Saturable reactor
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A saturable reactor in electrical engineering is a special form of inductor where the magnetic core can be deliberately saturated by means of a dc current flowing in a control winding. Once saturated, the inductance of the saturable reactor drops dramatically.
Saturable reactors provide a very simple means to remotely and proportionally control the flow of ac current through a load such as an incandescent lamp; the flow of ac is roughly proportional to the flow of dc in the control winding. In addition, because of the particular arrangement of the power windings, the control winding, and the core, the control winding is well-isolated from the ac power. The AC power windings are also usually configured so that they cancel out AC voltages that would otherwise be induced into the control winding.
Because the required inductance to achieve dimming varies with the size of the load, saturable reactors often have multiple taps, allowing a small inductance to be used with a large load or a larger inductance to be used with a smaller load. In this way, the required magnitude of the control current can be also held roughly constant, no matter what the load.
The principal disadvantages of saturable reactors are that they can be physically large, heavy, and comparatively expensive versus newer electronic power controllers. For this reason, they have largely been replaced by thyristor dimmers using triacs or SCRs.
