Reactors have been used for many years to solve problems in variable speed drive installations. About ten years ago the use of line reactors started to become more common as they helped to solve typical problems on the input (line side) of variable frequency drives (VFD) and SCR controllers. They often have been used as low cost substitutes for 1:1 isolation transformers. The typical problems that line reactors solved were drive nuisance tripping, voltage notch reduction (for SCR controllers) and harmonic attenuation. They were called “line reactors” because they were always used on the “line side” or input of a variable speed drive. Attempts to use “line reactors” on the output side of a drive tended to fail because the line reactors typically overheated due to the harmonic content of the output waveform.