Fault detection and diagnosis of asynchronous machine has become a central problem in industry over the past decade. A solution to tackle this problem is to use stator current for a condition monitoring, referred to as motor current signature analysis. This paper argues that bearing faults would have a negligible effect on motor currents and instead argues that the more likely reason why the faults can be detected in currents is because they entail a fluctuating resistive torque which acts immediately, in contrast to the radial displacement which takes time to integrate to a perceptible displacement even in response to a step change in velocity. In this context, we propose a new method for detecting bearing defects based on the exploitation of the instantaneous power factor that varies according to torque oscillations. Experimental results show the good performances of the proposed method which will be compared with the instantaneous power method to highlight the feasibility and advantages of this method.

In this paper, a lifetime model for bond wire contacts of Insulated Gate Bipolar Transistors (IGBT) power modules is reported. This model is based on power cycling tests obtained under accelerated conditions and a finite element model taking into account the electrical, thermal and mechanical coupling. It allows to estimate the bond-wires lifetime for a large scale of junction temperature swing amplitudes (ΔTj) and stress durations (ton). To build it, a numerical design of experiment was performed in both high and low stress values (ΔTj). Then, a strain-life curve has been constructed where average strain values on a defined volume around the contact areas between top-metallization and the most exposed bond-wires to fatigue and lift-off have been used. As result, it has been shown that the total strain is linearly dependent with ΔTj and power law dependent with ton The combination of the strain-life relation and the strain dependency with stress parameters leads to the lifetime relationship. The obtained lifetime model has been satisfactorily validated with some additional experimental points obtained from literature and with a large range of values for ton. This methodology can easily be replicated to other structures and is quite generic.