Transformers — devices used to convert alternating current and voltage. They are used in electric power, radio engineering, industrial automation, and electronics. The reliability and efficiency of such equipment largely depend on the properties of the materials from which it is made. A special role here is played by soft magnetic alloys, which ensure minimal energy losses and maximum performance. Let us consider how these materials affect the operation of various electric transformers and what unique solutions the PZPS plant offers.

The role of the magnetic circuit in transformer operation

The operating principle of a transformer is based on electromagnetic induction, which was first discovered and described by Michael Faraday. When alternating current passes through the primary winding, a changing magnetic field is created in it. This field, in turn, induces voltage in the secondary winding, converting the parameters of electric energy in accordance with the specified characteristics.

Main stages of the process:

1. Current flowing through the primary winding creates a changing magnetic field.
2. The magnetic flux created by the field is directed through the core (magnetic circuit) — an element made of a soft magnetic alloy — to the secondary winding.
3. Voltage is induced in the secondary winding, its magnitude proportional to the number of turns and the rate of change of magnetic flux.

The core plays a key role in this process. It concentrates and directs magnetic flux, which makes it possible to minimize energy losses and raise transformer efficiency. Alloys with high magnetic permeability, as well as low eddy-current and hysteresis losses, are used to make the magnetic circuit. These properties ensure optimal energy transfer and reliable device operation.

Current and voltage change in proportion to the number of turns in both windings, according to Faraday’s law:

​E=-Nt​

where:

• E — induced electromotive force, 
• N — number of turns,
• — magnetic induction flux,
• t — the time required for one phase of magnetic field change, 
• t — rate of flux change.

Thus, a transformer converts the parameters of electric energy, making it possible to adapt current and voltage levels in accordance with specified loads.

Transformer operating modes

When designing and operating electrical equipment, various operating modes are taken into account to ensure its reliability and efficiency.

1. No-load mode — operation without load.
   • Description: the primary winding is connected to an alternating voltage source, while the secondary winding remains without load.
   • Features: minimal current passes through the transformer, providing magnetization of the core. In this mode equipment parameters such as transformation ratio and hysteresis and eddy-current losses are measured.
   • Technical detail: to reduce losses, alloys with minimal hysteresis losses are used, for example 50Н and 50НП.
2. Load mode — the main operating mode.
   • Description: both circuits are connected to the load, and the device itself works to transfer energy to the consumer.
   • Features: the secondary voltage level depends on the load, and current increases as the load grows.
   • Technical detail: for efficient operation in this mode, alloys with high magnetic permeability and characteristic stability are used, for example 79НМ for weak fields.
3. Short-circuit (SC) mode — to determine winding losses and insulation strength.
   • Description: the secondary winding is short-circuited (connected to zero), while the primary remains under voltage.
   • Features: in this mode maximum current flows through the transformer, and all energy is spent on heating the conductors. This places high requirements on equipment strength and resistance to heating.
   • Application: SC mode is used to test equipment, including insulation strength tests. Alloys with a low level of eddy-current losses, for example 81НМА, ensure reliability under such loads.

Each mode requires cores that minimize energy losses and ensure stable equipment operation under various service conditions.

Physical phenomena in the magnetic circuit

The magnetic circuit serves as the basis for transferring and amplifying magnetic flux in a transformer. During operation the following physical phenomena occur in it:

Magnetic saturation

It arises when the core reaches the limiting magnetic flux density. This state is characterized by the fact that a further increase in winding current does not lead to significant field amplification.

To describe the process the equation is used:

B=μH

where:

• B — magnetic induction,
• μ — magnetic permeability of the medium,
• H — field strength.

When B approaches the maximum saturation value, the alloy permeability drops sharply. This leads to increased losses and reduced transformer efficiency. To avoid magnetic saturation, current and magnetic-circuit cross-section calculations are performed with a magnetizing-force margin.

Electromagnetic induction

Alternating current flowing through the primary winding creates an alternating magnetic field in the magnetic circuit. This field links the turns of the secondary winding, where an induced voltage arises in accordance with Faraday’s law. To raise device efficiency, core materials must have high magnetic permeability, which makes it possible to better guide flux between the windings.

Hysteresis 

This is a phenomenon in which alloy induction depends on its previous magnetization state. If the winding current changes direction, the process of field change in the magnetic circuit lags, which is linked to the internal resistance of the material’s domain structure. On hysteresis-loop plots it can be seen that energy is lost on each cycle of field change. These losses, called hysteresis losses, are expressed by the formula:

Pг​=η⋅f⋅Bmax2​

where:

• Pг​​ — hysteresis loss power,
• η — hysteresis coefficient depending on alloy properties,
• f — alternating-current frequency,
• Bmax2 — maximum magnetic induction.

To reduce these losses, transformer cores are made of special alloys containing silicon in their composition.

Eddy-current losses

An alternating field induces eddy currents in the magnetic circuit — closed currents forming inside the material. These currents create their own magnetic fields that oppose the original change. Because of this, part of the energy is spent maintaining eddy currents. These losses are reduced by using thin insulated sheets when making the core.

Thermal losses

Another source of losses is heat release in the magnetic circuit due to material resistance. These losses depend on the core’s specific resistance and external factors such as cooling. To reduce thermal losses, alloys with minimal resistance are used, and efficient transformer cooling is provided — oil or air.

Soft magnetic alloys produced by PZPS

The St. Petersburg Precision Alloys Plant offers a wide range of materials ideally suited for use in transformer cores:

1. 50Н and 50НП — distinguished by elevated magnetic permeability and high saturation induction. Used in producing power miniature and interstage transformers, as well as in equipment operating at high inductions with small bias or without it.
2. 79НМ — characterized by high permeability in weak magnetic fields, where saturation induction is from 0.65 to 0.75 T. Used in small models that operate in weak fields of magnetic shields. Strip 0.02 to 0.05 mm thick is used to minimize eddy losses in pulse-transformer cores.
3. 81НМА — an alloy with the highest magnetic permeability, elevated strength, and minimal sensitivity to mechanical deformation. Used in small equipment intended for work in weak magnetic fields.

Transformer operation is based on complex physical processes occurring in the magnetic circuit. Electromagnetic induction ensures energy transfer between windings. Hysteresis and magnetic saturation determine material behavior under alternating fields, while eddy-current and thermal losses limit device efficiency. Modern technologies make it possible to minimize these losses by selecting alloys with optimal physical and mechanical properties. 

To purchase alloys that best suit your projects, or to develop production technologies for new steel grades, call the phone numbers or leave a request on the website. Our specialists will contact you and help select materials that will ensure the reliability and efficiency of your equipment under any conditions.