Electrical Machines Courses

Losses of Transformers

HYSTERESIS LOSS :-

Each time the direction of magnetization is reversed, some useful energy is wasted in overcoming internal friction. This is known as "hysteresis loss" and it also produces heating in the core. Hysteresis loss is minimized by using special alloys known as "perm alloy" for core material.

EDDY CURRENTS:-

Due to variation in magnetic flux eddy currents are induced on the surface of iron core which in turn produce heating and therefore reduce the amount of power to the secondary coil. In order to avoid eddy currents , the core is laminated, made of thin sheets of soft iron. Each sheet is separated from the next by a layer of insulating varnish.

STRAY LOSS:-

When alternating current is used to measure the losses in the winding ,the result is always greater than the I²R measured with the direct current .The difference b/w the dc and ac losses in the windings is called stray loss. One portion of stray loss is called “eddy loss” and is created by eddy current circulating in the winding conductors. The other portion is generated outside of the windings, in frame member, tank walls etc.

NO/LOAD OR CORE LOSSES:-

Load losses vary according to the loading on the transformer. They include heat losses and eddy currents in the primary and secondary conductors of the transformer. Heat losses, or I²R losses, in the winding materials contribute the largest part of the load losses. They are created by resistance of the conductor to the flow of current or electrons. The electron motion causes the conductor molecules to move and produce friction and heat.