排管敷设电缆群暂态温度场和短时载流量数值计算

Numerical Calculation of Transient Temperature Field and Sort-term Ampaticty of Group of Cables in Ducts

地下排管敷设已经成为电缆敷设的主要形式,准确计算地下排管敷设电缆群的暂态温度场和短时载流量对合理调配电缆线路短时负荷具有重要的意义。为此,利用有限差分法将地下排管敷设电缆群暂态温度场计算过程分为离散的时间步,在每一个时间步内,利用有限元法计算地下排管敷设电缆群的温度场分布,最后给出了整个时间域内地下排管敷设电缆群的温度变化过程和最终暂态温度场分布,在此基础上,利用迭代法计算不超过绝缘短时耐受温度极限的地下排管敷设电缆群的短时载流量。利用地下穿管的发热管试验和仿真来模拟地下排管敷设电缆,试验结果与仿真计算结果基本相符,证明了利用有限差分法和有限元法计算地下排管敷设电缆群暂态温度场和短时载流量具有较高的精度,为工程实际提供了一种新的短时载流量计算方法。

In order to reasonably adjust short-time load of power cables, it is very important to calculate transient temperature field and short-time ampacity of underground power cables in ducts with high accuracy. Transient conduction equations and natural convection equations of simulation model were presented. The calculation process of transient temperature of underground power cables in ducts was divided into discrete transient time step using the fi- nite difference method （FDM）. At each time step, finite element method （FEM） was used to calculate the steadystate temperature distribution of underground power cables in ducts. The variation equations of natural convection were established by the vorticity-stream function and Galerkin method. Coupling of natural convection and conduction and radiation was realized by the iteration method. Between adjacent two time-steps, Grank-Nicolson difference formula was used to transfer parameters and conditions. At last, the temperature variation in whole time and the fi- nal transient temperature distribution of underground power cables in ducts were presented. The permitted shortterm ampacity of underground power cables in ducts was calculated by iteration approach. Trial and simulation of underground heat pipes in ducts was used to verify underground power cables in ducts. The trial test results are the same as the simulation results. The comparison proves that FDM with FEM possesses a high accuracy in calculating the transient temperature field and short-term ampacity of underground cables in ducts, and presents a new effective method to calculate short-time anapacity in engineering.