In order to investigate the heat dissipation efficiency of the separated cooling installations used in under-ground substation transformers

the layout modes of the cooling systems are investigated. The ODWF

OF/OF/ANand ONAN cooling types are commonly employed in underground substation transformers. Scale model heat dissipa-tion experimental simulations are carried out for ONAN type separated cooling installations in accordance with itspractical layout mode. The experiments are carried out on an 80 MVA/110 k V oil-immersed transformer with ONANtype separated cooling installation. The temperature rise at key points in the cooling system and on the windings aremeasured under different operating conditions

such as changing the horizontal distance between the transformermainbody and the panel-type radiator

lifting the panel-type radiator vertically to 5.75 m

etc. The analysis andcomparison of the experimental results show that under horizontal layout mode

changing the separate distance be-tween the transformer mainbody and the panel-type radiator has little influence on the cooling efficiency. However

lifting the panel-type radiator to 5.75 m would slowdown the oil flow in the cooling system and thus reduce the cool-ing efficiency

leading to a phenomenon that the temperature rise in the oil at the transformer top is still low but thetemperature rise at the windings has risen much higher. The conclusion of this paper has reference value for the ar-rangement of separated cooling installations and the improvement of temperature rise test of transformer.