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Combining the Best of Dry-Type and Liquid Cooling Mechanism

Depending on the insulation technology, transformers are broadly segregated into two categories – dry-type and liquid-filled or liquid-immersed. In the latter, the insulation liquid also acts as a cooling agent to disperse or absorb heat generated by the windings. In dry-type transformers, the windings are air-cooled. While liquid-filled transformers bring advantages in terms of size and weight, losses & efficiency, noise and overload capability to the table, dry-type transformers are preferred for fire safety, environmental safety, lower maintenance cost and short circuit strength.

But what if there was an opportunity to get the best of both technologies in one single transformer type?

Hitachi Energy introduces the CompactCool technology for transformers which combines the advantages of both liquid-filled and dry-type cooling technology. CompactCool retains the benefits of a dry-type transformer while reducing transformer size and weight by extracting losses in an innovative and controlled manner.

This makes CompactCool an ideal power transmission device for data center and renewable energy segments, where factors such as optimized footprint, safety and low maintenance are key to sustainable transformer operations. The CompactCool technology combines dry-type solid insulation with direct liquid-cooling to deliver:

CompactCool Technology

CompactCool leverages an advanced cooling mechanism where a K class liquid coolant is used inside of the coils to extract the losses out of windings and circulate them through an external heat exchanger.


The watts (heat) then get dissipated to an external ambience (to air or to a water circuit supply).


CompactCool does not require an enclosure.

Photo of CompactCool Transformer Technology by Hitachi Energy

CompactCool - Next-Gen Transformer Technology Promising Unmatched Efficiency and Reliability

Compact form factor and smaller transformer footprint requirements are often seen as a challenge in sectors like renewable energy production. In both onshore and offshore wind industry for instance, transformers need to be installed on the ground floor of wind towers, on the first level or inside of turbine nacelle platforms, since the available space for transformer installation is often limited. It is here where CompactCool technology creates a difference by solving the dimensional constraints of transformer installation, while offering ease of logistics, footprint optimization, and reduced installation costs.

The CompactCool technology from Hitachi Energy infuses safety and reliability into transformers through:

  • Optimized cooling
  • Loss Extraction in a controlled way
  • Minimized volume of liquid coolant
  • Low-cost maintainability and trouble-free operations

With CompactCool Technology, installing transformers in small enclosures or wind towers wouldn’t be an issue anymore. Join us as we orchestrate a transformer innovation that perfectly blends the value propositions of both dry-type and liquid-filled transformers.

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Dry-type transformers

Hitachi Energy offers a full range of dry-type transformers with primary voltages through 72.5 kV built according to all major standards including IEC and ANSI.


Hitachi Energy offers distribution and power transformers, dry-type and liquid-filled transformers as well as services, to be used in utility, industrial and commercial applications.

CompactCool Technology Product Brochure