Non-invasive monitoring system of synchronous generator using external field

Equipment for Monitoring Synchronous Generators Condition through External Magnetic Field Waveforms

“…Measurement of the external magnetic field The magnetic signature reflects physical and constructive characteristics of each machine, in addition to being associated with its operating condition [18]. These characteristics influence the machine internal magnetic field, of which the external field is a reflection.…”

“…When the sensor is not close to the stator frame, the intensity of the leakage field tends to be very low, inducing voltages in the order of millivolts or even microvolts in the induction field sensors, mainly due to the attenuation of the high frequency components by the stator frame. This fact leads to the need for analog conditioning steps, composed of amplification and filtering stages, to ensure a good signal-to-noise ratio and increase the signal amplitude for the analog-to-digital conversion step [18]. From the digitized signal, the external magnetic field time derivative can be obtained, as indicated in Fig.…”

“…The magnetic induction in the air gap B(t) can be modelled through analytical functions [5], [18], [28]. A simplified model for B(t) is given by (1), where mmf(t) is the function representing the magnetomotive force from the rotor and P(t) is the function characterizing the magnetic permeance along the air gap.…”

“…In later work, the investigation of the frequency spectrum of electrical and magnetic quantities have shown the presence of a spectral component corresponding to the mechanical rotation frequency of the synchronous machine and its harmonics, whose amplitude was sensitized when faults occurred [19], [20]. This research topic was outlined and complemented by theoretical and experimental studies that proved the existence of these spectral components from analytical models of the air gap magnetic induction, which showed the presence of these components due to the small asymmetries between the poles in real machines [18], [21]. The evaluation of the frequency spectrum of external magnetic field measurements on SGs for fault detection has been reported in several theoretical and experimental investigations in recent years [22]- [25], although no standard or commercial equipment for this end have been established.…”

“…This monitoring class is indicated as a trend in the faults diagnosis in electrical machines [11], mainly because it allows the development of non-invasive systems, that is, the sensors can be installed outside the machine without interrupting or disturbing its operation. This fault detection strategy is found mainly in applications involving induction motors [6], [12]- [15], although recent studies show that this application is also being investigated for synchronous machines [5], [16]- [18].…”