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OFAF transformer coolers

OFAF transformer coolers for extreme conditions

Our oil forced/air forced (OFAF) coolers help control the temperature of insulating oil in large transformers and other large high voltage equipment used across the power generation, transmission and distribution industries. Typically supplied to transformer manufacturers and maintenance companies, our OFAF coolers are customised to meet specific operating and environmental requirements.

Key benefits

  • Improved performance. Effective cooling helps transformers operate at peak efficiency while ensuring long life and reliability, with lower maintenance requirements. Our highly efficient fin block and fan design also ensures low sound levels and low energy consumption.

  • Rugged and robust. Designed to withstand vibration shock, seismic forces and thermal movement. Aluminium alloys, used as the standard for the tube, fin and tubeplate, minimise corrosion, with custom options available as required. Components supporting the fans and cooler elements are protected to C3 as standard, increased to C5-M(H) when conditions dictate.

  • Flexible. The modular construction of our OFAF range means the products fit all oil filled transformers. The highly configurable design is also able to meet all thermal requirements. Different materials, finishes and coatings are used to suit the most stringent operating conditions and to offer long service life.

How oil forced/air forced coolers work

OFAF Transformer cooler manufactured by Sterling Thermal TechnologyOur OFAF transformer coolers operate in ambient temperatures from -40oC to +50oC, with optional -45oC and +60oC limits available to order. The cooling element is made from materials suitable for the local environment and designed to ensure high levels of heat transfer. It is housed within a robust, long-lasting frame for protection against vibration and thermal shock.

The coolers can be custom designed and manufactured in lengths of 1 to 4 fan bays. Typical configurations include 1, 3 or 5 pass arrangements in a depth of 4 to 8 rows. A wide range of fans and motors is available to meet local electrical requirements, specified noise levels and ingress protection.

Fan construction is an external motor rotor with die-cast aluminium low noise blades, balanced to G6.3 standards or better as required. The fan housing is a robust composite and the discharge grill is electrostatically powder coated. All fan mountings are stainless steel. The ingress protection is IP54, with optional IP55, and the bearing life is expected to be more than 30,000 hours.

The standard cooler is produced without cabling.

Electrical options include:

  • Wiring of fan motors and pump to suit equipment layout
  • Electrical safety switches/isolators for easy isolation of fan motors during maintenance and replacement
  • Speed and sequence controls.

Additional options and accessories include:

  • Angled fans for efficient evacuation of hot air in confined spaces
  • Hinged/lift-off fans for easy coil cleaning and replacement
  • An inlet grid to prevent large particulates such as vegetation choking the element inlet face
  • Oil circulation pumps
  • Enhanced paint finishes
  • Mating flanges and gaskets
  • Customised packing for shipment.

OFAF Transformer Cooler with 2 x Ziehl-Abegg fan assemblies & oil circulation pump

Sterling OFAF transformer coolers are designed to be compact and low weight to ensure fast, easy implementation. We provide fully factory-assembled units with a wide range of mounting choices. All coolers are thoroughly tested to check vibration levels, electrical continuity and pressure. They are designed and manufactured as per our quality management system BS EN ISO 9001:2015.

Read our case study
We helped JST transformateurs to keep a colossal power plant cool in desert conditions.

Screen shot of the case study with JST Transformateurs about the OFAF designed and manufactured by Sterling Thermal Technology


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

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For this challenging project (Ghazlan II, Saudi Arabia), the biggest transformer we have ever developed, we needed to partner with a reliable manufacturer that could supply truly robust transformer oil coolers. Sterling understood our challenges and delivered everything we asked for – transformer oil coolers that fully satisfied our specifications.”

Jean-Claude Brantis, Sourcing and Supply Chain Leader, JST transformateurs

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