Tangential Coil Research Articles

Calibration of the Tangential Coil Sensor for the Measurement of Core Losses in Electrical Machine Laminations

The measurement of core losses in electrical steel laminations is considered an essential step in the machine design process. Accordingly, the calibration of the tangential field sensor for measurements of magnetic field strength H is of importance in core loss measurements for estimation of electrical machine efficiency. Due to the stray field between the lamination surface and the tangential coil, a concern is raised regarding the certainty of the measured field. This paper presents a reliable technical approach to calibrate the tangential field sensor used in the investigation of core losses in electrical machine laminations, which compensates for the drop in the actual field value. The proposed approach is based on developing a magnetizing circuit, which consists of two test laminations. An array of Hall Effect sensors is used in this study as a reference for the tangential field. The calibration results show that the magnetic field strength measured at the specimen surface by the tangential coil is scaled down by 4.57% of the actual field. The results are verified experimentally and validated by finite-element simulations. Based on the obtained results, a correction factor is applied on pulsating and rotational core losses to attain more accurate data.

Design optimisation of the ITER divertor magnetic probes using FEM analyses

This paper is focused on the design, simulation and optimisation of the ITER divertor magnetic tangential coils. The most critical issue for the divertor coils is to minimise RITES [G. Vayakis, et al., Radiation-induced thermoelectric sensitivity (RITES) in ITER prototype magnetic sensors, Rev. Sci. Instrum. 75 (10) (2004) 4324–4327] and TIEMF [R. Vila, E.R. Hodson, Thermally induced EMF in unirradiated MI cables, J. Nucl. Mater. 367–370 (Part 2) (2007) 1044–1047] by combining a proper choice of conductor with low temperature variation in the coil. Instead of mineral insulated cable (MIC), which was foreseen as the preferred winding, a winding made of ceramic-coated steel wire was recently proposed [G. Chitarin, L. Grando, S. Peruzzo, C. Tacconet, Design developments for the ITER in-vessel equilibrium Halo current sensors, 24th SOFT Conference, Warsaw, Poland, September 2006, Fusion Eng. Design, in press]. It is thought that, for this wire, maintaining a temperature variation in the wiring below 10 K will be sufficient to allow long-pulse operation. Variations of the divertor coil design have been simulated with the help of ANSYS. The aim was to keep the temperature variation in the winding pack within this limit. The optimisation of the coil based only on a cooling by conduction was not sufficient to meet the 10 K target. Therefore, an actively water-cooled coil was designed which finally met these requirements.

Measurements of the Field Quality in Superconducting Dipoles at High Ramp Rates

Several recent applications of superconducting magnets require the magnets to be operated at high ramp rates and at frequencies of several Hertz. Brookhaven National Laboratory (BNL) has recently designed and built prototypes of superconducting dipole magnets that can be ramped at a fairly high rate (1 T/s or more). For accelerator applications, it is also crucial that the magnets maintain good field quality even at high ramp rates. In order to characterize the field quality of magnets at high ramp rates, a measurement system consisting of 16 printed circuit tangential coils has been developed. The coil system is held stationary while the magnet is ramped. This paper describes the techniques used for the measurements and data analysis, and presents the results of measurements at ramp rates of up to 4 T/s in a prototype dipole built at BNL for GSI.

A novel device for the measurement of the mechanical and magnetic axes of superconducting magnet assemblies for accelerators

In the context of the LHC superconducting magnet production, especially for dipoles and quadrupoles due to their complexity, it is foreseen to perform acceptance tests, at an early production stage, to detect possible significant deviations from the design values. The knowledge of the magnetic field geometry is very important, especially for the main magnets. In order to get this information a new device has been conceived that measures the magnets at room temperature during different stages of construction. This device incorporates a sensitive measuring probe and an efficient data acquisition system because the coils are only powered at about 10/sup -5/ of the nominal D.C. current. It is dedicated to Quadrupole and Dipole [by using Quadrupole-Configured Dipole (QCD) transformation] magnets, but is also easily adaptable to higher order magnets (n = 3, 4 and 5) by specific orientation of the search coils. It is equipped with magnetic sensors (4 fixed tangential coils and AC excitation current for the magnet) and position sensors (3D-laser tracker and light reflector) that allow the simultaneous detection of the magnetic field axis and the cold bore axis. It is equipped as well with a set of 4 LEDs and associated with a CCD camera that allows both the measurement of the cold bore diameter and its position with respect to the mole. This paper describes the system and reports the first results measured on the pre-series magnets recently assembled.

Twin rotating coils for cold magnetic measurements of 15 m long LHC dipoles

We describe here a new harmonic coil system for the field measurement of the superconducting, twin aperture LHC dipoles and the associated corrector magnets. Besides field measurements the system can be used as an antenna to localize the quench origin. The main component is a 16 m long rotating shaft, made up of 13 ceramic segments, each carrying two tangential coils plus a central radial coil, all working in parallel. The segments are connected with flexible Ti-alloy bellows, allowing the piecewise straight shaft to follow the curvature of the dipole while maintaining high torsional rigidity. At each interconnection the structure is supported by rollers and ball bearings, necessary for the axial movement for installation and for the rotation of the coil during measurement. Two such shafts are simultaneously driven by a twin-rotating unit, thus measuring both apertures of a dipole at the same time. This arrangement allows very short measurement times (typically 10 s) and is essential to perform cold magnetic measurements of all dipoles. The coil surface and direction are calibrated using a reference dipole. In this paper we describe the twin rotating coil system and its calibration facility, and we give the typical resolution and accuracy achieved with the first commissioned unit.

Field and loss measurements in Epstein frame and sheet testers

The magnetic properties of sample sheets have been measured in an Epstein frame by the conventional method, and are compared with the results obtained simultaneously using a small tangential coil between the sheets in the Epstein frame. The loss values measured by the two methods on samples cut from oriented and non-oriented steels in the same Epstein frame do not differ significantly. A measure of the differences in the loss measurements can be defined as the differences in the predicted effective mass by averaging the losses arising in the legs and in the corner of the Epstein sample core. Thus, there is no reason why the measurements in the sheet testers and the Epstein frame should not be in good agreement.