I've seen that in some substations online transformer inspection is performed through partial discharge detection sensors. As partial discharge depends on voltage so I was wondering if these kind of devices would work for distribution transformer (11KV - 440V) inspection?
Yes it is Widely used, and there are many types of PD sensors and applications. These are caused by a voltage breakdown or detonation of tiny particles or voids in an otherwise homogeneous pure insulator.
With a small capacitance the particle charges faster and May breakdown or cause a tiny detonation. This can vary from 1 per minute to >1 per cycle and vary randomly in size. The result is carbon trails in epoxy and dissolved Hydrogen in oil.
On the outside it is called corona, where more contamination may occur from dust and Moisture.