The utility model discloses an iron core and low impedance transformer are rolled up to special opening of electric Railway, including the box, be equipped with iron core and the winding of cover on this iron core in this box, the iron core is single -phase opening and rolls up the iron core, and this box intussuseption is filled with insulating medium to and this iron core and low impedance transformer are rolled up to special opening of electric Railway's impedance voltage percentage is 3 -4%. The utility model has the advantages that: moderate, the energy -conserving effect of economic indicator is obvious, and can high -efficient batch production.