Abridgment of heat flow from underground electric power cables

The heat resistance of the soil surrounding underground cable ducts is usually large, and the path of the heat through the soil is not simple, especially when there are several adjacent ducts. This heat resistance and the path of the heat flow may be determined graphically, but except in the simpler cases, this method becomes very difficult. The heat resistance of any one of several ducts can be calculated theoretically by making assumptions of unknown magnitudes. To check these calculations by testing actual installations would be slow and expensive. Advantage may be taken of the similarity between the flow of heat and the flow of electricity to set up and test the electrical equivalent of any duct system. In this way, the theoretical results can be checked readily with a minimum outlay of equipment. Results obtained by this method show the theoretical calculations to be accurate even for close spacing and also give a picture of the actual path of the heat from a group of several ducts. Thus, the heat resistance of a duct may be found quite accurately if the specific heat resistance of the soil is known.