Ⅰ.What is Dry Type Transformer?
A dry type transformer is a type of transformer which never uses any insulating liquid where its winding or core are immerged in liquid. Rather, the windings and core are kept within a sealed tank that is pressurized with air.
Ⅱ.Types of Dry Type Transformers
The dry type transformer is of two types. They are:
1.Cast Resin Dry Type Transformer (CRT)
2.Vacuum pressure Impregnated Transformer (VPI)
Ⅲ.Cast Resin Dry Type Transformer (CRT)
Cast resin dry type transformer (CRT) is used in the high moisture prone areas. It is because of its primary and secondary windings are encapsulated with epoxy resin. This encapsulation helps to prevent moisture to penetrate to affect the winding material. Complete protection is achieved by this cast resin encapsulation so that the transformer can work without disruption in highly moisture prone area. Thus this transformer is non hygroscopic.
This type of transformer is available in ratings of 25 KVA to 12,500 KVA. with insulation class of F (90oC Temp. Rise).
This type of transformer has some featured advantages. They are
Better over load capacity.Low partial discharge along with low loss. Hence efficiency is very good.
As it is with non inflammable winding insulation, it offers zero risk to fire hazard. So it is suitable for indoor installation.
Can be fitted outdoor in IP 45 enclosure.
And off course non hygroscopic.
Ⅳ.Vacuum Pressure Impregnated Transformer (VPI)
This type of transformer is made with minimum flammable material as insulation of windings. The windings of this transformer are made in foil or strip in a continuous layer. But for higher voltages, the winding is made of disks that are connected in series or parallel as per power rating with respect to voltage level.
The insulation of the winding is void free impregnation that is made with class H polyester resin. The primary and secondary winding with core are laced safely within a vacuum protective box. Moisture Ingress Protection is high and it never gets affected by moisture.
This type of transformer is available from 5KVA to 30MVA with insulation grade F(155oC) and H(180oC). It's with Protection up to IP56.This type of transformer has several advantages. They are:
a.High mechanical strength.
b.Void free insulation.
c.No temperature fluctuation.
d.Easy maintenance.
e.Less prone to fire hazard.