Can Step Down Transformer Be Used as a Step Up One?


Can a step-down transformer be used as a step-up transformer? This involves not only the principle of the transformer, but also the specific components and their functions in circuit. In terms of working principle, the transformer can step down and step up. Does this mean they can be converted? But it is worth noting that the voltage grade, impedance characteristics, impedance voltage characteristics and winding current, etc. all determine whether the step-down transformer can be used for step-up. So here we will explain it in detail.

Step-up and Step-down Transformers Working & Applications



Ⅰ Electrical Transformer Working Principle

Ⅱ Differences between Step-down and Step-up Transformers

Ⅲ Example Analysis

Ⅳ Theoretical Analysis


Ⅰ Electrical Transformer Working Principle

Transformer is a common electrical equipment that can be used to transform a certain value of alternating voltage into another one with the same frequency. A step-up transformer is a device used to transform a low alternating voltage into another higher value with the same frequency. While the step-down transformer is a very important equipment in the power transmission and transformation system. That is, its normal operation is not only related to its own safety and reliable power supply for users, but also directly affects the stability of the power system.

Transformers generally have two functions, one is the buck-boost function, and the other is the impedance matching function. Let me talk about the former. Usually we use a variety of voltages in applications. For example, the life lighting power is 110V, the industrial safety lighting is 36V, and the voltage of the welding machine needs to be adjusted. These are inseparable from the transformer. For example, according to the principle of mutual inductance, the transformer passes through the main and auxiliary coils to reduce the voltage to the voltage we need.

EMF Formula

Figure 1. EMF Formula

The main parts of the transformer are the iron core and the windings on it. The two windings are only magnetically coupled but not electrically connected. Add an alternating voltage to the primary winding to generate alternating magnetic flux that links the primary and secondary windings, and induce the electromotive force (EMF) in the two windings respectively. As long as the number of turns of the primary and secondary windings is different, the purpose of voltage transformation can be achieved by transformer.

Ⅱ Differences between Step-down and Step-up Transformers

(1) The step-down transformer converts the higher voltage at the input of the power supply into a lower voltage for our normal use to achieve the purpose of step-down.

(2) The step-up transformer can convert a low voltage into a higher voltage. (Additionally, the inverter transformer is also a kind of step-up transformer).

In principle, the step-down transformer and the step-up transformer are the same, the specific difference is the inductance, copper consumption, and winding capacity of the high-voltage side and the low-voltage side. The same transformer, no matter it is used for step-up or step-down, the iron loss is the same. Under no-load conditions, the high-voltage side winding of the step-down transformer has many turns, large impedance, large inductance, small current and low copper loss, in addition, the high-voltage side winding has a larger capacity. At this time, it becomes a step-up transformer, the iron loss is the same, but the low-voltage side winding has a small number of turns and a small impedance. The inductance is small and the copper loss is small, and the primary side capacity is smaller than the secondary at this time.
But there is a question. When the step-down transformer is converted to a step-up transformer, can the rated parameters of the low-voltage side coil withstand the loss under no-load conditions? If so, how much power is left for the high-voltage side.
Whether to increase or decrease voltage depends on the ratio of the number of turns of the primary coil and the secondary coil. 1:1 is only for isolation. Therefore, the step-down transformer can be used as a step-up transformer, but it may not work in practice.

Transformer Voltage Conversion

Figure 2. Transformer Voltage Conversion

Ⅲ Example Analysis

As above mentioned, step-up transformer and step-down transformer cannot be used as a reverse conversion. Because the step-up transformer is equivalent to stepping up low-voltage power into high-voltage power. For the system, its low-voltage side is equivalent to absorbing electric energy, and the high-voltage side sending electric energy is equivalent to the power source. That is, the load of the system accepts the standard rated voltage, and the voltage output on the power supply side takes into account the voltage drop of the circuit and the transformer itself, about 10%. In order to ensure that the voltage delivered to the user is exactly the rated voltage, the voltage output on the high voltage side is 10% higher than the rated voltage.

For example, if the rated voltage of the low-voltage side of a step-up transformer is 20kV and the high-voltage side is 110kV, the receiving voltage of the low-voltage side is 20kV, and the high-voltage side is 10% higher, about 121kV. If you consider the transformation ratio, suppose that the low-voltage side has 20 turns, and the high-voltage side cannot be 110 turns but 121 turns. If this step-up transformer is used as a step-down transformer, its high-voltage side can be regarded as a load from the system and can only receive a rated voltage of 110kV, and meanwhile the output voltage of the low-voltage side cannot reach 20kV, which can’t work normally. Similarly, the step-down transformer cannot be used as a step-up transformer. In the actual application process, the structure and protection part of the step-down transformer is different from that of the step-up. So this action will slowly reduce the stability of the transformer and may affect its service life.

Of course, there is also a case where a step-down transformer can be used as a step-up one, as long as the voltage does not exceed the primary and secondary voltage.

Transformer Phase Change

Figure 3. Transformer Phase Change

Ⅳ Theoretical Analysis

Nowadays, it is very common that the voltage instability fluctuates during our usual mains electricity use. Therefore, each family needs to install a power supply device for its own power line. Considering that some people often use low voltage, and some people's home voltage is always high, so there are step-up transformers and step-down transformers.

