The following are the different types of windings used in transformers:
1.Multi Layer Helical Windings
Multilayer helical windings are typically used for high voltage ratings, such as 110kV and higher. Several cylindrical layers are wound concentrically and in series in these windings.The outer layers of these windings are shorter than the inner layers in order to distribute capacitance evenly. In essence, these windings improve the surge behavior of the transformer.
2.Helical Windings or Spiral Windings
In high-capacity transformers, there are a small number of low-voltage winding turns (20-30 turns or less), but the current is high, so the cross-section of the turns is large, requiring the use of many wires (6 or more). Since wires must be wound in the same layer in a cylindrical winding, many wires cannot be wound in parallel.
It is recommended that the strip’s cross-sectional area not be less than 75 mm to 100 mm square in order to protect sufficient mechanical power. 16 strips are the maximum number of strips that can be used to form a parallel conductor.There are three types of windings: single helix, double helix, and disc helix.
- Single Helical Winding：A single helical winding is an axial winding that follows a helix through a ramp. There is only one layer of turns in each of these windings.
- Double Helical Winding：As a result of the double helical coil, eddy current losses inside the conductor are reduced. Due to the reduced number of parallel conductors, these conductors are used radially.
- Disc-Helical Winding：In disk helical windings, the strips are connected radially from side to side, thereby absorbing the entire radial strength.
3.Disc Windings
By connecting several conductor discs in series, a disc winding can be designed. There is the possibility of winding the platters with different turns of insulated conductors and then coiling them in series. Partitions can be used to separate discs from each other.
Disc winding differs from helical winding in that helical winding involves only a simple twist of one parallel conductor per disc, whereas disc winding involves multiple turns. Transformers rated above 25 kV use disc windings. These windings are also mechanically strong, as is the helix.
4.Foil Windings
Generally, foil windings are constructed using thin aluminum or copper sheets, which are covered multiple times with thin insulating sheets to form multilayer spiral windings. On one side of the plane, the windings can be formed from single-piece or multi-piece windings. Transformers between 12 and 600 Amps are suitable for large capacity transformers.
5.Cylindrical Windings
Windings of this type are used for low voltage applications up to 6.6kV, and their current ratings range from 10-600A. Multiple layers of these windings are often used. To improve cooling conditions, we use round conductors wound with vertical strips. In this arrangement, tubing will be created to assist in the cooling process. With a maximum diameter size of 4mm, these windings are suitable for bare conductors with voltage ratings up to 33kV, 800kVA, and current ratings up to 80A.
6.Cross- Over Windings
Transformer cross windings for small transformers. In order to reduce the voltage between adjacent layers, these windings are divided into several coils that are axially separated by 0.5-1 millimeters. Ideally, the voltage between adjacent coils should not exceed 800-1000 volts.
A coil’s inner end is connected to the coil’s output end. Each coil has an axial length of approximately 50mm, and the spacing between the two coils is approximately 6mm, so that the block of insulating material can be accommodated. Coils have a width of 25 to 50 millimeters. Crossed windings are generally stronger than cylindrical windings. However, the cross has a lower pulse intensity than the columnar. Additionally, this winding consumes a greater amount of labor.
7.Disc & Continuous Disc Winding
In bulk transformers, this type of winding is commonly used where several disks or planar coils are arranged in series or parallel. It is possible to form these coils by winding rectangular strips in a radial direction. Conductor coils are wound on a horizontal plane in a parallel configuration.
Therefore, the formation of this conductor would enhance the strength of the structure
The conductor area ranges from 4 to 50 mm squared, and the current ranges from 12 to 600 amps. Transformer oil passages must have a minimum width of 6mm and are primarily used for 35kV transformers. In addition to providing maximum mechanical axial strength, these windings have another important advantage.
8.Aluminum Windings
There are several types of transformer windings used in North America, including dry and low voltage transformers. The main reason for choosing this aluminum winding is its low cost. Copper windings are the preferred winding material in most parts of the world.
It is easier to wind aluminium windings than copper windings, since aluminium windings are more flexible than copper windings. Due to aluminum’s maximum resistivity, windings contain less eddy current losses.As a result, hot spots are reduced. Transformers with aluminum windings and transformers with copper windings have the same losses and performance. Coils made of aluminum are larger than those made of copper.
