Dry Type Transformers

Working Principle of a Dry-type Transformer

A dry-type transformer features a primary and a secondary coil wrapped around a magnetic core. It operates on the principle of Faraday’s law of electromagnetic induction, where the alternating current (AC) induces electromagnetic force in a coil around the magnetic core. The induced current flows in the opposite direction on another wire coil wound on the same core. This results in the AC voltage conversion from the primary to the secondary winding. This process facilitates energy transfer between two circuits through electromagnetic energy transfer.

Types of Dry-type Transformers by Bruce Electric Equipment

Bruce Electric Equipment provides different types of dry-type transformers for sale and the following are a few prominent ones among them.

• Cast Resin Type (CRT) Dry-type Transformers: These transformers feature an epoxy resin and quartz powder mixture and are enclosed in an electrical insulator. This construction makes them ideal for areas where they may be exposed to moisture. Our CRT-type transformers are environment-friendly, reliable, crack resistant, have low load losses and offer a host of other advantages.
• Vacuum Pressure Impregnated (VPI) Dry-type Transformers: The core and windings of these transformers are immersed in the resin, which allows for excellent mechanical and electrical performance. The resin serves as the insulator that helps improve the electrical conductivity and mechanical strength of this transformer. VPI dry transformers are used in industrial and commercial environments where lasting electrical equipment is required. They are also suited for high moisture environments.
• Encapsulated Dry-type Transformers: These dry-type transformers are encapsulated in a protective covering made of epoxy resin, hence their name. Encapsulation offers protection against dust, moisture, and other contaminants. These devices are used in commercial and industrial settings, such as schools, shopping centers, and hospitals, where ambient environments exist, and low maintenance is a key requirement.
• Open Wound Dry-type Transformers: These dry-type transformers receive their name from the “dip and bake” production method employed in their construction. The conductor coils used in the transformer are preheated and dipped in varnish at high temperatures and baked to cure the varnish. This construction method makes the transformer suitable for high-temperature environments.
• Cast Coil Dry-type Transformers: These are low-loss cast resin dry-type transformers with low-voltage (LV) windings with either copper sheets or copper conductors and high-voltage (HV) windings with copper conductors. The copper sheets or conductors used in the LV winding are reinforced by glass fiber and cast with resin in a vacuum.

Advantages of Dry-type transformers  

There are several advantages of using Industrial dry-type transformers.

• These transformers do not contain toxic or flammable liquids, which can leak or catch fire.
• The transformers do not emit harmful or toxic gases, which makes them environmentally friendly.
• These transformers do not require any special foundations or vaults for installation.
• They can be placed near to the load, which reduces the need for costly cables.
• Dry-type transformers feature better thermal endurance and heat dissipation capabilities than liquid-filled transformers. They possess excellent capacity to support overloads.
• These transformers do not need fire protection systems and civil installation works, which helps reduce their installation costs.
• Dry-type transformers have high mechanical strength and low impedance. These properties offer an excellent resistance to short-circuit currents.
• These transformers have high-quality insulation materials that can withstand high temperatures without degrading.
• Dry-type transformers feature high moisture ingress protection and corrosion resistance, making them suitable for contaminated and damp areas.

Tips to Choose Dry-type Transformers  

Choosing the right used dry type transformer for your application involves several factors. Here are some tips that will help you make the right choice.

1. Consider the kVA/kW rating: You must consider the kW/kVA rating of the transformer. The kVA rating represents the apparent power, and kW is the real power. You can identify your application’s total kVA/kW rating by summing the power requirements of all devices connected to it. Always be sure to buy a dry-type transformer with a rating higher than the calculated power needs. This would aid you to plan for inrush currents or meet the future expansion demands.
2. Consider the primary and secondary voltage: Address your application’s input and output voltage requirements. You can choose the transformer whose primary voltage rating matches the incoming supply voltage. When choosing the secondary voltage, you should address the power requirements of the connected equipment. Depending on your application, some standard secondary voltages include 120V, 240V, and 480V.
3. Consider the harmonic Load: Some applications, such as LED lighting, computers, and variable frequency drives may introduce non-linear loads. If network features, these applications ensure to invest in a transformer with a K-Factor rating. This rating prevents the transformer from overheating when exposed to harmonics.
4. Analyze the cooling method: Dry-type transformers employ air circulation, unlike liquid-filled transformers. You can choose between a transformer with fan-assisted cooling or natural air convection cooling depending on your application’s kVA load or ambient temperature.
5. Focus on the enclosure type: Dry-type transformers are offered in enclosures. However, not all enclosures may suit your operational environment. In that case, you must consider the NEMA ratings that indicate the suitability of an enclosure for different environmental conditions. For instance, if you plan to install the transformer in a factory environment where it may be exposed to moisture or dust, you must invest in a transformer with a NEMA 4X or 3R enclosure. It shows their resistance to sleet, rain, and airborne dust.
6. Focus on standards compliance and certifications: Check if the transformer meets the relevant standards and certifications, such as UL, IEEE, ANSI, etc. Compliance with these standards or certifications ensures their reliability and safety in an operational environment.
7. Manufacturer reputation and warranty: Always ensure to buy the transformer from a manufacturer that offers excellent technical support, customer service, and warranty.
8. Consult the supplier: If you have yet to decide, consult an experienced supplier. If you have been considering any of the dry-type transformers listed on this page, you can contact our team of experts. They will work closely with you to understand the requirements and offer you the best solution.

Applications of Dry-type transformers

Dry-type transformers are used in the following industries.

• Manufacturing: Plastic and rubber molding, welding, sheet metal fabrication, machine shops
• Electrical Utilities: Distribution facilities, power plants, customer feeds, distribution units
• Hospitals and Medical Centers: Diagnostic centers, critical patient care, surgery units, laboratories
• Automation: Bottling units, paper mills, food processing facilities, metal processing mills

At Bruce Electric, we offer new, reconditioned, and used dry-type transformer for sale from different brands. Click on RFQ Now beside every transformer.

FAQ:

Are there any specific installation requirements for your dry-type transformers?

Yes, these transformers must be installed upright at a level in the area with free air circulation.

What is the shelf life of dry-type transformers?

If installed and maintained properly according to the manufacturer’s recommendation, these transformers can last more than 20 years. Ensure that they are installed in clean, dry, and well-ventilated areas.

What is the K-Factor rating in dry-type transformers?

K-factor rating refers to the transformer’s ability to handle harmonic currents produced by non-linear loads without increasing the unit’s temperature. Many applications add a significant amount of current to electrical systems, which, if not handled properly, can lead to overheating and failure of the transformer.

Can dry-type transformers be used outside?

Dry-type transformers are designed for indoor use and are protected by a weatherproof enclosure. Transformers exceeding 112 ½ kVA must be installed outside 12 inches of combustible materials. If your dry-type transformer has Class 155 insulation systems, it can be installed within 12 inches of combustible materials.

Is it safe to operate the dry-type transformer in an overloaded condition?

No, it is not recommended to operate the dry-type transformer in an overloaded condition. Overloading can lead to overheating, which can lead to rapid deterioration of insulation and coil failure.

Do these dry-type transformers work when reverse-connected?

Yes, dry-type transformers can be reverse-connected without losing the KVA rating. However, this reverse feeding imposes certain restrictions, such as increased inrush current or the need for larger breakers.