Dynamic impedance identification of slot-bars by means of pointwise electric field noisy time-finite observations

The effective resistance and inductance of electric machine armature conductors differ considerably from their direct current value. Their determination is at present of peculiar interest especially in connection with nonsinusoidal and aperiodic currents arising from transient operations. This paper describes a new computing method which enables to estimate both the magnetic vector potential and the current density distribution in the time domain at any point in the cross-section of a slot-bar. Such evaluation is crucial both in calculating the skin-effect resistance and reactance of the conductors and in the leakage flux analysis in the slots. The estimation procedure is carried out on the basis of pointwise noisy time-finite observations of the longitudinal electric field in one of the armature slot-bars, taking into account the eddy currents and the statistical information about the measurement noise. The method outlined results from a straightforward use of the state-variables approach and of the related concept of observability for an infinite dimensional system (i.e. a time-invariant distributed parabolic one). The computer program worked out by the author employing this technique is described in detail. Two different procedures are used within the above framework: modal analysis and weighted residual method. The striking differences between the two resulting systems are pointed out for different shaped slot-bars.