Dry Type Transformer Specifications


Dry-Type-TransformerTransformers change voltages from one level to another. Most commonly, that change involves very high power line transmission voltages (500 kV) being reduced to the much lower levels used in heavy industry (as much as 30 kV). Dry type, or air-cooled, transformers accomplish this function so safely and efficiently that they are commonly used for indoor applications where other transformer types are considered too risky. Electric Service Company (ELSCO) is the leading manufacturer of and repair facility for dry type transformers.


A dry type transformer, like all transformers, uses basic physical principles of electricity and magnetic coupling to produce any desired voltage level:

When a fluctuating electric current flows through a wire, it generates a fluctuating magnetic field or “magnetic flux” all around it.
When a magnetic field fluctuates around a piece of wire, it generates an electric current in the wire.
So, if a second wire is placed next to the first charged wire, within that fluctuating magnetic flux field, electric current is induced to flow in the second wire. Thus, electricity is “passed” from the first wire to the second without the two wires actually touching.

In all transformers, including dry type transformers, the first wire, or primary coil winding, is connected to an alternating current (AC) voltage source while wrapped around a magnetic core, producing a fluctuating current in the wire coil. That fluctuating current magnetizes the core. The second wire coil, or secondary winding, is wrapped around another part of the core. The fluctuating magnetic field in the core induces a current in the secondary coil. The relative number of turns each winding makes around the core determines how much voltage is produced in the secondary. Most commonly, transformers step voltage down from high to low; but turns ratios can also be arranged to step up voltage if necessary, for instance, to allow 240-V foreign appliances to work in the US where the voltage supplied is 120 V.

Dry-Type-Transformer Specs

Basic Transformer Core Layout

This electromechanical linkage in a transformer makes it possible for the same megavoltage source, like a dam, wind farm, or coal-powered generator, to supply power for both a high-demand steel mill and a low-demand kitchen toaster. The particular application will determine what size equipment is needed and which kind – a dry type transformer or some other technology. ELSCO can provide products, service and information covering many different transformer types, all of which contain copper windings, the most efficient coil wire material.

Note that while power sources are rated in kilovolts (kV) — the potential difference measured between two electrical points — transformers are rated in kilovolt-amperes, or kVA — the product of current and voltage, signifying the actual, or apparent, power consumed by an electrical load, that is, the energy required to actually run a device. Electric Service Company supplies dry type transformers from 500 kVA – the power necessary to run a school or small industrial building — to 5000 kVA, enough for a power plant.


But whatever specific transformer equipment is needed, major limiting factors to consider include heat, maintenance, and safety. Dry type transformers are especially valued for their stellar performance via these three important factors.

An intrinsic byproduct of the transformation process is heat, specifically, the “I2R” (I=Current, R=Resistance) heating that occurs when current runs through a conductive wire. Heat breaks down transformer composition materials and insulation, resulting in less efficiency and shorter service life. Transformer heat is best controlled by the oil used in oil filled transformers, which conducts the heat away from the heat-producing parts while protecting other internal transformer workings. That is why these transformers are used in the highest voltage applications like high-voltage transmission.

But with proper sizing and placement, as well as fans when appropriate, dry type transformers, which cool by air ventilation, provide excellent, low-heat service in tight enclosures and indoor situations where oil leakage could cause a fire or significant environmental hazard. Clearly, a system without these threats offers enhanced safety for indoor applications. A dry type transformer will typically incorporate a design with greater internal clearances to allow for better heat dissipation. No fireproofing, oil catch basins or venting of toxic gasses are required, and the transformer can be close to the load, minimizing secondary line losses. But a dry type transformer also reduces maintenance with no need to replace transformer oil while avoiding the contaminant and composition checks necessary for proper oil insulation and cooling.


These are the reasons why Electric Service Company provides so many dry type transformers to schools, institutions and commercial buildings where reliability and safety are mandatory. Relative ease of repair and smaller size if movement or removal are necessary further explain why a dry type transformer is often the choice for lower voltage applications. But ELSCO is also known for its complete stock and expert advice on selection and application of oil filled transformers. These transformers have the same level of craftsmanship and state of the art technology as Electric Service Company’s dry type transformers.