Solution Overview

ONAN Cooling for Space-Constrained Oil-Immersed Transformers

TengQi Technology’s ONAN cooling solution addresses limited radiator space and hotspot temperature-rise challenges in oil-immersed distribution and small-to-medium power transformers. Optimized radiator oil passages, inlet flow guidance and effective heat-transfer area support natural-circulation cooling without fans, with performance subject to project-specific calculation and verification.

Cooling mechanism: Natural oil circulation and natural air convection; no cooling fans or oil pumps
Installation constraint: Limited radiator dimensions and configuration quantity
Radiator type: Panel radiators with optimized internal oil passages
Design focus: Oil-flow capacity, flow distribution and effective heat-transfer area
Design inputs: Transformer capacity, oil temperature, interfaces, radiator dimensions and temperature-rise requirements
Cooling improvement target: Up to approximately 5%, subject to project-specific calculation and verification

Solution Highlights

Coordinate inlet flow, side passages, oil distribution and heat-transfer area to support cooling within fixed dimensional limits.

Enlarge Header Oil-Flow Openings

Larger header openings, reduced local inlet resistance

Enlarge Side Oil Passages

Wider side passages, improved access to side cooling sections

Guide Inlet Oil Distribution

Inlet guide grooves, directed flow toward side panels

Increase Effective Heat-Transfer Area

Additional panel oil channels, greater developed surface area

Natural-circulation cooling without additional fans or oil pumps

TengQi Technology’s ONAN cooling solution addresses the thermal-management needs of oil-immersed distribution and small-to-medium power transformers with limited installation space. It focuses on plate-type radiator design rather than adding forced-cooling equipment or simply increasing radiator dimensions.

ONAN means Oil Natural Air Natural: heated insulating oil circulates naturally from the transformer into the radiators, releases heat through the radiator surfaces to the surrounding air by natural convection, and returns to the transformer. Both the internal oil circuit and the external airflow conditions influence the available cooling capacity.

Why a larger radiator bank is not always the answer

Transformer dimensions, connection positions and site clearances can restrict radiator size and quantity. Within those limits, insufficient oil-entry capacity, uneven oil distribution and underused heat-transfer surfaces can make temperature-rise requirements more difficult to meet.

Small collector-pipe oil openings can restrict natural circulation.
Uneven flow between central and side passages can leave some radiator areas insufficiently utilized.
Unguided inlet flow can favor lower-resistance paths instead of distributing oil effectively.
Limited developed surface area can constrain the cooling capacity available within the permitted dimensions.

Four coordinated design measures

↔ Increase oil-entry capacity

Larger collector-pipe oil openings reduce local entry resistance and help prevent inlet restrictions from limiting the overall natural oil circulation.

⇄ Reinforce side passages

Enlarged side oil passages improve flow access to the radiator’s side regions, helping these heat-dissipating surfaces contribute more effectively.

↗ Guide incoming oil

Guide grooves at the oil inlet direct incoming hot oil toward the side radiator plates. This addresses flow distribution rather than relying on increased inlet capacity alone.

＋ Optimize effective area

Additional plate oil passages can increase developed surface area within the allowed dimensions. Passage count must remain balanced with flow resistance, structural strength and manufacturing feasibility.

What the approach can support

Combining improved circulation, more balanced oil distribution and effective heat-transfer area can help release more cooling capacity from each radiator. This supports hotspot temperature control and may create design flexibility to reduce radiator quantity, subject to the transformer’s total heat-dissipation requirement and project validation.

Because the solution does not use cooling fans, it avoids additional fan operating noise and fan-related maintenance tasks. It does not eliminate transformer operating noise or the need for routine transformer and radiator inspection.

A design target, not a universal performance guarantee

The solution targets an improvement in cooling capacity of up to approximately 5% through oil-path and surface-area optimization. Actual improvement depends on radiator specification, transformer loading, oil temperature, ambient conditions, installation and the agreed comparison and test conditions. Cooling performance and hotspot temperature effects require project-specific calculations, sample validation or agreed testing.

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