| dc.description.abstract | High voltage (HV) underground power cables are an important part of the power grid. In recent years, the necessity of optimization of power flow within the grid has increased significantly. The transition to renewable energy as well as the growth of electricity demand has resulted in high loads on the existing grid network. In order to optimize the ampacity of underground power cables, a good understanding of their thermal environment is needed. However, the occurrence and effect of wind flow in naturally ventilated cable tunnels has not been researched extensively. To further explore this phenomenon, two temperature sensors and a wind sensor were installed at an HVAC power cable tunnel site. The power cable site contains a three phase 2000 mm2 aluminum cable, rated for 132 kV, with cross-linked polyethylene (XLPE) insulation.
The collection of temperature and wind data were compared to theoretical models to investigate whether the models could be used for future estimation of wind speed in cable tunnels. A validation of the IEC 60287-2-31 [1] model, for calculating the ampacity rating, was also explored. The wind sensor registered a maximum wind speed of 0.7 m/s at the tunnel exit, which coincided with the theoretical calculations, for naturally induced wind. The calculations were made using an equivalent diameter as the tunnel diameter. However, more data is needed to verify the model.
The cable at the sensor site had a steady but low load. The load current was around 300 A, compared to the maximum permissible load of 985 A. A cable with a higher load current would have resulted in higher cable temperatures, leading to clearer wind data. The IEC model, used for ampacity and temperature calculations, correlated with the collected temperature data with an error of ca 20%, meaning that the IEC model is in good agreement with the collected data at this specific site. Thus the IEC model can be used to establish an ampacity rating for an HVAC cable laid in an underground tunnel. Furthermore, the calculation of naturally induced wind flow can be used as an indication of wind speed in cable tunnels, until further verified. | |
