Silicon Steel in Transformers

The main components of a transformer are the iron core and the windings. The core is primarily made of laminated silicon steel sheets. With a silicon content ranging from 0.8% to 4.8%, they possess strong magnetic permeability.

Pre-cut silicon steel sheets

When a transformer operates, it incurs power transmission losses. There are two main types of losses: one is copper loss, which occurs due to the resistance of the windings; and the other iron loss, which originates within the silicon steel sheets. Iron loss itself is caused by two main phenomena: hysteresis loss and eddy current loss.

 

transformer hysteresis curve

Hysteresis loss is the iron loss that occurs due to the hysteresis phenomenon during the magnetization process of the iron core. The magnitude of this loss is directly proportional to the area enclosed by the material's hysteresis loop. Silicon steel has a narrow hysteresis loop, so using it for the transformer core results in smaller hysteresis loss.

 

Transformer eddy-current loss

Eddy current loss is caused by circulating currents induced within the core material by the alternating magnetic flux. These currents flow in planes perpendicular to the magnetic flux and also result in heat generation. To reduce this loss, the iron core is constructed using laminated silicon steel sheets, which increases the resistance in the path of the eddy currents.

 

 

Silicon steel sheets determine the power loss of a transformer. As mentioned above, their size and shape are important factors influencing power loss. Theoretically, the thinner the silicon steel sheets and the narrower the laminated strips, the better the effect. However, the efficiency of lamination and the effective cross-section also need to be considered. Typically, transformer cores use cold-rolled silicon steel sheets, often in an "E" or "I" shape, with a standard thickness of 0.35mm.

Core for Oil Immersed Transformers

Transformers operate on the principle of electromagnetic induction. Two windings, a primary and a secondary, are wound around a closed iron core. When an alternating voltage is applied to the primary winding, an alternating current flows through it, creating a magnetomotive force (MMF). This MMF drives an alternating main magnetic flux through the silicon steel core.

 According to Lenz's law, the magnetic flux produced by the induced current will oppose the change in the original magnetic flux. When the primary magnetic flux increases, the magnetic flux produced by the induced current opposes it, and a lower-level alternating voltage appears in the secondary winding.

A. Low iron loss. This is the most critical indicator of quality. Global standards classify grades primarily based on iron loss values. The lower the iron loss, the higher the grade and the better the quality.

B. High magnetic induction. Silicon steel sheets that can achieve a higher magnetic induction under the same magnetic field will result in smaller and lighter transformer cores. This, in turn, saves silicon steel, copper wire, and insulating materials.

C. High stacking factor. Smooth, flat surfaces and uniform thickness in silicon steel sheets improve the packing density of the core. This leads to an increase in space efficiency and magnetic performance.

VKE's Silicon Steel Cutting Workshop

D. Good punching performance. This property is especially important for manufacturing cores used in small and micro motors.

E. Good adhesion and weldability of the surface insulation coating. A durable insulating coating that adheres well and allows for reliable welding is essential for core assembly and performance.

F. Magnetic aging resistance. The material should maintain stable magnetic properties over time and under operational stresses.

G. Required delivery condition. Silicon steel sheets must be supplied after annealing and pickling processes to ensure optimal magnetic and mechanical properties.