High power AC line reactors

Alongside the introduction of high power electronic drive systems or converters there has been an increase in demand for heavy current line reactors. These are fitted on the AC input of the electronic drive systems to add extra reactance. The benefits of this include: (i) attenuation of line harmonics, and (ii) improvement of current waveform. The first author describes a method now adopted by Power Transformers to wind the current carrying coils using foil or sheet conductors which dramatically reduces the time taken to produce the coils as opposed to multiples of smaller conductors. However due to the nature of continuously changing magnetic fields great care must be taken to avoid the introduction of induced eddy currents into the foil windings from around the air gaps in the core even at frequencies as low as 50 Hz. To lessen these eddy currents entails changing the core design so that any field that leaves the core and impinges on the winding is of low enough intensity to not be a problem. The second author discusses phase shifting transformers, double wound transformers, and polygonal autotransformers