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Rare earth permanent magnets can be reused directly as an alternative to traditional recycling methods, in which scrapped magnets are reprocessed into new magnets by undergoing many of the original energy-intensive and expensive production processes. Direct reuse entails using segmented magnet assemblies built by several small standard-sized magnets that can be reused directly in a number of different applications. A central part of the direct reuse strategy is to separate and demagnetize magnets by heating them to the Curie temperature. We investigated the validity of direct reuse as a rare earth magnet recycling strategy by evaluating the extent to which the heat-driven demagnetization cycles affected magnetic properties, as well as the integrity of the protective coating of Nd–Fe–B magnets. The experimental investigation consisted of four different tests, and was applied to 300 magnets that had either been heated once, five times, or none at all. The tests included $J$ – $H$ measurements, coating pull-off test, corrosion salt spray test, and optical microscopy of the interface between coating and magnet. Magnets coated with Zn, Epoxy, Ni–Cu–Ni, and Ni–Cu+Epoxy were investigated, of which Ni–Cu+Epoxy showed no degradation after heat treatment. Direct reuse as a recycling strategy could therefore be a valuable alternative to traditional recycling.

The design and construction of an easy-to-use test-rig for permanent magnet couplings is presented. Static torque of permanent magnet couplings as a function of angular displacement is measured of permanent magnet couplings through an semi-automated test system. The test-rig is capable of measuring torque up to 240 Nm (in increments of 0.1 Nm) at a angular step of 0.0011 degrees (mechanical). Axial, radial, and angular misalignment can be imposed on the coupling in order to study abnormal and faulty operating conditions. This can also be used to assess installation tolerances. Measured data is stored in a USB thumb-drive, and no additional software or hardware is needed to operate the test-rig. Tests of the aligned static torque performance of two different cylindrical couplings are presented along with radial and axial misalignment-tests of one. The results demonstrates the diversity and usefulness of the the designed test-rig. Furthermore, the coupling-performance shows a clear influence of end-effects for axially short couplings, and are found to be very robust to small misalignment.

A novel recycling strategy, direct reuse, for rare earth permanent magnets were investigated in this article. Direct reuse uses small, unit-cell (segmented) magnets to replace the normal solid pole configuration, which is not directly reusable due its unique shape and size. The unit-cell magnets are directly reusable due to their standard shape and size, and direct reuse effectively bypasses a number of the expensive and energy intensive processes of normal recycling. Based on a model of a 3 MW direct drive wind turbine generator, the finite element studies concluded that normal values of average output torque, torque ripple, and cogging torque are achievable with this segmentation technique. The influence of the thickness of the adhesive layer was analyzed, and a pole-shaping technique was applied to improve the torque characteristics. The simulation models were verified experimentally.

Recycling rare earth permanent magnets is becoming an important alternative source of supply of raw materials for neodymium-iron-boron (Nd-Fe-B) permanent magnets. This article documents a recycling case-study in which isotropic binder-free magnet powder is extracted and recycled from hermetically-sealed rotors. The extraction process is detailed, and the influence of demagnetization-temperature on the magnetic performance of the recycled product is studied and reported on. Both intrinsic coercivities and the squareness factor of the demagnetization curves are observed to decrease with demagnetization-temperature. Back-emf measurements of recycled rotors support the relatively low reduction in remanence flux density measured. The results suggest that a protective atmosphere is needed during the heat treatment, by which the rotors are demagnetized, in order to avoid oxidation of the powder.

This paper presents the methodology and subsequent findings of a performance-improvement routine that employs automated finite element (FE) analysis to increase the torque-per-kilogram-magnet (TPKM) of a permanent magnet coupling (PMC). The routine is applied to a commercially available cylindrical PMC with rectangular permanent magnets (PM), and a new design is discovered which increases TPKM by 15.6%. Furthermore, the study is repeated using concave/convex-shaped PMs, which results in an increase of TPKM of 57.6%. The FE models are validated against experimental measurements of the static torque-performance of the PMC selected for design improvements. The new designs are constrained such that they do not inflict any significant changes to the manufacturing process of the investigated PMC. The routine is found to be readily implementable for investigating existing PMC designs.

Characterization of five accuracy class 0.2 current transformers rated 600 A up to 2500 A is done by measurement of phase displacement and amplitude error as function of frequency and current. The test system is presented and the test procedure is described. The accuracy of test system voltage and current measurements is addressed and separate measurements on the transformer burden (load resistance) are carried using other test equipment. This enables an assessment of the test equipment measurement ability. Finally, measurements of the current error and phase displacement of five different current transformers with burden are carried out

Traditionally electrical motors have three phases, but multiphase motors have shown to improve motor performance and efficiency. This paper concentrates about the control algorithm for a six-phase induction motor with third harmonic current injection. The problem is that typically a seventh inverter branch and filter inductances is needed for stabilizing the midpoint potential of the series connected dc-capacitor link. A new control strategy that pre-calculates the allowed voltage ripple and controls the motor voltage accordingly (using two standard three phase inverter modules) is suggested. With this new control strategy the seventh branch and an inductance can be saved. It also opens the possibility to use two standard three-phase inverters to supply the six-phase motor. An experimental setup is build and the theory is verified in the test case. The proposed control strategy works satisfactory. A drawback is that the voltage ripple in the midpoint increases, if a third harmonic current is injected specially at low speed, which could demand a higher voltage rating of the capacitors. Another drawback is that the higher voltage ripple will stress the capacitors hence the lifetime may be shortened.