What is the Sandwich Winding Method for Transformers

Sandwich winding is very common in the manufacturing and designing of high-frequency power transformers. It involves alternating layers of two windings (usually primary and secondary) to increase the coupling area between them. This ensures effective performance and reduces high-frequency leakage inductance. The main characteristic of this method is the layer-by-layer winding in which one winding is sandwiched between the other two layers.

Types of Sandwich Winding For Transformers

The following are two types of methods used for sandwiching transformers:

Primary Sandwiched Secondary

This is also called PSS; in this, the primary winding is sandwiched between two layers of secondary winding. It helps in reducing the leakage inductance and also improves the efficiency of transformer performance. This method is best when magnetic flux needs to be contained, as it helps reduce energy losses.

Secondary Sandwiched Secondary 

This method is known as SSP, and the secondary winding is sandwiched between two layers of the primary winding. It is best suited for applications where primary winding has a high current rating compared to secondary winding. This helps in improving the thermal performance and efficiency of a transformer.

Pros and Cons of Sandwich Winding

Here are the pros and cons of sandwich winding:

Pros

Sandwich winding offers various benefits for a variety of industries. Some of them are as follows:

• Helps in Reducing Leakage Induction

This method is very beneficial in reducing the voltage stress in a transformer. It reduces the leakage inductance, which minimizes frequent energy loss. It increases the coupling area between the primary and secondary layers of winding. This keeps the performance in check, increasing overall efficiency. 

• Effective in Reducing Copper Loss

Secondary-sandwiched winding is effective in reducing copper loss, which causes a rise in temperature. The output is low voltage and high current, so heat generation is in check due to reduced winding length.

• Improves Thermal Performance

Smooth electric flow in a transformer is achieved by using the sandwich winding method. This reduces the chances of hotspots within the transformer. Due to this, such a method is best for improving thermal performance and effective heat distribution. 

• Compact Design

Unlike other methods, this is perfect for places with limited space. This design is suited to cramped spaces and allows a compact design ideal for various applications.

• Cost-Effective

Frequent repairs on copper can cause material costs and money on professional help. This winding method minimizes the need for copper during winding. Therefore, it is one of the most cost-effective winding methods. 

Cons

The sandwich winding method has some cons that must be kept in mind while using it:

• Complex Winding Design

Sandwiched winding is placed in different positions, making its design more complex. Primary-sandwiched-secondary and secondary-sandwiched-primary windings each have their pros and cons. If the wrong method is selected for winding, it may not be suitable for specific design and application requirements.

• Difficulty in Testing

The coupling capaciticies between primary and secondary windings make it difficult to measure the transformer performance. The mutual influence between these two parameters must be considered when measuring leakage inductance and other tests.

• Needs High-Process Requirements

Commonly, sandwich winding needs a flat winding to reduce the chances of leakage inductance and improve coupling. However, it is quite challenging to maintain the flatness during the winding process due to many factors. The design and manufacturing of high-frequency transformers require expertise and keen focus. 

Moreover, higher insulation is needed since the sandwich winding increases the coupling area between the primary and seconding layers. If this factor is neglected, it can result in leakage and frequent short circuits. 

• Increased Coupling Capacitance

This method increases the coupling capacitance in two winding layers. While the switching power supply is operating, these distributed capacities are frequently charged and discharged. This reduces the power supply efficiency and also disrupts the distributed inductance of the windings. Due to this, a ringing noise is produced, which can be irritating.

• Difficulty in Repair and Less Scalability

Sandwich windings can be difficult to repair or replace due to the complexity of their operation and design. This increases the maintenance cost and the frequency of regular checks. Additionally, this method of winding is less scalable, which makes it less suitable for very large transformers.

• Complex EMI Testing 

EMI refers to electromagnetic interference, which can be difficult to test due to the impact of sandwich winding. Due to the close winding of the two layers, there is a shielding effect that disrupts the accurate readings of EMI emissions. This also increases the risk of false readings as it is harder to get isolated signals. When conducting EMI tests, multiple factors should be considered, and measures must be taken to suppress EMI.

Concluding Words

Similar to any other winding method, sandwich winding offers advantages and disadvantages. While using this method in practical applications, all factors must be considered. If you are looking for the best professional sandwich winding, Jingda is the best. They offer high-end and industry-grade products for various applications.