We first look at the rectifier transformer. We found that the secondary wire on its surface is particularly thick, which is due to the larger current in the secondary circuit. It can be imagined from this that if the secondary circuit is used as the primary side, its impedance must be very small, and the power supply must provide a large current to obtain the required voltage on the secondary side of the transformer, resulting in low conversion efficiency. Ordinary transformers do have this possibility. For example, the electric energy generated by the user's self-provided low-voltage generator may pass the power transformer (step-down) back to the grid. So once the self-provided generator starts, you need to open the circuit breaker connected to the grid. Even with this possibility, it is not arbitrarily that the electric energy can be fed back to the grid through the transformer.

Let's look at the expression of AC voltage: AC Voltage. Note that U on the right side of the equal sign is the effective value of the voltage, and this voltage must meet the specified rated value, f is the frequency (which must also meet the condition of the standard value), and Φ is the phase difference.
We call these three parameters on the primary side of the transformer consistent with the grid requirements on the secondary side of the transformer, which is called synchronous operation. It is a necessary operation that must be performed for the power supply and the power grid to be combined. And the same period value must fully comply with the specific specification value given by the specification standard.
Since the synchronization parameters of the power grid are fixed, the generator must adjust its own synchronization value. The adjustment process of the same period is not very easy. The synchronous period can only be satisfied in an instant. We can only achieve as close as possible, that is, quasi-synchronous. If it is found that the quasi-synchronization is completed, immediately close the circuit breaker, and the electric energy generated by the generator can be boosted by the transformer and sent to the grid. It can be seen that this is not easy, and it can only be achieved by supporting a synchronous measuring instrument or a relay.
Pay attention to the wiring problem of the transformer, that is, the connection group of the transformer. Generally, the phase of the high-voltage side of the transformer is deviated from the low-voltage side. Standards and specifications are vividly expressed using a clock. For example, Y11 and Y0, respectively indicate the connection at 11 o'clock and 0 o'clock (11 o'clock means that the difference between the two is 30 degrees in electrical angle, and 0 o'clock has no deviation). Therefore, when doing synchronous operations, we must also consider what time the transformer wiring is. In U.S, many households have solar power generation devices as auxiliary power supplies to generate electricity for own use. When the electricity is enough, it can be fed back to the grid and get benefit. Obviously, there are synchronization devices and power transformers here.

Phase Deviation

Figure 4. Phase Deviation


1. What is a step up transformer used for?

In the National Grid, a step-up transformer is used to increase the voltage and reduce the current. The voltage is increased from about 25,000V to 400,000V causing the current to decrease. Less current means less energy is lost through heating the wire.

2. What is difference between step up and step-down transformer?
The main difference between the step-up and step-down transformer is that the step-up transformer increases the output voltage, while the step-down transformer reduces the output voltage.

3. How does a step up transformer work?
Generally, a step-up transformer comes with more turns of wire in the secondary coil that increases the received voltage in the secondary coil. ... Hence, in simple words, a step up transformer increases the electricity voltage from lower to higher in the secondary coil according to the requirement or the application.

4. What is an example of a step up transformer?
As an example, a 10:1 step-up transformer requires ten times the turns on the secondary winding: In this formula, we converted the voltage from 5V to 50V (step-up) in a transformer with ten turns on the primary winding, and 100 turns on the secondary winding.

5. What appliances use step up transformer?
While this is done to make it suitable for general use, there are certain appliances like electrical motorsmicrowavesX-ray machines etc. that require a high voltage to start. A step-up transformer is used to convert the existing power supply to the desired voltage.

6. What is the formula for step up transformer?
Using this formula, P = E x I, and its direct derivatives, I = P / E and E = P / I, all transformer attributes can be calculated. For example, if the transformer's rating is 10 KVA and has a 240-volt output, it has a current capacity of 41.67 amperes (10,000 watts / 240 volts = 41.67 amps).

7. What is the main function of a step down transformer?
Transformers are classified by their function, which is either step up or step down. Step-up transformers increase the voltage of the incoming current, while step-down transformers decrease the incoming current's voltage.

8. How does a step down transformer work?
Primarily, a step-down transformer works on the basic principle of electromagnetic induction. According to Faraday's first law of electromagnetic induction, a conductor when placed in a varying electromagnetic field will see an induced current based on the rate at which the flux changes.

9. Why do we use a step down transformer?
The higher the current, the more heat is lost. To reduce these losses, the National Grid transmits electricity at a low current. This needs a high voltage. ... These high voltages are too dangerous to use in the home, so step-down transformers are used locally to reduce the voltage to safe levels.

10. Where do we use step up and step down transformers?
Step-up and step-down transformers use electromagnetic induction to convert voltage between two circuits. We use both types in the distribution of power from supply stations to the end user, as well as to ensure that the appropriate voltage goes into a circuit on many personal devices.

11. Why do we need to step down voltage?
Increased voltage allows decreased current which dramatically reduces power loss. Once the power completes its journey, we decrease its voltage at a step-down transformer to make it safer and more useable in the neighborhood.

12. What is transformer explain step up and step down transformer?
A transformer that increases the voltage from primary to secondary (more secondary winding turns than primary winding turns) is called a step-up transformer. Conversely, a transformer designed to do just the opposite is called a step-down transformer.

13. How does a transformer step down voltage?
The concept of a step-down transformer is actually quite simple. The transfer has more turns of wire on the primary coil as compared to the turns on the secondary coil. This reduces the induced voltage running through the secondary coil, which ultimately reduces the output voltage.

14. Does step down transformer consume electricity?
Thus, if you plug a 300W load into a step-down transformer (assuming the transformer is rated for more than 300W), expect it to draw a little more, perhaps 325W - 375W depending on quality of construction.

15. Does step down transformer increase current?
A step-up transformer increases voltage and decreases current, whereas a step-down transformer decreases voltage and increases current.

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