Magnetoelectric smart current sensors for wireless condition monitoring applications

Abstract

Studies on the structure, working principle, physical modeling, fabrication, characterization, and performance of magnetoelectric (ME) sensing elements as well as investigations on the design, fabrication, and evaluation of ME passive current sensors and multichannel wireless communication units for wireless condition monitoring of electrical assets are presented and discussed in this thesis. Explorations of the fabrication, characterization, and physical properties of magnetostrictive and piezoelectric materials constituting the ME sensing elements are performed. Conclusions and suggestions for future work are also included. Original contributions reported in this research are stated as follows. (1) Tb₀.₃Dy₀.₇Fe₁.₉₂ (Terfenol-D) alloy plates and Terfenol-D short-barNdFeB magnetepoxy composite rings were used as the magnetostrictive constituent materials, while 0.7Pb(Mg₁/₃Nb₂/₃)O₃ 0.3PbTiO₃ (PMNPT) single-crystal plates/bars, PMNPT single-crystal transformers, and Pb(Zr, Ti)O₃ (PZT) ceramic rings were employed as the piezoelectric constituent materials, in the ME sensing elements. These constituent materials were fabricated into three characteristic types of ME sensing elements, including: (i) plate-shaped sensing elements with a PMNPT single-crystal plate having a thickness polarization sandwiched between two Terfenol-D alloy plates having a length magnetization; (ii) ring-shaped sensing elements with an inner Terfenol-D short-barNdFeB magnetepoxy composite ring having a circumferential magnetization and an internal magnetic biasing concentric to an outer PZT ceramic ring having a wall-thickness polarization; and (3) bar-shaped sensing elements with a Rosen-type or long-type PMNPT single-crystal transformer with its input part sandwiched between two Terfenol-D alloy plates having a length magnetization. (2) An existing physical model was applied to describe the working principle and to predict the ME voltage coefficient (αV=dV/dH) of the plate-shaped sensing elements, while novel physical models were developed for the ring-shaped and bar-shaped sensing elements. Good agreements were obtained between the theoretical and experimental results in all cases. The plate-shaped and ring-shaped sensing elements were found to be suitable for broadband nonresonance sensing, while the bar-shaped sensing elements were good for narrowband resonance sensing with increased sensitivity. (3) Novel surface mount-type and clamp-type ME passive current sensors with magnetic field biasing, electric field shielding, and thermal insulation capabilities were developed based on the plated-shaped and ring-shaped sensing elements, respectively. The effects of magnetic field biasing, electric field shielding, and thermal insulation on the performance of the current sensors were evaluated, both analytically and experimentally. The fabrication and performance of the current sensors were reported. (4) A short-range, 4-channel, 2.4 GHz wireless communication unit and a long-range, 3-channel, 3G/2G wireless communication unit were developed for integration with the ME passive current sensors. The hardware and software developments were described and the design features are highlighted. The performance of the two units was evaluated and disclosed in the laboratory using direct signals generated by an arbitrary waveform generator and indirect signals detected by ME passive current sensors. (5) Three distinct sets of wireless condition monitors were formed and deployed in three different field tests by suitably combining the developed ME passive current sensors and wireless communication units. In the first field test, four surface mount-type current sensors were integrated with the 2.4 GHz wireless communication unit for monitoring the electrical motor drives of the train traction system of a 12-cabin mainline train operated by MTR Corporation Limited and running between Hong Kong and Shenzhen, China on the East Rail Line. In the second field test, three surface mount-type current sensors were connected with the 3G/2G wireless communication unit for monitoring an ABB 400 V, 1,000 A, 3-phase electrical switchgear located in the Electrical Machines Laboratory (EF001a) of the Department of Electrical Engineering at PolyU. In the third field test, a clamp-type current sensor was inputted to the 2.4 GHz wireless communication unit for monitoring a 220 V, 13 A switching mode power supply used for driving personal computers. For all tests, the application background, field installation and implementation as well as test results and analysis were disclosed. A number of publications (please refer to the list of publications) were produced during four years of PhD studies, further elucidating the originality, significance, and excellence of the present work. In addition, the present work was led to the award of the Li Po Chun Charitable Trust Fund Scholarship 2011.