Forced Oil Cooling
When forced cooling becomes necessary in large high-voltage oil-immersed transformers.
The choice of the method of cooling will depend largely upon the conditions obtaining at
the site. Air-blast cooling can be used, a hollow-wailed tank being provided for the transformer and oil, the cooling air being blown through the hollow space. The heat removed from the inner walls of the tank can be raised to five or six times that dissipated naturally. A cheap method of forced cooling where a natural head of water is obtainable is the use of a cooling coil, consisting of tubes through which cold water is circulated, inserted in the top of the tank. This method has, however, the disadvantage that it introduces into the tank, system containing water under a head greater than that of the oil. Any leakage will be from the water to the oil, so that there is a risk of contaminating the oil and reducing its insulating value.