Guide to transformer cores: types, construction, purpose

The iron core in the transformer is composed of hot rolled or cold rolled silicon steel sheets with high silicon content and coated with insulating paint. The iron core and the coil wound on it constitute a complete electromagnetic induction system. The main role is to form the magnetic circuit of the transformer, so that the primary side of the transformer and the secondary side of the magnetic coupling.

transformer core

Type of transformer core

There are many types of transformer cores, and the following are the types of cores obtained according to different classification standards:

1. Classification by frequency of use

High-frequency type: High-frequency transformer core usually uses iron powder core, which is a ceramic magnet with spinel crystal structure. It is composed of iron oxide and other bivalent metal compounds, such as manganese zinc (MnZn) series, nickel zinc (NiZn) series. These materials have high permeability and impedance physical properties and can be used in a frequency range from 1kHz to more than 200kHz.

Low-frequency type: Low-frequency transformer core is often used silicon steel sheet. Silicon steel sheet has good magnetic permeability and low loss, which is suitable for low-frequency, high-power occasions. According to its production process, silicon steel sheet can be divided into forging (black) and no forging (white). According to its shape it can be divided into EI type, UI type, C type, mouth type and so on.

2. Sort by material

Silicon steel transformer core: Silicon steel core has low cost, good stability, low noise advantages. It is suitable for all voltage levels of transformers.

Amorphous transformer core: Amorphous alloy core has high energy saving, especially in no-load loss performance. The advantages of amorphous transformers include significant energy saving effects and low losses, but the cost of the same capacity is generally higher than that of silicon steel transformers.

3. Sort by structure

Shell and core: Shell core is the structure of the core surrounding the winding, while the core is the structure of the winding surrounding the core column. Most of the transformer core in our country adopts stacking core type.

Single-phase and three-phase core: Single-phase core has a single two-column stack core, single-phase single-column side yoke type four-column core and other forms; The three-phase core has a variety of forms, such as the three-phase column stack core and the three-phase side-yoke five-column core.

Three-dimensional and planar core: The core column and iron yoke of three-dimensional core are not in a plane. There are various forms of radial, involute, symmetrical and so on; The core of the flat type iron core and the iron yoke are in the same plane, which has high mechanical strength and good manufacturability.

4. Classification by manufacturing process

Stack core and roll core: Stack core is made of stack core and is a common manufacturing process. There are many forms of coiled core, such as involute core and so on.

transformer core

The main components and characteristics of transformer core

1. Iron yoke: As the main part of the iron core, the iron yoke carries the magnetic flux of the transformer. It is made of silicon steel sheet laminated and has low hysteresis loss and eddy current loss, thus improving the efficiency of the transformer. In addition, the shape and size of the yoke also have an important impact on the magnetic circuit design of the transformer.

2. Clamp: The main function of the clamp is to fix the yoke and winding to ensure that they will not be deformed or displaced during the operation of the transformer. The clamp is usually made of a high-strength, high-rigidity material, such as steel plate or cast steel.

3. Winding: Winding is another important part of the transformer, which is responsible for converting electrical energy from one voltage level to another voltage level. The winding is usually made of wire wound and arranged on the iron core in a certain way. The design and manufacture of windings have an important effect on the performance of transformers.

4. Insulation parts: Insulation parts are materials used to isolate different potential parts of the transformer. In the iron core, the insulation is mainly used to isolate the potential difference between the yoke and the winding to prevent electrical breakdown caused by excessive potential difference. Insulating parts are usually made of insulating paper, insulating paint and other materials, which has good insulation properties and high temperature resistance.

The role of the iron core in the transformer

‌Forming magnetic circuit: The transformer core is composed of silicon steel sheets to form a closed magnetic circuit. The role of the iron core is to form the magnetic circuit of the transformer, so that the primary side and the secondary side of the transformer are coupled through the magnetic circuit‌.

‌Pilot flux: When alternating current is passed to the primary side of the transformer, alternating flux is generated in the core. The function of the core is to guide the magnetic flux so that the magnetic flux forms a closed loop in the core, thus generating the induced electromotive force on the secondary side‌.

‌Reduce reluctance: The permeability of the iron core is much higher than that of the air. The use of the iron core can greatly reduce the reluctance and improve the efficiency of the magnetic flux‌.

‌Reduced iron loss: There is an insulating layer between the silicon steel sheets of the core, which reduces the generation of eddy currents and thus reduces iron loss‌.

Isolated electromagnetic interference: The iron core can also play a certain isolation role to reduce the electromagnetic interference between the primary side and the secondary side‌.