What is the cause of transformer loss?

　　Transformer loss is a concept in the field of modern physics, which refers to the sum of no-load loss P and short-circuit loss Pk.

　　No-load loss P: When the rated voltage is applied to one winding of the transformer and the other windings are open, the active power absorbed by the transformer is called no-load loss.

　　Short-circuit loss Pk: For a two-winding transformer, the active power absorbed by the transformer when the rated current passes through one winding of the transformer and the other winding is short-circuited is called the short-circuit loss of the transformer. For a multi-winding transformer, the short-circuit loss is based on a specified pair of windings.

　　There are two main reasons for transformer losses:

　　First, a large amount of copper wire is needed when winding the transformer. These copper wires have resistance. When current flows through, the resistance will consume a certain amount of power. This part of the loss is often consumed as heat. This loss is called "copper loss".

　　Second, when the primary winding of the transformer is energized, the magnetic flux generated by the coil flows in the iron core. Because the iron core itself is also a conductor, an electric potential will be induced on the plane perpendicular to the magnetic field line. This electric potential forms a closed loop on the cross section of the iron core and generates a current, which is called "eddy current". This "eddy current" increases the loss of the transformer, causing the iron core of the transformer to heat up and the temperature rise of the transformer to increase. The loss caused by "eddy current" is called "iron loss".

　　Therefore, the temperature rise of the transformer is mainly caused by iron loss and copper loss. Due to the iron loss and copper loss of the transformer, its output power is always less than the input power. The relationship between output power and input power is expressed by efficiency η: η = output power / input power.