Low-Voltage Transformer Loss-of-Life Assessments for a High Penetration of Plug-In Hybrid Electric Vehicles (PHEVs)

In the coming years, plug-in hybrid electric vehicles (PHEVs) will strongly penetrate the French car fleet. Their impact on each element of the electric distribution grid needs to be estimated. In this paper, the impact of PHEVs on the life duration of the medium-voltage/low-voltage (LV) transformer using a thermal model to estimate the hot-spot temperature is studied. Based on probabilistic algorithms, three penetration rates of PHEVs are studied. A stochastic method is applied to construct domestic daily load profiles of houses constituting an LV residential electric grid supplied by the transformer. Correlated with the initial load rate (without PHEVs) of the transformer, two indices are proposed; the D_{TR_PHEV_X} and V_{TR_PHEV_X} to calculate, respectively, the life duration and aging rate of transformer in the presence of PHEVs. It is shown that the aging rate of the transformer is quadratic in the presence of PHEVs.