedance into high AC voltage, small current, and high impedance accordingly. When there is an AC current in the primary coil, an alternating magnetic flux is generated in the iron core (or magnetic core) ), which induces a voltage (or current) in the secondary coil. The input of the transformer must be an alternating power, and its output voltage is proportional to the turns ratio of the output to input coils. If you use a battery, because it is DC, you must add a switch circuit to the input circuit to turn it into a constantly changing voltage. In this way, alternating high-voltage electricity can be obtained at the output end.

Formula and description: The numbers of turns of the two sets of coils of the transformer are N1 and N2 respectively, N1 is the primary, and N2 is the secondary. When an AC voltage is applied to the primary coil, an induced electromotive force is generated at both ends of the secondary coil. When N2 is greater than N1, the induced electromotive force is higher than the voltage applied by the primary, and this transformer is called a step-up transformer.

Step-Up Transformer Fabrication

How to make a step-up transformer? You can find the answer in the following part.

According to the calculation formula of power and iron core:

S=1.2×square P=1.2×square2000≈54（cm²）

The cross-section of the selected iron core, 40 cm², is too small, and it may not be able to accommodate the windings. According to the iron core section 54 cm² calculation steps:

When core permeability is 10000 Gauss, turns per volt:

N=45/S=45/54≈0.84 (turns)

The number of turns for primary 12V:

12×0.84≈10 (turns)

Secondary turns at 800V (influenced by transformer iron loss and copper loss, a 5% margin must be added):

800×0.84×1.05≈706 (turns)

Primary and secondary current:

I1=P/U=2000/12≈167(A)

I1=2000/800=2.5(A)

Primary and secondary wire diameters:

D=1.13×√I/δ

(The current density is 2.5~3A per square, takes 2.5A to calculate)

D1=1.13×√167/2.5≈9.2(MM)

D2=1.13×√2.5/2.5=1.13(MM)

The transformer only works on alternating current. If you use a 4V DC power supply to rise to 220V, you need an inverter circuit to convert it into a square wave or pulse waveform. This conversion process has a conversion efficiency problem. When designing, the transformer is a step-down transformer. Considering the loss of the transformer itself, the actual ratio of the number of turns of the primary and secondary is not equal to the theoretical calculation value, but the secondary coil is connected to a certain percentage to increase the number of turns. Now you want to use the primary and secondary in reverse, you have to consider a certain amount of voltage from the power supply voltage to achieve your purpose.

Step-Up Transformer Functions

What does a step-up transformer do? Learn more here.

A step-up transformer is a type of transformer which has the function of voltage compensation and boosting and is also called a step-up compensator. In fact, most transformers are divided into two categories: step-up transformers and step-down transformers according to different voltages. The two transformers are diametrically opposite in terms of voltage. A step-up transformer has more secondary turns than the primary, and a step-down transformer has fewer secondary turns than the primary.

The step-up transformer is a special isolation transformer, and it is also divided into single-phase and three-phase. The voltage levels are 220V, 380V, 400V, 415V, 480V, 500V, 515V, 660V, 690V, 1140V to 60KV and other voltage levels. It has good advantages of small size and reliable performance and it is widely used in construction projects where the voltage cannot meet the needs of the voltage used because the construction line is too long, as well as the use of undervoltage compensation on different occasions.

When the AC voltage U1 is applied to the primary side of the transformer, and the current flowing through the primary winding is I1, the current will generate an alternating magnetic flux in the iron core, so that the primary winding and the secondary winding are electromagnetically connected. According to the principle of electromagnetic induction, when the alternating magnetic flux passes through these two windings, an electromotive force will be induced, and its magnitude is proportional to the number of winding turns and the maximum value of the main magnetic flux. The side with more winding turns has a higher voltage, and the side with fewer winding turns has a lower voltage. When the secondary side of the transformer is open, that is, when the transformer is no-load, the voltage at the primary and secondary terminals is proportional to the number of turns of the primary and secondary windings, and the transformer serves the purpose of transforming the voltage.

When the secondary side of the transformer is connected to the load, under the action of the electromotive force E2, a secondary current will pass through, and the electromotive force generated by the current will also act on the same iron core to play a reverse demagnetization effect. The magnetic flux depends on the power supply voltage, and U1 remains basically unchanged, so the primary winding current will automatically increase a component to generate the magnetomotive force F1 to offset the magnetomotive force F2 generated by the secondary winding current. Under the action of L1 and L2, the total magnetomotive force acting on the iron core (excluding the no-load current I0), F1+F2=0, because F1=I1N1, F2=I2N2, so I1N1+I2N2=0, it can be seen from the formula, I1 and I2 are in the same phase, so I1/I2=N2/N1=1/K. It can be seen from the formula that the primary and secondary current ratio and the primary and secondary voltage ratio are reciprocal of each other, and the power of the primary and secondary windings of the transformer is basically unchanged (because the transformer itself The loss is relatively smaller than its transmission power), the size of the secondary winding current I2 depends on the needs of the load, so the size of the primary winding current I1 also depends on the needs of the load, and the transformer plays a role in power transmission.

Differences between a Step-Up Transformer and a Step-Down Transformer

A transformer is a common electrical device that can be used to convert an alternating voltage of a certain value into an alternating voltage of another value of the same frequency. A step-up transformer is a transformer used to convert a low-value alternating voltage into another higher-value alternating voltage of the same frequency. The so-called step-down transformer is to convert the higher voltage at the input end into a relatively low ideal voltage at the output, so as to achieve the purpose of step-down.

The basic principles of step-up transformers and step-down transformers are the same. The main difference is the number of turns of the primary and secondary windings: the number of turns of the main winding of the step-up transformer is less, and the number of turns of the primary winding of the step-down transformer is more.

There is no difference between a step-up transformer and a step-down transformer in theory, but there are differences in practice. Generally, there is no problem when the step-up transformer is used as a step-down transformer, but the step-down transformer is basically unworkable when used for stepping up. There is also a situation where a step-down transformer can be used as a step-up transformer, as long as the voltage does not exceed the voltage of the primary and secondary levels.

The difference between the step-up transformer and the step-down transformer lies in the number of turns of the primary coil and the secondary coil. 1:1 is neither up nor down, only for isolation. In theory, a step-down transformer can be used as a step-up transformer in reverse, but it may not work in practice.

The so-called step-up transformer naturally refers to increasing the value of the instantaneous voltage supply, while the step-down transformer converts the higher voltage at the input end of the power supply into a lower ideal voltage output for the normal use of our home appliances to achieve step-down. So can step-up transformers and step-down transformers be used interchangeably? Regarding this issue, it is not possible in principle, because the loss element needs to be considered in the design and packaging process of the equipment. When the primary coil is responsible for transferring the power to the secondary, it is also responsible for providing losses such as iron loss, while the secondary coil needs to increase the coil to offset the voltage loss, so the two cannot be used in reverse.

However, if there is a reason, it can be temporarily used as a substitute when there is an emergency, but the loss of the internal transformer will increase, the reliability of the equipment operation will gradually decrease, and the service life of the equipment may be shortened, so Here, Easybom does not recommend that you replace it for a long time.

Related: Power Transformer: A Basic Electronic Tutorial