Electrical Machine Permanent Magnets Health Monitoring and Diagnosis Using an Air-Gap Magnetic Sensor

Abstract

this study proposes a magnetic sensor design and application for monitoring the health of rotor magnets in permanent magnet (PM) electrical machines through in-situ observation of the air-gap magnetic flux density. The reported device employs the concept of Fibre Bragg Grating (FBG) strain sensing fusion with magnetostrictive material to deliver a machine stator slot wedge integrated sensor that allows straightforward installation and retrofit with no invasive action to core elements of the machine. The sensing theory, design, prototyping, calibration and installation of the proposed magnetic sensing scheme are detailed in the paper. The sensor was installed into an inverter driven surface mount PM synchronous machine (SPMSM) and its performance for in-situ observation of rotor PM magnetization conditions validated in a range of healthy and demagnetised PM conditions tests. The obtained experimental data demonstrate the reported device's capability to enable recognition of rotor PMs' magnetisation level and thus their health monitoring. Finally, a fault index is proposed and experimentally validated that allows the application of in-situ magnetic sensor measurements for relative quantification of PM demagnetization fault severity.

The Demagnetization Harmonics Generation Mechanism in Permanent Magnet Machines With Concentrated Windings

“…Those mentioned above also gave a motive for the development of techniques based on the extraction and process of signals obtained by commercial flux sensors, [24]- [28] or using a number of search coils having proper span along stator's circumference [18], [29]- [33]. Utilizing properly positioned coils has the advantage of exploiting the magnetic flux in specific points on machines' air-gap and taken advantage of the impact of the fault.…”

An End-to-End, Real-Time Solution for Condition Monitoring of Wind Turbine Generators

“…The modified rotor assembly was created using the original shaft, bearings and core; however, to enable the analysis of different magnetization conditions in a controlled fashion, the original healthy PM pole arc design was modified to be circumferentially segmented into six individual sections, as can be seen in the rotor of Figure 1. This facilitates controlled emulation of a range of typical conditions that can arise from different demagnetization processes [7,8] by appropriate magnetization of individual PM sections and their careful assembly into complete PM poles to be installed on the rotor [9].…”

Detecting Partial Demagnetization in AFPM Generators by Monitoring Speed and EMF Induced in a Supplemental Winding

“…Moreover, partial demagnetization increases the magnitude of higher force harmonic components leading tovibration and acoustic noise radiated from the machine [8] and alters the attraction between the rotor and the stator leading to a change in the machines' shaft trajectory [9]. Generally there is a significant amount of work that has been done on the detection of the partial demagnetization fault in the past two decades [3], [5], [10]- [12].…”

“…Flux-based fault detection techniques using commercial flux sensors [12], [18]- [20] or by using a number of search coils with a proper span [21]- [23] is a reliable, low-cost and industrial applied method to extract fault indicator quantities. Their major advantage is the ability to measure the flux at various points and for specific surfaces in an electric machine; as a result, making it possible to exploit the consequences of a fault.…”