This device was made in order to test the big amount of spoiled tools like drill or grinder. The device was made of a transformer from an old Russian TV set. The regulation used was on U2008 system, through which it regulates the opening angle of the triac. It has a practical application as in order to detect short circuits between the coils, doesn't require a full supply of electromagnet. Otherwise the rotor starts to move a little because of the connections inaccuracies.
The usage is quite simple. The rotor should be placed on forks and additionally, a piece of plate on it. When the short circuit occurs, the plate starts to vibrate. It should be done by rotating the rotor and placing the plate on every gouge.