What is a shell transformer

Three-phase transformer structure

A three-phase transformer is used to transmit a large amount of power. The three-phase transformer is required to build up and reduce the voltages at different stages of a network. The three-phase transformer is constructed in two ways.

  1. Three separate single-phase transformers are suitably connected for three-phase operation.
  2. A single three-phase transformer that combines the cores and windings of all three phases into a single structure.

The three single-phase transformers can be used as a three-phase transformer if their primary and secondary windings are connected together. The three-phase transformer supply has many advantages compared to three single-phase units as it takes up very little space and is also much smaller, smaller and cheaper. The three-phase transformer is mainly classified into two types; H. The core type transformer and the shell type transformer.

Core type three phase transformer

Imagine a three phase core type transformer at an angle of 120 ° to each other as shown in the figure below. When the balanced three-phase sinusoidal voltages are applied to the windings, the fluxes are φaφb and φc So wants to be sinusoidal and balanced. When the three legs that carry these rivers are combined, the total flow in the merged leg becomes zero. This leg can therefore be removed as it does not contain any river. This structure is not suitable for the core.

The core of the three-phase transformer is usually composed of three members in the same plane. This can be built up using stack lamination. Each leg of this core carries the low-voltage and high-voltage windings. The low-voltage windings are isolated from the core from the high-voltage windings.

The low windings are placed next to the core with suitable insulation between the core and the low voltage windings. The high voltage windings are placed over the low voltage windings with suitable insulation therebetween. The magnetic paths of legs a and c are larger than those of legs b, the construction is not symmetrical and there is an imbalance in the magnetizing current.

Shell-type three-phase transformer

The shell type 3-phase transformer can be constructed by stacking three single-phase shell transformers as shown in the following figure. The winding direction of the central unit b is opposite to that of the units a and c. When the system is aligned with the phase sequence a-b-c, the flow is also balanced

The size of this combined flow is equal to the size of each of its components. The cross-sectional area of ​​the combined yoke is the same as that of the outer leg and the upper and lower portions of the yoke. The imbalance in the magnetic path has very little influence on the performance of the three shell transformers. The windings of the three-phase transformer of the shell type are connected in delta or star as desired.

So see; Three transformer connections.