The impact of sympathetic magnetization transients on harmonic filters in auto-transformer fed railway traction applications

The operation of mixed fleets of modern PWMrectifier and older thyristor locomotives and the tightening ofharmonic emission standards globally will lead to more complexharmonic filter installations in railway applications. This papershows that track switching operations in an auto-transformer fedsystem can generate sympathetic transformer magnetizationcurrents that have very significant magnitudes, high harmoniccontent and last for some seconds. A sympathetic transient canoccur when un-energized auto-transformers are switched intoservice and paralleled with energized transformers at the feederstation or in adjacent track sections. The harmonic loads imposedby these currents need to be considered in the design of theharmonic filter elements and protection.