Investigation on the Thermal Impact of Low-Order Harmonics on Railway Power Supply Transformers

This work evaluates the thermal impact of low-order harmonics on transformer loading capabilities in the Swedish electric railway power system (ERPS). Using real power quality (PQ) measurements and standard methodologies from IEC and IEEE, it estimates the hot-spot temperature (HST), top-oil temperature (TOT), and ageing parameters to assess harmonic contributions to transformer loss of life (LOL). Results indicate that harmonic distortion can increase HST by up to 25°C and that over 50% of total ageing is attributed to harmonics. The findings align with the general view and values of the existing literature. While severe insulation degradation limits were not reached within the study period, future expansions in railway traffic may significantly elevate thermal stress, necessitating transformer derating. The study underscores the importance of harmonics in ERPS transformer health management and PQ performance.