Thermo-fluid analysis on forced air cooling of increase transmission capacity in underground pipeline section

Underground transmission facilities are difficult to maintain and require huge investment, although the necessity of underground transmission is increasing due to expansion of urban areas and the increase in electric demand. Therefore, technology to increase the capacity of transmission cable has been requested. In this paper, we suggested a cooling method using forced air cooling to increase the transmission capacity, and the direct cooling effect of this method was reviewed by thermo-fluid analysis. We modeled and analyzed cables as 3-dimensional, 2-dimensional axisymmetric, and 2-dimensional cross section models respectively, and we computed heat generation increasing rate in an environment maintaining maximum temperature when external air is supplied. Also, fan capacity was calculated to supply the exterior air considering safety factor. As a result of analysis, the allowable heat generation increase rate was increased to 9.2%, 23.4%, 24.3% compare with the condition that didn't performed cooling when fluid velocity was 1 m/s, 5 m/s, 10 m/s respectively. The fan capacity to flow required speed in a 30m cable was estimated as 0.013 kW, 0.977 kW, 6.993 kW respectively.