VARIABLE AUTOTRANSFORMER (VARYAK)
It is composed of a single-layer winding wound on a toroidal iron core. Variac is often used when we wish to obtain a variable AC voltage from a fixed-voltage AC source. A movable carbon brush ,which can be set in any position between 0 and 330°, sliding on the winding and serves as a variable tap. Manuel or motorized control can be possible
The secondary winding is actually part of the primary winding. In effect, a variac eliminates the need for a seperate secondary winding. As a result , autotransformers are always smaller,lighter, and cheaper than standart transformers of equal power output.
Their iron and copper losses are smaller and result of this their efficient beter than standart transformers.
Their leakege flux is smaller so their regulation ratio beter than standart transformers.