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The Different Parts of a Dry Type Transformer

The Different Parts of a Dry Type Transformer

Dry type transformers enable energy transfer through electromagnetic induction. They employ solid insulation and cooling mechanisms like natural convection or forced air. There are a few fundamental components to consider, from magnetic cores to insulation to cooling systems. Each piece works seamlessly together to enhance efficiency, safety and reliability in various applications. Understanding these elements offers valuable insights into the robust functioning of dry type transformers across industries.

What Is a Dry Type Transformer? 

Dry type transformers are electrical devices that transfer electrical energy from high-voltage primary sources to lower-voltage secondary circuits. Unlike oil-filled transformers that use oil for insulation and cooling, dry type transformers use solid insulation materials.

Here are some key points about dry type transformers:

  • Insulation technique: Dry type transformers employ insulation materials like polyester varnish or epoxy to insulate windings and the core and also to seal the core & coils and keep moisture out.
  • Cooling mechanism: Cooling fans regulate temperatures to prevent overheating. They use natural convection and forced air cooling to manage thermal conditions. 
  • Fire safety: An inherent advantage of dry type transformers is their superior fire safety compared to oil-filled transformers. The absence of flammable oil significantly minimizes the risk of fire.
  • Indoor installation suitability: Dry type transformers are particularly suitable for indoor installations since there are no containment requirements like there are for oil-filled transformers.
  • Maintenance: There’s no need to monitor or replace oil levels, simplifying maintenance procedures.
  • Environmental considerations: Dry type transformers are more eco-friendly since there is no chance of oil contaminating the soil or water.
  • Applications: Dry type transformers find extensive utility in commercial structures, industrial complexes, medical institutions, educational establishments and other settings where prioritizing fire safety and environmental integrity is imperative.
  • Voltage and power ratings: Dry type transformers are available in various voltage and power classifications, rendering them adaptable for diverse application scenarios.
Here are some key points about dry type transformers:

What Are the Different Parts of a Dry Type Transformer? 

A dry type transformer contains many interdependent components that enable energy transfer. Knowing these parts and their roles can help you understand how a transformer works. Here is a list of dry type transformer parts: 

Core and Windings

The primary winding, connected to the power source, conducts alternating current along a circular path around the core to generate a magnetic field. This field induces a voltage across the secondary winding, enabling energy transfer between the primary and secondary voltages. The precise number of turns within each winding determines the transformer’s voltage transformation ratio. Additional layers to the windings can enhance performance. 

  • Core: Laminated sheets of premium silicon steel minimize eddy current losses and magnetic hysteresis, enhancing energy efficiency.
  • Primary winding: Connected to the power source, it generates a magnetic field that initiates energy transfer.
  • Secondary winding: Induces voltage through electromagnetic induction via the core, transmitting energy to the load.


Solid insulation materials ensure electrical separation between the core, windings and winding layers. These materials separate the windings into multiple layers, mitigating potential short circuits and guaranteeing safe energy transmission. By covering windings and isolating them from the magnetic core, the insulation fortifies the transformer against voltage breakdowns, improves resistance to environmental stressors and enhances thermal performance.

Typical insulation materials include: 

  • Polyester varnish
  • SG-200 glastic sheets and winding combs
  • Dupont Nomex insulation
  • Advanced composites – GPO-3 fiberglass

Cooling Mechanisms

The cooling mechanisms, typically a blend of natural convection and forced air cooling techniques, maintain the transformer’s optimal operational temperature. Balancing these cooling mechanisms helps the transformer’s longevity and reliability.

  • Natural convection: Natural convection employs thermal buoyancy, where hot air rises and cool air falls. Vents and ducts facilitate the upward movement of hot air, drawing in cooler air for passive cooling. This heat transfer process and the strategic design of cooling ducts ensure effective dissipation.
  • Forced air cooling: Fan cooling amplifies airflow, actively dissipating heat and maintaining optimal temperatures.

Enclosure and Protection

The enclosure protects the core and windings from the elements and keeps personnel out for safety.

Terminals, Bushings and Connections

Terminals and supplementary components such as bus bars and bushings integrate the external circuits with the transformer’s internal windings and prevent flashovers. These components bolster electrical efficiency, promote isolation and fortify the transformer’s role within a larger electrical network.

  • Terminals: These parts ensure reliable energy transfer.
  • Bus bars: These robust conductors are designed for high-current applications and enhance electrical efficiency.
  • Bushings: These insulating components extend through the enclosure to facilitate secure external connections.

Tap Changer

A de-energized tap changer allows for voltage adjustment.  Its essential function is to alter the winding turns ratio for voltage adjustment. 

Grounding System

The grounding system redirects redirecting electrical faults away from the transformer, channeling them safely into the ground. This safety measure reduces the probability of electrical shocks, equipment harm, potential fires, injury and death. The grounding system contains a grounding electrode, surge arrestors and fault indicators.

  • Grounding bus: This component provides a low-resistance path for fault currents to safely dissipate into the ground.
  • Surge arrestors: These parts divert transient overvoltage, safeguarding the transformer against voltage spikes.

Temperature Monitoring and Protection

Temperature monitoring and protection mechanisms prevent overheating, a significant concern in transformer function, and take action if temperatures rise too high, preserving the transformer’s operational integrity. Integration with supervisory control and data acquisition (SCADA) systems facilitates real-time data relay, enabling remote monitoring and analysis of temperature trends.

  • Temperature sensors: Thermocouples monitor the temperature in each coil near the top where the hottest spot is. At certain set points it can kick the fans on and once the unit cools to a certain set point, kick the fans off.
  • Protection relays: Relays can activate alarms, shutdowns or remote communications in response to excessive temperatures.

Learn More About ELSCO Transformers 

Discover the advanced capabilities of ELSCO medium-voltage, dry type transformers tailored to your needs. Our experienced team can provide technical insights into the benefits of these transformers. In addition to transformer construction, we offer services like custom bus work, retrofitting and emergency replacements, addressing a wide range of transformer needs. New indoor dry type transformers come with an industry-leading five-year warranty. Additionally, we have never had a failure since we started building transformers in 1988.

Begin your inquiry by completing our online quote form to receive detailed pricing information about our products. For technical questions or additional product details, you can reach us at 513-275-5781.

Learn More About ELSCO Transformers