These transformers are those transformers which are used to protect power transformers against fluctuation. Fluctuation can be defined as sudden change in voltage or current. Fluctuation will cause increase in eddy current which in return increases over heating and apply sudden forces on conductors .Harmonics are one of the main reasons of fluctuation. Harmonics is caused when non linear loads are used. Non linear loads can be defined as those loads which don’t offer constant resistance but changes its impedance on changing any parameter of supply other than magnitude. When these loads are used then they change the waveform of supply which in turn disturbs the transformers that are used to control them. To avoid these types of problems reactor transformers are used.
The HV rating of both power and reactor transformer are same i.e. number of turns on hv of both transformers are same. The hv of power transformer is connected across the core of reactor transformer so that excitation can be provided to the reactor transformer. Through this excitation a less fluctuating waveform is generated and is supplied through winding of reactor transformer. It has only one set of winding.
The structure of core is responsible for its working. Its core has different structure than normal transformer’s core. Its limbs are made in discontinuous disks with some spacing in between them. These disks are laminated so as to reduce any chance of short . Due to this discontinuity high fluctuating flux reduces to less fluctuating flux.
In normal transformers the yoke and limbs are connected at an angle of 45o so as to give smooth flow to flux , but in reactor transformers this angle is increased to 90o so as to obstruct maximum and this also leads to reduction in high fluctuating flux.
And in this way a less fluctuating supply is maintained.