Q. Characteristics of Transformer?

The characteristics of most interest to power engineers are voltage regulation and ef?ciency. The voltage regulation of a transformer is a measure of the change in the magnitude of the secondary voltage as the current changes from no load to full load while the primary voltage is held ?xed. This is de?ned as

 in which the I²R loss is obviously load-dependent, whereas the core loss is considered to be constant and independent of the load. It can be shown that the core loss should be equal to the copper loss for maximum operating ef?ciency at a given load.

The rated core loss can be approximated by the power input in the open-circuit test in which one winding is open-circuited and rated voltage at rated frequency is applied to the other winding.

The rated copper loss (at full load) can be approximated by the power input in the short-circuit test, in which one winding is short-circuited and a reduced voltage at rated frequency is applied to the other winding such that the rated current results.

The energy ef?ciency generally taken over a 24-hour period, known as all-day ef?ciency,is also of interest. It is given by