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Transformer Oil Cooling

Forced Oil / Forced Air (FOA)

Forced Oil / Forced Air (FOA)

Forced Oil / Forced Water (OFW)

Forced Oil / Forced Water (OFW)



We offer air-cooled and water-cooled systems for Oil-Filled Transformers. Transformer oil cooling systems are critical equipment at power plants and substations, as well as chemical and metal refining facilities. The coolers, pumps and valves are specifically designed for transformer oil service and are unlike cooling equipment used in other applications. If you know your performance requirements, you can contact us by requesting a quote.


  • Power Plants
  • Main Output Transformers
  • Generator Stepup Transformers
  • Service Transformers
  • Power Grid
  • Stepdown transformers
  • Mobile emergency or de-bottlenecking cooling systems
  • Rectifier Transformers
  • Furnace Transformers

Air Cooled

(Type FOFA, FOA or OFP)

Unifin’s Forced Oil – Forced Air Transformer Oil Coolers can be standard units or custom designed to dissipate a particular heat load or meet a specific application requirement. Standard cooler lines are pre-engineered around industry standards with numerous custom features available as options.

Standard Features:

  • Extruded Aluminum finned tubes
  • Floating headers to accomodate thermal expansion
  • High efficiency, weather resistant motors
  • Enamel Finish

Optional Features:

  • Other tube and fin materials
  • Galvanized fan cabinets
  • Hinged fan cabinets
  • Backscreens
  • Control panels

These Coolers are also referred to as:

  • OFP
  • Forzair
  • FOA
  • FOFA

Custom coolers can be designed to provide additional cooling in the same space, replace radiators, or address operational concerns such as:

  • excessive fin fouling
  • corrosion
  • poor air distribution
  • higher ambient temperature than design

Unifin is in the unique position of having been the sole supplier to most of the major North American manufacturers of transformers for over 30 years. Unifin has the design and manufacturing information to provide form, fit and functional replacements or upgrades and improvements to the existing design.

In this cooler type, the oil is pumped through finned tubes while air is blown over the fins to cool the oil

Heat Sink

Heat Sink

The Heatsink is a self-contained cooling system complete with cooler, pumps, valves, expansion tank and all other components required to provide auxiliary cooling to an overheating transformer.

This series of Auxiliary coolers have been specifically designed to augment the cooling capacity of transformers in service. With recent years being some of the hottest on record, and with the high demand for electricity during the hottest part of the summer months, keeping transformers operating at capacity has become crucial to all utilities.

The portable Heatsink Auxiliary Transformer Cooler will allow increased overload, extend life and save money. When you install a Heatsink unit, you can eliminate present and future overload problems by reducing the temperature of the dielectric oil in the transformer. Heatsink Auxiliary Transformer Coolers can be installed quickly with little modification to the transformer. Using optional quick connect hoses, and the optional trailer, your Heatsink transformer cooler can be transferred easily from one overloaded substation to another.

Water Cooled

(Type OFW / ONW)

We provide water to transformer oil coolers with the unique leak detector feature that not only identifies a leak but captures and isolates the leaking fluid so the oil and water do not mix .

Forced Oil Flow (OFW)

An OFW Cooler is a forced-oil-forced water transformer oil cooler. This describes that an external pump is used to circulate the oil through both the transformer and the cooler to assist in cooling the oil. The OFW cooler may be mounted in either a horizontal or vertical orientation on the side of the transformer. This design is available in a standard or Leak Detector design – both include double tubesheets.

Natural Oil Flow (ONW)

Natural Oil Flow (ONW)

ONW Coolers are a shell & tube heat exchanger with natural oil convection on the shell side and water through the tube – no pump is used to move the oil through the transformer or cooler. A natural flow of oil is set up through the density change that occurs as the oil is heated in the transformer then cooled in the external cooler.

The ONW cooler is available with the exclusive Unifin leak detector feature which allows immediate detection of any water leaks before the safety of the transformer is compromised due to water penetrating into the oil and it protects the environment by preventing the oil from entering the water. Fifteen standard sizes are available in both conventional or leak detector design, both incorporating double tubesheet construction.


We offer Cardinal Pumps which are specifically designed for transformer oil. These pumps are self contained with no mechanical seals, so the risk of oil leaks and contamination is significantly reduced.

The Cardinal Transformer Oil Pump is offered in both centrifugal and axial flow models. These pumps have been the standard used on oil filled transformers in North America for decades. Cardinal took over the manufacturing when other suppliers such as GE, Westinghouse and Ingersoll Rand stopped manufacturing Transformer Oil Pumps.  

Flange sizes for centrifugal pumps range from 2″ x 2″ to 8″ x 8″.

Axial flow pumps are available in 6″ x 6″ and 8″ x 8″ sizes.

Eighteen standard models are available, all offered with a variety of customer specified optional features.

Standard Features:

  • Heavy Duty class 30 cast iron is used for the pump casing, motor enclosure and impeller to provide long life.
  • Pump and motor units are pressure tested to 50 psig to establish the integrity of the complete unit.
  • Motor windings Hi-Pot tested for 60 seconds at (2x voltage + 1000), to ensure the electrical integrity and continuity.
  • Impellers designed to permit thermosyphon flow (allows natural convection even when the pump is shut off).
  • The pumps continuous duty operating temperatures are -40ºc (-40°F) to + 100°c (+212°F).
  • Winding resistances of the motor are taken before and after the pump is built, to ensure the integrity of the product.

Optional Features:

  • Tecsonics® Bearing Wear Monitoring System.
  • Special motor insulation for transformer cooling liquids other than transformer oil.
  • Shaft rotation sight plugs to facilitate checking shaft rotation.
  • Metric sized flange connections for international compatibility.
  • Performance run-in testing and certified test curves.
  • Various connectors are available to suit customer’s specific requirements.
  • Motors available in single or dual voltage, single or three phase, 50 or 60 Hz frequencies.
  • Large thrust face bearing.
  • Custom designed transformer oil pumps that meet existing pump dimensions and performance requirements.
  • Transformer Pumps suitable for rail car service.

Information on Transformer Oil Pump inspection, maintenance, repair and replacement

Design factors to consider when specifying a Transformer Oil Pump

Heavy Duty Transformer Oil Valves

Unifin’s Cardinal Pumps & Exchangers also manufactures a line of heavy-duty transformer oil valves ranging from 2″ to 8″ in size including ANSI standard and OEM specific flange configuration (such as the GE square shown to the right) bolt hole patterns. These valves are designed specifically for use on new transformers or as replacements on existing electrical transformers.

Field retrofit kits available for Westinghouse and McGraw Edison valves.

Parts for Pumps

  • Replacement and upgraded pump connectors
  • Replacement power cords
  • Valve kits
  • Flow Gauges
  • Replacement gaskets and seals
  • Replacement fans and motors
  • OSHA compliant fanguards

Valves and Coolers

  • Replacement and upgraded pump connectors
  • Replacement power cords
  • Valve kits
  • Flow Gauges
  • Replacement gaskets and seals
  • Replacement fans and motors
  • OSHA compliant fanguards

Design Parameters for Transformer Oil Cooling Click Here

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