Abstract
The maximum temperature that cable insulation can withstand determines the maximum load that the cable conductor can carry, which is called cable ampacity. However, a temperature far from this value under normal load conditions affects the transients due to earth faults in the distribution network. Accordingly, error estimation in the fault location occurs, and the smart grids do not accept such errors. Considering heterogenous unearthed and compensated distribution networks, the temperature rise in different underground cables is estimated under different load conditions. These loads are full load, three quarters (3/4) load, one half (1/2) load, and one quarter (1/4) load. The generated heat in the cable conductor due to these loads is calculated, and the corresponding temperatures are estimated. The distribution of the temperature across XLPE is ascertained using COMSOL Multiphysics by an interface of heat transfer in solids. The impact of these temperature increases on the XLPE relative permittivity is investigated. Moreover, the impact of relative permittivity on the transients due to the earth faults is investigated. Time and frequency domains of the faulted currents are investigated to determine the effect of load. The effect of the load on the arrival time of traveling surge created due to the fault event is measured using a voltage transducer at the main busbar, and evaluated. Accordingly, the time arrival deviations due to effect of load produce an undesired error in the fault location determination using traveling wave principles. Simulations of the fault cases are implemented in ATPDraw, and Matlab is used to extract the surge arrival time. This work contributes to highlighting the errors involved in the fault location algorithms using network transients due to network service operation at different load conditions.