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Cooling systems protect the transformer from accelerated aging by lowering the operating temperature and therefore avoid insulation disruptions leading to transformer failure.

The effect of a malfunctioning cooling system could cause significant disruptions to the availability of the transformer as well as the remaining life. By upgrading the cooling capacity, capital optimization could also be achieved by increasing the rated capacity of the transformer. A well-functioned cooling system requires regular maintenance. Depending on the type, the life expectancy of the cooling devices can be much shorter than the transformer active part and tank.

Cooling system replacement/upgrades: The need to replace or upgrade the cooling system can emerge from a variety of situations, such as old age, “wear and tear,” the move of the transformer, and adaptation to new design technology. Upgrades of cooling systems enable an increase in the loading capacity of the transformer.

One-to-one Replacement

  • Single-tube to double tube
  • Oil-water to oil-air

Upgrades of existing cooling solution from original size to large size

  • From ONAN to ONAF
Cooling System Overhaul & Upgrade for Hitachi Energy Transformer Service

Scope of work

Coolers are cleaned by brushing inside the water tubes or by air-side vacuum cleaning when necessary. The need for cleaning is indicated by increased pressure loss, decreased temperature-difference oil/water/air in/out, increased transformer temperature, decreased water flow, etc. See the manufacturer’s documentation.

For cooling systems, our offering covers the following key components:

Installation Planned Preventive Maintenance Diagnostics Replacements and upgrades
  • Installation Report
  • External visual inspection; looking for rust, leaking gaskets, and noise.
  • External and internal cleaning; water that collects along the flanges and bolts (capillary effect) will eventually create rust, which, if nothing is done, will allow even more water to collect.
  • Replacement of gaskets; often occurs due to the aging of gaskets. Moisture can enter the transformer and create water in the oil and damp insulators. This will increase the aging of the transformer or can develop into a direct malfunction.
  • Maintenance report
  • External and internal inspection, e.g., through ultrasound
  • Diagnostics report

Transformer Component Upgrades

Transformers component upgrades are based on Hitachi Energy's decade-long experience in manufacturing and maintaining its products.

Bushing Replacements

Hitachi Energy offers repair of high-voltage condenser bushings that includes installation, preventive maintenance, condition assessment, and replacement or upgrades.

Tap-changer Overhaul and Upgrades

Hitachi Energy offers the best resource for all tap-changer service requirements and covers services ranging from documentation, design engineering, the latest testing and oil processing, and providing 100% OEM grade parts and life extension kits.


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Transformer service

Aging assets, rising energy demand, and the critical need to avoid unplanned outages are challenging worldwide utilities and industrials. The service portfolio of Hitachi Energy allows utilities and industrials to maximize the return on transformer assets by ensuring high reliability, reducing life cycle costs, and ensuring optimized performance while lowering environmental impact.
Hitachi Energy Power Transformers


Hitachi Energy offers distribution and power transformers, Dry-type and EconiQ™ Transformers as well as services, for industrial and commercial applications.