What are no-load and excitation current tests?

No-load losses (excitation losses) are the core losses of a transformer that are "excited" at rated voltage and frequency, but which do not supply load. No-load losses include core loss, dielectric loss, and losses in the windings due to exciting current. The transformer is excited at rated voltage with all other windings open circuited. The exciting current and no load loss is then measured.(Note: This is a standard test only on units over 500kVA. It will only be carried out on lower kVA units when specifically requested.)