In this paper, problems existing in present filter of the tested
transformer substation such as 3rd harmonic intensification and
capacitor overload are firstly discovered though spot tests. In
order to solve these problems, analysis and simulations are
then made to design and an effective filter. In conclusion, the
superiority of the designed filter is verified as 3rd harmonic is
weakened and the total harmonic current at 220kV side
decreases as well, moreover, its operating security at higher
bus voltage can be guaranteed since the chose capacitors
satisfy requirement of overload test. Consequently, power
quality threatened by the electric railway is ensured through
operating the designed filter