Modelling of ampacity and temperature of MV cables in presence of harmonic currents due to EVs charging in electrical distribution networks

Abstract

To meet the rapidly growing electric vehicle (EV) charging demand, it is important to determine maximum ampacity and avoid overloading of Medium Voltage (MV) cables in power distribution systems. Previous works on modelling and analysis of relationship between the load demand of MV cables and EV penetration level did not consider the contribution of harmonic currents. This paper presents a methodology for modelling and analysis of the impact of EV charging loads on cable ampacity and temperature in presence of different levels harmonic currents under two typical scenarios of EV charging modes, i.e., uncontrolled domestic charging scenario and uncontrolled off-peak domestic charging. The proposed method determines the ampacity and temperature of three-core cable taking account for cable geometry, harmonic levels, stochastic nature of the charging power, start time of individual charging, seasonal temperature under different EV penetrations. A generic urban distribution network with residential load ratio of 0.7, which is representative of urban residential distribution network in China, is adopted as an example. Results show that the ampacity of a 400 mm2 10 kV cross-linked polyethylene (XLPE) cable decreased by 10.79 A and 2.03% when the harmonic level is at the maximum allowed limit as given in IEC 61000-3-2. Meanwhile, the ampacity decreased by 23.34 A and 4.09% at the maximum limit given in IEC 61000-3-4. In presence of 36.15% and 41.66% total harmonic distortion current which are the most serious harmonic distortion in the example network with 30% EV penetration, cable ampacity decreased by 42.86 A, 8.06% and 61.35 A, 11.35% respectively.