The research activity of the Applied Electromagnetics Department covers a wide range of topics in the field of electromagnetism, from computational modelling to the development of references and measurement techniques of electromagnetic fields, high voltages and high currents.
Electrical machine diagnosis is becoming increasingly important, and has been addressed in cooperation with the Universities of Parma and Modena and the Politecnico di Torino. A dedicated machine, developed at INRIM, and the related Finite Element analysis have made it possible to investigate the stator and rotor current spectra. Spectrum lines evidence magnetic and electrical asymmetry, eccentricity, stator and rotor slotting and spatial harmonics in the magneto-motive wave, which have to be separated from actual fault conditions.
Computed and measured rotor current spectrum.
The modelling of a bearingless device has been developed in cooperation with the Brazilian UFRN University, focusing attention on a three-phase induction motor with divided windings, independently controlled to generate radial and rotational forces. Machine performances have been improved by a Finite Element model, validated with experiments carried out in Brazil.
Scheme of the current control strategy for the rotor positioning.
The ferroresonance in LCR electrical circuits has been investigated analyzing the influence of dynamic hysteresis and classical losses on the bifurcation diagrams and on the stability region of subharmonic resonance. The modelling analysis has evidenced and quantified the role of dissipative effects, which significantly reduce the appearance of ferroresonance, and of the initial state of the magnetic material, which modifies the current waveforms introducing subharmonics.
Appearance of ferroresonance at the decrease
of the electrical conductivity of the ferromagnetic core.
The application of homogenization techniques in computational electromagnetism, carried out in cooperation with the Departments of Mathematics and Electrical Engineering of Politecnico di Torino, has been extended to finely periodic structures for magnetic shielding applications. These devices range from grid shields, for enhancing thermal dissipation, to composite magnetic materials. Due to the finely periodic structure and to the different sizes of involved components, standard numerical techniques are inadequate to solve the problem. These difficulties have been advantageously overcome with homogenization techniques, transforming the non-homogeneous shield into an equivalent homogeneous one.
Scheme of the grid shield and magnetic field behaviour
along a transversal direction for different heights h above the shield.
A fully anechoic chamber (useful volume about 8 m × 4 m × 4 m) has recently been built to generate reference
electromagnetic fields in the radio frequency and microwave range. Both free-space normalised site attenuation and field homogeneity measurements have been performed to evaluate the test volume within the room.
Through the use of open-ended guide antennas and standard-gain horns, reference fields can be generated to
calibrate field sensors in a frequency range (500 MHz to 3 GHz) complementary to that in which TEM and GTEM cells
are employed.
A system for the generation of reference magnetic fields in the frequency range from 1 kHz up to
100 kHz has been set up. Magnetic flux densities up to 100 μT at 1 kHz and to 15 μT at 100 kHz are generated
with relative uncertainties ranging from 2·10-3 to 1·10-2.
As regards the traceability of EMC measuring equipment,
technical procedures have been developed to calibrate the main instruments and ancillary equipment recommended by
international standards (CISPR, CENELEC) for emission testing.
The anechoic chamber at I.N.RI.M.
A new measurement set-up has been developed for the investigation of the shielding properties of magnetic and pure conductive materials. Coupling experimental and numerical results, shielding mechanisms have been clarified for magnetic fields in the range (20-100) kHz. Moreover, studies on low frequency high power fields have been performed in cooperation with FIAT Research Center. Further work has been carried on with AEM S.p.A to mitigate the magnetic field of the "Urban 2" power line in Torino.
Magnetic Field Mitigation Set-up: A) generator, oscillator and chiller,
B) 2 m coil, C) magnetic sheet, D-E) probe and positioning plotter.
In collaboration with Centro Elettrotecnico Sperimentale Italiano (CESI) and TERNA S.p.A., in the framework of the Public Interest Energy Research Project named "Ricerca di Sistema" supported by Ministry for Production Activities (MAP, Decree of 28 February 2003), the characterisation of a reference measuring system (RMS) to be used for the on-site verification of current transformers for energy metering has been performed. The ratio errors and phase displacements of the RMS, which includes a Rogowski coil as a current transducer, special optically powered data links, a local unit for data acquisition and storage and a specific data analysis software developed by CESI, have been determined by comparison with a standard current transformer up to 4000 A. With reference to the environmental conditions, the temperature effect on the Rogowski coil and associated remote unit has been investigated in the range from 5 °C to 35 °C.
Temperature variation of the ratio error of the Rogowski coil
and associated remote unit with respect to the value measured at 25 °C.