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Types of transformer

There are several different types of transformers available in the world market, mainly divided by Power and tension supplied, but also depending on its application. Here we list the major differences trying to explain in general their advantages and applications.

SDT Small Distribution Transformers
Single phase transformers, made usually with wound core system and rectangular windings. Specially in use in the British Standard countries as in USA, particularly adapted for small power
Power range: Usually from 50 to 200 kVA within 35 kV
Main use: Distribution in rural areas and countryside
Main advantages: Small production costs with possibility of good automation

DST Distribution Transformers
Usually three phase transformers, immersed in liquid oil as dielectric insulation and enclosed in a tank with cooling system. Recently made hermetically sealed for reduced maintenance and better quality.

Power range: Usually from 250 to 2500 kVA within 35 kV
Main use: Distribution of energy in cities and centre with different houses
Main advantages: Great extension of use in different outdoor application

DTH Dry Type Transformers H class insulation
Usually three phase transformers, but instead of being immersed in oil, the HV side is impregnated into an insulating varnish which will be its dielectric insulation along with open air.

Power range: Usually from 250 to 2500 kVA within 35 kV
Main use: Underground systems, mines and skyscrapers.
Main advantages: Fireproof and explosion-proof, particularly adapted for Indoor applications

CRT Cast Resin Transformers
Usually three phase transformers, but instead of being immersed in oil, the HV side is cast into a resin which will be its dielectric insulation.
Power range: Usually from 250 to 5000 kVA within 35 kV
Main use: Underground systems, mines and skyscrapers.
Main advantages: Fireproof and explosion-proof, particularly adapted for Indoor applications

LDT - Large Distribution Transfomers 
Three phase transformers, usually immersed in liquid oil as dielectric insulation and enclosed in a tank with cooling system.

Power range: Usually from 2500 to 20000 kVA within 35 kV
Main use: Grid interconnections, Industrial application, special application as furnace or railway..
Main advantages: Big power within the tension of distribution 35 kV

SPT/MPT Small and Medium Power Transformers
Three phase transformers, adapted for grid interconnections for small distance Transmission lines till 220 kV.

Power range: Usually from 10 to 50 MVA within 220 kV 
Main use: Interconnecting grids.
Main advantages: Big power and high tension.

LPT Large Power Transformers
Three phase transformers, adapted for grid interconnections for large distance Transmission lines above 220 kV

Power range: Usually from 50 MVA and above 220 kV
Main use: Interconnecting grids and main power station.
Main advantages: Big power and high tension