Mains Transformers
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About mains transformers
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What are mains transformers?
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What types and types of mains transformers are available?
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Purchase criteria for mains transformers – what is important?
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Conclusion: How to buy the right mains transformer
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FAQ – Frequently asked questions about mains transformers
What are mains transformers?
Transformers, also called transformers or transformers, consist of at least two coil windings which are located on a common iron or ferrite core. Alternating voltage, which is fed on the input-side winding, converts a transformer on its output side into a lower, higher or identical voltage. The winding numbers of the input and output winding (primary and secondary sides) define the ratio of input and output voltage . For example, a transformer with a 10:1 winding ratio converts the common mains voltage from 230 volts to 23 volts on the secondary side. Of course, this also works in the opposite direction. Mains transformers are commonly referred to as transformers intended for use in low-voltage networks with frequencies of 50 or 60 Hertz.
What types and types of mains transformers are available?
The most well-known are the classical mains transformers, which transform the mains voltage from 230 V AC to significantly lower voltages in the most varied electrical and electronic devices and galvanically separate the input and output side. It is only through these low voltages, which are usually rectified, smoothed and stabilized, that the operation of electronic components and circuits becomes possible at all and safe for the user.
Control Transformers
Used to supply control circuits . In addition to any voltage adjustment required for the control circuit, such as 230 volts to 23 volts, they electrically separate the primary and secondary sides. Control transformers are often fitted with several taps on the input side to enable better voltage adaptation to the local power supply.
Isolating transformers
Are offered both with a ratio of 1:1 and with various other winding conditions. They ensure galvanic isolation from the input circuit to avoid dangerous contact voltages against earth.
Safety transformers:
Also perform an electrical separation between the input and output sides. Their output voltage is also limited to a maximum of 50 V AC without load when idling. They are often equipped with additional protective devices, for example in the form of fuses. Safety transformers are sometimes also short-circuit-proof.
In addition to the single-phase versions, isolating and autotransformers are also available as three-phase versions for operation in three-phase systems.
Purchase criteria for mains transformers – what is important?
Good mains transformers have a high electrical efficiency and have low no-load losses. The more powerful a transformer is, the more important these aspects are. Poor efficiency can lead to considerable additional costs over the years, as energy is converted into heat loss without any use. In addition, additional acquisition and operating costs may arise for the necessary heat dissipation.
For these reasons, it is important to design the mains transformer correctly, i.e. to size it as precisely as possible for the required electrical power. An undersized mains transformer will overload it and cause an early failure, while an oversize transformer will cause unnecessary procurement and operational costs.
Note that the output voltage(s) of transformers refer to the rated load specified . Accordingly, a transformer with a low load provides a higher output voltage, whereas an overloaded transformer experiences a voltage dip.
For most transformers, the power specified in the data sheet refers to operation at 40 °C ambient temperature and free-standing. If a transformer is installed in a housing, the usable power is reduced accordingly due to the poorer heat dissipation.
Depending on the intended use, the degree of protection of the mains transformer must be selected accordingly. If more difficult ambient conditions are to be expected, for example in the form of dust or moisture, fully encapsulated mains transformers are particularly suitable. Their hermetically sealed encapsulation protects the winding and core from harmful moisture entry and mechanical damage.
Conclusion: How to buy the right mains transformer
In addition to the purely electrical data, i.e. input and output voltage, output current and power, always observe the required type of mains transformer . The transformer must be designed to meet all safety requirements. For example, it is not permitted to replace a safety transformer with a normal transformer when replacing it.
As a rule, small to medium-sized mains transformers are installed in device housings or other enclosures. When replacing the transformer, make sure that the dimensions of the new transformer are correct and that the electrical connections are suitable or that they are as compatible as possible with the existing connectors or cables.
Make sure that the mains transformer has the required test marks and conforms to the applicable standards. The mains transformers offered by Conrad in the shop fulfill high quality requirements, are characterized by reliability, a high degree of efficiency and a long service life.
Our practical tip:
Autotransformers are not suitable if galvanic isolation between the primary and secondary sides is required. There is danger to life from dangerous contact voltages!
FAQ – Frequently asked questions about mains transformers
The transformer is humming or surfing quietly, is that normal?
Electromagnetic forces can cause windings and iron core to produce minimal vibrations, which can then be heard at 50 Hertz line frequency as a humming noise with a frequency of 100 Hz. In very sensitive applications, fully encapsulated transformers can be used, which cause less disturbing operating noise due to their encapsulation.
What is the advantage of autotransformers?
Autotransformers offer advantages in terms of weight, size and material, especially if the input and output voltage are relatively close together with a transmission ratio of approx. 3:1, this advantage is gradually reduced.
Can I replace a safety or isolation transformer with a normal mains transformer or an autotransformer?
No, this is not permitted under any circumstances!
Can a mains transformer be operated at a voltage higher than the specified rated input voltage?
No. Operation at higher voltages not only damages the mains transformer but can lead to electric accidents, as the winding insulation is not designed for this purpose and can lead to insulation failure.