I posted some information on Soviet protection research before, which included experiments spaced armour. Here is another such experiment, performed in the summer of 1943 at factory #112.
A drawing of the extra armour includes armour for the turret, but the prototype does not have it. Only the sides of the hull are equipped with additional armour.
The armour did not enter production. However, "everything old is new again" rang as true then as it does now, since the idea of skirt armour returned in 1945, this time to combat Panzerfausts. The additional armour was 6-8 mm thick and positioned 600 mm away from the main armour. A hit from a Panzerfaust created a 30 mm breach in the screen, but did not penetrate the main armour.