In what cases is it used?
The schematic construction of an open-loop version for a transformer is used quite often in production. The fact is that thanks to it you can use synchronization on power vehicles. Used to connect transformers with one phase if it is not possible to install a three-phase one. Protects mechanisms, including electric motors, from supplying two if there is no voltage in one of the phases. The only acceptable assembly scheme is if the rotor is installed in the stator bore.
