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Transformer Oil Water Coolers (OFWF)

OFWF – Double duty to keep your transformers cool

Our Hygard transformer oil water cooler is an enhanced shell and tube heat exchanger with the added benefit of a double wall arrangement. Integral leak protection for both tube and tube plates reduces cross-contamination and failures while providing early detection of faults. The shell and tube design is solid, robust, and versatile.

Key benefits

Hyguard - The Sterling Thermal Technology Transformer Oil Water Cooler
  • Safe: Isolates the oil from water circuits with a fail-safe detection of circuit damage.
  • Versatile:  Units are custom designed and made to match your needs in terms of shape, size and materials. They fit all oil filled transformers and can be built to meet all thermal requirements. Designed to be used around the world, passing all known standards and norms.
  • Robust: made for long life and low cost of ownership even in challenging environments and conditions. Based on the universally accepted shell and tube heat exchanger, our double wall configuration is the pinnacle in safety and reliability for critical equipment. With correct maintenance and cleaning, our coolers usually last 25 years or more.


How it works

The power generation, transmission and distribution industries use water-based transformer oil coolers to control the temperature of vital equipment when loads and ambient temperatures are high and where acoustic performance is important.

Power plants use transformers to convert electricity to a high voltage for efficient transportation. Oil is used to cool the transformer windings and dissipate heat. This oil must itself be cooled and recirculated. Water coolers offer an efficient and reliable solution. They also an essential role in controlling the temperature in electrical generation systems. However, it is vital that the cooling water does not have the opportunity to contaminate the oil as this could destroy the transformer.

‘Double barrier’ design for the safest operation

Transformer oil water cooler- Double tube -Design and manufacture by Sterling Thermal Technology
Double tube

Typical shell and tube heat exchangers are externally robust and built to withstand severe conditions. However, even with the most resilient tube material, poor water quality may ultimately cause failure. A double wall cooler, with double tube and tube plates, provides the all-important second barrier to prevent contamination of transformer oil and provide an early warning of a potential failure.

The two barriers separate flows preventing cross-contamination and subsequent machine failure. If one barrier fails, fluid drains away along a dedicated leak path, allowing the cooler to continue operating while you plan your intervention.

The thermal efficiency of the active areas is ensured by actively bonding the two surfaces together and introducing leakage path capillaries for detection.

Customised cooler design

We individually design the coolers to meet your thermal, mechanical and physical requirements. We include a thermal margin for fouling and a mechanical margin to a give long service life. Besides, we mitigate against corrosion and erosion through efficient and proactive design. We also use specially selected materials to match the water quality and arrange the tubes to meet thermal and pressure drop requirements.

Our range of coolers for OFWF (Oil Forced, Water Forced) transformers have capacities ranging from 40kW up to 2MW and can use water from both open and closed circuits.


If you feel you need another type of heat exchanger, visit our products and services page or contact us.

Customised heat exchangers

Over 100 years of design & manufacturing knowledge

Your partner for the entire lifecycle of your business

We value the added protection that we receive from the double tube design. Not only does it reduce failures, but these coolers even alert us to potential problems in advance. That helps to keep us up and running, which is vital in our industry.

A key player of the power transmission industry

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We customise our heat exchange solution to meet your requirements, so contact us today to discover the right equipment for you.

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