Dry-Type Transformers Improved Short Circuit Quality

A dry-type transformer is a type of transformer that never uses any insulating liquid where its winding or core is immersed in liquid. Rather the windings and core are kept inside a fixed tank that is pressurized with air.

Type of Dry Type Transformers

Dry-type transformers are of two types

1. Cast Resin Dry Type Transformer (CRT)

Cast resin dry type transformer (CRT) is used in high moisture zones. It is because of its primary and secondary windings are encased with epoxy resin. This encapsulation helps in hindering moisture to enter to impact the winding material. Complete security is achieved by this cast resin encapsulation so the transformer can operate without break in deep moisture inclined zone. Accordingly, this transformer is non-hygroscopic.

This type of transformer is available in ratings of 25 KVA to 12,500 KVA, with an insulation class of F (90 degrees C Temperature Rise).

This type of transformer has some featured advantages benefits.

  • Can be fitted outside in IP 45 enclosure.
  • Finally, it is non-hygroscopic.
  • Better overload capacity.
  • As it is with non-inflammable winding insulation, it offers zero peril to fire risk. Therefore, it is suitable for indoor installation.
  • Low partial release along with low loss. Accordingly, efficiency is very high.

2. Vacuum pressure Impregnated Transformer (VPI)

Minimum flammable material is used to make this type of transformer as insulation of windings. Foil or strip in a continuous layer is utilized to create the windings of this transformer. However, for higher voltages, the winding is made of plates that are connected in series or parallel as indicated by power rating according to the voltage level.

The primary and secondary winding with the core is bound safely inside a vacuum protective box. The protection of Moisture Ingress is high and it never gets impacted by moisture. This type of transformer is accessible from 5KVA to 30MVA with insulation grade F(155oC) and H(180oC). It comes with Protection up to IP56.

This type of transformer has a couple of advantages.

  • High mechanical quality.
  • Insulation that is void-free.
  • No temperature fluctuation.
  • Easy maintenance.
  • Less prone to fire risk.

Essential components to design a Dry Type Transformer

Insulation type Choice

Generally, an F and H class of insulation is used. We utilize these kinds of insulation to insulate the primary and secondary winding. It is because these classes have high temperatures withstand property, for instance, 155 degrees C for F and 180 degrees C for H class of insulation. Generally, varnish and polyester resin are used as insulation of the winding. Besides the temperature withstands capacity, mechanical strength; dielectric quality, and resistance to thermal shock are the essential abilities that must be fulfilled by the insulation selected for the windings.

Determination of Winding Material of Dry-Type Transformers

For the most part, copper and aluminum are used to make the winding or coil. However, copper is a better conductor, aluminum conductor wound transformer has negligible expense and weight. For a similar current rating, a copper conductor with a low cross-section is used as the winding material in the transformer. Better mechanical strength is provided by Copper coil than the aluminum coil.

Determination of Core Material with Low Hysteresis Loss in Dry-Type Transformers

Core material assurance is noteworthy in the plan of the transformer. Core material should have high permeability and less hysteresis loss. Nonetheless, both can’t be achieved in any core material. By and large, silicon steel, CRGO, and some more are used to allow minimum hysteresis loss with higher permeability.

Life Expectancy

The life of the transformer depends upon the breakdown of winding insulation due to temperature rising effect in winding due to overloading. Usually, the installation of class B, F, and H are preferred for dry type transformer to withstand higher temperature gradient including encompassing temperature. Thus, the design of the transformer must be done concerning the rise of the temperature of working full load conditions.


No-load losses mean loss of core and eddy current that is free of loading condition. Notwithstanding, in loading condition loss of copper occurs that includes the iron loss to grow the value of voltage regulation, for instance, poor voltage regulation. Leakage reactance and winding resistance must be within moderate value to restrict this loss and better voltage regulation, hence higher capability.


Dry-type transformers give safety against fire and leakage, which also lessens concerns related to the environment and health. These types of transformers are free of moisture and have upgraded impulse and short circuit quality. Dry-type transformers have wide importance in residential and industrials segments. Due to the different advantages of dry-type transformers, the market is most likely to see growth in the upcoming years.