I. Introduction
Mechanically driven circuit breakers (CBs) in medium voltage applications (cf. Fig.1 a)) are systems that are characterized by a very long service life, but may only be switched very rarely. Therefore, they are prone to certain mechanical failure cases for example due to corrosion, or grease degradation at shafts and bearings. From a functional point of view, their task is to interrupt current flow, even in case of short circuits and thus to protect equipment in the grid [1]. Establishing and breaking the contact is achieved by some drive unit and a linkage (e.g. levers or gears) transmitting the actuation force from the manual push buttons or automated trip coils to the electrical contact (Fig. 1 b) and c)). Among other mechanical issues [2], one possible failure is the jamming of certain shafts within the drive unit (compare Fig. 1 c)), preventing the whole system from operating correctly. A logical attempt to prevent such failures by maintenance can be taken when having a condition monitoring system, tracking the operation of the circuit breaker over time and detecting changes to its health state.