Heat Dissipation in Variable Underground Power Cable Beddings: Experiences from a Real Scale Field Experiment

Abstract

To prevent accelerated thermal aging or insulation faults in cable systems due to overheating, the current carrying capacity is usually limited by specific conductor temperatures. As the heat produced during the operation of underground cables has to be dissipated to the environment, the actual current carrying capacity of a power cable system is primarily dependent on the thermal properties of the surrounding porous bedding material and soil. To investigate the heat dissipation processes around buried power cables of real scale and with realistic electric loading, a field experiment consisting of a main field with various cable configurations, laid in four different bedding materials, and a side field with additional cable trenches for thermally enhanced bedding materials and protection pipe systems was planned and constructed. The experimental results present the strong influences of the different bedding materials on the maximum cable ampacity. Alongside the importance of the basic thermal properties, the influence of the bedding’s hydraulic properties, especially on the drying and rewetting effects, were observed. Furthermore, an increase in ampacity between 25% and 35% was determined for a cable system in a duct filled with an artificial grouting material compared to a common air-filled ducted system.

Evolution of Temperature Field around Underground Power Cable for Static and Cyclic Heating

“…The underground power cables in previous studies are modelled with a heated cylinder with defined heat flux, or temperature [17,45]. However, temperature-controlled tests offer better control and are closely related to insulation melting condition.…”

“…However, the effect of the boundary conditions and accumulation of generated heat in the surrounding soil mass due to limited size, resulted in a higher temperature field near the heater and excess moisture near the boundaries due to diffusion moisture transfer [36]. Therefore, large-scale boxes fitted with single [2] and multiple heaters [45] are built to eliminate the boundary effect, and have sufficient heat dissipation characteristics. The multiple heater setup offers a better understanding of the interacting temperature and moisture fields around the UGPS.…”

Experiment-Based Study of Heat Dissipation from the Power Cable in a Casing Pipe

“…The power cable performance is a function of the ampacity, which represents its maximum electrical current carrying capacity. This is limited by the critical insulation temperature [13]. The heat loss in the cables results from resistive losses in the conductors and dielectric losses in the insulation.…”

“…The release of thermal energy in the cable leads to an increase in its temperature and an increase in the resistance of the cable. As a consequence, this leads to a limitation in the allowable electricity that can be transmitted via a given cable line [13]. The condition for good heat dissipation from the cable is the use of proper filling of the space outside the cable.…”

“…Casing pipes are used in underground power lines, mainly in the sections of the transition from the cable buried in the ground to overhead lines or ground infrastructure facilities, in culverts under roads or between dense underground infrastructure in cities. A cable duct bank with casing pipes is one of the construction methods that can protect underground power cables from damage due to penetration and traffic above the duct [13]. The outer space of the pipe in the trench is filled with a material that can improve the thermal properties of the underground power system.…”