Power Transformer Cooling Methods: ONAN, ONAF, OFAF, OFWF

Power Transformer Cooling Methods

ONAN

Oil Natural Air Natural

Oil: natural convection

Air: natural convection

Feature: No pump, no fan; silent & maintenance-free

Use: Small & medium distribution transformers

ONAF

Oil Natural Air Forced

Oil: natural convection

Air: forced draft by fans

Feature: Higher cooling capacity than ONAN

Use: Medium power transformers, allow short-time overload

OFAF

Oil Forced Air Forced

Oil: forced circulation by oil pump

Air: forced cooling by fans

Feature: High cooling efficiency

Use: Large main power transformers, substation & power plant transformers

OFWF

Oil Forced Water Forced

Oil: forced by oil pump

Water: forced cooling by water circulation

Feature: Highest heat dissipation

Use: Extra-large transformer, underground substation, heavy-load station

Quick Comparison Summary

ONAN: Oil natural + Air natural

ONAF: Oil natural + Air forced

OFAF: Oil forced + Air forced

OFWF: Oil forced + Water forced