Considerations regarding the behaviour of power transformers in transient regimes at no-load and short-circuit connection

Within paper are analysed the transient processes both on high voltage transformers used in power stations. In order to eliminate the undesired effects, there are analysed means and methods of limiting the current peak are presented experiments performed on single-phase and three-phase transformers through optimal establishing connection angle. Comparatively are analysed transient regime at short-circuit operation of power transformer in two cases: a) the transformer has secondary windings short-circuited and the nominal voltage are suddenly applied (pre-established short-circuit) and b) the transformer is operating in no-load regime and is suddenly short-circuited (post-established short-circuit). The methods of checking the operation in these two cases are recommended by IEC 60076-5.