Dry Type Transformer

What is a Dry Type Transformer?

Is an electrical machine (air cooled) to step up or step down AC voltages, to adapt them to the operating conditions of the connected devices within a voltage range (upper and lower), they also have the ability to galvanically separate both levels of voltage, all this safely without affecting the frequency. The windings of a dry type transformer are in a physical medium of air, cast resin or completely enclosed, that is, they are not impregnated or immersed in any liquid such as oils, silicones or similar materials.

Dry type transformers are commonly used for medium voltage, such as auxiliary service transformers in large plants or electrical systems, supply of industries and companies of all kinds, shopping centers, schools, institutions, residential distribution/supply, and an extensive list of other uses. These Transformers are static machines that do not have moving parts, which contributes to lengthening their useful life and minimizing maintenance

They are the most important device in an electrical system, for this reason we must protect them as much as possible. We are experts in protection relays, we manufacture protection relays specialized in dry type transformers with hundreds of thousands of units installed around the world, click below to know about it:

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Difference between dry type transformer and oil type transformer

The differences between this two kinds of transformers are:

Maintenance: Oil type transformers require oil maintenance. The oil needs to be sampled, but the dry type transformers do not contain oil.

Efficiency: Dry type has higher energy loss. Oil transformers have a better energy efficiency, and as a result longer lifespan.

Operation Costs (energy):Dry type transformers have higher energy (loss) costs than Oil type transformers.

Noise: Oil type transformers have a lower operating noise level.

Recyclability: Oil transformer has an easier Metal/copper recyclability.

Voltage Capabilities: Dry transformers are designed for small to medium power applications (lower voltages than oil types). Oil transformers handle higher loads at higher voltages.

Location safety: Dry type is used in buildings, because they are environmentally safer, and are less flammable, ideal for shopping malls, hospitals,residential complexes. Oil transformers are used in outdoor installations due to the possibility of oil leakage with a higher fire risk, but these units are more environmentally friendly.

Preventive maintenance checklist for dry type transformer

The following steps are essential for the preventive maintenance of dry type transformers the checklist is:

- Clean the HV and LV windings from dust deposits, dirt and condensation. Use a vacuum cleaner to avoid dispersion of dirt and dust on the transformer.

- Room cleaning and check windows shield for breaks 

- Room roof check for water infiltration

- Check for temperature rise of coils in normal conditions.

- Check cables and busbars are tightened

- Inspect insulation for any discoloration or signs of heat damage

- Isolation dampers should be monitored for signs of deterioration

- Clean and check cooling fans functionality

Dry type transformer tap changer

A tap changer is always located in the center part of the HV coil and is a busbar switch used to change the output voltage of a transformer. By altering the position of the Tap changer you will change the ratio of the transformer.   In normal operations, voltages in medium voltage are not always nominal.

There are 2 common types:  de-energized tap changer (DETC) and an on-load tap changer (LTC)

Dry type transformer clearance requirements and hs code

Importing documents is important to avoid problems with local authorities.  Correct HS code must be provided by the manufacturer by the time of the purchase order.   Local rules on transport security and insurance coverage must be investigated prior to purchase order, and HS code is always required.

Harmonized System (HS) Codes are commonly used throughout the export process for goods.  The Harmonized System is an international nomenclature for the classification of products. It allows countries to classify traded goods for customs purposes. At the international level, the Harmonized System (HS) is a six-digit code system.

Dry type transformer dimensions and weight

During transport, the Dry type transformer must be adequately fixed as indicated by the manufacturer. HV and LV con- nections must not be stressed by the retaining straps. Once the transformer is at its destination, it is highly recommended to carefully examine it.  In particular the HV and LV terminals and connections, presence of scratches and/or cracks on the windings of MV, integrity of the protection enclosure, presence of impurities, dirt, foreign body, moisture or water.

High voltage dry type transformer

Dry type transformers are normally found with a primary voltage of 30KV, 20KV, 15KV and 10KV.   The high voltage winding (HV winding) requires  enormous technical know-how.   Cast resin transformers are characterized by the conductors of the HV winding being embedded completely in an enclosed cast resin body.   Surge-proof double-layer winding enables the handling of high surge voltages.  These special features imply a high degree of safety both regarding operation and security.

3 phase dry type transformer

3 phase dry type transformers are used to convert the 3-phase mains Medium voltage into a low voltage. To cater for the wide range of application areas involved,these transformers are essentially available in the same kinds of designs as the single-phase transformers:

• Three-phase dry-type transformer: separate winding version

• Three-phase series transformer: autotransformer winding version

• Three-phase safety, isolating, mains or insulating transformer: separate winding version

Coils of a dry type transformer are under  cast resin or completely enclosed, and are not immersed in any liquid such as oils, silicones or similar materials.

3 Phase dry type transformers are commonly used for medium voltage, such as auxiliary service transformers in the supply of industries, shopping centers, institutions, residential, and an extensive list of other uses. These Transformers are static machines that do not have moving parts, which contributes to lengthening their useful life and minimizing maintenance

Cast Resin Transformer information