No Load Excitation Current in Transformer 1

[KS20]

What is the practical Importance of No load Excitation current and what exactly it tells about the transformer. Is there any limit of this current. When test engineer specify this as % age on test report than whether its the %age of LV or % of HV or it depends which side we are giving excitation based on step up or step down?

 

[prc]

Today, its significance is very little as the excitation current is very low, Power Transformers (20-800 MVA) 0.1% to 0.04% of rated full load current. For distribution transformers, the typical value is around 0.5 % and 2-3 % for very small distribution transformers. But during the initial days of transformers, it was very high, 10-20 %, limiting the total load current that can be drawn from a transformer.

In the transformer test report, when it is mentioned as a %, it usually refers to LV's rated current. LV (winding near to core) excitation current as a percentage will be slightly higher than HV excitation current %, but insignificant.